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Volatile communication between plants that affects herbivory: A meta-analysis
Abstract
Volatile communication between plants causing enhanced defence has been controversial. Early studies were not replicated, and influential reviews questioned the validity of the phenomenon. We collected 48 well-replicated studies and found overall support for the hypothesis that resistance increased for individuals with damaged neighbours. Laboratory or greenhouse studies and those conducted on agricultural crops showed stronger induced resistance than field studies on undomesticated species, presumably because other variation had been reduced. A cumulative analysis revealed that early, non-replicated studies were more variable and showed less evidence for communication. Effects of habitat and plant growth form were undetectable. In most cases, the mechanisms of resistance and alternative hypotheses were not considered. There was no indication that some response variables were more likely to produce large effects. These results indicate that plants of diverse taxonomic affinities and ecological conditions become more resistant to herbivores when exposed to volatiles from damaged neighbours.
... Plastic changes that are induced by plant-to-plant communication could affect roots through byproducts of physiological mechanisms. Plant-to-plant communications often lead to increases in the content of secondary chemical metabolites in leaves [7][8][9][10][11][12][13][14][15][16] or changes in shoot-to-root allocation 17 . The increase in secondary chemical metabolites may affect the microbial community associated with roots because secondary chemical metabolites have anti-microbial properties [18][19][20][21] . ...
... Similar to many previous studies 6,7,11 , our experiment demonstrated that the plant-to-plant communication induced changes in plant quality. Although plant biomass, shoot-to-root ratio and total phenolics in leaves were not affected (Fig. 1a-c), the saponins in both leaves and roots were significantly higher in the VOC-exposed plants (Fig. 1e,f). ...
... Our results are consistent with those of Shiojiri et al. 11 who showed that the VOCs from cut goldenrod increase the defense of soybean plants against the herbivore, S. litura. The response of soybean plants may reduce leaf damage through resistance effects [6][7][8] or alteration of herbivore behavior 9 . ...
Aboveground communication between plants is well known to change defense traits in leaves, but its effects on belowground plant traits and soil characteristics have not been elucidated. We hypothesized that aboveground plant-to-plant communication reduces root nodule symbiosis via induction of bactericidal chemical defense substances and changes the soil nutrient environment. Soybean plants were exposed to the volatile organic compounds (VOCs) from damaged shoots of Solidago canadensi s var. scabra , and leaf defense traits (total phenolics, saponins), root saponins, and root nodule symbiosis traits (number and biomass of root nodules) were measured. Soil C/N ratios and mineral concentrations were also measured to estimate the effects of resource uptake by the plants. We found that total phenolics were not affected. However, plants that received VOCs had higher saponin concentrations in both leaves and roots, and fewer root nodules than untreated plants. Although the concentrations of soil minerals did not differ between treatments, soil C/N ratio was significantly higher in the soil of communicated plants. Thus, the aboveground plant-to-plant communication led to reductions in root nodule symbiosis and soil nutrient concentrations. Our results suggest that there are broader effects of induced chemical defenses in aboveground plant organs upon belowground microbial interactions and soil nutrients, and emphasize that plant response based on plant-to-plant communications are a bridge between above- and below-ground ecosystems.
... Apart from influencing atmospheric chemistry and climate feedback, biogenic VOCs have multiple ecological functions, for example attracting and/or repelling herbivorous insects, recruiting natural enemies of the attacking herbivores, and mediating between-and within-plant communication, among others (De Moraes et al., 1998;Karban et al., 2014;Li and Blande, 2017;Tooker and Hanks, 2006). Moreover, some plant VOCs, such as isoprene and monoterpenes, have been shown to confer plants with thermal protection against high temperature-induced oxidative stress Loreto and Fineschi, 2015). ...
... The lack of a clear effect of gall-infestation on isoprene emissions observed in our study might be due to VOC-mediated withinand between-plant signalling. VOCs emitted from herbivoredamaged plants have been well documented to induce and/or prime VOC emissions from undamaged tissues of the same damaged plants as well as from neighbouring undamaged plants (Karban et al., 2014;Li and Blande, 2017). In hybrid aspen, for instance, herbivoreinduced VOCs were observed to enhance isoprene emissions from undamaged branches of the damaged saplings (Li and Blande, 2017). ...
... In hybrid aspen, for instance, herbivoreinduced VOCs were observed to enhance isoprene emissions from undamaged branches of the damaged saplings (Li and Blande, 2017). The galled and ungalled branches in our experimental plots were spaced 20-70 cm apart, which falls within the distance over which VOCmediated within-and between-plant signalling can occur in nature (Karban et al., 2014), and further, the branches might be connected to each other below ground. Therefore, it is possible that gall-infested branches might have stimulated isoprene emissions from neighbouring uninfested branches via both vascular and airborne signals, which in turn may have overshadowed the direct effects of gall infestation on isoprene emissions. ...
Climate change is altering high-latitude ecosystems in multiple facets, including increased insect herbivory pressure and enhanced emissions of volatile organic compounds (VOCs) from vegetation. Yet, joint impacts of climatic drivers and insect herbivory on VOC emissions from the Arctic remain largely unknown. We examined how one-month warming by open-top plastic tents, yielding a 3–4 °C air temperature increase, and the natural presence of gall-forming eriophyoid mites, Aculus tetanothrix, individually and in combination, affect VOC emissions from whortle leaved willow, Salix myrsinites, at two elevations in an Arctic heath tundra of Abisko, Northern Sweden. We measured VOC emissions three times in the peak growing season (July) from intact and gall-infested branches using an enclosure technique and gas chromatography–mass spectrometry, and leaf chemical composition using near-infrared reflectance spectroscopy (NIRS). Isoprene accounted for 91% of the VOCs emitted by S. myrsinites. Isoprene emission rates tended to be higher at the high than low elevation during the measurement periods (42 μg g⁻¹ DW h⁻¹ vs. 23 μg g⁻¹ DW h⁻¹) even when temperature differences were accounted for. Experimental warming increased isoprene emissions by approximately 54%, but decreased emissions of some minor compound groups, such as green leaf volatiles (GLVs) and (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT). In contrast, gall-infestation did not affect isoprene emissions but stimulated emissions of DMNT, sesquiterpenes and GLVs, particularly under ambient conditions at the low elevation. The NIRS-based chemical composition of the leaves varied between the two elevations and was affected by warming and gall-infestation. Our study suggests that under elevated temperatures, S. myrsinites increases emissions of isoprene, a highly effective compound for protection against oxidative stress, while an infestation by A. tetanothrix mites induces emissions of herbivore enemy attractants like DMNT, sesquiterpenes and GLVs. Under both conditions, warming effects on isoprene remain but mite effects on DMNT, sesquiterpenes and GLVs diminish.
... For instance, herbivore-induced VOCs can attract natural enemies of herbivores (Sabelis, 1999), provide protection against pathogens (Shiojiri et al., 2006), and repel herbivores (Heil, 2004), potentially defending plants against their enemies (Kessler and Baldwin, 2001). Moreover, undamaged neighboring plants can recognize VOCs emitted from attacked plants and use them as a cue to mobilize their own defense systems (Kobayashi and Yamamura, 2003;Karban, 2008;Karban et al., 2014). Plant communication can be influenced by climate because VOC production, volatility and, consequently, VOC movement at the leaf surface, are controlled by temperature (Niinemets et al., 2004). ...
... These effects were largely as predicted across elevation and time, and support the idea of plant-plant communication, with both MeJA-treated and untreated neighboring ramets up to 5 m away evidently activating their defense systems, at least in 2016 when the plants were treated. Our results are consistent with other studies showing that above- (Tamogami et al., 2008;Rodriguez-Saona et al., 2009;Moreira et al., 2018b;Kalske et al., 2019) and belowground (Jassbi et al., 2010;Falik et al., 2011;Rasmann et al., 2012;Elhakeem et al., 2018) signals emitted by induced plants can activate the defense system of uninduced neighbors (Dicke and Bruin, 2001;Baldwin et al., 2002;Pickett et al., 2003;Karban et al., 2014;Delory et al., 2016). Moreover, these effects were more pronounced and consistent in the sub-montane and mid-montane climatic zones (Low and Medium sites) than in the subalpine zone (High sites), suggesting that plant-plant communication in bilberry, either through airborne or belowground signaling from MeJA-treated ramets, is apparently modulated by climatic conditions. ...
The activation of plant defense systems in response to herbivory or experimentally applied methyl jasmonate (MeJA) involves the production of chemical defense substances functioning as warning signals to repel herbivores and protect against pathogens. They also serve as signals detectable by undamaged neighboring plants, a phenomenon called plant-plant communication. We studied how altitudinal variation in temperature and timing of snowmelt affected herbivore resistance, growth and reproduction of untreated bilberry (Vaccinium myrtillus L.) 20-500 cm from MeJA-treated ramets. Across 2 years, responses of MeJA-treated and untreated bilberry ramets were recorded twice per season along an elevational gradient in a boreal system. At low and medium altitudes, untreated bilberry showed increased herbivore resistance and reduced growth and reproduction up to 500 cm from MeJA-treated ramets. In the warmer sites at these altitudes, the effects persisted for 2 years for ramets up to 100 cm from the treated ramets. At high altitudes, however, only untreated ramets growing 20-100 cm from the treated ramets showed increased resistance to insect herbivores and reduced reproduction, but these effects did not persist into the second year. Altitudinal variation in climate affected trade-offs between plant defense, growth, and reproduction. Our findings indicate that plant-plant communication is also influenced by the combination of changes in climate and time after induction. Adaptations of plants growing under increasing temperature in high-latitude environments can profoundly impact ecosystem functioning, especially where bilberry, the key plant species in the boreal system, interacts with its herbivores.
... Plants emit volatile organic compounds (VOCs) in response to leaf damage caused by herbivorous arthropods or mechanical damage such as weeding (Takabayashi & Shiojiri, 2019). When neighboring plants receive such VOCs, they often induce defenses against herbivores; this phenomenon is referred to as plant-plant communication (Heil & Bueno, 2007;Heil & Karban, 2010;Karban et al., 2000Karban et al., , 2014Shiojiri & Karban, 2008b;Tscharntke et al., 2001;Yoneya & Takabayashi, 2014). For example, field-grown sagebrush trees (Artemisia tridentata) which were exposed to VOCs from clipped conspecific plants in the early season experienced less herbivore damage in the following seasons (Shiojiri & Karban, 2008a). ...
... Lima bean (Phaseolus lunatus) plants exposed to VOCs from herbivore-damaged conspecific plants increased the amount of extrafloral nectar that attracts carnivorous arthropods (Choh et al., ,2004Heil & Kost, 2006). Plant-plant communication mediated by VOCs has been observed in >40 plant species, most of which are herbaceous (Heil & Karban, 2010;Karban et al., 2014;Li, 2016;Yoneya & Takabayashi, 2014). However, the first evidence of the phenomenon was found in tree species such as sugar maple and poplar (Baldwin & Schultz, 1983). ...
In response to volatiles emitted from a plant infested by herbivorous arthropods, neighboring undamaged conspecific plants become better defended against herbivores; this is referred to as plant‒plant communication. Although plant‒plant communication occurs in a wide range of plant species, most studies have focused on herbaceous plants. Here, we investigated plant‒plant communication in beech trees in two experimental plantations in 2018 and one plantation in 2019. Approximately 20% of the leaves of a beech tree were clipped in half in the spring seasons of 2018 and 2019 (clipped tree). The damage levels to leaves in the surrounding undamaged beech trees were evaluated 90 days after the clipping (assay trees). In both years, the damage levels decreased with a reduction in the distance from the clipped tree. In 2019, we also recorded the damage levels of trees that were not exposed to volatiles (nonexposed trees) as control trees and found that those that were located <5 m away from clipped trees had significantly less leaf damage than nonexposed trees. By using a gas chromatograph–mass spectrometer, ten and eight volatile compounds were detected in the headspaces of clipped and unclipped leaves, respectively. Among them, the amount of (Z)-3-hexenyl acetate in clipped leaves was significantly higher than that in nonclipped leaves. Our result suggests that green leaf volatiles such as (Z)-3-hexenol and (Z)-3-hexenyl acetate and other volatile organic compounds emitted from clipped trees induced defenses in the neighboring trees within the 5 m radius. The effective distances of plant‒plant communication in trees were discussed from the viewpoint of the arthropod community structure in forest ecosystems.
... Aboveground signalling interactions are mediated by air-borne chemicals (Farmer, 2001), while root exudates drive belowground plant-plant signals (Semchenko, Saar, & Lepik, 2014). Aboveground signalling interactions by air-borne chemicals have been substantially clarified, particularly in the context of herbivore-induced volatiles that can be perceived by neighbouring plants and "warn" them of imminent attack (Baldwin et al., 2006;Karban, Yang, & Edwards, 2014). Air-borne chemicals, including ethylene, methyl jasmonate and salicylate, indole and several volatile terpenes, are largely responsible for aboveground plant-plant signalling interactions (Baldwin et al., 2006;Erb et al., 2015). ...
... JA is a common signalling chemical that elicits the production of defensive metabolites in plants against attacking microbes, feeding herbivores or plant competitors Martinez-Medina et al., 2017). The role and mechanism of JA in aerial signalling interactions are well established (Baldwin et al., 2006;Heil & Karban, 2010;Karban, Yang, & Edwards, 2014), but less information is available on JA as a root-secreted signalling chemical. A few studies have indicated that plants release JA from roots, inducing allelochemical production of neighbouring plants Li et al., 2020;Li, Xia, & Kong, 2016). ...
Plant-to-plant signaling is a key mediator of interactions among plant species. Plants can perceive and respond to chemical cues emitted from their neighbors, altering survival and performance, impacting plant coexistence and community assembly. An increasing number of studies indicate root exudates as key players in plant-to-plant signaling. Root exudates mediate root detection and behavior, kin recognition, flowering and production, driving inter- and intra-specific facilitation in cropping systems and mixed-species plantations. Altered interactions may be attributed to the signaling components within root exudates. Root ethylene, strigolactones, jasmonic acid, (-)-loliolide and allantoin are signaling chemicals that convey information on local conditions in plant-plant interactions. These root-secreted signaling chemicals appear ubiquitous in plants and trigger a series of belowground responses inter- and intra-specifically, involving molecular events in biosynthesis, secretion and action. The secretion of root signals, mainly mediated by ATP-binding cassette transporters, is critical. Root-secreted signaling chemicals and their molecular mechanisms are rapidly revealing a multitude of fascinating plant-plant interactions. However, many root signals, particularly species-specific signals and their underlying mechanisms, remain to be uncovered due to methodological limitations and root-soil interactions. A thorough understanding of root-secreted chemical signals and their mechanisms will offer many ecological implications and potential applications for sustainable agriculture. This article is protected by copyright. All rights reserved.
... The capacity to perceive and respond to environmental cues is essential to all life on earth (Erb 2018). According to a meta-analysis, 40 out of 48 studies of plant-plant communication via herbivoreinduced volatile organic compounds (VOCs) have found evidence of communication that affects herbivory (Karban et al. 2014), which indicates volatiles act as positive regulators of plant defenses. However, some studies suggest that volatiles may also act as defense suppressors (Erb 2018). ...
Plants have evolved sophisticated defense mechanisms to overcome their sessile nature. However, if and how volatiles from cold stressed plants can trigger interplant communication is still unknown. Here, we provide the first evidence for interplant communication via inducible volatiles in cold stress. The volatiles, including nerolidol, geraniol, linalool, and methyl salicylate, emitted from cold‐stressed tea plants play key role(s) in priming cold tolerance of their neighbors via a CBF‐dependent pathway. The knowledge will help us to understand how plants respond to volatile cues in cold stress and agricultural ecosys.
This article is protected by copyright. All rights reserved.
... They also play a role in repelling herbivores that avoid inducible plant defenses and conspecific or heterospecific competition (De Moraes et al., 2001;Knolhoff and Heckel, 2014;Anderson et al., 2011;Jiao et al., 2018) or they can attract specialist herbivores that aggregate to collectively overcome the defense of their hosts (Loughrin et al., 1995;Weed, 2010;Robert et al., 2012). HIPVs can also be detected by neighboring plants and help them to anticipate an incoming attack (Arimura et al., 2000;Heil and Ton, 2008;Engelberth et al., 2004;Karban et al., 2014;Sugimoto et al., 2014;Nagashima et al., 2018). Hence, HIPVs provide information to all players in a plant's ecological network and through these various effects, HIPVs play a major role in determining the composition of insect communities in the field (Xiao et al., 2012;Zhu et al., 2015;Poelman and Dicke, 2014;Blubaugh et al., 2018;Schuman and Baldwin, 2018). ...
Plants typically release large quantities of volatiles in response to herbivory by insects. This benefits the plants by, for instance, attracting the natural enemies of the herbivores. We show that the brown planthopper (BPH) has cleverly turned this around by exploiting herbivore-induced plant volatiles (HIPVs) that provide safe havens for its offspring. BPH females preferentially oviposit on rice plants already infested by the rice striped stem borer (SSB), which are avoided by the egg parasitoid Anagrus nilaparvatae, the most important natural enemy of BPH. Using synthetic versions of volatiles identified from plants infested by BPH and/or SSB, we demonstrate the role of HIPVs in these interactions. Moreover, greenhouse and field cage experiments confirm the adaptiveness of the BPH oviposition strategy, resulting in 80% lower parasitism rates of its eggs. Besides revealing a novel exploitation of HIPVs, these findings may lead to novel control strategies against an exceedingly important rice pest.
... Communication between plants has been extensively studied above ground, with a focus on HI-VOCs (herbivore-induced volatile organic compounds; Karban et al., 2014a, b). These compounds are released as plants are wounded by herbivores and can be directly repellent to herbivores or attractive to predators and parasites of herbivores that can decrease levels of damage inflicted by herbivory (reviewed by Karban et al., 2014b). In addition, VOCs can be perceived by proximate neighbours that eavesdrop on the volatile signals emitted by the herbivore-damaged plant. ...
Communication between plants mediated by herbivore-induced volatile organic compounds has been extensively studied aboveground. However, the role of root herbivory in belowground plant-plant communication is much less understood. We here investigated whether root herbivores can trigger plant roots to emit warning signals to neighbouring plants that are not yet in direct contact with them.
We used a split-root system and infected half of the roots of Agrostis stolonifera plants with root-knot nematodes (Meloidogyne minor) and left the other half uninfected. As a control, we grew plants without nematodes in separate pots. Leachates from each split-root soil compartment and from soils with control plants were applied to separate pots with A. stolonifera plants, of which biomass allocation and morphological traits were measured one month after leachate addition.
Plants receiving leachates from the soil with the nematode-free roots of the nematode-infected plants showed a significantly larger total biomass, more root branches, and deeper rooting than plants receiving leachates from the soil with the nematode-infected roots or from soil with control plants. Plants were taller and the root/shoot ratio was higher in plants receiving leachates from soil with the nematode-free roots than in plants receiving leachates from soil with nematode-infected roots. Shoot tiller number was higher in plants receiving leachates from either root compartment of the nematode-infected plants than in plants receiving control leachates.
Our results suggest that an overcompensation response was triggered by systemically induced root-derived compounds from nematode-free roots of a plant locally infected with root-feeding nematodes. Signals from directly attacked roots of the same nematode-infected plant only caused receiver plants to develop more shoot tillers, possibly for future stolon development to grow away from the infected area. This may indicate an anticipatory tolerance response to root feeders that are still distant and an additional generalized escape response to root feeding.
... Criticism regarding the lack of true replication and artificial experimental conditions (Fowler and Lawton, 1985) resulted in the rejection of this popular phenomenon known as "talking trees." It took almost 20 years to revisit and revive the concept of plant-plant communicating via volatile cues by intensely searching for evidence of VOCinduced plant protection against herbivory (Heil and Karban, 2010;Karban et al., 2014). This review focuses specifically on wounding-/damage-induced plant volatiles that fulfill the criteria of DAMPs in stricto sensu. ...
Damage-associated molecular patterns (DAMPs) are an ancient form of tissue-derived
danger or alarm signals that initiate cellular signaling cascades, which often initiate
defined defense responses. A DAMP can be any molecule that is usually not exposed
to cells such as cell wall components, peptides, nucleic acid fragments, eATP and other
compounds. DAMPs might be revealed upon tissue damage or during attack. Typically,
DAMPs are derived from the injured organism. Almost all eukaryotes can generate and
respond to DAMPs, including plants. Besides the molecules mentioned, certain volatile
organic compounds (VOCs) can be considered as DAMPs. Due to their chemical nature,
VOCs are supposed to act not only locally and systemically in the same plant but
also between plants. Here, we focus on damage-induced volatiles (DIVs) that might
be regarded as DAMPs; we will review their origin, chemical nature, physiochemical
properties, biological relevance and putative function in plant–plant communications.
Moreover, we discuss the possibility to use such airborne DAMPs as eco-friendly
compounds to stimulate natural defenses in agriculture in order to avoid pesticides.
... In this case, plants may still recognise kin by root signalling (Chen, During, & Anten, 2012) . Second, root signals (e.g., exudates, see review by Chen et al., 2012) and/or volatiles (Karban, Yang, & Edwards, 2014) may enable plants to determine the genetic relatedness of a neighbour. Third, the way light signals change over time may provide information on the nature of neighbours. ...
Plant foliage selectively absorbs and scatters light, resulting in changes in light spectral composition in surroundings. Plants have evolved to use these spectral changes as signals to predict the competitive strength of neighbouring plants, by adapting their developmental pattern. Both strength and direction of such light signals may contain messages on competition. Studies on light-mediated plant neighbour detection generally focus on strength of light signals coming from the top and/or from the sides, representing shading by an overhead canopy or by similarly sized neighbours. However, light signals could also come from below, reflected by smaller neighbours or by the plant's own foliage, which may not pose a threat. Whether and how plants respond to light signals coming from below and the ecological consequences for plant performance have received little attention. We argue that light signals from below should be considered in studies on light-mediated plant neighbour detection, in which signal reliability is highly relevant. We discuss plant responses to light signals from below that potentially maximize fitness and desirable crop responses to such signals in different ecological settings or crop systems. We put forward a 3D plant simulation approach to aid in the analysis of light signals from below. This article is protected by copyright. All rights reserved.
... Plants perceive and respond to complex blends of VOCs emitted by conspecific and heterospecific neighboring plants (53,74). Such responses frequently involve either priming or defense induction by receiver plants when exposed to VOCs released by herbivore-damaged neighbors (emitters), which ultimately results in heightened resistance on the part of the receiver against subsequent herbivory (71). ...
Ecological research conducted over the past five decades has shown that increasing tree species richness at forest stands can improve tree resistance to insect pest damage. However, the commonality of this finding is still under debate. In this review, we provide a quantitative assessment (i.e., a meta-analysis) of tree diversity effects on insect herbivory and discuss plausible mechanisms underlying the observed patterns. We provide recommendations and working hypotheses that can serve to lay the groundwork for research to come. Based on more than 600 study cases, our quantitative review indicates that insect herbivory was, on average, lower in mixed forest stands than in pure stands, but these diversity effects were contingent on herbivore diet breadth and tree species composition. In particular, tree species diversity mainly reduced damage of specialist insect herbivores in mixed stands with phylogenetically distant tree species. Overall, our findings provide essential guidance for forest pest management.
Expected final online publication date for the Annual Review of Entomology, Volume 66 is January 11, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... Communication between plants has been extensively studied above ground, with a focus on HI-VOCs (herbivore-induced volatile organic compounds; Karban et al., 2014a, b). These compounds are released as plants are wounded by herbivores and can be directly repellent to herbivores or attractive to predators and parasites of herbivores that can decrease levels of damage inflicted by herbivory (reviewed by Karban et al., 2014b). In addition, VOCs can be perceived by proximate neighbours that eavesdrop on the volatile signals emitted by the herbivore-damaged plant. ...
Communication between plants mediated by herbivore-induced volatile organic compounds has been extensively studied aboveground. However, the role of root herbivory in belowground plant-plant communication is much less understood. We here investigated whether root herbivores can trigger plant roots to emit warning signals to neighbouring plants that are not yet in direct contact with them.
We used a split-root system and infected half of the roots of Agrostis stolonifera plants with root-knot nematodes ( Meloidogyne minor ) and left the other half uninfected. As a control, we grew plants without nematodes in separate pots. Leachates from each split-root soil compartment and from soils with control plants were applied to separate pots with A. stolonifera plants, of which biomass allocation and morphological traits were measured one month after leachate addition.
Plants receiving leachates from the soil with the nematode-free roots of the nematode-infected plants showed a significantly larger total biomass, more root branches, and deeper rooting than plants receiving leachates from the soil with the nematode-infected roots or from soil with control plants. Plants were taller and the root/shoot ratio was higher in plants receiving leachates from soil with the nematode-free roots than in plants receiving leachates from soil with nematode-infected roots. Shoot tiller number was higher in plants receiving leachates from either soil of the nematode-infected plants than in plants receiving control leachates.
Our results suggest that an overcompensation response was triggered by systemically induced root-derived compounds from nematode-free roots of a plant locally infected with root-feeding nematodes. Signals from directly attacked roots of the same nematode-infected plant only caused receiver plants to develop more shoot tillers, possibly for future stolon development to grow away from the infected area. This may indicate an anticipatory tolerance response to root feeders that are still distant and an additional generalized escape response to root feeding.
... Research on inter-plant communication via volatiles is fascinating and most of the evidence for this comes from upregulation of defence-related genes upon exposure to herbivore-induced plant volatiles from neighbouring plants (Karban et al. 2014). However, the role of FVOCs in plantplant communication is relatively less studied. ...
Floral scents are important traits which mediate interactions within biotic communities. These volatiles perform diverse functions, ranging from attracting pollinators, repelling florivores or herbivores, as well as controlling the growth of pathogens. Therefore, floral volatiles are under constant selection to balance attraction and repellence in accordance with local communities and this has led to the evolution of highly complex volatile profiles. To date, more than 1000 volatile compounds have been identified from flowers, which ultimately ensure plant reproduction by attracting pollinators. Plant–pollinator interactions mediated by floral volatiles can range from highly generalized to extremely specialized systems. By evolving exclusive relationships with pollinators that are most abundant or efficient, plants increase reproductive success. On the other hand, attracting many kinds of insects by providing generic cues and rewards leads to generalization, where plants benefit by taking advantage of pollinator diversity. Such interactions of varied strength could be achieved through tailoring different floral volatile blends. Floral scents vary widely among plants but despite the variation, there are mainly three major classes of floral volatile organic compounds (FVOCs) based on their origin, function and biosynthesis. They are terpenoids, benzenoids or phenylpropanoids, and fatty acid derivatives. Along with these, certain flowers also produce unusual compounds, which attract pollinators by mimicking food or brood sources. The production, composition, quantity and timing of volatile emissions are tightly regulated by biotic and abiotic factors that help in fine-tuning the ecological interactions mediated by FVOCs. This chapter updates the current knowledge on these aspects and emphasizes the ecological importance of floral volatiles. Further, the various methods for collection and analyses of FVOCs are also described.
... They also play a role in repelling herbivores that avoid inducible plant defenses and conspecific or heterospecific competition (De Moraes et al., 2001;Knolhoff and Heckel, 2014;Anderson et al., 2011;Jiao et al., 2018) or they can attract specialist herbivores that aggregate to collectively overcome the defense of their hosts (Loughrin et al., 1995;Weed, 2010;Robert et al., 2012). HIPVs can also be detected by neighboring plants and help them to anticipate an incoming attack (Arimura et al., 2000;Heil and Ton, 2008;Engelberth et al., 2004;Karban et al., 2014;Sugimoto et al., 2014;Nagashima et al., 2018). Hence, HIPVs provide information to all players in a plant's ecological network and through these various effects, HIPVs play a major role in determining the composition of insect communities in the field (Xiao et al., 2012;Zhu et al., 2015;Poelman and Dicke, 2014;Blubaugh et al., 2018;Schuman and Baldwin, 2018). ...
Plants typically release large quantities of volatiles in response to herbivory by insects. This benefits the plants by, for instance, attracting the natural enemies of the herbivores. We show that the brown planthopper (BPH) has cleverly turned this around by exploiting herbivore-induced plant volatiles (HIPVs) that provide safe havens for its offspring. BPH females preferentially oviposit on rice plants already infested by the rice striped stem borer (SSB), which are avoided by the egg parasitoid Anagrus nilaparvatae, the most important natural enemy of BPH. Using synthetic versions of volatiles identified from plants infested by BPH and/or SSB, we demonstrate the role of HIPVs in these interactions. Moreover, greenhouse and field cage experiments confirm the adaptiveness of the BPH oviposition strategy, resulting in 80% lower parasitism rates of its eggs. Besides revealing a novel exploitation of HIPVs, these findings may lead to novel control strategies against an exceedingly important rice pest.
... They also play a role in repelling herbivores that avoid inducible plant defenses and conspecific or heterospecific competition (De Moraes et al., 2001;Knolhoff and Heckel, 2014;Anderson et al., 2011;Jiao et al., 2018) or they can attract specialist herbivores that aggregate to collectively overcome the defense of their hosts (Loughrin et al., 1995;Weed, 2010;Robert et al., 2012). HIPVs can also be detected by neighboring plants and help them to anticipate an incoming attack (Arimura et al., 2000;Heil and Ton, 2008;Engelberth et al., 2004;Karban et al., 2014;Sugimoto et al., 2014;Nagashima et al., 2018). Hence, HIPVs provide information to all players in a plant's ecological network and through these various effects, HIPVs play a major role in determining the composition of insect communities in the field (Xiao et al., 2012;Zhu et al., 2015;Poelman and Dicke, 2014;Blubaugh et al., 2018;Schuman and Baldwin, 2018). ...
Plants typically release large quantities of volatiles in response to herbivory by insects. This benefits the plants by, for instance, attracting the natural enemies of the herbivores. We show that the brown planthopper (BPH) has cleverly turned this around by exploiting herbivore-induced plant volatiles (HIPVs) that provide safe havens for its offspring. BPH females preferentially oviposit on rice plants already infested by the rice striped stem borer (SSB), which are avoided by the egg parasitoid Anagrus nilaparvatae, the most important natural enemy of BPH. Using synthetic versions of volatiles identified from plants infested by BPH and/or SSB, we demonstrate the role of HIPVs in these interactions. Moreover, greenhouse and field cage experiments confirm the adaptiveness of the BPH oviposition strategy, resulting in 80% lower parasitism rates of its eggs. Besides revealing a novel exploitation of HIPVs, these findings may lead to novel control strategies against an exceedingly important rice pest.
... The simple nature of common VOC signals would also allow eavesdropping by unrelated neighbours (Karban, Maron, Felton, Ervin, & Eichenseer, 2003;Ninkovic et al., 2013). This unintentional sharing of information with unrelated neighbours may not be maladaptive (since reducing overall herbivory/pathogen pressure may benefit the emitting plant), but could also have led to the evolution of VOCs "chemotypes" in a number of plant species (Gouinguene, Degen, & Turlings, 2001;Karban, Yang, & Edwards, 2014;Ninkovic, 2003). There is evidence that VOC-mediated herbivory defence is more effective if signalled by related conspecific plants (Karban et al., 2013) even though the emission of VOCs may be reduced in conspecific stands (Kigathi, Weisser, Veit, Gershenzon, & Unsicker, 2013 ...
Plants were traditionally seen as rather passive actors in their environment, interacting with each other only in so far as they competed for the same resources. In the last 30 years, this view has been spectacularly overturned, with a wealth of evidence showing that plants actively detect and respond to their neighbours. Moreover, there is evidence that these responses depend on the identity of the neighbour, and that plants may cooperate with their kin, displaying social behaviour as complex as that observed in animals. These plant–plant interactions play a vital role in shaping natural ecosystems, and are also very important in determining agricultural productivity. However, in terms of mechanistic understanding, we have only just begun to scratch the surface, and many aspects of plant–plant interactions remain poorly understood. In this review, we aim to provide an overview of the field of plant–plant interactions, covering the communal interactions of plants with their neighbours as well as the social behaviour of plants towards their kin, and the consequences of these interactions. We particularly focus on the mechanisms that underpin neighbour detection and response, highlighting both progress and gaps in our understanding of these fascinating but previously overlooked interactions.
... Herbivore-induced and control branches were kept about 2 m apart in the same climate chamber, which was continuously ventilated by an airstream from bottom to top. It has been shown for many plant species that HIPVs emitted by herbivore-infested plants can prime defense in neighboring plants (Karban, Yang, & Edwards, 2014). However, studies on the distance over which such plant-plant signaling works revealed that plant-plant communication via leaf volatiles is limited within a very close radius, usually not exceeding 1 m (Holopainen, 2004;Simpraga, Takabayashi, & Holopainen, 2016). ...
Several studies have shown that insectivorous birds are attracted to herbivore‐damaged trees even when they cannot see or smell the actual herbivores or their feces. However, it often remained an open question whether birds are attracted by herbivore‐induced changes in leaf odor or in leaf light reflectance or by both types of changes. Our study addressed this question by investigating the response of great tits (Parus major) and blue tits (Cyanistes caeruleus) to Scots pine (Pinus sylvestris) damaged by pine sawfly larvae (Diprion pini). We released the birds individually to a study booth, where they were simultaneously offered a systemically herbivore‐induced and a noninfested control pine branch. In the first experiment, the birds could see the branches, but could not smell them, because each branch was kept inside a transparent, airtight cylinder. In the second experiment, the birds could smell the branches, but could not see them, because each branch was placed inside a nontransparent cylinder with a mesh lid. The results show that the birds were more attracted to the herbivore‐induced branch in both experiments. Hence, either type of the tested cues, the herbivore‐induced visual plant cue alone as well as the olfactory cues per se, is attractive to the birds. Both great tits and blue tits were attracted to systemically herbivore‐damaged pines when they could only see or only smell the experimental branches. This is the first ever study to show that both vision and olfaction alone are enough for attraction of insectivorous birds to herbivore‐damaged trees.
... Many studies have shown that volatiles can activate or prime defense responses (Bouwmeester et al., 2019). A previous meta-analysis has shown that adjacent plants exposed to volatiles from damaged neighbors become more resistant to herbivores (Karban, Yang, & Edwards, 2014). However, tomato plants infested by whiteflies produce a volatile blend that makes neighboring plants more susceptible to whiteflies . ...
Herbivore‐induced plant volatiles play important ecological roles in defense against stresses. However, if and which volatile(s) are involved in the plant‐plant communication in response to herbivorous insects in tea plants remains unknown. Here, plant‐plant communication experiments confirm that volatiles emitted from insects‐attacked tea plants can trigger plant resistance and reduce the risk of herbivore damage by inducing jasmonic acid (JA) accumulation in neighboring plants. The emission of six compounds was significantly induced by geometrid Ectropis obliqua , one of the most common pests of the tea plant in China. Among them, (E) ‐4,8‐dimethyl‐1,3,7‐nonatriene (DMNT) could induce the accumulation of JA and thus promotes the resistance of neighboring intact plants to herbivorous insects. CsCYP82D47 was identified for the first time as a P450 enzyme, which catalyzes the final step in the biosynthesis of DMNT from (E) ‐nerolidol. Down‐regulation of CsCYP82D47 in tea plants resulted in a reduced accumulation of DMNT and significantly reduced the release of DMNT in response to the feeding of herbivorous insects. The first evidence for plant‐plant communication in response to herbivores in tea plants will help to understand how plants respond to volatile cues in response to herbivores and provide new insight into the role(s) of DMNT in tea plants.
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... This scepticism occurred despite the well-known facts that plants can sense and respond to the presence of other plants, for example, through light signals (Pierik & de Wit, 2014) and physical contact (de Wit et al., 2012). Plants can even detect the status of neighbours, for example, whether a neighbour is attacked by a herbivore being conveyed through volatiles (Karban, Yang, & Edwards, 2014) or whether the neighbour is stressed by drought being conveyed through sounds (Jeong et al., 2014). The fact that plants can distinguish between self-and non-self, and are thus capable of some level of identity recognition, has been evident from the observation that many species prevent self-pollination (Fujii, Kubo, & Takayama, 2016). ...
... Furthermore, upon stress, plants release above-and below-ground info-chemicals, including volatile organic compounds (VOCs) or root exudates, which function in direct defense against the attacking herbivores or pathogens, in indirect defense to recruit natural enemies, or serve as chemical cues to neighboring plants (Bais et al., 2006;Dicke & Baldwin, 2010;Delory et al., 2016;Ninkovic et al., 2019). Plants that 'eavesdrop' on the chemical status of the attacked neighbors may benefit from the emitted signals by priming or pre-inducing their own defenses against the oncoming attack, thereby reducing future damage (Heil & Karban, 2010;Karban et al., 2014). Moreover, interplant signals may not only benefit the receiver but also increase the inclusive fitness of the emitter, and, thus, could be considered as mutually beneficial plant-toplant chemical communication (Kalske et al., 2019). ...
Recognition of plant pathogens or herbivores activate a broad‐spectrum plant defense priming in distal leaves against potential future attacks, leading to systemic acquired resistance (SAR). Additionally, attacked plants can release aerial or belowground signals that trigger defense responses, such as SAR, in neighboring plants lacking initial exposure to pathogen or pest elicitors. However, molecular mechanisms involved in inter‐plant defense signal generation in sender plants and decoding in neighboring plants are not fully understood. We previously reported that Pieris brassicae eggs induce intra‐plant SAR against the foliar pathogen Pseudomonas syringae in Arabidopsis thaliana. Here we extend this effect to neighboring plants by discovering an egg‐induced inter‐plant SAR via mobile root‐derived signal(s). The generation of egg‐induced inter‐plant SAR signal requires pipecolic acid (Pip) pathway genes ALD1 and FMO1 but occurs independently of salicylic acid (SA) accumulation in sender plants. Furthermore, reception of the signal leads to accumulation of SA in the recipient plants. In response to insect eggs, plants may induce inter‐plant SAR to prepare for potential pathogen invasion following feeding‐induced wounding or to keep neighboring plants healthy for hatching larvae. Our results highlight a previously uncharacterized belowground plant‐to‐plant signaling mechanism and reveals genetic components required for its generation.
... These include cues directly associated with herbivores, such as herbivore movement on leaf surfaces (Peiffer et al. 2009), the presence of insect eggs on plant tissues (Beyaert et al. 2012;Bandoly et al. 2016;Hilker & Fatouros 2016;Lortzing et al. 2019) and olfactory cues emitted by herbivores, such as pheromones (Helms et al. 2013;Helms et al. 2017;Bittner et al. 2019). In addition, plants may respond to indirect cues that reveal information about the presence of herbivores, most notably herbivore-induced volatile emissions from plant tissues that are already under attack, which have been shown to prime plant defences in a wide range of systems Frost et al. 2008a;Dicke & Baldwin 2010;Karban et al. 2014) and which appear to play a signalling function within plants (Frost et al. 2007;Heil & Silva Bueno 2007), as well as serving as cues for neighbouring plants of the same or different species (Karban & Maron 2002;Kessler et al. 2006;Zhang et al. 2019). ...
Plants can detect cues associated with the risk of future herbivory and modify defence phenotypes accordingly; however, our current understanding is limited both with respect to the range of early warning cues to which plants respond and the nature of the responses. Here we report that exposure to volatile emissions from plant tissues infested with herbivore eggs promotes stronger defence responses to subsequent herbivory in two Brassica species. Furthermore, exposure to these volatile cues elicited an apparent shift from growth to reproduction in Brassica nigra, with exposed plants exhibiting increased flower and seed production, but reduced leaf production, relative to unexposed controls. Our results thus document plant defence priming in response to a novel environmental cue, oviposition‐induced plant volatiles, while also showing that plant responses to early warning cues can include changes in both defence and life‐history traits
... Frequently, a single host plant is exploited concurrently by several herbivore species belonging to different guilds, which create additional attracting or repelling cues. The emission of volatile compounds is perhaps the most studied of these cues (see Karban et al. 2014). Co-occurrence of herbivores, for instance, has been reported in super-host plants, which support several species of galling insect simultaneously (e.g. ...
• Host plant selection by herbivores is driven by a complex array of cues, including leaf traits and previous leaf damage. Herbivore-associated cues to host selection at the plant and leaf scale aid understanding of mechanisms responsible for host preference that might translate into increased performance, as well as processes structuring herbivore populations mediated by interactions. We investigated how changes induced by a galling insect in the tropical fern Cyathea phalerata act as repellent or attractant cues for sawfly feeding and the effects of leaf size on herbivory levels.
• We recorded gall abundance, damage by chewers, leaf size, plant nutritional quality, phenolic concentration and leaf anatomical traits between galled and non-galled leaf samples.
• Galled samples contained less N, higher levels of phenolics and higher C/N ratio. However, leaf-chewing damage did not differ between galled and non-galled leaves. The gall structure was avoided by chewers, as it had high concentrations of phenolics, lignification and suberization. Larger leaves sustained higher gall abundance, but leaf size did not have a significant effect on chewer damage. A co-occurrence index calculated for both guilds indicated that galls and chewers exhibited a distribution that did not differ from random, reinforcing that the two guilds on C. phalerata do not show patterns of repulsion such as those maintained by interspecific competition.
• Sawflies dismissing chemical cues indicate that the increase in phenolics caused by galling insects does not generate increased protection of the galled pinnules. Our results highlight ferns as key resources for herbivores and as a potential plant group to study new research avenues on plant–insect interactions.
... First, terpenes mediate a number of ecological interactions (Abbas et al., 2017). Conifer terpenes are important parts of both constitutive and inducible defense systems against insects and pathogens (Abbas et al., 2017;Blande et al., 2009;Keeling and Bohlmann, 2006;Madmony et al., 2018;Markó et al., 2011), and may also be involved in competitive plant-plant interactions (Karban et al., 2014;Li and Blande, 2017). As such, it's no surprise that rates of terpene emission increase in response to many biotic challenges (Abbas et al., 2017;Keeling and Bohlmann, 2006). ...
Conifer terpenes mediate a number of ecological roles such as deterring herbivory and allelopathic (plant-plant) communication. These terpenes also effect air quality and climate models and are used in chemotaxonomic studies. Herein we report on variation in both intra- and interspecific spruce terpenes using static headspace gas chromatography mass spectrometry (HS-GC-MS) and principal component analysis (PCA) of ‘fingerprint’ volatile profiles. Samples of blue spruce (Picea pungens), Norway spruce (P. abies), and cedar of Lebanon (Cedrus libani), an outgroup control, were analyzed by HS-GC-MS using both chiral and achiral GC columns. Headspace sampling parameters, temperature and heating time, were optimized to maximize detected terpenes. PCA of terpene ‘fingerprint’ profiles showed differences by species, by individual trees, but perhaps surprisingly not by environmental conditions. Analysis of blue and Norway spruce over several months show that volatile emissions remained remarkably constant unlike cedar of Lebanon, which showed a much greater variation in volatile profiles. Branches and buds from both spruces were found to release greater amounts of terpenes than samples of needles. The enantiomeric compositions of seven chiral monoterpenes were found to be largely similar between the three conifers with the exception of (−)-α-pinene, which was the dominant enantiomer released by Norway spruce and cedar of Lebanon, while (+)-α-pinene slightly predominated in blue spruce. While not the primary focus of this work, we believe this constitutes the first report on the enantiomeric composition of terpenes in cedar of Lebanon.
... Naturally occurring environmental stimuli that may reliably indicate impending herbivory and prime plants for improved defense against attack by herbivorous arthropods are, for example, volatile compounds released by herbivorous insects or by herbivore-infested plants. Exposure of plants to insect sex pheromones (Helms et al., 2014(Helms et al., , 2017Bittner et al., 2019), to herbivory-induced plant volatiles (HIPVs, e.g., Heil and Kost, 2006;Dicke and Baldwin, 2010;Karban et al., 2014), or to insect OIPVs (Pashalidou et al., 2020) has been shown to render a plant's anti-herbivore defense more effective. Furthermore, herbivory preceding further herbivory (e.g., Rasmann et al., 2012) and insect egg deposition preceding larval feeding damage Fatouros, 2015, 2016) are known to enhance plant defenses against the feeding stages of the herbivores. ...
Plants can respond to eggs laid by herbivorous insects on their leaves by preparing (priming) their defense against the hatching larvae. Egg-mediated priming of defense is known for several plant species, including Brassicaceae. However, it is unknown yet for how long the eggs need to remain on a plant until a primed defense state is reached, which is ecologically manifested by reduced performance of the hatching larvae. To address this question, we used Arabidopsis thaliana, which carried eggs of the butterfly Pieris brassicae for 1–6 days prior to exposure to larval feeding. Our results show that larvae gained less biomass the longer the eggs had previously been on the plant. The strongest priming effect was obtained when eggs had been on the plant for 5 or 6 days, i.e., for (almost) the entire development time of the Pieris embryo inside the egg until larval hatching. Transcript levels of priming-responsive genes, levels of jasmonic acid-isoleucine (JA-Ile), and of the egg-inducible phytoalexin camalexin increased with the egg exposure time. Larval performance studies on mutant plants revealed that camalexin is dispensable for anti-herbivore defense against P. brassicae larvae, whereas JA-Ile – in concert with egg-induced salicylic acid (SA) – seems to be important for signaling egg-mediated primed defense. Thus, A. thaliana adjusts the kinetics of its egg-primed response to the time point of larval hatching. Hence, the plant is optimally prepared just in time prior to larval hatching.
... This scepticism occurred despite the well-known facts that plants can sense and respond to the presence of other plants, for example, through light signals (Pierik & de Wit, 2014) and physical contact (de Wit et al., 2012). Plants can even detect the status of neighbours, for example, whether a neighbour is attacked by a herbivore being conveyed through volatiles (Karban, Yang, & Edwards, 2014) or whether the neighbour is stressed by drought being conveyed through sounds (Jeong et al., 2014). The fact that plants can distinguish between self-and non-self, and are thus capable of some level of identity recognition, has been evident from the observation that many species prevent self-pollination (Fujii, Kubo, & Takayama, 2016). ...
The phenomenon that organisms can distinguish genetically related individuals from strangers (i.e. kin recognition) and exhibit more cooperative behaviors towards their relatives (i.e. positive kin discrimination) has been documented in a wide variety of organisms. However, its occurrence in plants has only been recently considered. Despite the concerns about some methodologies used to document kin recognition, there is sufficient evidence to state that it exists in plants. Effects of kin recognition go well beyond reducing resource competition between related plants, and involve interactions with symbionts (e.g. mycorrhizal networks). Kin recognition thus likely has important implications for evolution of plant traits, diversity of plant populations, ecological networks and community structures. Moreover, as kin selection may result in less competitive traits and thus greater population performance, it holds potential promise for crop breeding. Exploration of these evo‐ecological and agricultural implications requires: adequate control for‐ and measurements of relatedness, sufficient replication at genotypic level and comprehensive measurements of performance/fitness effects of kin discrimination. The primary questions that need to be answered are: when, where and by how much positive kin discrimination improves population performance.
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... These compounds may, for instance, protect plants against biotic and abiotic stresses [12][13][14]. VOCs can also include defense mechanisms to control growth of neighboring plants [15]. The aroma of wine is one of the main factors that determines its quality, and derives from both the VOCs present in the berries [16], and those produced during the fermentation and aging [17,18]. ...
Abscisic acid (ABA) plays a crucial role in the plant responses to environmental signals, in particular by triggering secondary metabolism. High-altitude vineyards in Mendoza, Argentina, are exposed to elevated solar ultraviolet-B (UV-B) levels and moderate water deficits (WD), thus producing grapevine berries with high enological quality for red winemaking. Volatile organic compounds (VOCs) and phenolic compounds (PCs) accumulate in the berry skins, possess antioxidant activity, and are important attributes for red wine. The aim of the present study was to analyze the role of ABA in the modulation of these compounds in Vitis vinifera L. cv. Malbec wines by comparing the independent and interactive effects of UV-B, WD, and ABA. Two UV-B treatments (ambient solar UV-B or reduced UV-B), two watering treatments (well-watered or moderate water deficit) and two ABA treatments (no ABA and sprayed ABA) were given in a factorial design during one growing season. Sprayed ABA, alone and/or in combination with UV-B (specially) and WD (to a lower degree) increased low molecular weight polyphenols (LMWP), anthocyanins, but most noticeably the stilbenes trans-resveratrol and piceid. Under these treatments, VOCs were scarcely affected, and the antioxidant capacity was influenced by the combination of UV-B and WD. From a technological point of view, ABA applications may be an effective vineyard management tool, considering that it elicited a higher content of compounds beneficial for wine aging, as well compounds related to color.
... From earlier studies we know that winter browsing by red deer on bilberry did not result in the same systematic plant responses indicative of induced defences as did chemical treatment . Most studies of induced plant defences point to herbivory by insects as the main inducer of plant resistance (Howe & Jander, 2008;Karban, Yang & Edwards, 2014), and even if ungulate browsing may modify plant quality it may be by other mechanisms than induced defences. ...
Ecological theory predicts the strongest ecosystem effects of herbivory when dominant and ecologically important species are consumed. Bilberry, Vaccinium myrtillus, is such a key plant species, attractive to many other species in the boreal forests, for example ungulate and invertebrate herbivores. Large herbivores may remove substantial biomass and alter plant quality and therefore affect abundance and populations of invertebrate animals sharing the same food plant. We combined experimental exclusion of ungulates with a browsing intensity gradient to investigate the 15-year effect of ungulate (Cervus elaphus and Ovis aries) browsing on bilberry plant size and on bilberry-feeding herbivorous larvae (Lepidoptera and Symphyta), in a Norwegian old growth boreal forest ecosystem. Bilberry ramets in exclosure plots had nearly nine times higher dry mass and three times higher abundance of invertebrates feeding on them than in ungulate-access plots. Sweep-netting data verified these findings as larval numbers were twice as high in exclosure plots. The pattern in the large herbivore effects on bilberry size and abundance of herbivorous larvae were identical along the browsing gradient. Differences in larval abundance between treatments, as indicated by leaf-chewing, increased during the 15-year study period, and the community fluctuations were larger when ungulate herbivores were excluded. The browsing effect was moderated by plant quality as larval densities were lowest on both heavily-browsed and non-browsed plants, and highest on ramets that had 50-74% of annual shoots browsed. Our study supports previous findings in that bilberry is relatively disturbance tolerant and may recover quickly, and that ungulates may compete with herbivorous larvae for food biomass. Additionally, our results strongly indicated that population insect community peaks and fluctuations are dampened by ungulate consumption. Our findings add to the understanding on how ungulates may structure forest ecosystems directly and indirectly.
... A bee will perform her waggle dance to encode certain specific information that may easily be decoded by observing bees who share the bee-code. 17 All across the animal kingdom (and arguably in parts of the plant world too, see: Karban, Yang and Edwards, 2014;Manusco, 2018), communication is achieved in this way. What is essential for this code-based communication to work, is that the signifier remains consistently wedded to the signified. ...
A central diagnostic and anecdotal feature of autism is difficulty with social communication. Traditionally, these difficulties are regarded as autistic impairments, related to proposed cognitive and social deficits. From this perspective the onus of failures in mutual understanding
is placed within the mind/brains of the autistic individuals involved. However, recent research in the social sciences and critical autism studies is beginning to demonstrate that non-autistic people have challenges in understanding autistic people too, and to reframe the communicative difficulties as a two-way double empathy problem.
A survey of the literature reveals the need for further empirical investigation of the proposed double empathy problem. This thesis builds on contemporary studies examining intersubjectivity between autistic and non-autistic people, and moves this research into the domain of cognitive linguistics. It explores, theoretically, whether relevance theory (a cognitive account of utterance interpretation) might help make sense of what is happening pragmatically during these breakdowns in mutual understanding. It also examines whether a radical reframing of these breakdowns as akin to intercultural problems might provide any valuable insights.
The thesis begins with an interdisciplinary literature review that outlines the central constructs and themes contained within. To begin, the thesis presents an overview of autism research, covering both traditional biomedical theories and more recent phenomenological perspectives informed by the neurodiversity paradigm. Autistic minds are considered as autistically embodied agents navigating a social world comprised of non-autistically shaped norms. Relevance theory
is then introduced within the wider context of cognitive pragmatics, and its application to interactions across dispositional borders (i.e. between autistic and non-autistic individuals) technically explored.
The second half of the thesis reports on and discusses the results of a small-scale linguistic ethnographic case study. Eight core autistic participants engaged in three naturalistic conversations around the topic of loneliness with; (1) a familiar, chosen conversation partner;
(2) a non-autistic stranger and (3) an autistic stranger. Relevance theory is utilized as a frame for the linguistic analysis of the interactions to investigate where mutual understanding is and is not
achieved.
There is increasing acknowledgement of the importance of autistic stakeholder involvement in autism research. In order to bring my own autistic insights more centrally into this work, I have taken an autoethnographic approach. This method draws on the lived experience of the researcher as a member of the group being studied, and as such offers an emancipatory mechanism for raising up previously marginalized voices.
... We confirmed that the attractant did not affect the oviposition behaviour of DBM adults on mizuna plants (the number of eggs), the pupation rate and the pupal weight of DBM larvae on mizuna plants (electronic supplementary materials and figure S2). Thus, in contrast with other studies [28][29][30][31][32][33][34], the attractant did not affect the performance of either DBM adults or larvae. We could therefore focus solely on the C. vestalis-attracting function of the HIPV dispensers. ...
We investigated the recruitment of specific parasitoids using a specific blend of synthetic herbivory-induced plant volatiles (HIPVs) as a novel method of pest control in greenhouses. In the Miyama rural area in Kyoto, Japan, diamondback moth (DBM) ( Plutella xylostella , Lepidoptera: Plutellidae) larvae are an important pest of cruciferous crops in greenhouses, and Cotesia vestalis (Hymenoptera: Braconidae), a larval parasitoid of DBM, is found in the surrounding areas. Dispensers of HIPVs that attracted C. vestalis and honey feeders were set inside greenhouses (treated greenhouses). The monthly incidence of DBMs in the treated greenhouses was significantly lower than that in the untreated greenhouses over a 2-year period. The monthly incidences of C. vestalis and DBMs were not significantly different in the untreated greenhouses, whereas monthly C. vestalis incidence was significantly higher than monthly DBM incidence in the treated greenhouses. Poisson regression analyses showed that, in both years, a significantly higher number of C. vestalis was recorded in the treated greenhouses than in the untreated greenhouses when the number of DBM adults increased. We concluded that DBMs were suppressed more effectively by C. vestalis in the treated greenhouses than in the untreated greenhouses.
... However, pest management by genetic manipulation of volatiles in the plant is not always successful in the field due to its complex context-dependency (Bruce et al., 2015). In another line of defense, plants communicate danger signals to other plants (Karban et al., 2006;Karban et al., 2014;Kalske et al., 2019). For example, the volatile homoterpene compound (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) mediates plant-plant communication in sweet potato (Ipomoea batatas) and triggers systemic and jasmonic acid (JA)-independent anti-herbivore defenses in neighboring plants. ...
Insect pests negatively affect crop quality and yield; identifying new methods to protect crops against insects therefore has important agricultural applications. Our analysis of transgenic Arabidopsis thaliana plants showed that overexpression of PENTACYCLIC TRITERPENE SYNTHASE 1 ( PEN1 ), encoding the key biosynthetic enzyme for the natural plant product (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), led to significant resistance against a major insect pest, Plustella xylostella . DMNT treatment severely damaged the peritrophic matrix (PM), a physical barrier isolating food and pathogens from the midgut wall cells. DMNT repressed the expression of PxMucin in midgut cells and knocking down PxMucin resulted in PM rupture and P. xylostella death. A 16S RNA survey revealed that DMNT significantly disrupted midgut microbiota populations and that midgut microbes were essential for DMNT-induced killing. Therefore, we propose that the midgut microbiota assists DMNT in killing P. xylostella . These findings may provide a novel approach for plant protection against P. xylostella .
... It cannot be completely ruled out that volatiles released by the nearby leek plant could have directly enhanced induced sweet pepper defense mechanisms toward M. persicae. Certain VOCs have been shown to stimulate neighboring plants to adjust their defenses at the right time and subsequently reduce herbivore feeding damages [45][46][47] . The physiological studies were carried out both in clip-cages and in Petri dishes. ...
Combining a non-host plant (companion plant or CP) with a target cultivated plant is considered as a promising strategy to reduce pest pressure. Among the companion plants (CP) commonly used in integrated systems, those belonging to the Amaryllidaceae family (chives, garlic, onion, leek) exhibit characteristics related to certain volatile organic compounds (VOCs) with promising repellent potentialities. The aim of this work was to investigate the potential disruption of sweet pepper (host plant) colonization by the green peach aphid (Myzus persicae) when exposed to leek (Allium porrum) as a CP. Retention/dispersion, EPG and clip-cage/Petri dish laboratory experiments were thus performed to study the effect of leek VOCs on aphid settlement/migration, feeding behavior and life history traits parameters, respectively. This work revealed that leek as a CP had a negative effect on aphid feeding behavior, by disturbing the balance between phloem and xylem sap ingestion, but had no influence concerning aphid settlement. Surprisingly, leek as a CP triggered some unexpected probiotic effects on certain life history traits such as aphid survival, biomass, and fecundity, suggesting a possible hormetic effect of leek VOCs on aphid physiology. The possibility of experience-induced preference of aphids for leek VOCs was also discussed.
... Its release into the air constitutes a volatile defence signal that activates the resistance of neighbouring tobacco plants (Shulaev et al., 1997). Karban et al. (2014), who combined the results of 48 studies, confirmed the existence of "chemical communication" between plants. MeSA is therefore an indicator of diseased plants (Jansen et al., 2011) and has been evidenced as biomarker of grapevine leaves infected with downy mildew caused by Plasmopara viticola (Chalal et al., 2015). ...
Methyl salicylate (MeSA) is a plant metabolite that induces plant defence resistance and an odorous volatile compound presenting green nuances. This volatile compound was shown to be present in wine samples, sometimes at concentrations above its olfactory detection threshold. MeSA is localized in grapes, particularly in the skins and stems, and is extracted during red wine vinification. It was detected at the highest concentrations in wines of several grape varieties, made from grapes affected by cryptogamic diseases, namely downy mildew caused by Plasmopara viticola, and black rot caused by Guignardia bidwellii. It has also been detected in wines from vines affected by Esca, a Grapevine Trunk Disease. MeSA can also be considered to be a chemical marker in grapes and wine indicative of the level of development of several vine cryptogamic diseases.
... Recognition of these airborne chemicals in turn triggers molecular and physiological cascades that can induce trait changes related to resistance. Intriguingly, there is evidence that other plants (of the same or different species) may "eavesdrop" on such chemical signals, exhibiting trait changes in response to perceived enemy risk (reviews by Karban et al., 2014;Ameye et al., 2018;Bouwmeester et al., 2019). For example, undamaged, neighboring lima bean plants were able to recognize HIPVs from attacked plants, activating a defensive response in the form of extra-floral nectaries to attract enemies of herbivores (Kost and Heil, 2006). ...
Predators kill and consume prey, but also scare living prey. Fitness of prey can be reduced by direct killing and consumption, but also by non-consumptive effects (NCEs) if prey show costly risk-induced trait responses (RITRs) to predators, which are meant to reduce predation risk. Recently, similarities between predators and parasites as natural enemies have been recognized, including their potential to cause victim RITRs and NCEs. However, plant-herbivore and animal host-parasite associations might be more comparable as victim-enemy systems in this context than either is to prey-predator systems. This is because plant herbivores and animal parasites are often invertebrate species that are typically smaller than their victims, generally cause lower lethality, and allow for further defensive responses by victims after consumption begins. Invertebrate herbivores can cause diverse RITRs in plants through various means, and animals also exhibit assorted RITRs to increased parasitism risk. This synthesis aims to broadly compare these two enemy-victim systems by highlighting the ways in which plants and animals perceive threat and respond with a range of induced victim trait responses that can provide pre-emptive defense against invertebrate enemies. We also review evidence that RITRs are costly in terms of reducing victim fitness or abundance, demonstrating how work with one victim-enemy system can inform the other with respect to the frequency and magnitude of RITRs and possible NCEs. We particularly highlight gaps in our knowledge about plant and animal host responses to their invertebrate enemies that may guide directions for future research. Comparing how potential plant and animal victims respond pre-emptively to the threat of consumption via RITRs will help to advance our understanding of natural enemy ecology and may have utility for pest and disease control.
... In response to damages caused by herbivorous arthropods, plants start emitting herbivory-induced plant volatiles (HIPVs) (Takabayashi and Shiojiri, 2019). When uninfested conspecific plants received HIPVs, they become more defensive against herbivores [for review see Karban et al. (2014) and Yoneya and Takabayashi (2016)]. Besides responding to HIPVs, plants also respond to volatiles from artificially damaged plants. ...
It is known that undamaged plants that have been exposed to volatiles from damaged con- or heterospecific plants become more resistant against herbivores. This is one of the plants’ induced resistant responses against herbivores. To test whether this response can be used for rice production, we conducted the following experiments over 2 years (2012 and 2013). Rice seedlings were first planted in the rice seedling bed for 2 weeks in early May. There, half of the rice seedlings were exposed to artificially damaged weed volatiles three times for 12 days (treated plants). Weeds were randomly collected from the areas that were >100 m away from the seedling bed and the rice paddy fields. The remaining seedlings were not exposed (control plants). In the middle of May, bunches (ca. three seedlings per bunch) were transplanted to the rice paddy field. In July, leaf damage was observed. The total number of leaves in the treated and control plants was not significantly different. In contrast, the total number of damaged leaves in the treated plants was significantly lower than that in the control plants. In September, rice grains were harvested. The average weight of a rice grain from the treated and control plants was not significantly different. However, the weight of grains per bunch of treated plants was significantly higher than that of control plants; this indicated a significant increase of the number of grains by 23% in 2012 and by 18% in 2013 in the treated plants compared to that in the control plants. The volatiles emitted from the weeds included monoterpenoids (40.4% in total), green leaf volatiles (46.5%), short-chain alcohols (5.3%), short-chain ketone (5.4%), short-chain acetate (0.5%), short-chain aldehyde (1.1%), and hydrocarbon (0.7%). These results suggest that exposure of volatiles from artificially damaged weeds to rice seedlings has the potential to increase rice production.
... Understanding the plant-insect interactions is of utmost importance for developing effective pest management approaches. Direct damage to the plant or exposure to volatiles results in induced resistance 8 . Induced defense responses compromise less plant fitness and are more durable as compared to constitutive defense mechanisms 9 . ...
Pink stem borer (PSB) causes considerable yield losses to maize. Plant–insect interactions have significant implications for sustainable pest management. The present study demonstrated that PSB feeding, mechanical wounding, a combination of mechanical wounding and PSB regurgitation and exogenous application of methyl jasmonate have induced phenolic compound mediated defense responses both at short term (within 2 days of treatment) and long term (in 15 days of treatment) in leaf and stalk tissues of maize. The quantification of two major defense related phenolic compounds namely p-Coumaric acid (p-CA) and ferulic acid (FA) was carried out through ultra-fast liquid chromatography (UFLC) at 2 and 15 days after imposing the above treatments. The p-CA content induced in leaf tissues of maize genotypes were intrinsically higher when challenged by PSB attack at V3 and V6 stages in short- and long-term responses. Higher p-CA content was observed in stalk tissues upon wounding and regurgitation in short- and long-term responses at V3 and V6 stages. Significant accumulation of FA content was also observed in leaf tissues in response to PSB feeding at V3 stage in long-term response while at V6 stage it was observed both in short- and long-term responses. In stalk tissues, methyl jasmonate induced higher FA content in short-term response at V3 stage. However, at V6 stage PSB feeding induced FA accumulation in the short-term while, wounding and regurgitation treatment-induced defense responses in the long-term. In general, the resistant (DMRE 63, CM 500) and moderately resistant genotypes (WNZ ExoticPool) accumulated significantly higher contents of p-CA and FA content than susceptible ones (CM 202, BML 6) in most of the cases. The study indicates that phenolic mediated defense responses in maize are induced by PSB attack followed by wounding and regurgitation compared to the other induced treatments. Furthermore, the study confirmed that induced defense responses vary with plant genotype, stage of crop growth, plant tissue and short and long-term responses. The results of the study suggested that the Phenolic acids i.e. p-CA and FA may contribute to maize resistance mechanisms in the maize-PSB interaction system.
... This population-specific effect was found in both of the sites where the experiments were conducted showing that cues vary geographically in their effectiveness and suggesting that sagebrush has a stronger response to local than to foreign dialects. The investigators also observed that the volatiles emitted by damaged sagebrush plants were characterized into two heritable chemotypes (dominated by either thujone or camphor) and that following leaf damage, individuals of the same chemotype communicated more effectively than individuals of differing chemotypes [96,97]. These findings seem to indicate that chemotypes can be considered examples of language differences based on relatedness, suggesting that language is shaped by the context in which it is used and in which it develops [84]. ...
The linguistic behavior of humans is usually considered the point of reference for studying the origin and evolution of language. As commonly defined, language is a form of communication between human beings; many have argued that it is unique to humans as there is no apparent equivalent for it in non-human organisms. How language is used as a means of communication is examined in this essay from a biological perspective positing that it is effectively and meaningfully used by non-human organisms and, more specifically, by plants. We set out to draw parallels between some aspects characterizing human language and the chemical communication that occurs between plants. The essay examines the similarities in ways of communicating linked to three properties of language: its combinatorial structure, meaning-making activities and the existence of dialects. In accordance with the findings of researchers who have demonstrated that plants do indeed communicate with one another and with organisms in their environment, the essay concludes with the appeal for an interdisciplinary approach conceptualizing a broader ecological definition of language and a constructive dialogue between the biological sciences and the humanities.
... Volatiles Volatiles from damaged neighbours increase resistance against herbivores across plant species [92] The parasitic plant fiveangled dodder (Cuscuta pentagona) exhibits directed growth toward volatiles of the potential plant host [93] Nonvolatile exudates Root-secreted JA is involved in neighbour detection and plant-plant communication in common wheat (Triticum aestivum) ...
To achieve ecological and reproductive success, plants need to mitigate a multitude of stressors. The stressors encountered by plants are highly dynamic but typically vary predictably due to seasonality or correlations among stressors. As plants face physiological and ecological constraints in responses to stress, it can be beneficial for plants to evolve the ability to incorporate predictable patterns of stress in their life histories. Here, we discuss how plants predict adverse conditions, which plant strategies integrate predictability of biotic stress, and how such strategies can evolve. We propose that plants commonly optimise responses to correlated sequences or combinations of herbivores and pathogens, and that the predictability of these patterns is a key factor governing plant strategies in dynamic environments.
... phytophagous insects in over 30 plant species, including agricultural crops and tree species (Heil & Karban, 2010;Karban et al., 2014), and is now recognized as an important (and potentially widespread) modulator of plant defensive responses and induced resistance. ...
Plant communication in response to insect herbivory has been increasingly studied, whereas that involving pathogen attack has received much less attention. We tested for communication between potato (Solanum tuberosum) plants in response to leaf infection by the fungal pathogen Sclerotinia sclerotiorum. To this end, we measured the total amount and composition of volatile organic compounds (VOCs) produced by control and infected emitter plants, as well as tested for induced resistance of receiver plants exposed to VOCs from emitters. We further tested for changes in the expression of defensive genes due to pathogen infection. Fungal infection did not significantly affect the total amount or composition of VOCs produced by emitter plants. Correspondingly, we found no evidence of higher resistance to the pathogen in receiver plants exposed to VOCs from infected emitters relative to control emitters. Molecular analyses indicated that pathogen infection drove a down‐regulation of genes coding for VOC precursors, potentially explaining the absence of pathogen effects on VOC emissions and thus of communication. Overall, these results indicate no evidence of airborne communication between potato plants in response to fungal infection and point at pathogen inhibition of VOC emissions as a likely explanation for this result.
1. Induced plant responses to herbivory are common and we have learned a lot about the mechanisms of induced resistance and their effects on herbivore performance. We know less about their effects on herbivore behavior and especially on spatial patterns of damage. 2. Theoretical models predict that induced responses can cause patterns of damage to become aggregated, random, or even. A recent model predicted that informed herbivore movement coupled with communication between plants would make damage more even within individual plants. We tested these predictions in the field using a specialist beetle (Trirhabda pilosa) that feeds on sagebrush (Artemisia tridentata). Both the beetle and the plant are well‐documented to respond to damage‐induced volatile cues. 3. Beetle larvae were more likely to move from damaged leaves and leaves that had been exposed to volatiles from nearby damaged leaves compared to undamaged control leaves. Previous lab results indicated that beetles were more likely to choose undamaged leaves compared to damaged leaves or those exposed to volatile cues of damage. 4. A comparison of damage patterns early in the season and after completion of beetle feeding revealed that variance in damage among branches decreased as the season progressed; i.e., damage became more evenly distributed among the branches within a plant. Larvae damaged many leaves on a plant but removed relatively little tissue from each leaf. 5. Herbivore movement and the spatial patterns of damage that it creates can be important in determining effects on plant fitness and other population processes. Dispersion of damage deserves more consideration in plant‐herbivore studies.
Herbivore-induced plant volatiles prime neighboring plants to respond more strongly to subsequent attacks. However, the key volatiles that trigger this state and their priming mechanisms remain largely unknown. The tea geometrid Ectropis obliqua is one of the most devastating leaf-feeding pests of tea plants. Here, plant–plant communication experiments demonstrated that volatiles emitted from tea plants infested by E. obliqua larvae triggered neighboring plants to release volatiles that repel E. obliqua adult, especially mated females. Volatile analyses revealed that the quantity of eight volatiles increased dramatically when plants were exposed to volatiles emitted by infested tea plants, including (Z)-3-hexenol, linalool, α-farnesene, β-Ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT).The results of behavioral bioassays demonstrated that β-Ocimene strongly repelled mated E. obliqua females. Individual volatile compound exposure experiments revealed that (Z)-3-hexenol, linalool, α-farnesene, and DMNT triggered the emission of β-Ocimene from tea plants. Chemical inhibition experiments demonstrated that the emission of β-Ocimene induced by (Z)-3-hexenol, linalool, α-farnesene, and DMNT was dependent on Ca²⁺ and JA signaling. These findings help us to understand how E. obliqua moths respond to volatiles emitted from tea plants and provide new insight into volatile-mediated plant–plant interactions. They have potential significance for the development of novel insect and pest control strategies in crops
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It is well established that plants emit, detect and respond to volatile organic compounds; however, knowledge on the ability of plants to detect and respond to volatiles emitted by non-plant organisms is limited. Recent studies indicated that plants detect insect-emitted volatiles that induce defence responses; however, the mechanisms underlying this detection and defence priming is unknown. Therefore, we explored if exposure to a main component of Plutella xylostella female sex pheromone namely (Z)-11-hexadecenal [(Z)-11-16:Ald] induced detectable early and late stage defence-related plant responses in Brassica nigra. Exposure to biologically relevant levels of vapourised (Z)-11-16:Ald released from a loaded septum induced a change in volatile emissions of receiver plants after herbivore attack and increased the leaf area consumed by P. xylostella larvae. Further experiments examining the effects of the (Z)-11-16:Ald on several stages of plant defence-related responses showed that exposure to 100 ppm of (Z)-11-16:Ald in liquid state induced depolarisation of the transmembrane potential (Vm), an increase in cytosolic calcium concentration [Ca2+]cyt, production of H2O2 and an increase in expression of reactive oxygen species (ROS)-mediated genes and ROS-scavenging enzyme activity. The results suggest that exposure to volatile (Z)-11-16:Ald increases the susceptibility of B. nigra to subsequent herbivory. This unexpected finding, suggest alternative ecological effects of detecting insect pheromone to those reported earlier. Experiments conducted in vitro showed that high doses of (Z)-11-16:Ald induced defence-related responses, but further experiments should assess how specific the response is to this particular aldehyde.
Fluxes of matter, energy, and information over space and time contribute to ecosystems’ functioning. The meta-ecosystem framework addresses the dynamics of ecosystems linked by these fluxes, however, to date, meta-ecosystem research focused solely on fluxes of energy and matter, neglecting information. This is problematic due to organisms’ varied responses to information, which influence local ecosystem dynamics and can alter spatial flows of energy and matter. Furthermore, information itself can move between ecosystems. Therefore, information should contribute to meta-ecosystem dynamics, such as stability and productivity. Specific subdisciplines of ecology currently consider different types of information (e.g., social and cultural information, natural and artificial light or sound, body condition, genotype, and phenotype). Yet neither the spatiotemporal distribution of information nor its perception are currently accounted for in general ecological theories. Here, we provide a roadmap to synthesize information and meta-ecosystem ecology. We begin by defining information in a meta-ecological context. We then review and identify challenges to be addressed in developing information meta-ecology. Finally, we present new hypotheses for how information could impact dynamics across scales of spatio-temporal and biological organization.
Since the early 1990s, ecologists and evolutionary biologists have aggregated primary research using meta-analytic methods to understand ecological and evolutionary phenomena. Meta-analyses can resolve long-standing disputes, dispel spurious claims, and generate new research questions. At their worst, however, meta-analysis publications are wolves in sheep's clothing: subjective with biased conclusions, hidden under coats of objective authority. Conclusions can be rendered unreliable by inappropriate statistical methods, problems with the methods used to select primary research, or problems within the primary research itself. Because of these risks, meta-analyses are increasingly conducted as part of systematic reviews, which use structured, transparent, and reproducible methods to collate and summarise evidence. For readers to determine whether the conclusions from a systematic review or meta-analysis should be trusted - and to be able to build upon the review - authors need to report what they did, why they did it, and what they found. Complete, transparent, and reproducible reporting is measured by 'reporting quality'. To assess perceptions and standards of reporting quality of systematic reviews and meta-analyses published in ecology and evolutionary biology, we surveyed 208 researchers with relevant experience (as authors, reviewers, or editors), and conducted detailed evaluations of 102 systematic review and meta-analysis papers published between 2010 and 2019. Reporting quality was far below optimal and approximately normally distributed. Measured reporting quality was lower than what the community perceived, particularly for the systematic review methods required to measure trustworthiness. The minority of assessed papers that referenced a guideline (~16%) showed substantially higher reporting quality than average, and surveyed researchers showed interest in using a reporting guideline to improve reporting quality. The leading guideline for improving reporting quality of systematic reviews is the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement. Here we unveil an extension of PRISMA to serve the meta-analysis community in ecology and evolutionary biology: PRISMA-EcoEvo (version 1.0). PRISMA-EcoEvo is a checklist of 27 main items that, when applicable, should be reported in systematic review and meta-analysis publications summarising primary research in ecology and evolutionary biology. In this explanation and elaboration document, we provide guidance for authors, reviewers, and editors, with explanations for each item on the checklist, including supplementary examples from published papers. Authors can consult this PRISMA-EcoEvo guideline both in the planning and writing stages of a systematic review and meta-analysis, to increase reporting quality of submitted manuscripts. Reviewers and editors can use the checklist to assess reporting quality in the manuscripts they review. Overall, PRISMA-EcoEvo is a resource for the ecology and evolutionary biology community to facilitate transparent and comprehensively reported systematic reviews and meta-analyses.
Polyploids often display a variety of phenotypic novelties when compared to their diploid progenitors, some of which may represent ecological advantages, especially regarding tolerance to biotic and abiotic factors. Plants cope with environmental factors by producing chemicals such as volatile organic compounds (VOCs) and specific amino acids (AAs). In potato, the third most important food crop in the world, gene introgression from diploid wild relative species into the genetic pool of the cultivated species (tetraploid) would be of great agronomical interest. The consequences of allopolyploidization on the potato VOCs and AAs profiles have not been yet analyzed. In this work, the effects of whole genome duplication on VOCs and AAs contents in leaves of potato allo- and autotetraploids and cultivated varieties were studied. The polyploids were obtained by chromosomal duplication of a genotype of the wild diploid species S. kurtzianum (autopolyploid model), and a diploid interspecific hybrid between the cultivated species S. tuberosum and S. kurtzianum (allopolyploid model). Almost all compounds levels varied greatly among these tetraploid lines; while all tetraploids showed higher contents of non-isoprenoids compounds than diploids, we found either increments or reductions in terpenes and AAs content. The results support the idea that genome duplication is a stochastic source of variability, which might be directly used for introgression in the 4x gene pool of the cultivated potato by sexual hybridization.
Abstract Plants respond to insect eggs with transcriptional changes, resulting in enhanced defence against hatching larvae. However, it is unknown whether phylogenetically distant plant species show conserved transcriptomic responses to insect eggs and subsequent larval feeding. We used Generally Applicable Gene set Enrichment (GAGE) on gene ontology terms to answer this question and analysed transcriptome data from Arabidopsis thaliana, wild tobacco (Nicotiana attenuata), bittersweet nightshade (Solanum dulcamara) and elm trees (Ulmus minor) infested by different insect species. The different plant–insect species combinations showed considerable overlap in their transcriptomic responses to both eggs and larval feeding. Within these conformable responses across the plant–insect combinations, the responses to eggs and feeding were largely analogous, and about one-fifth of these analogous responses were further enhanced when egg deposition preceded larval feeding. This conserved transcriptomic response to eggs and larval feeding comprised gene sets related to several phytohormones and to the phenylpropanoid biosynthesis pathway, of which specific branches were activated in different plant–insect combinations. Since insect eggs and larval feeding activate conserved sets of biological processes in different plant species, we conclude that plants with different lifestyles share common transcriptomic alarm responses to insect eggs, which likely enhance their defence against hatching larvae.
During herbivory, insects recognize their host plant based on specific chemical cues, whereas the plants induce various chemical and morphological defense responses to resist this attack. However, the seemingly bidirectional insect–plant interaction involves various confounding aspects that influence the performance and fitness of the two participants. These interactions are often mediated by associated microbiota, competitors, predators, and parasitoids that interact in either obligate or facultative manner. Insect endosymbionts play a crucial role in the perception, nutrition, metabolism as well as reproduction of their host, which together determine its survival and fitness on the plant. Endosymbionts also help their host to overcome plant defenses by detoxifying plant metabolites. On the contrary, plant-associated microbes contribute in induced systemic plant resistance by enhancing chemical and morphological defense. These interactions determine the association of insect and plant, not only with the high trophic levels but also with the ecosystem as a whole. Thus, insect–plant interaction is a multilayered relationship extending to various micro- and macro-organisms associated either temporally or spatially. All these relationships may be considered to obtain a wholesome perspective of the natural environment.
Plants can adjust defence strategies in response to signals from neighbouring plants attacked by aboveground herbivores. Whether similar responses exist to belowground herbivory remains less studied, particularly regarding the spatiotemporal dynamics of such belowground signalling. We grew the grass Agrostis stolonifera with or without root-feeding nematodes (Meloidogyne minor). Leachates were extracted at different distances from these plants and at different times after inoculation. The leachates were applied to receiver A. stolonifera plants, of which root, shoot, and total biomass, root/shoot ratio, shoot height, shoot branch number, maximum rooting depth and root number were measured 3 weeks after leachate application. Receiver plants allocated significantly more biomass to roots when treated with leachates from nematode-inoculated plants at early infection stages. However, receiver plants’ root/shoot ratio was similar when receiving leachates collected at later stages from nematode-infected or control plants. Overall, early-collected leachates reduced growth of receiver plants significantly. Plants recently infected by root-feeding nematodes can thus induce increased root proliferation of neighbouring plants through root-derived compounds. Possible explanations for this response include a better tolerance of anticipated root damage by nematodes or the ability to grow roots away from the nematode-infected soil. Further investigations are still needed to identify the exact mechanisms.
In the process of avoiding predation, prey are faced with potentially fitness‐compromising trade‐offs that have implications for their survival and reproduction. The nature and strength of these non‐consumptive effects at the population level can be equivalent, or even greater, than consumptive effects. Many prey species have evolved defence mechanisms that are induced by predation risk. These inducible defences can be morphological or behavioural in nature. Extensive research has detected these defences in predator–prey communities across freshwater, marine and terrestrial ecosystems. Among this vast research however, an influential portion of these systems has not been widely considered. Humans inhabit a level in trophic systems above apex predators. In that position, humans have been referred to as a hyperkeystone or super predator species as they have shown a capacity to consume animals at rates many times higher than any other non‐human species. However, the extent to which humans induce adaptive defences in animals is not as clear. Systems involving large mammals may be particularly well‐suited for the study of human‐induced defences given that these species have been disproportionately exploited (for food and competition) over evolutionary time by humans. To begin this process we first had to examine the context in which large mammals could adaptively evolve inducible defences in relation to human lethality. With the plausibility of these conditions satisfied, we then conducted an extensive review to document the inducible defences that have been detected in large mammals. All of the 187 studies reviewed documented the behavioural plasticity of large mammals to human lethality. No morphological adaptive defences were detected. However, the extent to which the observed behavioural plasticity of large mammals is representative of adaptive inducible defences remains unclear because the fitness trade‐offs (i.e. costs), an integral condition for inducible defences to evolve, were implied rather than quantified among close to 92% of this research. We make recommendations for renewed ingenuity in the development of field experiments that can quantify these costs and discuss the implications of human lethality on the ecology, conservation and management of large mammals. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.
Volatile compounds released by different plant species are involved in a vast array of adaptive and physiological functions including attraction of pollinators, seed dispersers, and natural enemies, defense against herbivorous insects, predators/parasitoids and microbial attack, and as communication signals in plant-plant and plant-microbe interactions. Monitoring changes in emission patterns of these compounds over time may represent a potential approach for early detection and solving many agricultural problems in the field. In this chapter we will highlight the potentials of these compounds as sustainable solutions to improve crop growth and production, exploring their antimicrobial, herbicidal, resistance priming, allelopathic, plant growth promoting/suppressing effects, and their applications in smart agriculture practices.
The ability of many animals to recognize kin has allowed them to evolve diverse cooperative behaviours; such ability is less well studied for plants. Many plants, including Artemisia tridentata, have been found to respond to volatile cues emitted by experimentally wounded neighbours to increase levels of resistance to herbivory. We report that this communication was more effective among A. tridentata plants that were more closely related based on microsatellite markers. Plants in the field that received cues from experimentally clipped close relatives experienced less leaf herbivory over the growing season than those that received cues from clipped neighbours that were more distantly related. These results indicate that plants can respond differently to cues from kin, making it less likely that emitters will aid strangers and making it more likely that receivers will respond to cues from relatives. More effective defence adds to a growing list of favourable consequences of kin recognition for plants.
cis-Jasmone, or (Z)-jasmone, is well known as a component of plant volatiles, and its release can be induced by damage, for example during insect
herbivory. Using the olfactory system of the lettuce aphid to investigate volatiles from plants avoided by this insect, (Z)-jasmone was found to be electrophysiologically active and also to be repellent in laboratory choice tests. In field studies,
repellency from traps was demonstrated for the damson-hop aphid, and with cereal aphids numbers were reduced in plots of winter
wheat treated with (Z)-jasmone. In contrast, attractant activity was found in laboratory and wind tunnel tests for insects acting antagonistically
to aphids, namely the seven-spot ladybird and an aphid parasitoid. When applied in the vapor phase to intact bean plants,
(Z)-jasmone induced the production of volatile compounds, including the monoterpene (E)-β-ocimene, which affect plant defense, for example by stimulating the activity of parasitic insects. These plants were more
attractive to the aphid parasitoid in the wind tunnel when tested 48 h after exposure to (Z)-jasmone had ceased. This possible signaling role of (Z)-jasmone is qualitatively different from that of the biosynthetically related methyl jasmonate and gives a long-lasting effect
after removal of the stimulus. Differential display was used to compare mRNA populations in bean leaves exposed to the vapor
of (Z)-jasmone and methyl jasmonate. One differentially displayed fragment was cloned and shown by Northern blotting to be up-regulated
in leaf tissue by (Z)-jasmone. This sequence was identified by homology as being derived from a gene encoding an α-tubulin isoform.
The effects of defoliation of alder (Alnus glutinosa) on subsequent herbivory by alder leaf beetle (Agelastica alni) were studied in ten alder stands in northern Germany. At each site, one tree was manually defoliated (c. 20% of total foliage) to simulate herbivory. Subsequent damage by A. alni was assessed on ten alders at each site on six different dates from May to September 1994. After defoliation, herbivory by A. alni increased with distance from the defoliated tree. Laboratory experiments supported the field results. Not only leaf damage in the field, but also the extent of leaf consumption in laboratory feeding-preference tests and the number of eggs oviposited per leaf in another laboratory test were positively correlated with distance from the defoliated tree. Resistance was therefore induced not only in defoliated alders, but also in their undamaged neighbours. Consequently, defoliation of alders may trigger interplant resistance transfer, and therefore reduce herbivory in whole alder stands.
Plants are capable of acquiring information from other plants, but are they able to send signals and communicate with them?
Evolutionary biologists define biological communication as information transmission that is fashioned or maintained by natural
selection and signals as traits whose value to the signaler is that they convey information to receivers. Plants, then, can
be said to communicate if the signaling plant derives a fitness benefit from conveying information to other plants. Examples
for interplant communication that fit these definitions potentially include territorial root communications, self/non-self
recognition between roots and associated with self-incompatibility, volatile signals that induce defenses against herbivores,
signals from ovules to mother plants, signals associated with root graft formation, and male to female signals during pollen
competition. Natural selection would favor signals that are costly to the signaler and therefore are likely to convey reliable
information because they cannot be easily faked. Toxins in low concentrations may commonly act as signals between plants rather
than as inhibitory allelochemicals. This explains why toxic concentrations of plant allelochemicals are rarely found in natural
coevolved systems.
Populations of grasses exposed to grazing by vertebrates often exhibit reduced stature, increased tillering, reduced flowering,
and other morphological differences which distinguish them from ungrazed populations. These differences frequently are interpreted
as an adaptive response that reduces grazing damage; however, there are few experimental tests of this hypothesis. This paper
describes a field experiment designed to determine whether morphological variation among genotypes of the grass Bouteloua gracilis is related to variation in their responses to grazing. Eleven genotypes differing in morphological and reproductive characters
were transplanted into a shortgrass steppe community near Fort Collins, Colorado. Replicates of each genotype were subjected
to clipping treatments intended to realistically simulate three grazing intensities. After two growing seasons, different
genotypes still maintained significant differences in a wide range of morphological and demographic characters. However, there
were few significant effects of grazing treatment, and no significant genotype×treatment interactions. These results suggest
that for B. gracilis clipped in simulation of natural grazing, defoliation has few short-term effects on fitness components, and intrapopulation
morphological variation has few consequences for defoliation resistance.
The possibility of communication between plants was proposed nearly 20 years ago, although previous demonstrations have suffered from methodological problems and have not been widely accepted. Here we report the first rigorous, experimental evidence demonstrating that undamaged plants respond to cues released by neighbors to induce higher levels of resistance against herbivores in nature. Sagebrush plants that were clipped in the field released a pulse of an epimer of methyl jasmonate that has been shown to be a volatile signal capable of inducing resistance in wild tobacco. Wild tobacco plants with clipped sagebrush neighbors had increased levels of the putative defensive oxidative enzyme, polyphenol oxidase, relative to control tobacco plants with unclipped sagebrush neighbors. Tobacco plants near clipped sagebrush experienced greatly reduced levels of leaf damage by grasshoppers and cutworms during three field seasons compared to unclipped controls. This result was not caused by an altered light regime experienced by tobacco near clipped neighbors. Barriers to soil contact between tobacco and sagebrush did not reduce the difference in leaf damage although barriers that blocked air contact negated the effect.
Meta-analysis provides formal statistical techniques for summarizing the results of independent experiments and is increasingly being used in ecology. The response ratio (the ratio of mean outcome in the experimental group to that in the control group) and closely related measures of proportionate change are often used as measures of effect magnitude in ecology. Using these metrics for meta-analysis requires knowledge of their statistical properties, but these have not been previously derived. The authors give the approximate sampling distribution of the log response ratio, discuss why it is a particularly useful metric for many applications in ecology, and demonstrate how to use it in meta-analysis. The meta-analysis of response-ratio data is illustrated using experimental data on the effects of increased atmospheric CO{sub 2} on plant biomass responses.
Paths of water flow in trees and shrubs of different sizes and chorotypes were investigated with injected dyes. Aged shrubs possessed a sectorial ascent. Young specimens of these species showed a sectorial turning into a ring ascent. Species with large and tall crowns showed either a spiral pattern or sectorial straight pattern. Since independence of branches or trunk segments is characteristic of shrubs, it is suggested that woody species exhibiting a sectorial pattern of water movement should be considered chamaephytes.
We develop fast algorithms for estimation of generalized linear models with convex penalties. The models include linear regression, two-class logistic regression, and multi- nomial regression problems while the penalties include âÂÂ_1 (the lasso), âÂÂ_2 (ridge regression) and mixtures of the two (the elastic net). The algorithms use cyclical coordinate descent, computed along a regularization path. The methods can handle large problems and can also deal efficiently with sparse features. In comparative timings we find that the new algorithms are considerably faster than competing methods.
Plants respond to attack by herbivores or pathogens with the release of volatile organic compounds. Neighbouring plants can receive these volatiles and consecutively induce their own defence arsenal. This 'plant communication', however, appears counterintuitive when it benefits independent and genetically unrelated receivers, which may compete with the emitter. As a solution to this problem, a role for volatile compounds in within-plant signalling has been predicted. We used wild-type lima bean (Phaseolus lunatus) to quantify under field conditions the distances over which volatile signals move, and thereby determine whether these cues will mainly trigger resistance in other parts of the same plant or in independent plants. Independent receiver plants exhibited airborne resistance to herbivores or pathogens at maximum distances of 50 cm from a resistance-expressing emitter. In undisturbed clusters of lima bean, over 80 per cent of all leaves that were located around a single leaf at this distance were other leaves of the same plant, whereas this percentage dropped below 50 per cent at larger distances. Under natural conditions, resistance-inducing volatiles of lima bean move over distances at which most leaves that can receive the signal still belong to the same plant.
In this paper we present the R package deSolve to solve initial value problems (IVP) written as ordinary differential equations (ODE), differential algebraic equations (DAE) of index 0 or 1 and partial differential equations (PDE), the latter solved using the method of lines approach. The differential equations can be represented in R code or as compiled code. In the latter case, R is used as a tool to trigger the integration and post-process the results, which facilitates model development and application, whilst the compiled code significantly increases simulation speed. The methods implemented are efficient, robust, and well documented public-domain Fortran routines. They include four integrators from the ODEPACK package (LSODE, LSODES, LSODA, LSODAR), DVODE and DASPK2.0. In addition, a suite of Runge-Kutta integrators and special-purpose solvers to efficiently integrate 1-, 2- and 3-dimensional partial differential equations are available. The routines solve both stiff and non-stiff systems, and include many options, e.g., to deal in an efficient way with the sparsity of the Jacobian matrix, or finding the root of equations. In this article, our objectives are threefold: (1) to demonstrate the potential of using R for dynamic modeling, (2) to highlight typical uses of the different methods implemented and (3) to compare the performance of models specified in R code and in compiled code for a number of test cases. These comparisons demonstrate that, if the use of loops is avoided, R code can efficiently integrate problems comprising several thousands of state variables. Nevertheless, the same problem may be solved from 2 to more than 50 times faster by using compiled code compared to an implementation using only R code. Still, amongst the benefits of R are a more flexible and interactive implementation, better readability of the code, and access to R’s high-level procedures. deSolve is the successor of package odesolve which will be deprecated in the future; it is free software and distributed under the GNU General Public License, as part of the R software project.
When infested by herbivorous mites, cotton seedlings produce volatile cues that elicit attraction of predatory mites. Experiments were carried out to elucidate how downwinduninfested conspecific seedlings are affected by these volatiles. It was found that the rate of oviposition of herbivorous mites was reduced on seedlings exposed to volatiles from infested seedlings. Moreover, predatory mites were attracted by exposeduninfested seedlings. These results strongly suggest that uninfested plants are better protected against herbivore attack when exposed to airborne chemicals released by their infested neighbours.
When maize plants, Zea mays L., are mechanically damaged and the damaged sites are treated with caterpillar regurgitant, the plants will release a specific blend of volatiles. It is known that these volatiles can be attractive to natural enemies of herbivores. We hypothesise that the plant volatiles constitute part of the induced plant defence and that herbivores will be affected by the odours as well. In laboratory and semi-field studies this hypothesis was tested for the aphid Rhopalosiphum maidis (Fitch) (Rhynchota, Sternorrhyncha, Aphididae).
In spite of initial doubts about the reality of 'talking trees', plant resistance expression mediated by volatile compounds that come from neighboring plants is now well described. Airborne signals usually improve the resistance of the receiver, but without obvious benefits for the emitter, thus making the evolutionary explanation of this phenomenon problematic. Here, we discuss four possible non-exclusive explanations involving the role of volatiles: in direct defense, as within-plant signals, as traits that synergistically interact with other defenses, and as cues among kin. Unfortunately, there is a lack of knowledge on the fitness consequences of plant communication for both emitter and receiver. This information is crucial to understanding the ecology and evolution of plant communication via airborne cues.
Corn seedlings release large amounts of terpenoid volatiles after they have been fed upon by caterpillars. Artificially damaged seedlings do not release these volatiles in significant amounts unless oral secretions from the caterpillars are applied to the damaged sites. Undamaged leaves, whether or not they are treated with oral secretions, do not release detectable amounts of the terpenoids. Females of the parasitic wasp Cotesia marginiventris (Cresson) learn to take advantage of those plant-produced volatiles to locate hosts when exposed to these volatiles in association with hosts or host by-products. The terpenoids may be produced in defense against herbivores but may also serve a secondary function in attracting the natural enemies of these herbivores.
Herbivore feeding activates plant defenses at the site of damage as well as systemically. Systemic defenses can be induced internally by signals transported via phloem or xylem, or externally transmitted by volatiles emitted from the damaged tissues. We investigated the role of herbivore-induced plant volatiles (HIPVs) in activating a defense response between branches in blueberry plants. Blueberries are perennial shrubs that grow by initiating adventitious shoots from a basal crown, which produce new lateral branches. This type of growth constrains vascular connections between shoots and branches within plants. While we found that leaves within a branch were highly connected, vascular connectivity was limited between branches within shoots and absent between branches from different shoots. Larval feeding by gypsy moth, exogenous methyl jasmonate, and mechanical damage differentially induced volatile emissions in blueberry plants, and there was a positive correlation between amount of insect damage and volatile emission rates. Herbivore damage did not affect systemic defense induction when we isolated systemic branches from external exposure to HIPVs. Thus, internal signals were not capable of triggering systemic defenses among branches. However, exposure of branches to HIPVs from an adjacent branch decreased larval consumption by 70% compared to those exposed to volatiles from undamaged branches. This reduction in leaf consumption did not result in decreased volatile emissions, indicating that leaves became more responsive to herbivory (or "primed") after being exposed to HIPVs. Chemical profiles of leaves damaged by gypsy moth caterpillars, exposed to HIPVs, or non-damaged controls revealed that HIPV-exposed leaves had greater chemical similarities to damaged leaves than to control leaves. Insect-damaged leaves and young HIPV-exposed leaves had higher amounts of endogenous cis-jasmonic acid compared to undamaged and non-exposed leaves, respectively. Our results show that exposure to HIPVs triggered systemic induction of direct defenses against gypsy moth and primed volatile emissions, which can be an indirect defense. Blueberry plants appear to rely on HIPVs as external signals for inter-branch communication.
Volatile phytohormones or other chemicals can affect processes in distal plant parts but may also influence neighboring plants, and thereby function allelopathically. While this hypothesis has been widely discussed, rigorous tests are lacking. Transgenic plants, silenced in the production of an emitted chemical, are ideal tools to test the hypothesis that the release of a chemical can negatively influence the growth of neighbors (allelopathy). We used isogenic wild type (WT) and genetically transformed plants that lacked the ability to produce ethylene (ir-aco), as both "emitters" and "receivers" of this volatile phytohormone in experiments where receiver plants were only exposed to the headspace of WT or ir-aco emitters, in order to evaluate if natural ethylene releases can function allelopathically. Root growth (a proxy of plant fitness) of WT receivers correlated negatively with the number of WT emitters and headspace ethylene concentrations. Reducing ethylene concentrations in the headspace with the ethylene scrubber, KMnO(4), and using ir-aco seedlings as emitters restored root growth of WT receiver seedlings. 1-Aminocyclopropane-1-carboxylic acid (ethylene biosynthesis substrate) supplementation to WT but not ir-aco emitters inhibited root growth of ir-aco, but not WT receivers, suggesting increased sensitivity to exogenous ethylene of ir-aco seedlings. We conclude that plants genetically silenced in the production of a putative allelochemical are useful in determining if the emitted chemical functions allelopathically.
In response to herbivore damage, several plant species emit volatiles that attract natural predators of the attacking herbivores. Using spider mites (Tetranychus urticae) and predatory mites (Phytoseiulus persimilis), it has been shown that not only the attacked plant but also neighbouring plants are affected, becoming more attractive to predatory mites and less susceptible to spider mites. The mechanism involved in such interactions, however, remains elusive. Here we show that uninfested lima bean leaves activate five separate defence genes when exposed to volatiles from conspecific leaves infested with T. urticae, but not when exposed to volatiles from artificially wounded leaves. The expression pattern of these genes is similar to that produced by exposure to jasmonic acid. At least three terpenoids in the volatiles are responsible for this gene activation; they are released in response to herbivory but not artificial wounding. Expression of these genes requires calcium influx and protein phosphorylation/dephosphorylation.
Herbivore attack is known to increase the emission of volatiles, which attract predators to herbivore-damaged plants in the
laboratory and agricultural systems. We quantified volatile emissions fromNicotiana attenuata plants growing in natural populations during attack by three species of leaf-feeding herbivores and mimicked the release
of five commonly emitted volatiles individually. Three compounds (cis-3-hexen-1-ol, linalool, and cis-α-bergamotene) increased egg predation rates by a generalist predator; linalool and the complete blend decreased lepidopteran
oviposition rates. As a consequence, a plant could reduce the number of herbivores by more than 90% by releasing volatiles.
These results confirm that indirect defenses can operate in nature.
Plants respond to insect herbivory by synthesizing and releasing complex blends of volatile compounds, which provide important host-location cues for insects that are natural enemies of herbivores. The effects of these volatile blends on herbivore behaviour have been investigated to only a limited extent, in part because of the assumption that herbivore-induced volatile emissions occur mainly during the light phase of the photoperiod. Because many moths-whose larvae are some of the most important insect herbivores-are nocturnal, herbivore-induced plant volatiles have not hitherto been considered to be temporally available as host-location cues for ovipositing females. Here we present chemical and behavioural assays showing that tobacco plants (Nicotiana tabacum) release herbivore-induced volatiles during both night and day. Moreover, several volatile compounds are released exclusively at night and are highly repellent to female moths (Heliothis virescens). The demonstration that tobacco plants release temporally different volatile blends and that lepidopteran herbivores use induced plant signals released during the dark phase to choose sites for oviposition adds a new dimension to our understanding of the role of chemical cues in mediating tritrophic interactions.
Many plants invest carbon to form isoprene. The role of isoprene in plants is unclear, but many experiments showed that isoprene may have a role in protecting plants from thermal damage. A more general antioxidant action has been recently hypothesized on the basis of the protection offered by exogenous isoprene in nonemitting plants exposed to acute ozone doses. We inhibited the synthesis of endogenous isoprene by feeding fosmidomycin and observed that Phragmites australis leaves became more sensitive to ozone than those leaves forming isoprene. Photosynthesis, stomatal conductance, and fluorescence parameters were significantly affected by ozone only in leaves on which isoprene was not formed. The protective effect of isoprene was more evident when the leaves were exposed for a long time (8 h) to relatively low (100 nL L(-1)) ozone levels than when the exposure was short and acute (3 h at 300 nL L(-1)). Isoprene quenched the amount of H(2)O(2) formed in leaves and reduced lipid peroxidation of cellular membranes caused by ozone. These results indicate that isoprene may exert its protective action at the membrane level, although a similar effect could be obtained if isoprene reacted with ozone before forming active oxygen species. Irrespective of the mechanism, our results suggest that endogenous isoprene has an important antioxidant role in plants.
R package for Data Analysis using multilevel/hierarchical model
Red alder (Alnus rubra) and Sitka willow (Salix sitchensis) trees subjected to attack by tent caterpillars (Malacosoma californicum pluviale) or webworms (Hyphantria cunea), respectively, exhibited a change in foliage quality such that bioassay insects fed leaves from the attacked trees grew more slowly than those fed leaves from unattacked control trees. In contrast, bioassay of leaf quality of S. sitchensis, subjected to attack by tent caterpillars, indicated that altered leaf quality had been induced not only in the attacked trees but also in nearby unattacked control trees. This suggests that S. sitchensis is sensitive to and can respond to signals generated by attacked trees or the caterpillars. Since no evidence was found for root connections between attacked and control willows, the message may be transferred through airborne pheromonal substances.
Plants 'forage' for light in plant canopies using a variety of photosensory systems. Far-red radiation (FR) reflected by neighbours is an early signal of competition that elicits anticipatory shade-avoidance responses. In Arabidopsis and cucumber, perception of reflected FR requires phytochrome B. Horizontal blue (B) light gradients also guide plant shoots to canopy gaps in patchy vegetation, and these B light signals are perceived by specific photoreceptors. When plants are shaded by neighbours they undergo extensive reprogramming of their morphological development. Although phytochromes and B light receptors are certainly involved in these responses to shading, other sensory systems probably play important roles in the field. Recent studies of plant-plant signalling are unveiling a paradigm of sensory diversity and sophistication, which has important implications for understanding the functioning of plant populations and communities.
In many plants, defence systems against herbivores are induced through the octadecanoid pathway,, which may also be involved in recruiting natural enemies of herbivores. This pathway can beinduced by treating plants with jasmonic acid or by natural herbivory, and increases resistance against herbivorous insects intomato plants, in part by causing production of toxic and antinutritive proteinase inhibitors and oxidative enzymes. Herbivore-infested tomato plants release increased amounts of volatiles and attract natural enemies of the herbivores, as do other plants. The octadecanoid pathway may regulate production of these volatiles, which attract host-seeking parasitic wasps,. However, plant resistance compounds can adversely affect parasitoids as well as herbivores. It is unclear whether the combination of increased retention and/or attractiveness of parasitic wasps to induced plants and the adverse effects of plant defence compounds on both caterpillars and parasitoids results in a net increase in parasitization of herbivores feeding on induced plants.Here I show that inducing plants with jasmonic acid increases parasitism of caterpillar pests in an agricultural field twofold. Thus, elicitors of plant resistance may become useful in agriculture.
Reviews the evidence that rapidly induced chemical changes in damaged leaves for example, after attack by insects, 1) significantly influence the population dynamics of herbivorous insects and mites in the field, and 2) significantly reduce damage to plants by such herbivores. We also review the evidence for 'talking trees', ie following experimental damage to tree foliage, chemical changes are induced in adjacent undamaged trees that mirror those in damaged trees. There is only one field study demonstrating significant effects of rapidly induced defenses on insect population dynamics. Evidence that foliage damage is overdispersed on tree leaves, interpreted as possibly caused by induced defenses, is equivocal and subject to several plausible alternative explanations. Two experiments (Baldwin and Schultz 1983; Rhoades 1983) purport to show intertree communication after experimental damage. One of these studies is statistically flowed (Baldwin and Schultz 1983); results from Rhoades' study may be due to and infectious disease transmitted between caterpillars and not to inter-tree communication. We report on a field experiment in which we look for reductions in herbivore damage levels in birch Betula pubescens saplings following experimental defoliations of 5% and 25%. We found no evidence either that experimental defoliation reduces subsequent levels of herbivore attack or that trees communicate.-from Authors
Summary1. Plants commonly attract predatory and parasitoid organisms, and may thereby increase resistance against antagonistic herbivores. Mechanisms for indirect resistance include the provision of resources (e.g. food and shelter) for predators as well as the provision of information (e.g. herbivore-induce volatiles) on the location of hosts and prey that can facilitate the foraging behaviour of natural enemies of herbivores.2. These ecologically divergent mechanisms for attracting bodyguards should also differ fundamentally in their evolution, particularly in how herbivores and their predators select on plant resistance traits. However, these different strategies are typically lumped together in theoretical discussions of indirect defences.3. Here we highlight the fundamental differences between resource-mediated and information-mediated indirect resistance and discuss the relative evolutionary impacts of the interacting organisms as agents of natural selection in shaping indirect defence traits of plants.4. We review clear evidence for a defensive function of resource-mediated indirect resistance, and recognize a significant lack of evidence for an adaptive function of information-mediated traits. A comparison of the underlying factors driving coevolution in each category of indirect defences, suggests that information-mediated indirect resistance is less likely to be subject to coevolution between plants and the third trophic level.
We conducted a meta-analysis of 68 studies published between 1982 and 2000 in which the responses of woody plants to natural or simulated herbivore damage and/or insect herbivore performance on control and damaged plants were measured. Cumulative meta-analyses revealed dramatic temporal changes in the magnitude and direction of the plant and herbivore responses reported during the last two decades. Studies conducted in the 1980s reported increase in phenolic concentrations, reduction in nutrient concentrations and negative effect on herbivore performance, consistently with the idea of induced resistance. In contrast, in the early 1990s when the idea that some types of plant damage may result in induced susceptibility was generally accepted, studies reported non-significant results or induced susceptibility, and smaller effects on herbivores. The above changes may reflect paradigm shifts in the theory of induced defenses and/or the differences between study systems used in the early and the more recent studies. Overall, plant growth and carbohydrate concentrations were reduced in damaged plants despite enhanced photosynthetic rates. Damage increased the concentrations of carbon and phenolics, while terpene concentrations tended to decrease after damage; changes in nutrient concentrations after damage varied according to nutrient mobility, inherent plant growth rate, ontogenetic stage and plant type (deciduous/evergreen). Early season damage caused more pronounced changes in plants than late season damage, which is in accordance with the assumption that vigorously growing foliage has a greater capacity to respond to damage. Insect growth rate and female pupal weight decreased on previously damaged plants, while herbivore survival, consumption and male pupal weight were not significantly affected. The magnitude and direction of herbivore responses depended on the type of plant, the type of damage, the time interval between the damage and insect feeding (rapid/delayed induced resistance), and the timing of the damage.
Previous experiments showed that wild tobacco plants with experimentally clipped sagebrush neighbors experienced less damage by grasshoppers than tobacco plants with unclipped sagebrush neighbors. This result could have been caused by grasshoppers preferring not to feed near clipped sagebrush. This hypothesis was tested in field choice experiments using six grasshopper species feeding on an unresponsive and uniformly palatable food. When offered food that was either close to clipped sagebrush or close to unclipped sagebrush, grasshoppers showed no preference. When offered food that was either close to sagebrush (3 cm) or far from sagebrush (30 cm), grasshoppers preferred to feed far from sagebrush. However, this preference was similar whether or not the sagebrush had been clipped. Avoidance of feeding near clipped sagebrush, independent of changes in tobacco, was not found to contribute to our earlier result that tobacco near clipped sagebrush suffered less herbivory than tobacco near unclipped sagebrush.
We assayed the quality of red alder trees for western tent caterpillar growth and survival to test the hypothesis that caterpillar feeding stimulates plant defenses in both attacked and adjacent trees. Three years of high tent caterpillar density were necessary before deterioration in foliage quality occurred, and even then only foliage from trees which were almost completely defoliated in the current year reduced the growth of caterpillars. Both tent size and mean egg mass size increased after the second year of high density which indicates that good conditions still existed for tent caterpillars after 2 to 3 years of heavy feeding.
Egg masses which were moved to areas where trees had not recently supported a high caterpillar population produced significantly smaller tents than endemic controls in 1982. Therefore the small tent and egg mass size of the high density population in 1982 was inherent to the insects rather than modified by food source. In 1983 the tents from introduced egg masses were as large as naturally occurring tents.
If lightly attacked trees within areas of high caterpillar density are better defended against insect attack, this does not show up in their ability to support caterpillar growth and survival. We found no evidence to support the hypothesis that trees communicate insect attack and stimulate chemical defenses in adjacent trees. Reduced foliage quality seems to be a result of extensive insect damage rather than a defense against insect damage.
During the last several decades, traditional approaches to host-plant resistance have shown that a number of plant natural products act as constitutive bases of resistance against insects. More recently, it has been realized that plant resistance against insects also consists of inducible and dynamic elements triggered by insect-feeding damage. These inducible elements of resistance have been found to be both plant enzymes and their end-products. The potential use of such enzymes and their products as bases of resistance against insects is discussed.
Plants ‘forage’ for light in plant canopies using a variety of photosensory systems. Far-red radiation (FR) reflected by neighbours is an early signal of competition that elicits anticipatory shade-avoidance responses. In Arabidopsis and cucumber, perception of reflected FR requires phytochrome B. Horizontal blue (B) light gradients also guide plant shoots to canopy gaps in patchy vegetation, and these B light signals are perceived by specific photoreceptors. When plants are shaded by neighbours they undergo extensive reprogramming of their morphological development. Although phytochromes and B light receptors are certainly involved in these responses to shading, other sensory systems probably play important roles in the field. Recent studies of plant–plant signalling are unveiling a paradigm of sensory diversity and sophistication, which has important implications for understanding the functioning of plant populations and communities.
Herbivore damage is generally detrimental to plant fitness, and the evolu- tionary response of plant populations to damage can involve either increased resistance or increased tolerance. While characters that contribute to resistance, such as secondary chem- icals and trichomes, are relatively well understood, characters that contribute to a plant's ability to tolerate damage have received much less attention. Using Helianthus annuus (wild sunflower) and simulated damage of Haplorhynchites aeneus (head-clipping weevil) as a model system, we examined morphological characters and developmental processes that contribute to compensatory ability. We performed a factorial experiment that included three levels of damage (none, the first two, or the first four inflorescences were clipped with scissors) and eight sires each mated to four dams. We found that plants compensated fully for simulated head-clipper damage and that there was no variation among plant families in compensatory ability: seed production and mean seed mass did not vary among treat- ments, and sire X treatment interactions were not significant. Plants used four mechanisms to compensate for damage: (1) Clipped plants produced significantly more inflorescences than unclipped plants. Plants produced these additional inflorescences on higher order branches at the end of the flowering season. (2) Clipped plants filled significantly more seeds in their remaining heads than did unclipped plants. (3) Clipped plants, because they effectively flowered later than unclipped plants, were less susceptible to damage by seed- feeding herbivores other than Haplorhynchites. (4) In later heads, seed size was greater on clipped plants, which allowed mean seed size to be maintained in clipped plants. Although there was genetic variation among the families used in this experiment for most of the characters associated with compensation for damage (seed number, mean seed size, mean flowering date, length of the flowering period, and branching morphology), in analyses of these characters, no sire X treatment interactions were significant indicating that all of the families relied on similar mechanisms to compensate for damage.
Chemical information conveyance between organisms has been well established for a wide range of organisms including protozoa, invertebrates, vertebrates and plant-parasitic plants. During the past 20 years, various studies have addressed whether chemical information conveyance also occurs between damaged and undamaged plants and many interesting pieces of evidence have been presented. To date, this research field has been restricted to the question whether and how plants (in general) are involved in plant-to-plant communication. However, apart from mechanistic questions, evolutionary questions should be addressed asking why plants do (or do not) exploit their neighbour's information and whether their strategy is affected by e.g. environmental conditions or previous experience. Recent progress in the field of chemical information conveyance between damaged and undamaged plants warrants an intensified study of this exciting topic in chemical ecology.
1. Resource delivery within plants depends on supply pathways. Some species have relatively constrained (sectored) vascular connections, while others have relatively unconstrained (integrated) vascular connections.
2. In this study, patterns of vascular hydraulic sectoriality, anatomy and ecological tolerance were examined for 18 Northern Hemisphere temperate woody species growing at Arnold Arboretum, Jamaica Plain, MA, USA. A hydraulic technique was used to measure axial and tangential conductivity on branch segments. From a ratio of these values, a sectoriality index was calculated.
3. Species that were more hydraulically sectored had greater vessel size, variation in vessel area and tangential nearest-neighbour distance, as well as lower vessel density, than did integrated species.
4. Ecologically, higher tolerance to drought and wind was correlated with being sectored, while higher tolerance to flood and shade was correlated with being integrated.
5. These results suggest that sectored species should be especially prominent in xeric environments where sectoriality may reduce embolism spread by minimizing vessel-to-vessel contact and pitting, and integrated species should be especially prominent when resources are spatially patchy or heterogeneous.
Generalized linear mixed models provide a flexible framework for modeling a range of data, although with non-Gaussian response variables the likelihood cannot be obtained in closed form. Markov chain Monte Carlo methods solve this problem by sampling from a series of simpler conditional distributions that can be evaluated. The R package MCMCglmm implements such an algorithm for a range of model fitting problems. More than one response variable can be analyzed simultaneously, and these variables are allowed to follow Gaussian, Poisson, multi(bi)nominal, exponential, zero-inflated and censored distributions. A range of variance structures are permitted for the random effects, including interactions with categorical or continuous variables (i.e., random regression), and more complicated variance structures that arise through shared ancestry, either through a pedigree or through a phylogeny. Missing values are permitted in the response variable(s) and data can be known up to some level of measurement error as in meta-analysis. All simu- lation is done in C/ C++ using the CSparse library for sparse linear systems.
Phytophagous mites are a serious threat to their host plants; in absence of predators they tend to overexploit their food source. To prevent such a crash and maintain as much leaf area as possible host plants may defend themselves in various ways, one of which is to increase the effectiveness of natural enemies of the phytophagous mites. Predatory mites are considered to be very important natural enemies of plant-feeding mites and there is evidence for a mutualistic interaction with plants. Examples of how plants obtain and arrest predatory mites as bodyguards are discussed. It is known for a long time that some plant species provide pollen that appear to be a very profitable food source for some species of predatory mites: it does not only promote survival, but also allows development and egg production. In doing so, plants ensure themselves of bodyguards even before any damage is inflicted. Recently, evidence has been obtained that plants under attack by spider mites provide information by releasing a blend of volatile chemicals that are helpful to predatory mites in locating their prey. Plant-predator interactions are not always of a mutualistic nature. Some plant species invest in a rigorous defence against spider mites, even though this may be to the detriment of the predators: glandular hairs of some plant species entrap not only spider mites, but also their predators. The evolutionary implications of these various plant-predator interactions are discussed.
In response to arthropod herbivory, plants release volatile organic compounds (VOCs), which are attractive to natural enemies. Consequently, VOCs have been interpreted as co-evolved plant-natural enemy signals. This review argues that, while these data are necessary, they are not sufficient to demonstrate a VOC plant-natural enemy signaling function. We propose that evidence that (1) plant fitness is increased as a consequence of natural enemy recruitment, and either (2A) natural enemies preferentially learn prey-induced VOCs or (2B) natural enemies respond innately to the VOCs of the prey-host plant complex, is also required. Whereas there are too few studies to rigorously test hypotheses 1 and 2A, numerous studies are available to test hypothesis 2B. Of 293 tests of natural enemy responses to VOCs, we identified only 74 that were unambiguous tests of naïve natural enemies; in the remainder of the tests either natural enemies were experienced with their host in the presence of VOCs, or experience could not be ruled out. Of those 74 tests with naïve natural enemies, attraction was observed in 41 and not in 33. This review demonstrates that empirical support for the hypothesized VOC plant-natural enemy signaling function is not universal and presents alternative hypotheses for VOC production.
A genetical mathematical model is described which allows for interactions between relatives on one another's fitness. Making use of Wright's Coefficient of Relationship as the measure of the proportion of replica genes in a relative, a quantity is found which incorporates the maximizing property of Darwinian fitness. This quantity is named “inclusive fitness”. Species following the model should tend to evolve behaviour such that each organism appears to be attempting to maximize its inclusive fitness. This implies a limited restraint on selfish competitive behaviour and possibility of limited self-sacrifices.Special cases of the model are used to show (a) that selection in the social situations newly covered tends to be slower than classical selection, (b) how in populations of rather non-dispersive organisms the model may apply to genes affecting dispersion, and (c) how it may apply approximately to competition between relatives, for example, within sibships. Some artificialities of the model are discussed.
Powerful volatile regulators of gene expression, pheromones and other airborne signals are of great interest in biology. Plants are masters of volatile production and release, not just from flowers and fruits, but also from vegetative tissues. The controlled release of bouquets of volatiles from leaves during attack by herbivores helps plants to deter herbivores or attract their predators, but volatiles have other roles in development and in the control of defence gene expression. Some of these roles may include long-distance signalling within and perhaps between plants.
Inducible defensive responses in plants are known to be activated locally and systemically by signaling molecules that are produced at sites of pathogen or insect attacks, but only one chemical signal, ethylene, is known to travel through the atmosphere to activate plant defensive genes. Methyl jasmonate, a common plant secondary compound, when applied to surfaces of tomato plants, induces the synthesis of defensive proteinase inhibitor proteins in the treated plants and in nearby plants as well. The presence of methyl jasmonate in the atmosphere of chambers containing plants from three species of two families, Solanaceae and Fabaceae, results in the accumulation of proteinase inhibitors in leaves of all three species. When sagebrush, Artemisia tridentata, a plant shown to possess methyl jasmonate in leaf surface structures, is incubated in chambers with tomato plants, proteinase inhibitor accumulation is induced in the tomato leaves, demonstrating that interplant communication can occur from leaves of one species of plant to leaves of another species to activate the expression of defensive genes.
In this study, we used plant vascular architecture as a framework from which to predict induced changes in resource quality for Lema trilinea feeding on the host plant Solanum dulcamara at both low and high levels of herbivory. The systemic patterns of allocation of dye from a capillary tube inserted onto the petiole of the first true leaf and sections of the stem were used to establish the degree of vascular connectivity among different leaf positions. Induced changes in the activity of two defensive proteins, proteinase inhibitor (PI) and polyphenol oxidase (PPO), as well as larval L. trilinea performance, were measured in weakly or strongly connected leaves on plants with the first leaf damaged or undamaged by adult L. trilinea. At high levels of herbivory, larval performance decreased on the sixth leaf, which has strong vascular connections to the first leaf, yet increased on the fifth leaf, which has weak vascular connections to the first leaf. PPO activity increased in both the fifth and sixth leaf, while PI activity decreased in the fifth leaf although remaining unchanged in the sixth leaf. At low levels of herbivory, a decrease in larval performance was observed in the sixth leaf, but no change occurred in the weakly connected fifth leaf. Hence, plant vascular architecture clearly predicted within-plant changes in resource quality following only small amounts of herbivore damage.