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BENEFITS AND COSTS OF INDUCED PLANT DEFENSE FOR LEPIDIUM VIRGINICUM (BRASSICACEAE)
Ecology
... Plant defence against herbivores is often effective but it imposes energy costs associated with its production (Agrawal, 2000;Agrawal et al., 2002). As optimal defence theory predicts (Rhoades, 1979;Stamp, 2003), plants thus evolve defensive levels that are positively associated with herbivory level and negatively associated with allocation and/or ecological cost. ...
... Plant defence against herbivores imposes a high cost for chemical production, resulting in decreased growth and reproduction (Agrawal, 2000;Agrawal et al., 2002). If low-defended plants can successfully escape from herbivory under the patronage of neighbouring high-defended plants, they can effectively grow and reproduce without any costs against herbivores. ...
There is increasing evidence that herbivore–plant interactions on a focal plant species are influenced by interspecific neighbourhood effects via neighbouring plants (i.e. an associational effect). However, intraspecific neighborhood effects imposed by plant traits have been less appreciated. Specifically, the significance of intraspecific neighbourhood effects in population‐level consequences of plants has been totally overlooked.
Using two varieties of Nicotiana tabacum (high‐ and low‐nicotine), we evaluated the neighbourhood effects based on patch‐level interactions in a split‐plot 3 × 3 factorial experiment that manipulated number of plants (4, 9 and 16 plants) and culture type (monoculture plots with high‐ and low‐nicotine plants, and polyculture plot) in an experimental garden.
We found that herbivore visits on plants varied depending on the number of plants per patch and culture type. Presence of more high‐nicotine plants decreased herbivore visits in the four plant plots, and presence of high‐nicotine plants in the nine plant plots decreased herbivore visits on both high‐ and low‐nicotine plants. In contrast, in the 16 plant plots, herbivore visits on high‐nicotine plants in polyculture plots were lower than others, including those on high‐nicotine plants in monoculture plots.
Our findings clearly demonstrated that the intraspecific neighbourhood effect could occur depending on the aggregation of highly defended plants (i.e. high density and/or plant‐spacing). This study suggests that multiple mechanisms for the neighbourhood effect simultaneously worked, depending on the patch size and composition of defensive traits of individual plants, and that intraspecific neighbourhood effects may influence population‐level consequences for plant–herbivore interaction.
A free Plain Language Summary can be found within the Supporting Information of this article.
... These interactions can be direct, such as competition for limited resources, or indirect, mediated through changes in the host plant metabolism (Biere & Goverse, 2016). The outcome of these plant-mediated interactions might depend on the feeding guild of the herbivores and has been widely reported for leafchewing herbivores versus piercing-sucking aphids (Agrawal, 2000;Li et al., 2014;Poelman et al., 2008;Rodriguez-Saona et al., 2005;Soler et al., 2012). For instance, females of the European corn borer (ECB), Ostrinia nubilalis, were shown to avoid plants infested with aphids for oviposition, a behaviour that benefits the performance of their progeny (Harmon et al., 2003). ...
The selection of oviposition sites by female moths is crucial in shaping their progeny performance and survival, and consequently in determining insect fitness. Selecting suitable plants that promote the performance of the progeny is referred to as the Preference−Performance hypothesis (or ‘mother‐knows‐best’). While root infestation generally reduces the performance of leaf herbivores, little is known about its impact on female oviposition. We investigated whether maize root infestation by the Western corn rootworm (WCR) affects the oviposition preference and larval performance of the European corn borer (ECB). ECB females used leaf volatiles to select healthy plants over WCR‐infested plants. Undecane, a compound absent from the volatile bouquet of healthy plants, was the sole compound to be upregulated upon root infestation and acted as a repellent for first oviposition. ECB larvae yet performed better on plants infested below‐ground than on healthy plants, suggesting an example of ‘bad motherhood’. The increased ECB performance on WCR‐infested plants was mirrored by an increased leaf consumption, and no changes in the plant primary or secondary metabolism were detected. Understanding plant‐mediated interactions between above‐ and below‐ground herbivores may help to predict oviposition decisions, and ultimately, to manage pest outbreaks in the field.
... This zig-zag model, which has been described by Jones and Dangl [6], proposes distinct phases, including "pathogen-associated molecular pattern-triggered immunity"; "effector-triggered susceptibility in overcoming pathogen-associated molecular pattern-triggered immunity"; "effector-triggered immunity that further protects the plant against microbial infection"; "countermoves, where the pathogen may evolve to escape recognition by either alteration to the binding specificity of the effector or by the evolution of novel host-defense suppression". The research on this topic, particularly involving toxic plants defending from herbivore attacks, has been highly productive over the past 50 years (e.g., [7][8][9][10][11][12][13][14][15][16][17][18]). Currently, the molecular tools allow us to unravel the detailed mechanisms that herbivores or plants use during their interactions [19][20][21][22]. ...
Citation: Aluja, M.; Vázquez-Rosas-Landa, M.; Cerqueda-García, D.; Monribot-Villanueva, J.L.; Altúzar-Molina, A.; Ramírez-Vázquez, M.; Velázquez-López, O.; Rosas-Saito, G.; Alonso-Sánchez, A.G.; Ortega-Casas, R.; et al. Assessment of the Molecular Responses of an Ancient Angiosperm against Atypical Insect Oviposition: The Case of Hass Avocados and the Tephritid Fly Anastrepha ludens. Int. J. Mol. Sci. 2023, 24, 2060. https:// (M.A.); enrique.ibarra@inecol.mx (E.I.-L.) † These authors contributed equally to this work and share first authorship. Abstract: Anastrepha spp. (Diptera: Tephritidae) infestations cause significant economic losses in commercial fruit production worldwide. However, some plants quickly counteract the insertion of eggs by females by generating neoplasia and hindering eclosion, as is the case for Persea americana Mill., cv. Hass (Hass avocados). We followed a combined transcriptomics/metabolomics approach to identify the molecular mechanisms triggered by Hass avocados to detect and react to the oviposition of the pestiferous Anastrepha ludens (Loew). We evaluated two conditions: fruit damaged using a sterile pin (pin) and fruit oviposited by A. ludens females (ovi). We evaluated both of the conditions in a time course experiment covering five sampling points: without treatment (day 0), 20 min after the treatment (day 1), and days 3, 6, and 9 after the treatment. We identified 288 differentially expressed genes related to the treatments. Oviposition (and possibly bacteria on the eggs' surface) induces a plant hypersensitive response (HR), triggering a chitin receptor, producing an oxidative burst, and synthesizing phytoalexins. We also observed a process of cell wall modification and polyphenols biosynthesis, which could lead to polymerization in the neoplastic tissue surrounding the eggs.
... Here, we found some parasitoid-exposed DBM larvae on the wall of the VPW enclosures but not on the wall of the cabbage enclosures, suggesting that the hostsearching intensity of D. insulare may have been greater on VPW and hence induced a greater avoidance or escape response in DBM. Parasitoid behavior on VPW and cabbage likely stems from differences in both plant structures and chemical compositions [44][45][46]. ...
Enemy-risk effects (i.e., non-consumptive effects) describe the non-lethal fitness costs incurred by animals when they perceive a risk of predation. These effects can result from fear-associated changes in behavior and physiology. Diamondback moth larvae (Plutella xylostella) are known to violently wriggle backwards and drop from their host plants, usually suspending themselves with a silk thread, when threatened by predators and parasitoids. Here, we investigated the developmental costs associated with this behavior when larvae were exposed to its specialist parasitoid wasp (Diadegma insulare). Additionally, the structural and chemical properties of plants are well-known to influence predation and parasitism rates of herbivorous insects. Yet, few studies have examined the influence of plants on enemy-risk effects. Therefore, we examined the developmental costs associated with parasitism risk on two host plants. Diamondback moth larvae were placed on either cabbage or Virginia pepperweed plants and exposed to gravid parasitoids with truncated ovipositors, which prevented piercing of the host cuticle without affecting host searching and attacking behaviors. On Virginia pepperweed, risk of parasitism resulted in reduced larval weight gain, longer development time, and smaller adult size compared to larvae that were not exposed to parasitoids. However, on cabbage, parasitoid exposure prolonged development time but had no significant effects on larval weight gain and adult size. On both plants, parasitoid-exposed larvae were found feeding on older foliage than younger foliage. Our findings demonstrate that the enemy-escape behavior of diamondback moths has developmental costs and that plants may mediate the intensity of these enemy-risk effects.
... Previous work has found that while nitrogen fertilization of B. oleracea plants can benefit both caterpillars and aphids (e.g., (Chen, Lin, Wang, Yeh, & Hwang, 2004b;Letourneau & Fox, 1989;Staley et al., 2010), less is known about plantmediated effects of P enhancement on these herbivores. On B. oleracea, prior feeding by caterpillars has been shown to induce plant defenses that harm the generalist aphid M. persicae, but that benefit the specialist aphid B. brassicae (Agrawal, 2000, but see Staley et al., 2011. So, while a great deal is known about plant-mediated interactions between pairs of these herbivore species, or about the effects of fertilizers on one or two of the herbivore species, the full diversity of nutrient-plant-herbivore-herbivore interactions possible in the system have not been examined in the complexity likely to be seen on working farms. ...
Soil fertility is tightly linked with herbivore pressure because it affects the nutritional status of host plants as well as the production of anti-herbivore defenses. This in turn can influence whether herbivores in different feeding guilds render plants more or less susceptible to one another. Thus, growers’ fertility management choices may impact herbivores through a variety of indirect channels. We examined relationships between soil fertility and interactions between phloem-feeding and leaf-chewing herbivores on broccoli (Brassica oleracea) plants in the greenhouse, taking advantage of natural variation in nitrogen (N) and phosphorus (P) in soils from 20 working organic vegetable farms. Next, we experimentally fertilized soil in a field trial with N and/or P to examine the consequences of these nutrients for growth of and interactions between specialist and generalist herbivores. Soils on our cooperating farms varied widely in P and N concentrations, with 40% exceeding recommended pre-plant N concentrations and 90% exceeding P recommendations. In single-herbivore infestations, augmenting N in the soil increased caterpillar (Pieris rapae) growth, augmented N and P additively enhanced generalist green peach aphid (Myzus persicae) colonization, and augmented P (but not N) increased specialist cabbage aphid (Brevicoryne brassicae) growth. In dual-guild herbivore infestations, caterpillars facilitated specialist cabbage aphid growth in the absence of fertilizer, but this pattern disappeared under augmented N, and reversed under augmented P. We found that a complex web of indirect effects linked soil fertility to herbivore performance, depending on the identity of the nutrients being altered, the ecological roles of responding herbivore species (i.e., specialist versus generalist), and indirect interactions between chewing and sucking herbivores. More generally, we highlight that successful use of fertility management to improve pest resistance requires careful consideration of herbivore feeding niches and herbivore-herbivore interactions.
... Although there are costs associated with inducible defense, it may be relatively cheap, since response to damage enhances the competitiveness of plants, and many of the secondary compounds are only synthesized when needed (Agrawal 2000;Miranda et al. 2007). ...
The responses in growth and defense after tissue damage are highly variable in plants depending on species, damaged-tissue type and the intensity of damage. The prevailing abiotic conditions can also influence these responses. In this study, our aim was to examine how the removal of lateral vegetative buds affects the growth and accumulation of phenolics in saplings of the dioecious Populus tremula grown under simulated climate change. For three growing seasons, the saplings were grown under ambient conditions (control), elevated temperature (+2°C) and elevated UV radiation (30%) (UVB and UVA as its control), or a combination of these. In the fourth growing season, all saplings were grown under ambient conditions. The bud removal was performed twice - in summer and autumn - in the third year. The responses of growth and the accumulation of phenolics to the bud removal were measured at the end of the fourth growing season. Removal of 5% of the lateral buds resulted in higher leaf, stem and total plant biomass in both sexes of P. tremula saplings, compared to intact plants. The effects were greater in the temperature-treated plants, especially in the temperature-treated females. The concentrations of flavonoids and condensed tannins were higher in the bud-removed individuals. The concentration of condensed tannins was also higher in the males than in the females, opposite to the concentration of phenolic acids. There was no significant interaction between bud removal and UVB treatment on either growth or phenolics. Our results suggest that plants can allocate resources to both growth and defense simultaneously in response to tissue loss, and that global warming can modify the responses to some extent.
... The induction of such plant defences can result in the allocation of fewer resources to vegetative growth and flower production. Induced plant defences are often assumed to be costly because of this reallocation (Agrawal, 2000;Zangerl et al., 1997), but there is mixed evidence for such costs (Gianoli and Niemeyer, 1997;Karban, 1993;Strauss et al., 2002;Thaler, 1999). The results presented here suggest that plant performance is not negatively affected by the presence of M. pygmaeus on the plant or by the induction of plant defences by the omnivore. ...
Plant feeding by omnivorous predators can induce plant defences, which decreases the performance of herbivores and influence behaviour of other predators. However, it is not known what are the consequences of this feeding for the plant and how this, in turn, affects the omnivore. We therefore investigated the effects of plant feeding by the omnivorous predator Macrolophus pygmaeus on plant development and reproduction. We also assessed the effects of these plant changes on survival and reproduction of the omnivore. Sweet pepper plants exposed to M. pygmaeus had significantly lower numbers of leaves and open flowers than clean plants, but numbers of fruits were similar. Moreover, the presence of the omnivore significantly shortened the period for flowers to become fruits. The dry weights of leaves plus stems and fruits were similar on clean plants and plants with the omnivore. Significantly higher numbers of seeds were found in fruits from plants with the omnivore than on clean plants. The survival rates of M. pygmaeus females and nymphs increased with numbers of flowers. Our results show that the presence of this omnivorous predator can benefit plants by increasing seed production, but the changes in plant phenology do not seem to benefit the omnivore.
Plants produce a great number of phytochemicals serving a variety of different functions. Recently, the chemodiversity of these compounds (i.e., the diversity of compounds produced by a plant) has been suggested to be an important aspect of the plant phenotype that may shape interactions between plants, their environment, and other organisms. However, we lack an agreement on how to quantify chemodiversity, which complicates conclusions about the functional importance of it. Here, we discuss how chemodiversity (deconstructed into components of richness, evenness and disparity) may relate to different ecologically relevant aspects of the phenotype. Then, we systematically review the literature on chemodiversity to examine methodological practices, explore patterns of variability in diversity across different levels of biological organization, and investigate the functional role of this diversity in interactions between plants and other organisms. Overall, the reviewed literature suggests that high chemodiversity is often beneficial for plants, although a heterogeneity of methodological approaches partly limits what general conclusions can be drawn. Importantly, to support future research on this topic, we provide a framework with a decision tree facilitating choices on which measures of chemodiversity are best used in different contexts and outline key questions and avenues for future research. A more thorough understanding of chemodiversity will provide insights into its evolution and functional role in ecological interactions between plants and their environment.
Insect–plant interactions are complex and dynamic relationships that have evolved over millions of years. Plants have developed various adaptations to deter insect herbivores, including physical, chemical, and induced defences. In response, insects have evolved detoxification mechanisms, behavioural adaptations, and physiological adaptations to overcome these defences. This coevolutionary arms race has shaped the interactions between plants and insects, leading to a diverse array of strategies and counter-strategies. Additionally, other associated organisms such as endosymbionts and rhizosphere microbes have been shown to play a critical role in these interactions. Endosymbionts can alter the nutritional quality of plant tissue and confer resistance to environmental stressors, while rhizosphere microbes can influence plant growth and nutrient uptake. Understanding the coevolutionary arms race and the role of associated organisms in insect–plant interactions has important implications for plant protection and management. By leveraging these relationships, we can develop sustainable and eco-friendly approaches to crop protection and pest management.
Although the typical framework for studies and models of bloom dynamics in toxigenic phytoplankton is pre- dominantly based on abiotic determinants, there is mounting evidence of grazer control of toxin production. We tested for the effect of grazer control of toxin production and cell growth rate during a laboratory-simulated bloom of the dinoflagellate Alexandrium catenella. We measured cellular toxin content and net growth rate when cells were exposed to copepod grazers (direct exposure), copepod cues (indirect exposure), and no co- pepods (control) throughout the exponential, stationary, and declining phases of the bloom. During the simu- lated bloom, cellular toxin content plateaued after the stationary phase and there was a significantly positive relationship between growth rate and toxin production, predominantly in the exponential phase. Grazer-induced toxin production was evident throughout the bloom, but highest during the exponential phase. Induction was greater when cells were directly exposed to grazers rather than their cues alone. In the presence of grazers toxin production and cell growth rate were negatively related, indicating a defense-growth trade-off. Further, a fitness reduction associated with toxin production was more evident in the presence than the absence of grazers. Consequently, the relationship between toxin production and cell growth is fundamentally different between constitutive and inducible defense. This suggests that understanding and predicting bloom dynamics requires considering both constitutive and grazer-induced toxin production.
Plants of Eruca sativa from a desert population produce less vegetative biomass, flower earlier and possess higher density of trichomes than plants from a more mesic Mediterranean habitat. When eliciting plant defense mechanisms with methyl-jasmonate (MJ), trichome formation was exclusively enhanced in plants of the Mediterranean ecotype. To test the relative costs of defenses, ecologically-important traits were monitored in non-elicited plants of the two ecotypes and when defenses were induced by MJ. Opposing the expected tradeoffs of induced defense, MJ- elicitation significantly delayed bolting and flowering in plants of the desert ecotype but not in the Mediterranean ones. Moreover, MJ did not impose costs on fitness- related traits, i.e. fruit and seed production, nor differences between plants of the two ecotypes were found. It is suggested that early flowering in plants of the desert ecotype provide a mean to escape both the abiotic stressful environment as well herbivory, while induced defense in the Mediterranean ecotype was favored in habitats of more stressful biotic interactions. The results are discussed in light of the optimal defense theory and resource availability hypothesis.
Plant secondary metabolites (PSMs) such as terpenes and phenolic compounds are known to have numerous ecological roles, notably in defence against herbivores, pathogens and abiotic stresses and in interactions with competitors and mutualists. This book reviews recent developments in the field to provide a synthesis of the function, ecology and evolution of PSMs, revealing our increased awareness of their integrative role in connecting natural systems. It emphasises the multiple roles of secondary metabolites in mediating the interactions between organisms and their environment at a range of scales of ecological organisation, demonstrating how genes encoding for PSM biosynthetic enzymes can have effects from the cellular scale within individual plants all the way to global environmental processes. A range of recent methodological advances, including molecular, transgenic and metabolomic techniques, are illustrated and promising directions for future studies are identified, making this a valuable reference for researchers and graduate students in the field.
Plant secondary metabolites (PSMs) such as terpenes and phenolic compounds are known to have numerous ecological roles, notably in defence against herbivores, pathogens and abiotic stresses and in interactions with competitors and mutualists. This book reviews recent developments in the field to provide a synthesis of the function, ecology and evolution of PSMs, revealing our increased awareness of their integrative role in connecting natural systems. It emphasises the multiple roles of secondary metabolites in mediating the interactions between organisms and their environment at a range of scales of ecological organisation, demonstrating how genes encoding for PSM biosynthetic enzymes can have effects from the cellular scale within individual plants all the way to global environmental processes. A range of recent methodological advances, including molecular, transgenic and metabolomic techniques, are illustrated and promising directions for future studies are identified, making this a valuable reference for researchers and graduate students in the field.
Plant secondary metabolites (PSMs) such as terpenes and phenolic compounds are known to have numerous ecological roles, notably in defence against herbivores, pathogens and abiotic stresses and in interactions with competitors and mutualists. This book reviews recent developments in the field to provide a synthesis of the function, ecology and evolution of PSMs, revealing our increased awareness of their integrative role in connecting natural systems. It emphasises the multiple roles of secondary metabolites in mediating the interactions between organisms and their environment at a range of scales of ecological organisation, demonstrating how genes encoding for PSM biosynthetic enzymes can have effects from the cellular scale within individual plants all the way to global environmental processes. A range of recent methodological advances, including molecular, transgenic and metabolomic techniques, are illustrated and promising directions for future studies are identified, making this a valuable reference for researchers and graduate students in the field.
Plant secondary metabolites (PSMs) such as terpenes and phenolic compounds are known to have numerous ecological roles, notably in defence against herbivores, pathogens and abiotic stresses and in interactions with competitors and mutualists. This book reviews recent developments in the field to provide a synthesis of the function, ecology and evolution of PSMs, revealing our increased awareness of their integrative role in connecting natural systems. It emphasises the multiple roles of secondary metabolites in mediating the interactions between organisms and their environment at a range of scales of ecological organisation, demonstrating how genes encoding for PSM biosynthetic enzymes can have effects from the cellular scale within individual plants all the way to global environmental processes. A range of recent methodological advances, including molecular, transgenic and metabolomic techniques, are illustrated and promising directions for future studies are identified, making this a valuable reference for researchers and graduate students in the field.
Weeds can play numerous important roles in pest suppression in agroecosystems. These include influencing the host searching behaviors of herbivorous pests and their natural enemies and providing shelter and alternative food sources for predators and parasitoids. Virginia pepperweed, Lepidium virginicum, is a widespread naturalized weed in Hawaii and can often be found in and around agricultural fields. It is a member of the Brassicaceae family and is a known host plant of the diamondback moth (DBM), Plutella xylostella. In this study, we found that DBM preferentially oviposit on L. virginicum (vegetative stage) when presented with a choice of cabbage. Using laboratory and semi-field trials, we investigated the responses of the natural enemies of DBM to the vegetative stage of L. virginicum and cabbage infested with DBM larvae. When DBM-infested plants were placed in the field for 48 h, more spiders and parasitized DBM larvae were recovered from the L. virginicum than from cabbage. In laboratory choice experiments, we demonstrated that the dominant DBM parasitoid species in Hawaii (Cotesia vestalis) oviposited in more host larvae on L. virginicum compared to cabbage, though this had no particular benefit for parasitoid development (adult size and sex ratio). Our findings suggest that the presence of L. virginicum in cabbage agroecosystems could be beneficial by serving to divert DBM oviposition away from cabbage and promoting predator and parasitoid populations.
Plant metabolic pathways and gene networks involved in the response to herbivory are well-established, but the impact of epigenetic factors as modulators of those responses is less understood. Here, we use the demethylating agent 5-azacytidine to uncover the role of DNA cytosine methylation on phenotypic responses after short-term herbivory in Thlaspi arvense plants that came from two European populations with contrasting flowering phenotypes expected to differ in the response to experimental demethylation. The experimental design followed a 2×3 factorial design, that was replicated for each flowering-type. First, half the seeds were submerged in a water solution of 5-azacytidine and the other half only in water, as controls. Then, we assigned control and demethylated plants to three herbivory categories (i) insect herbivory, (ii) artificial herbivory, and (iii) undamaged plants. The effects of the demethylation and herbivory treatments were assessed by quantifying genome-wide global DNA cytosine methylation, concentration of leaf glucosinolates, final stem biomass, fruit and seed production, and seed size. For most of the plant traits analysed, individuals from the two flowering-types responded differently. In late-flowering plants, global DNA methylation did not differ between control and demethylated plants but it was significantly reduced by herbivory. Conversely, in early-flowering plants, demethylation at seed stage was still evident in leaf DNA of reproductive individuals whereas herbivory did not affect their global DNA methylation. In late-flowering plants, artificial herbivory imposed a stronger reduction than insect herbivory in global DNA methylation and final stem biomass, and induced higher concentration of aliphatic glucosinolates. In early-flowering plants, the effects of herbivory were non-significant for the same traits. Finally, the effect of herbivory on reproductive parameters varied with the level of demethylation and the plant flowering-type. Although further investigations with more populations and families are required to confirm our results, they suggest that the genetic background of experimental plants and timing of damage can affect the response to herbivory and point towards multifaceted genetic-epigenetic interactions in determining herbivory-induced phenotypic plasticity.
Polyploid species possess more than two sets of chromosomes and may show high gene redundancy, hybrid vigor, and masking of deleterious alleles compared to their parent species. Following this, it is hypothesized that this makes them better at adapting to novel environments than their parent species, possibly due to phenotypic plasticity. The allopolyploid Arabidopsis suecica and its parent species A. arenosa and A. thaliana were chosen as a model system to investigate relationships between phenotypic plasticity, fitness, and genetic variation. Particularly, we test if A. suecica is more plastic, show higher genetic diversity, and/or have higher fitness than its parent species. Wild Norwegian populations of each species were analyzed for phenotypic responses to differences in availability of nutrient, water, and light, while genetic diversity was assessed through analysis of AFLP markers. Arabidopsis arenosa showed a higher level of phenotypic plasticity and higher levels of genetic diversity than the two other species, probably related to its outbreeding reproduction strategy. Furthermore, a general positive relationship between genetic diversity and phenotypic plasticity was found. Low genetic diversity was found in the inbreeding A. thaliana. Geographic spacing of populations might explain the clear genetic structure in A. arenosa, while the lack of structure in A. suecica could be due to coherent populations. Fitness measured as allocation of resources to reproduction, pointed toward A. arenosa having lower fitness under poor environmental conditions. Arabidopsis suecica, on the other hand, showed tendencies toward keeping up fitness under different environmental conditions. Does polyploid species outrange their parents in phenotypic response range, genetic diversity, and fitness? We investigated the allopolyploid Arabidopsis suecica and its diploid parents A. thaliana and A. arenosa and found no indications of this.
Premise:
Plant responses to herbivores and their elicitors include changes in traits associated with phenology, defense, and reproduction. Induced responses by chewing herbivores are known to be hormonally mediated by the jasmonate pathway and can cascade and affect late-season seed predators and pollinators. Moreover, herbivore-induced plant responses can be transmitted to the next generation. Whether herbivore-induced transgenerational effects also apply to phenological traits is less well understood.
Methods:
Here, we explored responses of wild lima bean plants (Phaseolus lunatus) to herbivory and jasmonate treatment and possible transgenerational effects of herbivore-induced early flowering. In a controlled field experiment, we exposed lima bean plants to herbivory by leaf beetles or methyl jasmonate sprays (MJ). We then compared plant development, phenology, reproductive fitness and seed traits among these treatments and undamaged, untreated control plants.
Results:
We found that MJ and leaf herbivory induced similar responses, with treated plants growing less, flowering earlier, and producing fewer seeds than undamaged plants. However, seed size, phenolics and cyanogenic glycosides concentrations did not differ among treatments. Seed germination rates and flowering time of the offspring were similar among maternal treatments.
Conclusions:
Overall, the results confirm that responses of lima bean to herbivory by leaf beetles are mediated by jasmonate; however, effects on phenological traits are not transmitted to the next generation. We discuss why transgenerational effects of herbivory might be restricted to traits that directly target herbivores.
Plants face multiple biotic and abiotic stressors simultaneously. Many species can tolerate and resist stress, but countermeasures differ between roots and leaves. Since herbivores and environmental conditions modulate costs and benefits of plant defence traits, stress responses are context‐dependent. We examined whole‐plant tolerance and resistance responses to individual and combined effects of above and belowground herbivory under variable water conditions.
We manipulated water availability and access by two common herbivores (Spodoptera exigua caterpillars and Meloidogyne incognita nematodes) to Solanum lycocarpum. Plants were either watered based on historical regional averages or the 30% reduction predicted by IPCC studies. Herbivory treatments included isolated above (AG) and belowground (BG) attacks, simultaneous (AGBG) attacks and no‐herbivory controls. We then parameterized generalized linear mixed‐effects models with data on plant survival, leaf and root biomass accumulation, root complexity and terpenoid concentration.
Foliar herbivory increased terpenoid concentrations in roots relative to no‐herbivory plants under control water but decreased concentrations in both roots and leaves under drought. Similarly, root feeders increased concentrations of terpenoids in leaves under control water but decreased concentrations only in roots under drought. Plants challenged with AGBG herbivory had greater whole‐plant biomass (i.e. tolerance) and lower total concentrations of defensive compounds (i.e. resistance) than plants exposed to no‐herbivore controls, regardless of water conditions. Importantly, the capacity of plants to grow or produce terpenoids changes when herbivory level is considered. In plants exposed to AGBG herbivory, greater nematode infection was related to decreases in whole‐plant biomass and marginal increases in total terpenoid concentration. Ultimately, accounting only for individual AG and BG responses would have led to different conclusions and underestimated the magnitude of S. lycocarpum's compensatory responses. A ‘whole‐plant’ approach revealed that belowground herbivory is the primary driver of tolerance in plants surviving moderate water stress.
Synthesis. Whole‐plant responses to stress in variable environments are complex, and their comprehensive understanding requires accounting for belowground herbivores and root responses.
Interaction between herbivores and plants is essential for ecosystem functioning. Phytochemical variation in plants is one of the most fascinating yet bewildering properties of the natural world and has important implications for both human health and the functioning of the ecosystem. One of the key aspects of plant phytochemical research is to study the insects that feed on plants which are one of the driving forces behind the development of chemical diversity in plants. Decoding their interaction from molecular to the ecological level is important for developing a comprehensive understanding of their interaction that has shaped their evolutionary history. Applications of advanced technologies and collaborative work between molecular biologists, geneticists, ecologists, evolutionary biologists, and biochemists will unravel their complex interactions for meeting future challenges. In this chapter, we have emphasized on the ecological perspective of the two interacting system and how it has led to evolution of certain traits in them.
The sections in this article are
Introduction
Access to the Plant Surface
Recognition Cues for Insects
Mimicry
Methods of Investigation
Application in Biological Pest Management
Conclusion
Plants defend themselves against attack by herbivores with a variety of physical and chemical defences, some of which also work by recruiting partners from the third trophic level. Despite the known or potential benefits of possessing defence traits, the expression of defence traits varies among tissues within individual plants, within and among plant populations, and across biotic and abiotic environments. The central explanation for such variation is that the expression of defence traits is costly to fitness in the absence of benefits. Here, we review how cost‐benefit trade‐offs have been incorporated in several hypotheses about the ecology and evolution of plant defences. We then describe several approaches that have been used to examine costs, and the empirical evidence that has been attained through their use. After 30 years of study, a consensus has emerged through a variety of approaches that expression of defence traits is, indeed, costly, but that the magnitude and importance of costs are context‐dependent.
Many plant species protect themselves against herbivores through mechanical or chemical so‐called inducible defences (ID). These are regulated via a hormonal cascade which may be under epigenetic control and in which jasmonic acid (JA) plays a prominent role. In this study, we indirectly tested the role of DNA methylation in the production of ID and the synthesis of hormones involved in the ID signalling cascade. Using different intensities of 5‐azacytidine application, we aimed to produce plants of Trifolium repens with different levels of DNA methylation alteration. We then elicited the plants together with controls, i.e. plants with natural DNA methylation status, with JA and then indirectly recorded ID production in herbivore‐choice trials in which the leaves of plants with different DNA methylation statuses were provided to caterpillars of a generalist herbivore, Spodoptera littoralis. We also analysed the balance of several key defence hormones such as jasmonates, abscisic acid (ABA), indole‐3‐acetic acid (IAA) and salicylic acid in the plants. We found that the S. littoralis preferred demethylated plants over non‐demethylated controls. Demethylation also reduced production of JA, ABA and IAA. We conclude that DNA methylation modulates expression of ID likely via regulation of signalling hormones involved in the establishment of defence.
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Environmental gradients serve as powerful settings to elucidate the ecological and evolutionary processes driving changes in species diversity, trait evolution, and ecosystem function. Classic theory holds that stronger plant-herbivore interactions under more stable and warmer climates towards the equator and sea level have resulted in stronger selection on plant defences. We hereby address latitudinal and elevational gradients in plant defences and herbivory follow these predictions for a number of dominant taxa of temperate trees. Many of these taxa include species that span broad latitudinal and elevational ranges and thus represent useful models for testing clinal variation in plant defences and herbivory. First, we review recent studies testing for latitudinal and elevational gradients in temperate tree defences and herbivory. Second, we analyse these results in the light of classical theory and discuss potential deviations from expected patterns and candidate mechanisms. Third, we analysed the use of genomic tools for assessing the genetic basis of clinal evolution in plant defences, a promising alternative toward reducing inconsistencies and identifying commonalities in ecological and evolutionary processes. Our review indicates considerable variation in the strength and direction of elevational and latitudinal gradients in temperate tree defences and herbivory. Strikingly, patterns that are opposite to classic predictions are equally common and, in some cases, even more common than expected patterns. In light of these findings, we argue for a need to apply consistent methods across studies, conduct more comprehensive assessments of plant defensive phenotypes, and explicitly consider the role of abiotic factors. Furthermore, as future research closes these gaps, the adoption of genomic tools will open an unprecedented opportunity to launch a new generation of studies. To achieve this, there is a need to merge research on landscape genetics and ecological studies of plant-intraspecific clines in plant-herbivore interactions to unveil the genetic basis of clinal evolution in plant defences. Likewise, analyses of the molecular level evolution of target genes associated with plant defence also hold a large potential for assessing plant defence macro-evolutionary patterns along environmental clines. Applying these tools will help elucidate the mechanisms of adaptive evolution in plant defence along environmental clines and contribute to develop new theory by uncovering patterns not apparent previously from studies based solely on measurements of plant phenotypes and species interactions.
Aims The plant-herbivore interaction is one of the most fundamental interactions in nature. Plants are sessile organisms, and consequently rely on particular strategies to avoid or reduce the negative impact of herbivory. Here, we aimed to determine the defense strategies against insect her-bivores in the creeping invasive plant Alternanthera philoxeroides. Methods We tested the defense response of A. philoxeroides to herbivory by a leaf-feeding specialist insect Agasicles hygrophila and a poly-phagous sap-feeding insect Planococcus minor. We also tested the mechanisms triggering defense responses of A. philoxeroides by including treatments of artificial leaf removal and jasmonic acid application. Furthermore, we examined the effect of physiological integration on these defense strategies. Important Findings The combination of artificial leaf removal and jasmonic acid application produced a similar effect to that of leaf-feeding by the real herbivore. Physiological integration influenced the defense strategies of A. philoxeroides against herbivores, and increased biomass allocation to aboveground parts in its apical ramets damaged by real herbivores. Our study highlights the importance of physiological integration and modular plasticity for understanding the consequences of herbivory in clonal plants.
Death camas (Zigadenus spp.) is a common poisonous plant in North America with plants occurring in a wide variety of habitats with species of toxic concern occurring primarily in meadows, grasslands, shrublands, and mountains. The toxicity of Zigadenus species has been attributed to a series of steroidal alkaloids. The objective of this study was to evaluate zygacine and total steroidal alkaloid concentrations in different plant tissues of Zigadenus paniculatus as a function of plant maturity. Death camas plants were collected at two locations at different developmental growth stages representing vegetative, flower, seed pod, and shattered seed pod stages. Zygacine represented greater than 50% of the total steroidal alkaloids at all developmental stages. In bulbs, total steroidal alkaloid and zygacine concentrations did not change significantly as a function of plant phenology, and concentrations were lower than what were observed in above ground plant parts. Total steroidal alkaloid and zygacine concentrations in above ground parts were highest at early vegetative growth stages and decreased over the growing season. In plant reproductive parts, total steroidal alkaloid and zygacine concentrations increased until maturity and then decreased as the plant senesced. The concentrations of steroidal alkaloids reported here suggest that the toxic risk associated with death camas is greatest in the early vegetative growth stages followed by the flower and pod stages. There is a toxic risk to livestock as long as the plant is present, and caution should be taken when grazing livestock in areas with death camas until the plant senesces.
Water hemlock (Cicuta spp.) plants are typically found in wet areas and are toxic to all species of livestock. The toxic components in water hemlock are C17 polyacetylenes, with cicutoxin being the most studied. The objective of this study was to evaluate the variation in cicutoxin and total C17 polyacetylene compounds in water hemlock populations across western North America. Cicutoxin and total C17 polyacetylene concentrations varied among the six collection locations and among plant parts. Tubers contained the highest cicutoxin and total C17 polyacetylene concentrations of all plant parts. Green seeds contained the second most abundant total C17 polyacetylene concentrations. Total C17 polyacetylene and cicutoxin concentrations were also compared in different plant parts at several different phenological stages over the growing season. Cicutoxin and total C17 polyacetylene concentrations in the tubers increased until the green seed stage whereupon the concentrations decreased as the seeds matured and the plant began to senesce. Concentrations of secondary compounds in the stems were consistent with the optimal defense theory in which secondary compounds were higher in stems in earlier development stages compared to later stages and concentrations in seeds were higher than other above ground parts. The toxic compounds are found in all plant parts, with tubers posing the most significant risk of livestock poisoning. Results presented in this study suggest that the toxic risk to livestock likely does not differ between water hemlock (Cicuta maculata) populations across western North America under similar circumstances of ingestion.
Plants defend themselves against herbivore attack by constitutively producing toxic secondary metabolites, as well as by inducing them in response to herbivore feeding. Induction of secondary metabolites can cross plant tissue boundaries, such as from root to shoot. However, whether the potential for plants to systemically induce secondary metabolites from roots to shoots shows genetic variability, and thus, potentially, is under selection conferring fitness benefits to the plants is an open question. To address this question, we induced 26 maternal plant families of the wild species Cardamine hirsuta belowground (BG) using the wound-mimicking phytohormone jasmonic acid (JA). We measured resistance against a generalist (Spodoptera littoralis) and a specialist (Pieris brassicae) herbivore species, as well as the production of glucosinolates (GSLs) in plants. We showed that BG induction increased AG resistance against the generalist but not against the specialist, and found substantial plant family-level variation for resistance and GSL induction. We further found that the systemic induction of several GSLs tempered the negative effects of herbivory on total seed set production. Using a widespread natural system, we thus confirm that BG to AG induction has a strong genetic component, and can be under positive selection by increasing plant fitness. We suggest that natural variation in systemic induction is in part dictated by allocation trade-offs between constitutive and inducible GSL production, as well as natural variation in AG and BG herbivore attack in nature.
Organisms of the third trophic level can indirectly interact with plants. However, whether parasitoids of herbivores have a positive effect on plant fitness has been controversial. In addition to possible effects on plant fitness, parasitoid‐mitigated herbivory can modify plant physiological responses and thereby alter the plant‐mediated indirect interactions between different herbivore species. These types of indirect multitrophic interactions remain largely unexplored. Thus, to understand the full effect of the third trophic level on plants, it is necessary to consider the context of the community of interacting species, both herbivores and their enemies.
Here, we investigated whether parasitoids of leaf‐feeding caterpillars affect plant fitness (seed quantity and quality) and the consequences for seed‐dwelling insects at the second and third trophic levels through plant‐mediated effects. To test this, we exposed lima bean plants (Phaseolus lunatus), under controlled field conditions, to caterpillars (Spodoptera latifascia) that were unparasitized or parasitized by the parasitoid species Cotesia marginiventris. Later in the season, we measured seed production and infestation by seed beetles and their parasitoids.
We found that parasitoids significantly reduced the leaf damage inflicted by the caterpillars, such that the plants suffered no loss in seed production. Yet, parasitoids had no effect on the emergence of seed beetles (Zabrotes subfasciatus and Acanthoscelides obtectus), which was equally reduced in plants attacked by unparasitized and by parasitized caterpillars. Seeds from undamaged plants were significantly more attacked by Z. subfasciatus beetles. Parasitism rates of seed beetle larvae were similar for all treatments.
Although parasitized caterpillars did not damage the plants enough to reduce seed production (unlike unparasitized caterpillars), the damage they inflicted induced resistance against other herbivores. Taken together, these results show how parasitoids can indirectly enhance plant fitness in the context of the local multitrophic ecological networks. These findings have significant implications for natural and agricultural systems since they reveal that the indirect interaction between plants and parasitoids can be beneficial in communities with multiple herbivore species.
Crop domestication and selective breeding have altered plant defense mechanisms, influencing insect-plant interactions. A reduction in plant resistance/tolerance against herbivory is generally expected in domesticated species, however, limited efforts have been made to compare inducibility of plant defenses between wild and domesticated genotypes. In the present study, the inducibility of several plant defense mechanisms (e.g. defensive chemicals, trichomes, plant volatiles) were investigated, and the performance and preference of the herbivore Helicoverpa zea were measured in three different tomato genotypes; a) wild tomato, Solanum pimpinellifolium L. (accession LA 2093), b) cherry tomato, S. lycopersicum L. var. cerasiforme (accession Matts Wild Cherry), and c) cultivated tomato, S. lycopersicum L. var. Better Boy). Enhanced inducibility of defensive chemicals, trichomes, and plant volatiles in the cultivated tomato, and a higher level of constitutive plant resistance against herbivory in the wild genotype was observed. When comparing the responses of damaged vs. undamaged leaves, the percent reduction in larval growth was higher on damaged leaves from cultivated tomato, suggesting a higher induced resistance compared to other two genotypes. While all tomato genotypes exhibited increased volatile organic compound (VOCs) emissions in response to herbivory, the cultivated variety responded with generally higher levels of VOCs. Differences in VOC patterns may have influenced the ovipositional preferences, as H. zea female moths significantly preferred laying eggs on the cultivated versus the wild tomato genotypes. Selection of traits during domestication and selective breeding could alter allocation of resources, where plants selected for higher yield performance would allocate resources to defense only when attacked.
Elevational gradients have been highly useful for understanding the underlying forces driving variation in plant traits and plant-insect herbivore interactions. A widely held view from these studies has been that greater herbivory under warmer and less variable climatic conditions found at low elevations has resulted in stronger herbivore selection on plant defences. However, this prediction has been called into question by conflicting empirical evidence, which could be explained by a number of causes such as an incomplete assessment of defensive strategies (ignoring other axes of defence such as defence inducibility) or unaccounted variation in abiotic factors along elevational clines. We conducted a greenhouse experiment testing for inter-specific variation in constitutive leaf chemical defences (phenolic compounds) and their inducibility in response to feeding by gypsy moth larvae (Lymantria dispar L., Lepidoptera) using saplings of 18 oak (Quercus, Fagaceae) species. These species vary in their elevational distribution and together span >2400 m in elevation, therefore allowing us to test for among-species elevational clines in defences based on the elevational range of each species. In addition, we further tested for elevational gradients in the correlated expression of constitutive defences and their inducibility and for associations between defences and climatic factors potentially underlying elevational gradients in defences. Our results showed that oak species with high elevational ranges exhibited a greater inducibility of phenolic compounds (hydrolysable tannins), but this gradient was not accounted for by climatic predictors. In contrast, constitutive defences and the correlated expression of constitutive phenolics and their inducibility did not exhibit elevational clines. Overall, this study builds towards a more robust and integrative understanding of how multivariate plant defensive phenotypes vary along ecological gradients and their underlying abiotic drivers.
Plants defend themselves against diverse communities of herbivorous insects. This requires an investment of limited resources, for which plants also compete with neighbours. The consequences of an investment in defence are determined by the metabolic costs of defence as well as indirect or ecological costs through interactions with other organisms. These ecological costs have a potentially strong impact on the evolution of defensive traits, but have proven to be difficult to quantify.
We aimed to quantify the relative impact of the direct and indirect or ecological costs and benefits of an investment in plant defence in relation to herbivory and intergenotypic competition for light. Additionally, we evaluated how the benefits of plant defence balance its costs in the context of herbivory and intergenotypic competition.
To this end, we utilised a functional‐structural plant (FSP) model of Brassica nigra that simulates plant growth and development, morphogenesis, herbivory and plant defence. In the model, a simulated investment in defences affected plant growth by competing with other plant organs for resources and affected the level and distribution of herbivore damage.
Our results show that the ecological costs of intergenotypic competition for light are highly detrimental to the fitness of defended plants, as it amplifies the size difference between defended and undefended plants. This leads to herbivore damage counteracting the effects of intergenotypic competition under the assumption that herbivore damage scales with plant size. Additionally, we show that plant defence relies on reducing herbivore damage rather than the dispersion of herbivore damage, which is only beneficial under high levels of herbivore damage.
We conclude that the adaptive value of plant defence is highly dependent on ecological interactions and is predominantly determined by the outcome of competition for light.
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Premise of the Study
The rapid leaf movement of Mimosa pudica is expected to be costly because of energetic trade‐offs with other processes such as growth and reproduction. Here, we assess the photosynthetic opportunity cost and energetic cost of the unique leaf closing behavior of M. pudica.
Methods
In the greenhouse, we employed novel touch‐stimulation machines to expose plants to one of three treatments: (1) untouched control plants; (2) plants touch‐stimulated to close their leaves during the day to incur energetic costs associated with leaf movement and reduced photosynthesis; (3) plants touched at night to assess the effects of touch alone. M. pudica is nyctinastic and closes its leaves at night; thus, touching at night does not impart additional costs. We directly assessed costs by comparing physical traits. Leaf re‐opening response was measured to assess the potential for plant behavioral plasticity to impact photosynthetic opportunity costs.
Key Results
The cost of rapid leaf closure behavior was expressed as a 47% reduction in reproductive biomass accounting for the effect of touch. Touch itself changed physical traits such as biomass, with touched plants being generally bigger. Plants touched at night re‐opened their leaflets 26% quicker than plants touched during the day.
Conclusions
We reason that the reproductive allocation costs incurred by M. pudica can be attributed to a combination of photosynthetic opportunity cost and the energetic cost associated with increased stimulation of leaf movement and that behavioral plasticity has the potential to alter photosynthetic opportunity costs.
Several studies have shown that pre-infestation with aphids can improve plant quality for herbivorous caterpillars. This effect is often explained by the negative crosstalk between specific plant defence, signal-transduction pathways induced by aphids and caterpillars, respectively. However, in these studies caterpillars are introduced on the plants by the researcher, whereas in nature, the adult mother often chooses the food plants for her offspring. According to the preference–performance hypothesis adult females should choose oviposition sites that result in optimal performance and survival of their offspring. In this study, we investigated whether three lepidopteran species–Pieris brassicae (L.) (Pieridae), Plutella xylostella L. (Plutellidae) and Mamestra brassicae L. (Noctuidae)–prefer aphid-infested over clean plants. Adult females of the three species was given the choice between wild cabbage (Brassica oleracea L., Brassicaceae) plants infested with aphids, Brevicoryne brassicae (L.) (Hemiptera: Aphididae) for 3, 7, or 14 days vs. non-infested clean plants. Pieris brassicae females was also given the choice between plants dually infested with B. brassicae aphids and P. xylostella caterpillars when the order of infestation was varied. For oviposition, adult females of all three species did not discriminate between aphid-infested and clean plants, irrespective of the duration of aphid infestation. Also, P. brassicae females did not discriminate between sets of dually infested plants, irrespective of the order of infestation. Several mechanisms are discussed that could explain this lack of preference.
Phenotypic plasticity is thought to impact evolutionary trajectories by shifting trait values in a direction that is either favored by natural selection (“adaptive plasticity”) or disfavored (“nonadaptive” plasticity). However, it is unclear how commonly each of these types of plasticity occurs in natural populations. To answer this question, we measured glucosinolate defensive chemistry and reproductive fitness in over 1,500 individuals of the wild perennial mustard Boechera stricta, planted in four common gardens across central Idaho, USA. Glucosinolate profiles—including total glucosinolate concentration as well as the relative abundances and overall diversity of different compounds—were strongly plastic both among habitats and within habitats. Patterns of glucosinolate plasticity varied greatly among genotypes. Plasticity among sites was predicted to affect fitness in 27.1% of cases; more often than expected by chance, glucosinolate plasticity increased rather than decreased relative fitness. In contrast, we found no evidence for within‐habitat selection on glucosinolate reaction norm slopes (i.e., plasticity along a continuous environmental gradient). Together, our results indicate that glucosinolate plasticity may improve the ability of B. stricta populations to persist after migration to new habitats.
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Maternal effects play important evolutionary and ecological roles. Amictic female mothers of monogonont rotifer Brachionus calyciflorus can transmit predatory information of Asplanchna brightwellii in their environment to their offspring by changing the offspring's defensive morphology to increase their fitness. However, it remains unclear whether such maternal effects also exist during sexual reproduction of a mictic mother. This study explored the maternal effect in mictic mothers using the B. calyciflorus and A. brightwellii as a prey-predator model. We collected resting eggs from two groups of mictic mothers that previously experienced environments with (P environment) or without (NP environment) Asplanchna kairomones. Stem females from the resting eggs of each maternal group were also hatched and reared in P and NP environments. The population growth rate of offspring who experienced the same environment as their mictic mothers was significantly higher than those that experienced a different environment. When exposed to a gradient of predator kairomone levels, the posterolateral spine of the offspring elongated with increasing kairomone concentration. Offspring from the P mictic mother showed significantly shorter posterolateral spines than those from the NP mictic mother at each predator kairomone level. Offspring originating from NP mictic mothers clearly elongated their posterolateral spines at low concentrations of predator kairomones, while those from P mothers elongated their posterolateral spines only at the highest levels of predator kairomone. Our findings highlight the existence of anticipatory maternal effects during the sexual process via resting eggs of B. calyciflorus in response to predator kairomone.
Background
Plants and insects have coexisted for million years and evolved a set of interactions which affect both organisms at different levels. Plants have developed various morphological and biochemical adaptations to cope with herbivores attacks. However, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has become the major pest threatening tomato crops worldwide and without the appropriated management it can cause production losses between 80 to 100%. ResultsThe aim of this study was to investigate the in vivo effect of a serine proteinase inhibitor (BTI-CMe) and a cysteine proteinase inhibitor (Hv-CPI2) from barley on this insect and to examine the effect their expression has on tomato defensive responses. We found that larvae fed on tomato transgenic plants co-expressing both proteinase inhibitors showed a notable reduction in weight. Moreover, only 56% of these larvae reached the adult stage. The emerged adults showed wings deformities and reduced fertility. We also investigated the effect of proteinase inhibitors ingestion on the insect digestive enzymes. Our results showed a decrease in larval trypsin activity. Transgenes expression had no harmful effect on Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae), a predator of Tuta absoluta, despite transgenic tomato plants attracted the mirid. We also found that barley cystatin expression promoted plant defense by inducing the expression of the tomato endogenous wound inducible Proteinase inhibitor 2 (Pin2) gene, increasing the production of glandular trichomes and altering the emission of volatile organic compounds. Conclusion
Our results demonstrate the usefulness of the co-expression of different proteinase inhibitors for the enhancement of plant resistance to Tuta absoluta.
Many plants respond to herbivory by increasing expression of defensive traits. The defensive response of plants can vary depending on plant condition, seasonality, and time of day. Due to a lack of field-based studies, it is unclear how temporal variability in defensive response may alter future rates of herbivory within ecological communities. In a series of simulated herbivory experiments, I quantified how the timing of leaf damage in mountain sagebrush (Artemisia tridentata ssp. vaseyana) affects future herbivory. An identical leaf damage treatment was applied across 12 time windows to test how the effectiveness of response to herbivore damage changes along 3 interacting temporal scales: diel, seasonal, and annual. In contrast to several studies demonstrating induced resistance to herbivory in sagebrush, prevention of future herbivory was only detected following summer afternoon leaf damage in one of three years. These findings suggest that the timing of experimental leaf damage is one of many factors contributing to variability in field-based plant defensive induction studies. This article is protected by copyright. All rights reserved.
How herbivores respond to resource heterogeneity is important for predicting plant resistance to herbivores. Experimental studies thus far have revealed that herbivore responses differ depending on whether herbivores are offered single or multiple plant types, but the reports have rarely been combined. Here, we conducted a meta-analysis of 47 publications on choice and no-choice experiments to reveal how the presence/absence of multiple plants (i.e., choice/no-choice conditions) alters the extent of behavioral avoidance by herbivores. The herbivore diet breadth and response traits (feeding, growth, or oviposition) explained a significantly large amount of heterogeneity in the herbivore response under choice and no-choice conditions. In contrast, a small amount of heterogeneity was explained by the herbivore types (vertebrates, exophagous, or endophagous invertebrates), plant resistance traits (chemical or nonchemical), plant life form, and relatedness of plant pairs (intraspecific or interspecific) as well as interactions between the herbivore and plant characteristics. Compared with the no-choice conditions, specialist herbivores further avoided suboptimal plants under choice conditions. Generalist herbivores more evenly utilized optimal and suboptimal plants under choice conditions. The avoidance of suboptimal plants under choice conditions was the most prominent in oviposition response. Thus, our meta-analysis found that herbivore characteristics rather than plant traits were more responsible for driving behavioral avoidance by herbivores to a particular plant. The contrasting response between specialist and generalist herbivores to plant heterogeneity may be more ubiquitous than previously thought.
Populations of herbivorous insects are naturally consumed by other predacious or predatory insect species. These entomophagous insects are thus plant-dwelling organisms that use the plant for several vital functions and are affected by plant traits at the evolutionary, organism and population levels. Many entomophagous species are used for the biological control of insect pests worldwide. The aim of this chapter is to provide an exhaustive review of mechanisms underlying the interactions between plants and entomophagous insects, including those governing life history traits at the individual level, as well as those acting on population and community structure and dynamics. We detail how properties of host-infested plants determine parasitism behaviour, development (in the case of parasitoids) and nectar consumption by adult entomophagous insects. We detail how plants respond to and benefit from natural enemies attacking insect herbivores. We also illustrate how plant architecture, the vegetation communities and their climatic correlates can influence predator and parasitoid behaviour and populations. This chapter considers the biology and ecology of the interactions and mentions some implications for the biological control of plant pests.
The combination of defensive traits leads to the evolution of 'plant defense syndromes' which should provide better protection against herbivores than individual traits on their own. Defense syndromes can be generally driven by plant phylogeny and/or biotic and abiotic factors. However, we lack a solid understanding of (i) the relative importance of shared evolution vs. convergence due to similar ecological conditions and (ii) the role of induced defense strategies in shaping defense syndromes. We investigate the relative roles of evolutionary and ecological factors shaping the deployment of pine defense syndromes including multiple constitutive and induced chemical defense traits. We performed a greenhouse experiment with seedlings of eighteen species of Pinaceae family, and measured plant growth rate, constitutive chemical defenses and their inducibility. Plant growth rate, but not phylogenetic relatedness, determined the deployment of two divergent syndromes. Slow-growing pine species living in harsh environments where tissue replacement is costly allocated more to constitutive defenses (energetically more costly to produce than induced). In contrast, fast-growing species living in resource-rich habitats had greater inducibility of their defenses, consistent with the theory of constitutive-induced defense trade-offs. This study contributes to a better understanding of evolutionary and ecological factors driving the deployment of defense syndromes.
Ecological theory indicates that warmer and more stable climates should result in stronger biotic interactions. Therefore, plant species growing at lower elevations and experiencing greater herbivore pressure should invest in higher levels of defences than those at higher elevations. Nonetheless, there are a number of studies that have found no effect of elevational gradients on plant defensive traits. Several factors might explain the lack of consistency for the altitude–defence relationships, including (i) the reduction of all defensive traits into one measure of resistance; (ii) not considering plant defence as the simultaneous expression of several defensive traits; and (iii) not considering the relative influence of biotic (e.g. herbivory) and abiotic (e.g. climate and soil conditions) factors associated with the ecological gradient.
Here, we present a comprehensive test of the effects of elevation and its associated biotic and abiotic factors on the individual and simultaneous expression of constitutive direct and indirect defences and their inducibility (i.e. expression of defences after herbivore attack). Specifically, we estimated climatic and soil variables and measured herbivore damage and constitutive and jasmonic acid‐induced glucosinolate levels in the leaves as a proxy for direct defences, and volatile emission as a proxy for indirect defences in 16 Cardamine species naturally growing along the steep elevational gradient of the Alps.
Within a phylogenetic comparative framework, we found that species growing at lower elevations invested more in the simultaneous inducibility of both direct and indirect defences, whereas species growing at higher elevations invested more in constitutive direct defences. Although we found strong elevational gradients in herbivory and climatic and soil variables, these biotic and abiotic factors only partially explained elevational patterns in plant defences.
Synthesis . These results highlight that the complex regulation of multiple defence traits strongly vary across elevational gradients and build towards a better understanding of the multiple mechanisms underlying trait evolution and species interactions along ecological gradients.
Introduction Ecologists have traditionally recognized the consequences that direct interactions between species have on the functioning of ecological communities and on the flow of energy through food webs (Pimm 2002). However, ecological communities are among the most complex natural systems, and thus the interactions between species are far from simple. In this respect, the importance of indirect effects (those effects transmitted from one species to another through one or more intermediate species) as a determinant of the structure and dynamics of ecological communities has been clearly acknowledged only in recent years (Wootton 1994, Abrams 1995, Abrams et al. 1996). Indirect effects are those transmitted from one species to another through one or more intermediate species. These indirect effects can be propagated through food webs as a consequence of changes in the density of the intervening species, a mechanism known as density-mediated indirect interaction (DMII) (Abrams 1995, Werner and Peacor 2003). Nevertheless, indirect effects can also occur through changes in the phenotypes of the interacting organisms, a mechanism known as trait-mediated indirect interaction (TMII) (Werner and Peacor 2003, Schmitz et al. 2004). Although DMIIs have been traditionally considered to be the main source of any variation in ecological communities, ecologists are progressively more conscious of the essential role played by TMIIs (Bolker et al. 2003, Dill et al. 2003, Luttbeg et al. 2003, Trussell et al. 2003, Werner and Peacor 2003; and chapters throughout this volume). © Cambridge University Press 2007 and Cambridge University Press, 2009.
The emission of fragrances can qualitatively and quantitatively differ in different parts of flowers. A detailed analysis was initiated to localize the floral tissues and cells which contribute to scent synthesis in Stephanotis floribunda (Asclepiadaceae) and Nicotiana suaveolens (Solanaceae). The emission of scent compounds in these species is primarily found in the lobes of the corollas and little/no emission can be attributed to other floral organs or tissues. The rim and centre of the petal lobes of S. floribunda contribute equally to scent production since the amount of SAMT (salicylic acid carboxyl methyltransferase) and specific SAMT activity compensate each other in the rim region and centre region. In situ immunolocalizations with antibodies against the methyl benzoate and methyl salicylate-synthesizing enzyme indicate that the adaxial epidermis with few subepi-dermal cell layers of S. floribunda is the site of SAMT accumulation. In N. suaveolens flowers, the petal rim emits twice as much methyl benzoate due to higher total protein concentrations in the rim versus the petal centre; and, both the adaxial and ab-axial epidermis house the BSMT (salicylic acid/benzoic acid car-boxyl methyltransferase).
Higher plants synthesize an amazing diversity of phenolic secondary metabolites. Phenolics are defined secondary metabolites or natural products because, originally, they were considered not essential for plant growth and development. Plant phenolics, like other natural compounds, provide the plant with specific adaptations to changing environmental conditions and, therefore, they are essential for plant defense mechanisms. Plant defensive traits are costly for plants due to the energy drain from growth toward defensive metabolite production. Being limited with environmental resources, plants have to decide how allocate these resources to various competing functions. This decision brings about trade-offs, i.e., promoting some functions by neglecting others as an inverse relationship. Many studies have been carried out in order to link an evaluation of plant performance (in terms of growth rate) with levels of defense-related metabolites. Available results suggest that environmental stresses and stress-induced phenolics could be linked by a transduction pathway that involves: (i) the proline redox cycle; (ii) the stimulated oxidative pentose phosphate pathway; and, in turn, (iii) the reduced growth of plant tissues.
The evaluation and use of endogenous soybean genes is an effective strategy to minimize the yield losses caused by insects. Allene oxide cyclase (AOC) catalyzes the most important step in the biosynthesis of jasmonate (JA), which plays a crucial role in plant defense against insects. In this study, the role of GmAOC3 in plant insect resistance was evaluated. Real-time PCR results indicate that GmAOC3 was uniquely and rapidly activated and attained peak expression in leaves after attack by the common cutworm (CCW). In insect bioassays, transgenic lines overexpressing GmAOC3 were significantly less damaged than wild-type plants, and the relative growth rate of CCW fed with leaves from transgenic lines was significantly lower than that of CCW fed with leaves from wild-type plants. Electron microscopy revealed that the density of leaf trichomes in transgenic lines overexpressing GmAOC3 was greater than that in wild-type tobacco. Several physiological and morphological indicators, including JA, phenolic content and the relative expression levels of the putrescine N-methyltransferase (PMT) and proteinase inhibitor (PI) genes, phenylalanine ammonia lyase (PAL) activity and volatile substances, increased in the transgenic plants overexpressing GmAOC3. Our findings indicate that GmAOC3 plays an important role in soybean resistance to CCW and can be used as a resource for plant breeding. © 2015, Korean Society of Plant Biologists and Springer-Verlag Berlin Heidelberg.
Selfing can evolve if the transmission advantage of selfers outweighs the negative effects of inbreeding depression. It has been hypothesised that on the long term, selfing lineages are an evolutionary dead end, in part due to genetic degradation resembling that of Muller’s ratchet in asexual lineages. There is a lack of empirical evidence for costs of selfing due to genetic degradation in recently evolved selfers. We tested whether such costs are apparent in recently established selfing populations of the generally outcrossing species Arabidopsis lyrata. Specifically, we compared selfing and outcrossing populations in their growth performance, and for traits that play a putative role in defence against herbivores. In line with our expectations, selfing populations had reduced germination rates, growth however was similar to outcrossing populations. Plants from selfing populations showed no consistent reduction in herbivore-defence traits, and were equally palatable to caterpillars of the moth Mamestra brassicae. There were also no differences between outcrossers and selfers in phenotypic plasticity for putative defence traits and palatability after induction by herbivores. Overall, we interpret our results as showing some evidence for persistent costs of selfing due to drift or inbreeding load in terms of reduced seedling establishment, but providing no support for the hypothesis that selfing populations should be more susceptible to generalist herbivores, or rely more on induced defence.
Aims This systematic review highlights the relative support and implications of the attractant-decoy and repellent-plant hypotheses,
discussing important linkages between these theories and the opportunity for novel integration into ecological and applied
research.
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