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Flowers with caffeinated nectar receive more pollination
Abstract
Floral nectar functions to attract insects, so the inclusion of toxic compounds calls for explanation. Recent work shows that honeybees prefer nectars with low concentrations of caffeine and nicotine, and that associative learning by honeybees is enhanced by caffeine, prompting speculation that pollination service could be enhanced. We directly tested caffeine’s effect on pollination service by allowing bumblebee colonies to feed on arrays of artificial flowers that offer nectar while also dispensing and receiving dye particles as pollen analogues. With caffeine levels signaled by flower color (blue, green, or yellow) in a factorial design, flowers offering nectar with 10−5 M caffeine received significantly more pollen analogue than did those with 10−4 M caffeine or with no caffeine. Effects of caffeine were unaffected by which colors were associated with which caffeine levels: Color alone had no significant effect, and there was no interaction between color and caffeine level. In cases where greater pollination service translates to increased fitness, we would expect stabilizing selection to maintain nectar caffeine at intermediate levels.
... Unlike previous work (Table 1), we did not assess the effects of OA and TA in isolation, since we always found them together in Citrus nectar, while CA presence varied. We examined the effects of these biogenic amines on four behaviors previously studied in the context of nectar chemistry (Si et al., 2005;Singaravelan et al., 2005;Thomson et al., 2015;Wright et al., 2013), with relevance for plant fitness (Burns, 2005;Cayenne Engel and Irwin, 2003): sucrose responsiveness, floral visitation rate, floral preferences, and early long-term memory performance. ...
... At the concentrations we found in Citrus x meyeri, bees had an aversion to CA, generally agreeing with previous findings. For example, Thomson et al. (2015) found indirect evidence for dose-dependent CA preferences in bumblebees: flowers with a low concentration of CA (0.01mM) received more pollen than flowers containing either a higher concentration (1mM) or no CA (Thomson et al., 2015). The concentration of CA in our free-flying experiment (0.04 mM) lies between the two concentrations of CA used in that study. ...
... At the concentrations we found in Citrus x meyeri, bees had an aversion to CA, generally agreeing with previous findings. For example, Thomson et al. (2015) found indirect evidence for dose-dependent CA preferences in bumblebees: flowers with a low concentration of CA (0.01mM) received more pollen than flowers containing either a higher concentration (1mM) or no CA (Thomson et al., 2015). The concentration of CA in our free-flying experiment (0.04 mM) lies between the two concentrations of CA used in that study. ...
Nectar chemistry can influence the behavior of pollinators in ways that affect pollen transfer, yet basic questions about how nectar chemical diversity impacts plant-pollinator relationships remain unexplored. For example, plants’ capacity to produce neurotransmitters and endocrine disruptors may offer a means to manipulate pollinator behavior. We surveyed 15 plant species and discovered that two insect neurotransmitters, octopamine and tyramine, were widely distributed in floral nectar. We detected the highest concentration of these chemicals in Citrus, alongside the well-studied alkaloid caffeine. We explored the separate and interactive effects of these chemicals on insect pollinators in a series of behavioral experiments on bumblebees (Bombus impatiens). We found that octopamine and tyramine interacted with caffeine to alter key aspects of bee behavior relevant to plant fitness (sucrose responsiveness, long-term memory, and floral preferences). These results provide evidence for a means by which synergistic or antagonistic nectar chemistry might influence pollinators.
... Nevertheless, a large body of empirical work examines how herbivores can indirectly affect pollinator visitation via physical and chemical changes in the plant's trait expression (Strauss et al. 1996;Krupnick et al. 1999;Kessler et al. 2011;Schiestl et al. 2011;Barber et al. 2012;Ghyselen et al. 2016;Chautá et al. 2017). In some cases, traits involved in herbivore defense, such as toxic secondary metabolites, can also affect pollinator visitation (Adler 2000;Gegear et al. 2007;Adler et al. 2012;Thomson et al. 2015;Jones and Agrawal 2016). Therefore, plant-pollinator-herbivore interactions provide a test case to examine how eco-evolutionary feedbacks between two species shape evolutionary responses of traits that mediate another kind of species interaction, as well as how feedbacks from one trait may affect two kinds of interactions. ...
... When τ < 0, increasing a plant's constitutive toxin level z (R) Tox has a negative direct effect on pollinator foraging (e.g., toxin is present in the nectar and acts as a deterrent to nectar feeders, Gegear et al. 2007). When τ > 0, increasing a plant's constitutive toxin level z (R) Tox has a positive direct effect on pollinator foraging (e.g., toxin in nectar attracts pollinators to forage more, Ehlers and Olesen 1997;Kevan et al. 2015;Thomson et al. 2015). The pollinator also has a conversion efficiency for converting harvested nectar into pollinator offspring, denoted as the parameter b, and an intrinsic death rate, denoted as the parameter f . ...
... Conversely, when the pollinator is attracted by toxins (τ > 0), the plant's abundance increases, causing the plant to evolve lower nectar provisioning but higher toxin levels. Certain chemical compounds found in nectar, such as caffeine and alcohols, can attract pollinators to forage more frequently and to prefer individuals with these defense compounds in their nectar (Ehlers and Olesen 1997;Couvillon et al. 2015;Kevan et al. 2015;Thomson et al. 2015). Hypothetically, plants could also evolve mechanisms to exclude deterrent toxins from floral resources (Adler et al. 2012;Manson et al. 2012;Cook et al. 2013). ...
Eco‐evolutionary feedbacks among multiple species occur when one species affects another species’ evolution via its effects on the abundance and traits of a shared partner species. What happens if those two species enact opposing effects on their shared partner's population growth? Further, what if those two kinds of interactions involve separate traits? For example, many plants produce distinct suites of traits that attract pollinators (mutualists) and deter herbivores (antagonists). Here, we develop a model to explore how pollinators and herbivores may influence each other's interactions with a shared plant species via evolutionary effects on the plant's nectar and toxin traits. The model results predict that herbivores indirectly select for the evolution of increased nectar production by suppressing plant population growth. The model also predicts that pollinators indirectly select for the evolution of increased toxin production by plants and increased counter‐defenses by herbivores via their positive effects on plant population growth. Unless toxins directly affect pollinator foraging, plants always evolve increases in attraction and defense traits when they interact with both kinds of foragers. This work highlights the value of incorporating ecological dynamics to understand the entangled evolution of mutualisms and antagonisms in natural communities. This article is protected by copyright. All rights reserved
... Plants produce a wide variety of secondary metabolic compounds such as alkaloids that mediate plant-animal interactions (Schoonhoven et al., 2005). These phytochemicals are found in nectar and in plant tissues at different concentrations and, although the dose-dependent role of some of them in attracting and rewarding pollinators has been demonstrated (Stevenson et al., 2017;Wright et al., 2013), they are generally regarded as defense mechanisms to reduce damage from non-adapted phytophagous animals, because they are bitter tasting and toxic (Adler, 2000;Muñoz et al., 2020;Mustard, 2020;Szentesi & Wink, 1991;Thomson et al., 2015). In the context of evolutionary arms race, the complex mechanisms of secondary metabolite production evolved by plant species to resist herbivory have, in return, made herbivores adapt a wide range of mitigation processes of their negative effects (Dearing et al., 2005). ...
... (Malvales: Tiliaceae) (Naef et al., 2004) in temperate regions. Caffeine effects are well documented on the animal brain and body, including on arthropods (Mustard, 2014;Thomson et al., 2015). Its role in protecting plants against herbivores and pathogens (Ashihara et al., 2008;Sano et al., 2013), and in influencing herbivore and pollinator behaviours is well understood (Couvillon et al., 2015;Prado et al., 2021;Wright et al., 2013). ...
... At high doses, caffeine is toxic for phytophagous insects, it can shorten life span, and deter pollinators from visiting plants and reduce their memory (Ashihara et al., 2008;Mustard, 2014;Nikitin et al., 2008). At low doses in laboratory studies, caffeine enhances pollinator memory of reward and increases pollination (Thomson et al., 2015;Wright et al., 2013). ...
Secondary metabolites are central to understanding the evolution of plant-animal interactions. Direct effects on phytophagous animals are well-known, but how secondary consumers adjust their behavioral and physiological responses to the herbivore's diet remains more scarcely explored for some metabolites. Caffeine is a neuroactive compound that affects both the behaviour and physiology of several animal species, from humans to insects. It is an alkaloid present in nectar, leaves and even sap of numerous species of plants where it plays a role of chemical defenses against herbivores and pathogens. Caffeine effects have been overlooked in generalist herbivores, that are not specialized on coffee or tea plants. Using a host-parasitoid system, we show that caffeine intake at relatively low dose affects longevity and fecundity of the primary consumer, but also indirectly of the secondary one, suggesting that this alkaloid and/or its effects can be transmitted through trophic levels and persist in the food chain. Parasitism success was lowered by ≈16% on hosts fed with caffeine, and parasitoids of the next generation that have developed in hosts fed on caffeine showed a reduced longevity, but no differences in mass and size were found. This study helps at better understanding how plant secondary metabolites, such as caffeine involved in plant-animal interactions, could affect primary consumers, could have knock-on effects on upper trophic levels over generations, and could modify interspecific interactions in multitrophic systems.
... This has been exploited, for example, to isolate the influence of shape, color, odor, and chemical rewards in plant pollination. While flower nectar is an attractant and reward (Thomson, Draguleasa, & Tan, 2015), some nectar also contains caffeine, which both a stimulant and toxic to most organisms. While flower nectar is an attractant and reward, many plants produce nectar that is toxic or repellent to some floral visitors (Adler, 2000). ...
... Investigating this counterintuitive pairing in nature had proved almost impossible and previous studies reported mixed results. However, Thomson et al. (2015) used 3D prints to mimic the function of a flower's anther and stamen in collecting and depositing pollen. They printed small hoppers that deposited dye onto a bee when it brushed under the hopper to reach the nectar. ...
... By measuring the amount of dye transferred, the authors found that the higher the caffeine content of the nectar the more bee visits (Thomson et al., 2015), possibly due to the improvement in memory formation provided by caffeine (Wright et al., 2013). ...
In the commercial and medical sectors, 3D printing is delivering on its promise to enable a revolution. However, in the fields of Ecology and Evolution we are only on the brink of embracing the advantages that 3D printing can offer. Here we discuss examples where the process has enabled researchers to develop new techniques, work with novel species, and to enhance the impact of outreach activities. Our aim is to showcase the potential that 3D printing offers in terms of improved experimental techniques, greater flexibility, reduced costs and promoting open science, while also discussing its limitations. By taking a general overview of studies using the technique from fields across the broad range of Ecology and Evolution, we show the flexibility of 3D printing technology and aim to inspire the next generation of discoveries.
... First, many floral compounds attract pollinators, but repel ants and other non-pollinating insects (Stephenson 1982, Junker and Bl€ uthgen 2010, Galen et al. 2011, Junker et al. 2011a) and inhibit microbes (Dobson and Bergstrom 2000, Huang et al. 2012, Junker and Tholl 2013. In some cases, however, nectar chemicals can deter consumption by pollinators (Hagler et al. 1990, Hagler and Buchmann 1993, Kessler et al. 2008, Barlow et al. 2017), with negative as well as positive effects on plant reproduction in different systems (Adler and Irwin 2005, Kessler et al. 2008, Thomson et al. 2015). Second, the same compound can have different consequences at different doses. ...
... Second, the same compound can have different consequences at different doses. For example, low concentrations of caffeine in nectar improved pollinator memory and increased pollination services to artificial flowers (Wright et al. 2013, Thomson et al. 2015, but high concentrations of caffeine and other compounds deterred pollinators (Singaravelan et al. 2005, Wright et al. 2013). Third, compounds may have different effects in the context of chemical mixtures. ...
... Although qualitative assays of particular compound classes date back many decades (Baker 1977, Dobson 1988, quantitative assessments are still limited to a handful of plant species, and often target particular compounds. Within species, chemical composition of floral rewards can vary at the scale of individual plants, patches, and populations (Kessler et al. 2012, and this variation can influence plant-pollinator interactions (Kessler et al. 2012, Thomson et al. 2015, Barlow et al. 2017). However, even in well-studied species, little is known about the extent of, or contributors to, intraspecific variation in nectar and pollen chemistry. ...
Floral chemistry mediates plant interactions with pollinators, pathogens, and herbivores, with major consequences for fitness of both plants and flower visitors. The outcome of such interactions often depends on compound dose and chemical context. However, chemical diversity and intraspecific variation of nectar and pollen secondary chemistry are known for very few species, precluding general statements about their composition. We analyzed methanol extracts of flowers, nectar, and pollen from 31 cultivated and wild plant species, including multiple sites and cultivars, by liquid‐chromatography–mass‐spectrometry. To depict the chemical niche of each tissue type, we analyzed differences in nectar and pollen chemical richness, absolute and proportional concentrations, and intraspecific variability. We hypothesized that pollen would have higher concentrations and more compounds than nectar, consistent with Optimal Defense Theory and pollen's importance as a male gamete. To investigate chemical correlations across and within tissues, which could reflect physiological constraints, we quantified chemical overlap between conspecific nectar and pollen, and phenotypic integration of individual compounds within tissue types. Nectar and pollen were chemically differentiated both across and within species. Of 102 compounds identified, most occurred in only one species. Machine‐learning algorithms assigned samples to the correct species and tissue type with 98.6% accuracy. Consistent with our hypothesis, pollen had 23.8‐ to 235‐fold higher secondary chemical concentrations and 63% higher chemical richness than nectar. The most common secondary compound classes were flavonoids, alkaloids, terpenoids, and phenolics (primarily phenylpropanoids including chlorogenic acid). The most common specific compound types were quercetin and kaempferol glycosides, known to mediate biotic and abiotic effects. Pollens were distinguished from nectar by high concentrations of hydroxycinnamoyl‐spermidine conjugates, which affect plant development, abiotic stress tolerance, and herbivore resistance. Although chemistry was qualitatively consistent within species and tissue types, concentrations varied across cultivars and sites, which could influence pollination, herbivory, and disease in wild and agricultural plants. Analyses of multivariate trait space showed greater overlap across sites and cultivars in nectar than pollen chemistry; this overlap reflected greater within‐site and within‐cultivar variability of nectar. Our analyses suggest different ecological roles of nectar and pollen mediated by chemical concentration, composition, and variability.
... By having captive bees visit arrays of two 'species' of artificial flowers with different nectar rewards, we achieved complete control over spacing, context and reward. By devising the flowers to dispense and receive different colours of powdered food dyes serving as pollen analogues ( Fig. 1A; see also Thomson et al., 2015), we could analyse 'stigma loads' colourimetrically to determine how much conspecific and heterospecific 'pollen' the flowers received. ...
... We used artificial flowers that were co-sexual ( Fig. 1A; for further description and photographs, see Thomson et al., 2015), unlike an earlier 'diclinous' design with separate sexes . Briefly, a squat screw-top jar serves as a reservoir for sucrose solution. ...
... After bees have interacted with the flowers for an experimental period, we remove each stigma, dissolve the dye in a known volume of water and determine the amounts of each dye by spectrophotometry. The amounts of the two dye colours can be determined by mathematically decomposing the combined absorption spectra (details in Thomson et al., 2015). ...
Background and aims:
If two plant species share pollinators, it has been proposed that the interaction between them may range from competitive to facilitative, depending on the way in which they intermingle. In particular, the presence of a rewarding plant species may increase the rate of pollinator visitation to a less rewarding species in its vicinity, but the beneficial increase in visitation may be counteracted by a detrimental increase in heterospecific pollen transfer. We assessed this trade-off using bumble-bees foraging over a gradual spatial transition between two plant species in an indoor cage experiment.
Methods:
We used two 'species' of artificial flowers - one more rewarding than the other - in arrays that varied in the degree of species intermingling. The flowers dispensed and received powdered food dyes serving as pollen analogues. Captive bumble-bees visited to collect sucrose solution. We quantified dye delivery to the adhesive-tape 'stigmas' in flowers by spectrophotometry.
Key results:
Across the spatial transition between species, the less attractive species received more dye (more bee visits) when in proximity to the more attractive species than it did when alone, but the larger dye loads were less pure (more heterospecific pollen transfer). The decline in purity cancelled out the gain in acquisition, so conspecific pollen receipt by the less attractive species was neutrally affected. The more attractive species received fewer visits when surrounded by the less attractive species, so the interaction between the two species was amensalism when considering conspecific pollen reception.
Conclusions:
Pollinator-mediated interactions between plant species depend on pollination quantity and purity, both of which can depend on spatial intermingling.
... For example, caffeine causes bees to form stronger, longer-lasting associations between odours and rewards, although such effects tend to be shortlived (Wright et al. 2013;Arnold et al. 2021). Additionally, it leads to bees overestimating resource quality, increasing foraging frequency and recruitment (Singaravelan et al. 2005;Couvillon et al. 2015;Thomson et al. 2015). ...
... Increased pollination of flowers offering moderate concentrations of caffeine in nectar (Thomson et al. 2015). ...
Argentine ants Linepithema humile are one of the most damaging invasive alien species worldwide. Enhancing or disrupting cognitive abilities, such as learning, has the potential to improve management efforts, for example by increasing preference for a bait, or improving ants’ ability to learn its characteristics or location. Nectar-feeding insects are often the victims of psychoactive manipulation, with plants lacing their nectar with secondary metabolites such as alkaloids and non-protein amino acids which often alter learning, foraging, or recruitment. However, the effect of neuroactive chemicals has seldomly been explored in ants. Here, we test the effects of seven potential neuroactive chemicals—two alkaloids: caffeine and nicotine; two biogenic amines: dopamine and octopamine, and three nonprotein amino acids: β-alanine, GABA and taurine—on the cognitive abilities of invasive L. humile using bifurcation mazes. Our results confirm that these ants are strong associative learners, requiring as little as one experience to develop an association. However, we show no short-term effect of any of the chemicals tested on spatial learning, and in addition no effect of caffeine on short-term olfactory learning. This lack of effect is surprising, given the extensive reports of the tested chemicals affecting learning and foraging in bees. This mismatch could be due to the heavy bias towards bees in the literature, a positive result publication bias, or differences in methodology.
... Plant chemicals also manipulate learning in bees to augment pollination. Nectar caffeine, for example, enhances memory in honeybees for floral traits associated with food rewards increasing revisitation to food rewards and increased pollen transfer to caffeinated flowers (Couvillon et al. 2015;Thomson et al. 2015;Wright et al. 2013). ...
... Further, learning is likely to be important in mediating responses by insects. In the case of pollinators, honeybees especially are well known to employ learning to optimise foraging (Couvillon et al. 2015;Thomson et al. 2015;Wright et al. 2013), and interpretation of homoterpene detection may involve integration with visual cues. This is important because a pollinator attracted to a plant by homoterpenes within HIPV blends (rather than as floral synomones) will encounter a plant under herbivore attack and this may reduce the plant's capacity to produce nectar and pollen so rendering it less rewarding than an uninfested plant that was not releasing homoterpene-containing HIPVs. ...
The homoterpenes 4,8‐dimethyl‐1,3,7‐nonatriene (DMNT) and 4,8,12‐trimethyl‐1,3,7,11‐tridecatetraene (TMTT) are volatile products of plant metabolism reported from diverse plant taxa and multiple plant tissues. As such, they have a range of potential ecological functions. Here, we review the key literature to assess evidence for roles in contrasting plant–arthropod interactions. TMTT, and DMNT especially, have been reported as sometimes dominant constituents of floral scents from angiosperm taxa ranging from primitive Magnoliales to more advanced, taxonomic orders of economic significance such as Fabales and Sapindales. Although all taxa producing TMTT and DMNT in floral scents are entomophilous (‘insect pollinated’), experimental evidence for an assumed role of these homoterpenes in pollinator attraction is limited. Representing a trade‐off, in some cases, homoterpenes in floral scents have been shown to act as kairomones, attracting herbivores. Additionally, both TMTT and DMNT are released by plant foliage in response to arthropod feeding, mechanical damage simulating feeding, or even egg deposition. Evidence for a functional role in herbivore‐induced plant volatile (HIPV) blends comes from a wide range of angiosperm orders, including anemophilous (‘wind pollinated’) taxa, as well as from gymnosperms. We conclude by considering how TMTT and DMNT function in community‐level interactions and highlighting research priorities that will reveal how plants avoid trade‐offs from contrasting ecological functions of DMNT and TMTT release and how homoterpene production might be exploited to develop improved crop varieties.
... This can be taken still further. Research over the last decade, building on earlier work, has demonstrated that both honeybees and bumblebees have behavioural responses to caffeine (Couvillon et al., 2015;Thomson et al., 2015). Tethered honeybees formed longer-lasting memory associations with odour when provide with caffeine during training ; caffeinated artificial flowers received more visits by bumblebees (Thomson et al., 2015). ...
... Research over the last decade, building on earlier work, has demonstrated that both honeybees and bumblebees have behavioural responses to caffeine (Couvillon et al., 2015;Thomson et al., 2015). Tethered honeybees formed longer-lasting memory associations with odour when provide with caffeine during training ; caffeinated artificial flowers received more visits by bumblebees (Thomson et al., 2015). Thus, not only could caffeine enhance learning and memory of floral odours, but it could furthermore still have this effect when ingested by commercial pollinators in the nest, away from the target crop. ...
This chapter introduces the background and theory underpinning use of odours by insects in pollination, discusses how flowers produce odours and highlights issues specific to crops such as selective breeding. It then explores current technologies and case studies in which natural or synthetic odours on or near the crop, and the interaction with insects, influences visitation, pollination success and yield.
... It has therefore been proposed that low concentrations of caffeine in nectar have positive repercussions for plant pollination, but this has not been studied directly. The most relevant study showed that the presence of caffeine in nectar at 10 −5 M (but not 10 −4 M) increased bumblebee deposition of artificial pollen (Thomson et al. 2015), but this study did not record individual bee visits or behavior; therefore, the mechanism for this increase in pollen deposition remains unknown. One way that caffeine in nectar may alter pollinator behavior to benefit plant pollination is by increasing bee floral preference or constancy. ...
... Caffeine is present in the flowers of several species, across at least three botanical families (Wright et al. 2013) and has been shown under some conditions to enhance honeybee learning, memory (Si et al. 2005;Wright et al. 2013), and social recruitment behavior (Couvillon et al. 2015). The presence of caffeine at 10 −5 M can also increase bumblebee deposition of artificial pollen (Thomson et al. 2015), and at 10 −4 M improves memory for floral odor (Arnold et al. 2021). Our bees experiencing 10 −5 M caffeine (what occurs in citrus nectar) in the nectar of white flowers showed no color preference in mixed arrays unlike the sucrose control on white flowers, or bees experiencing caffeine on blue flowers. ...
Caffeine and ethanol are naturally occurring compounds in floral nectar. We examined how these compounds influenced pollinator behaviors including floral preference, floral constancy, and social behavior using bumblebees, Bombus impatiens, which were given prior experience foraging on either human blue or human white (hereafter blue and white) artificial flowers. Because flower color influenced bee behavior, with strong preferences for blue, we focused on the interaction between nectar chemistry and flower color. Bees that had experience with blue flowers preferred blue regardless of nectar chemistry. In contrast, for bees that had prior experience with white flowers, only the control treatment preferred white, while bees exposed to caffeine and ethanol showed no preference. The effects of nectar compounds may therefore only occur when bees are already foraging on a less-preferred color. We also examined the impact of nectar chemistry on the social behavior of joining other bees at flowers. In the same treatments for which bees showed a preference for previously experienced flower colors (all of the blue treatments and only the white control), bees also preferentially visited unoccupied flowers. In the treatments where bees showed no color preference, however (the white caffeine and ethanol treatments), bees showed no preference for unoccupied flowers. We show that the impacts of field-realistic levels of caffeine and ethanol in nectar on pollinator behavior depend on flower color, highlighting that the potential costs and benefits of nectar chemistry to plants are likely to be dependent on bee behavioral biases for other floral traits.
Significance statement
Flower nectar often contains toxic compounds hypothesized to impact pollination, but little research has shown their effects on the behavioral decisions of free-flying bees. Caffeine and alcohol occur in the nectar of some flowers. We found that bee response to these nectar compounds depends on the flower color. Bees preferentially visited blue flowers regardless of nectar chemistry, but the presence of caffeine or alcohol reduced bee color preference when bees had experience foraging on white flowers. The bumblebee’s social behavior of joining other bees at flowers showed related effects; in treatments where bees showed a preference for flower type, they also preferred to forage alone. This research highlights that bees make decisions based on the interaction between multimodal cues including nectar chemistry, and therefore the strength of selection on nectar chemistry is dependent on bee behavioral biases for other floral traits.
... NSMs are chemically diverse and widespread across plant taxa (Palmer-Young et al., 2019). Beyond their ability to attract or deter floral visitors, some NSMs such as caffeine may promote pollen transfer (Thomson et al., 2015) and enhance bees' recall of floral stimuli (Wright et al., 2013). Because many NSMs are also mechanisms of chemical defence against herbivores, they can be toxic (Adler, 2000) potentially filtering the identity of floral visitors (Stevenson et al., 2017). ...
... Pesticides in nectar may also be ecologically consequential for plants, silently altering the eco-evolutionary fine-tuning of plantpollinator interactions. Caffeine, for example, in the nectar of plants such as Citrus, Coffea and Onobrychis (sainfoin) increases bee activity (e.g. Figure 2c), reduces parasite load (Folly et al., 2021) and promotes pollen transfer (Thomson et al., 2015). The addition of IMD, which B. impatiens workers do not show any preference for on its own (Muth et al., 2020), and which limits activity (Figure 2c,d), would likely result in lowered visitation rate with potential negative impacts on plant fitness. ...
Neonicotinoid pesticides in the nectar and pollen of managed crops and wildflowers contribute to the global declines of bees. These chemicals can have detrimental effects on bees’ physiology, behavior, and reproduction. Floral nectar also contains secondary chemistry with its own effects on bee health. How nectar secondary chemistry may act additively or synergistically with neonicotinoids is unknown. Here, we asked how an acute exposure to a common neonicotinoid, imidacloprid (IMD) affected the longevity, immune function, and behavior of bumble bee (Bombus impatiens) workers maintained on diets enriched with one of three nectar secondary metabolites (NSMs; the alkaloid caffeine, the terpenoid thymol, or the cardiac glycoside digoxin). A factorial design allowed us to assess the potential for additive and interactive effects of each NSM and IMD combination on multiple health outcomes. Without IMD exposure, different dietary NSMs each had positive effects on lifespan (caffeine), immune function (digoxin), and activity levels (caffeine, thymol), although these came with trade‐offs. A single sublethal IMD exposure overshadowed these NSM effects, and in two cases, an NSM‐enriched diet magnified the negative effects of pesticide exposure. In summary, we show that even a single acute exposure to a pesticide has the potential to reshape interactions between pollinators and plants mediated by nectar secondary chemistry.
... Pollen from all Ranunculus, Echium and Asteraceae species contain metabolites for defense mechanisms that result high mortality rates for pollinators (Bergstrom et al., 1995;Kempf, 2010). Thomson et al., 2015) and is pesticide that prevents insect feeding (Nathanson, 1984) as the same as in Dipsacusspecies (Faizal and Geelen, 2013). This is alsotrue in Lupinus perennis and L.albus, Phalaenopsis, Delphinium species (e.g. ...
... According to (Thomson et al., 2015), honey from poisonous plants has detrimental effect on honeybees and human beings. This can be from macrostachyus, Sobralia violacea, Sobralia rosea, and Justiciaschimperiana (Cingel, 2001;Pij and Dodson, 1966). ...
Introduction: Ethiopia is one of the world's hotspot areas in biodiversity including poisonous, useful and medicinal higher honey bee plants. However, some are poisonous and lethal to honey bees and humans. This attracts attentions across the globe. There are major gaps in knowledge of exploring local poisonous, useful and medicinal honey bee flora of the country. Aim: The main purpose of this review was so survey of poisonous, medicinal and useful honey bee plant species, document the most common poisonous plant species to Ethiopia and the world; and then to reach on conclusion in comparison of different authors findings. Methods: Various studies from different electronic data bases(Google scholar, Science direct, PubMed, Scopus) and from repositories were searched and assessed on the poisonous, useful and medicinal honey bee plants of Ethiopia. Discussion: Flowering plants provide nectar and pollen or both for bees. However, some species are poisonous to honey bees. Sixty nine poisonous honey bee plant species belonging to 33 families were found as result. Highest number of species were recorded in Ericaceae (7) followed by Solanaceae (6) and Fabaceae (6). Ranunculaceae and Solonaceae represented with 5 species each. Most of them exist as exotic (37) whilst 26 of them were nativespecies. Datura stramonium, corynocarpus laevigata, piptadenia stipulate, Echium plantagineum, Erythrina fusca, Thevetia peruviana etc. are invasive species while Euphorbia heterophylla, Lupinus perennis, Lupin albus L, Brugmansia aurea, Euphorbia cotinifolia, Nerium oleander, Delphinium elatumand Asclepias syriaca L are mainly planted for Ornamental purposes. And also, few of them are Invasive and parasitic plants (Lathraea clandestine where it parasites the root of various plants especially legumes, Cuscuta species like Cuscuta abyssinica A. Rich, C. australis and C. acutaetc. In Conclusion, Future studies that look into the simultaneous impacts of poisonous, useful and medicinal bee plants on bee keeping activity would more accurately illuminate our understanding of the underlying relationships. Ahmed Hassen, Meseret Muche
... Recent research has suggested that nectar SMs may play a key role in plantpollinator interactions by enhancing the quality and the quantity of pollination services received by plants [11][12][13][14]. For instance, it has been demonstrated that nectar alkaloids and diterpenes enhanced plant fitness by increasing pollen transfer among conspecific flowers, repelling nectar thieves and retaining specialist pollinators [12,[15][16][17]. This evidence, together with the fact that the composition of nectar precursors supplied to the nectaries is modified by selective secretion [18], progressively casted doubts on the pleiotropy hypothesis. ...
... Yet, so far, little work has been done to better understand their ecological role and their physiological mode of action. Several nectar SMs have been shown to increase plant fitness by increasing pollinators' visitation rate or by filtering out undesirable pollinators [14,16,64]. Our results suggest that also NPAAs in floral nectar may increase plants' ...
Floral nectar is a pivotal element of the intimate relationship between plants and pollinators and its chemical composition is likely to have been shaped by strong selective pressures. Nectars are composed of a plethora of nutritionally valuable compounds but also hundreds of secondary metabolites (SMs) whose ecological role is still not completely understood. Here we performed a set of behavioural experiments to study whether five ubiquitous nectar non-protein amino acids (NPAAs: β-alanine, GABA, citrulline, ornithine and taurine) interact with gustation, feeding preference, and learning and memory in the pollinator Apis mellifera. We showed that harnessed foragers were unable to discriminate NPAAs from water when only accessing antennal chemo-tactile information and that freely moving bees did not exhibit innate feeding preferences for NPAA-laced sucrose solutions. Also, dietary consumption of NPAAs did not alter food consumption or longevity in caged bees over 10 days. Taken together our data suggest that ecologically relevant concentrations of NPAAs did not alter nectar palatability to bees. Olfactory conditioning assays showed that honey bees were more likely to learn a scent when it signalled a sucrose reward containing either β-alanine or GABA, and that GABA also enhanced specific memory retention. Conversely, when ingested two hours prior to conditioning, GABA, β-alanine, and taurine weakened bees' acquisition performances but not specific memory retention, which was enhanced in the case of β-alanine and taurine. Neither citrulline nor ornithine affected learning and memory. Our study
... Pollen quality can also influence bee preference (Vaudo et al., 2016) -plants which depend solely on insect pollination often have a higher pollen protein content than facultative insect pollinated plants (Hanley et al., 2008). Plants can also secure pollinator fidelity by providing insects with secondary metabolites, such as alkaloids, in their nectar (Singaravelan et al., 2005;Wright et al., 2013;Thomson et al., 2015). One such alkaloid is caffeine. ...
... One such alkaloid is caffeine. In laboratory studies, caffeine enhanced pollinator learning and memory of reward (Wright et al., 2013), resulting in increased pollen receipt (Thomson et al., 2015). Of the two commercially produced coffee species, Coffea canephora contains higher caffeine concentrations in its nectar than C. arabica (Wright et al., 2013;Prado et al., 2019). ...
As agriculture expands to meet the needs of a growing global population, natural ecosystems are threatened by deforestation and habitat fragmentation. Tropical agroforestry systems offer a sustainable alternative to traditional agriculture by providing food for production while also supporting biodiversity and ecosystem services. Previous studies have shown that these systems may even improve crop pollination, but the mechanisms of how these improvements occur are still poorly understood. Using coffee as a focal crop, we explored how microcli-matic conditions affected nectar traits (sugar and caffeine concentration) important for pollinator visitation. We also studied how microclimate, floral traits, floral availability at the coffee plant level, availability of floral resources provided by other plant species in the agroecosystem ("neighborhood floral availability"), and the presence of other bees affected the amount of time bees spent foraging on coffee flowers and the proportion of coffee pollen carried on their bodies. We explored these factors using the two dominant coffee species farmed on Puerto Rico, Coffea canephora and C. arabica, under sun and shade management. We found that high nectar sugar concentration and temperature were important predictors of short floral visits (<15s), while increased numbers of bees and open coffee flowers were important predictors of longer floral visits (16-180 seconds). High nectar caffeine concentration was an important predictor of longer visits on C. arabica flowers while the opposite was observed for C. canephora flowers. For both species, high coffee floral availability was the main predicting factor for the proportion of coffee pollen on the bees' bodies. Surprisingly, neither neighborhood floral availability nor the type of coffee plantation (agroforest/shade or sun) were important predictors of bee visitation. These results suggest non-coffee flowering plants in coffee plantations were neither competitors nor facilitators of coffee plants for pollinators. Additionally, most of the bees surveyed were carrying ≥80 % pollen from one species (C. arabica or C. canephora), likely resulting in little heterospecific pollen deposition between Coffea and non-Coffea flowers. Shade trees in coffee plantations do not detract from pollinator visitation to coffee flowers, suggesting that the provision of multiple ecological and wildlife conservation benefits by shade trees is not in conflict with a grower's ability to maximize the benefits of insect pollination on fruit production.
... Remarkably, there is also recent evidence that some alkaloids may be able to manipulate the behaviour of pollinators pharmacologically, leading to enhanced pollination services 21,22 . Alkaloids at high concentrations are known to be potent neurobiological agents, able to interfere with neural pathways including sensory and motor functions, cognitive abilities and learning processes in both vertebrates and invertebrates [23][24][25][26] . ...
... Bees have innate flower signal preferences that can be altered quickly depending on flower rewards, and bee visitation patterns become highly consistent once learned. Our study supports the idea that nectar alkaloids may increase pollinator constancy 21,22,24 . An enhanced memory of a rewarding flower type is likely to increase the rate of visitation to that plant species as bees are more inclined to visit flowers they have already learned to be rewarding than novel flower types 43 . ...
Many plants defend themselves against herbivores by chemical deterrents in their tissues and the presence of such substances in floral nectar means that pollinators often encounter them when foraging. The effect of such substances on the foraging behaviour of pollinators is poorly understood. Using artificial flowers in tightly-controlled laboratory settings, we examined the effects of the alkaloid nicotine on bumblebee foraging performance. We found that bumblebees confronted simultaneously with two equally rewarded nicotine-containing and nicotine-free flower types are deterred only by unnaturally high nicotine concentrations. This deterrence disappears or even turns into attraction at lower nectar-relevant concentrations. The alkaloid has profound effects on learning in a dose-dependent manner. At a high natural dose, bees learn the colour of a nicotine-containing flower type more swiftly than a flower type with the same caloric value but without nicotine. Furthermore, after experiencing flowers containing nicotine in any tested concentration, increasing numbers of bumblebees stay more faithful to these flowers, even if they become a suboptimal choice in terms of reward. These results demonstrate that alkaloids enhance pollinator flower constancy, opening new perspectives in co-evolutionary process between plants and pollinators.
... The presence of secondary metabolites and microbes in nectars are first reported [64,[279][280][281][282][283] and similar studies continue to present day [27,68,73,74,77,[125][126][127][128][129][130][131][132][133][134][135][136][137][138][139][140][141][142][143][146][147][148][149][150][151][152][153][154][155][156][157][158][159][160]. 1990s ...
... Much as in the case of amino acids, honey bees will tolerate high nicotine levels in nectars if sugar concentrations are also high, which can actually benefit honey bee health [128,129]. Caffeine is another alkaloid identified in citrus and coffee nectars that benefit both pollinators and plants by increasing foraging memory in honey bees [130] and increasing pollination efficiency [131]. ...
Plants attract mutualistic animals by offering a reward of nectar. Specifically, floral nectar (FN) is produced to attract pollinators, whereas extrafloral nectar (EFN) mediates indirect defenses through the attraction of mutualist predatory insects to limit herbivory. Nearly 90% of all plant species, including 75% of domesticated crops, benefit from animal-mediated pollination, which is largely facilitated by FN. Moreover, EFN represents one of the few defense mechanisms for which stable effects on plant health and fitness have been demonstrated in multiple systems, and thus plays a crucial role in the resistance phenotype of plants producing it. In spite of its central role in plant-animal interactions, the molecular events involved in the development of both floral and extrafloral nectaries (the glands that produce nectar), as well as the synthesis and secretion of the nectar itself, have been poorly understood until recently. This review will cover major recent developments in the understanding of (1) nectar chemistry and its role in plant-mutualist interactions, (2) the structure and development of nectaries, (3) nectar production, and (4) its regulation by phytohormones.
... 34 Honey bees prefer solutions containing low concentrations of caffeine and have even been found to increase visitation rates and learn flower characteristics faster accordingly. 35,36 In the case of larvae and worker bees fed caffeine at levels comparable to those in Camellia oleifera pollen, caffeine showed no significant effect on larvae (from 2 to 8 day-old larvae) and worker bee survival rates compared to the CG group (Table S12, comparisons no. 2; Table S14, comparisons no. 2) (Table S13; Figure 4A,B). ...
Identifying the components of Camellia oleifera honey and pollen and conducting corresponding toxicological tests are essential to revealing the mechanism of Camellia oleifera toxicity to honey bees. In this research, we investigated the saccharides and alkaloids in honey, nectar, and pollen from Camellia oleifera, which were compared with honey, nectar, and pollen from Brassica napus, a widely planted flowering plant. The result showed that melibiose, manninotriose, raffinose, stachyose, and lower amounts of santonin and caffeine were found in Camellia oleifera nectar, pollen, and honey but not in B. napus nectar, pollen, and honey. Toxicological experiments indicated that manninotriose, raffinose, and stachyose in Camellia oleifera honey are toxic to bees, while alkaloids in Camellia oleifera pollen are not toxic to honey bees. The toxicity mechanism of oligosaccharides revealed by temporal metabolic profiling is that oligosaccharides cannot be further digested by honey bees and thus get accumulated in honey bees, disturbing the synthesis and metabolism of trehalose, ultimately causing honey bee mortality.
... A flowering plant whose flowers secrete nectar and pollen can promote the pollination success of the flowers of adjacent species, which cannot secrete nectar and pollen or secrete less nectar and pollen (Thomson 1978;Ferdy et al. 1998;Juillet et al. 2007). Toxic nectar may serve as a filter against ineffective pollinators (Masters 1991), while toxic nectar can, in this context, preserve nectar for legitimate pollinators (Masters 1991;Gosselin et al. 2013;Nicolson et al. 2015;Thomson et al. 2015). Toxins in nectar are probably a strategy developed by T. hypoglaucum to reduce the cost of pollination during reproduction, and attract the most effective pollinator. ...
Honeybees play a significant role in the plant-pollinator interactions of many flowering plants. The ecological and evolutionary consequences of plant-pollinator interactions vary by geographic region, and the effects of honeybees on the reproduction of toxic plants have not been well studied. We measured the florescence of toxic plants, the flower-visiting behaviour of honeybees, and the effects of pollination on the fertility, weight and moisture content of seeds. The effects of climatic factors on the number of flowers, and the spatial and temporal variation in pollinator visits were evaluated, and the effects of pollinator visits on seed quality were evaluated. Flower visitors were diverse, climatic factors had a great impact on spatiotemporal flowering variation, and the number of bee visits was strongly correlated with the spatiotemporal variation in the number of flowers. Honeybees strongly increase the fullness and weight of seeds. Our study demonstrated a good ecological fit between the spatiotemporal variation in the flowering of toxic plants and the general validity of honeybee pollination syndrome in the south of Hengduan Mountain in East Asia. A linear relationship between honeybee visitation and plant reproduction can benefit the stabilization of plant reproduction.
... Conversely, biologically active compounds in nectar may have benefits for pollination, for example by optimizing specialized pollinator syndromes through selective toxicity (Barlow et al., 2017) or, as in the case of caffeine, increasing pollinator memory for floral traits and thereby increasing visitation to target flowers and nestmate recruitment (Arnold et al., 2021;Couvillon et al., 2015;Thomson et al., 2015;Wright et al., 2013). When these nectar metabolites are biologically active against microorganisms, they may also protect nectar-feeding animals from disease . ...
Floral nectar and pollen commonly contain diverse secondary metabolites. While these compounds are classically thought to play a role in plant defense, recent research indicates that they may also reduce disease in pollinators. Given that parasites have been implicated in ongoing bee declines, this discovery has spurred interest in the potential for ‘medicinal’ floral products to aid in pollinator conservation efforts. We review the evidence for antiparasitic effects of floral products on bee diseases, emphasizing the importance of investigating the mechanism underlying antiparasitic effects, including direct or host-mediated effects. We discuss the high specificity of antiparasitic effects of even very similar compounds, and highlight the need to consider how nonadditive effects of multiple compounds, and the post-ingestion transformation of metabolites, mediate the disease-reducing capacity of floral products. While the bulk of research on antiparasitic effects of floral products on bee parasites has been conducted in the lab, we review evidence for the impact of such effects in the field, and highlight areas for future research at the floral product-bee disease interface. Such research has great potential both to enhance our understanding of the role of parasites in shaping plant-bee interactions, and the role of plants in determining bee-parasite dynamics. This understanding may in turn reveal new avenues for pollinator conservation.
... Note however that other food compounds can influence bee nutritional choices. In particular, foragers can be tricked by secondary metabolites such as caffeine and nicotine, that despite their relatively low amounts in nectar attract bees to flowers with nectar and/or pollen of suboptimal nutritional values (Thomson et al. 2015, Baracchi et al. 2017). ...
Honey bees are crucial pollinators. A plethora of environmental stressors, such as agrochemicals, have been identified as contributors to their global decline. Especially, these stressors impair cognitive processes involved in fundamental behaviours. So far however, virtually nothing is known about the impact of metal pollutants, despite their known toxicity to many organisms. Their worldwide emissions resulting from human activities have elevated their concentrations far above natural baselines in the air, soil, water and flora, exposing bees at all life stages. The aim of my thesis was to examine the effects of metallic pollution on honey bees using a multiscale approach, from brain to colonies, in laboratory and field conditions. I first observed that bees exposed to a range of concentrations of three common metals (arsenic, lead and zinc) in the laboratory were unable to perceive and avoid, low, yet harmful, field-realistic concentrations of those metals in their food. I then chronically exposed colonies to field-realistic concentrations of lead in food and demonstrated that consumption of this metal impaired bee cognition and morphological development, leading to smaller adult bees. As metal pollutants are often found in complex mixtures in the environment, I explored the effect of cocktails of metals, showing that exposure to lead, arsenic or copper alone was sufficient to slow down learning and disrupt memory retrieval, and that combinations of these metals induced additive negative effects on both cognitive processes. I finally investigated the impact of natural exposure to metal pollutants in a contaminated environment, by collecting bees in the vicinity of a former gold mine, and showed that individuals from populations most exposed to metals exhibited lower learning and memory abilities, and development impairments conducing to reduced brain size. A more systematic analysis of unexposed bees revealed a relationship between head size, brain morphometrics and learning performances in different behavioural tasks, suggesting that exposure to metal pollutants magnifies these natural variations. Hence, altogether, my results suggest that honey bees are unable to avoid exposure to field-realistic concentrations of metals that are detrimental to development and cognitive functions; and call for a revision of the environmental levels considered as ‘safe’. My thesis is the first integrated analysis of the impact of several metal pollutants on bee cognition, morphology and brain structure, and should encourage further studies on the contribution of metal pollution in the reported decline of honey bees, and more generally, of insects.
... This pseudo replication reduces the cost considerably and facilitates experimental setup as a single honeybee hive is used. In addition, concentrations of caffeine and dopamine much higher than those found naturally were employed [5,[51][52][53]. This facilitated a drug-induced detectable phenotype. ...
Apis mellifera (honeybees) are a well-established model for the study of learning and cognition. A robust conditioning protocol, the olfactory conditioning of the proboscis extension response (PER), provides a powerful but straightforward method to examine the impact of varying stimuli on learning performance. Herein, we provide a protocol that leverages PER for classroom-based community or student engagement. Specifically, we detail how a class of high school students, as part of the Ryukyu Girls Outreach Program, examined the effects of caffeine and dopamine on learning performance in honeybees. Using a modified version of the PER conditioning protocol, they demonstrated that caffeine, but not dopamine, significantly reduced the number of trials required for a successful conditioning response. In addition to providing an engaging and educational scientific activity, it could be employed, with careful oversight, to garner considerable reliable data examining the effects of varying stimuli on honeybee learning.
... Yet, so far, little work has been done to better understand their ecological role and their physiological mode of action. Several nectar SMs have been shown to increase plant fitness by increasing pollinators' visitation rate or by filtering out undesirable pollinators 14,16,64 . Our results suggest that also NPAAs in floral nectar may increase plants' reproductive success by facilitating learning of relevant flower features by pollinators. ...
Floral nectar is a pivotal element of the intimate relationship between plants and pollinators. Nectars are composed of a plethora of nutritionally valuable compounds but also hundreds of secondary metabolites (SMs) whose function remains elusive. Here we performed a set of behavioural experiments to study whether five ubiquitous nectar non-protein amino acids (NPAAs: β-alanine, GABA, citrulline, ornithine and taurine) interact with gustation, feeding preference, and learning and memory in Apis mellifera . We showed that foragers were unable to discriminate NPAAs from water when only accessing antennal chemo-tactile information and that freely moving bees did not exhibit innate feeding preferences for NPAAs. Also, NPAAs did not alter food consumption or longevity in caged bees over 10 days. Taken together our data suggest that natural concentrations of NPAAs did not alter nectar palatability to bees. Olfactory conditioning assays showed that honey bees were more likely to learn a scent when it signalled a sucrose reward containing either β-alanine or GABA, and that GABA enhanced specific memory retention. Conversely, when ingested two hours prior to conditioning, GABA, β-alanine, and taurine weakened bees’ acquisition performances but not specific memory retention, which was enhanced in the case of β-alanine and taurine. Neither citrulline nor ornithine affected learning and memory. NPAAs in nectars may represent a cooperative strategy adopted by plants to attract beneficial pollinators.
... A similar concentration of caffeine (200 ppm) supplied in sucrose diet, however, improved the memory of honey bee foragers, thereby enhancing flower visitation (Si et al., 2005;Wright et al., 2013). In two other separate studies, caffeinated nectar enhanced its quality, attracting more honey bees and leading to more efficient pollination (Couvillon et al., 2015;Thomson et al., 2015). ...
During nectar feeding, mosquitoes ingest a plethora of phytochemicals present in nectar. The ecological and physiological impacts of these ingested phytochemicals on the disease vectors are poorly understood. In this study, we evaluated the effects of three nectar phytochemicals-- caffeine, p-coumaric acid, and quercetin--on longevity, fecundity, and sugar-feeding behavior of the Asian tiger mosquito (Aedes albopictus). Adult females of Ae. albopictus were provided continuous access to 10% sucrose supplemented with one of the three phytochemicals and their fecundity, longevity, and the amount of sucrose consumed determined. Transcriptome response of Ae. albopictus females to p-coumaric acid and quercetin was also evaluated. Dietary quercetin and p-coumaric acid enhanced the longevity of female Ae. albopictus, while caffeine resulted in reduced sugar consumption and enhanced fecundity of gravid females. RNA-seq analyses identified 237 genes that were differentially expressed (DE) in mosquitoes consuming p-coumaric acid or quercetin relative to mosquitoes consuming an unamended sucrose solution diet. Among the DE genes, several encoding antioxidant enzymes, cytochrome P450s, and heat shock proteins were upregulated, whereas histones were downregulated. Overall, our findings show that consuming certain nectar phytochemicals can enhance adult longevity of female Asian tiger mosquitoes, apparently by differentially regulating the expression level of genes involved in longevity and xenobiotic metabolism; this has potential impacts not only on life span but also on vectorial capacity and insecticide resistance.
... In addition, caffeine has been shown to enhance a pollinator's memory of reward [56], resulting in increased visitation rates by altering the foraging behaviour of bees. Our results suggest that such manipulation of pollinator behaviour by caffeine, resulting in repeated flower visitations [74], may also indirectly benefit foraging bumblebees by reducing the incidence and distribution of a key parasite, N. bombi, within a given environment. However, it should be noted that under field conditions caffeine consumption may lead to suboptimal foraging strategies, as caffeine-producing plants have been linked to an overestimation of forage quality in honeybees [75], which, if replicated in bumblebees, may have a negative impact on colony fitness through nutritional deficiencies. ...
Emergent infectious diseases are one of the main drivers of species loss. Emergent infection with the microsporidian Nosema bombi has been implicated in the population and range declines of a suite of North American bumblebees, a group of important pollinators. Previous work has shown that phytochemicals found in pollen and nectar can negatively impact parasites in individuals, but how this relates to social epidemiology and by extension whether plants can be effectively used as pollinator disease management strategies remains unexplored. Here, we undertook a comprehensive screen of UK agri-environment scheme (AES) plants, a programme designed to benefit pollinators and wider biodiversity in agricultural settings, for phytochemicals in pollen and nectar using liquid chromatography and mass spectrometry. Caffeine, which occurs across a range of plant families, was identified in the nectar of sainfoin (Onobrychis viciifolia), a component of UK AES and a major global crop. We showed that caffeine significantly reduces N. bombi infection intensity, both prophylactically and therapeutically, in individual bumblebees (Bombus terrestris), and, for the first time, that such effects impact social epidemiology, with colonies reared from wild-caught queens having both lower prevalence and intensity of infection. Furthermore, infection prevalence was lower in foraging bumblebees from caffeine-treated colonies, suggesting a likely reduction in population-level transmission. Combined, these results show that N. bombi is less likely to be transmitted intracolonially when bumblebees consume naturally available caffeine, and that this may in turn reduce environmental prevalence. Consequently, our results demonstrate that floral phytochem-icals at ecologically relevant concentrations can impact pollinator disease epidemiology and that planting strategies that increase floral abundance to support biodiversity could be co-opted as disease management tools.
... In addition, caffeine has been shown to enhance a pollinator's memory of reward [56], resulting in increased visitation rates by altering the foraging behaviour of bees. Our results suggest that such manipulation of pollinator behaviour by caffeine, resulting in repeated flower visitations [74], may also indirectly benefit foraging bumblebees by reducing the incidence and distribution of a key parasite, N. bombi, within a given environment. However, it should be noted that under field conditions caffeine consumption may lead to suboptimal foraging strategies, as caffeine-producing plants have been linked to an overestimation of forage quality in honeybees [75], which, if replicated in bumblebees, may have a negative impact on colony fitness through nutritional deficiencies. ...
Emergent infectious diseases are a principal driver of biodiversity loss globally. The population and range declines of a suite of North American bumblebees, a group of important pollinators, have been linked to emergent infection with the microsporidian Nosema bombi. Previous work has shown that phytochemicals in pollen and nectar can negatively impact parasites in individual bumblebees, but how this relates to social epidemiology and by extension whether plants can be effectively used as disease management strategies remains unexplored. Here we show that caffeine, identified in the nectar of Sainfoin, a constituent of agri-environment schemes, significantly reduced N. bombi infection intensity in individual bumblebees and, for the first time, that such effects impact social epidemiology, with colonies reared from wild caught queens having lower prevalence and intensity of infection. Furthermore, infection prevalence was lower in foraging bumblebees from these colonies, suggesting a likely reduction in population-level transmission. Our results demonstrate that phytochemicals can impact pollinator disease epidemiology and that planting strategies, which increase floral abundance to support biodiversity could be co-opted as disease management strategies.
... Nectar and pollen SMs in many plants and their effect on honey bees were studied: High nectar concentrations of gelsemine (terpenoidal alkaloids) found in Gelsemium sempervirens (nectar) associated with reduced pollen receipt (Stevenson et al. 2017). Pollination of caffeinated flowers enhanced with the production of caffeine due to better recruitment and foraging on caffeinated food sources (Thomson et al. 2015). Damage on Glycine max foliage infected with spider and mite elevate lipid peroxidation, lipoxygenase (LOX), and peroxidase (POX), but the levels of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) were not affected (Heath et al. 2013). ...
Plants being sessile entities are often subjected to varied environmental stresses. They have developed an alternative defense mechanism that involves a vast variety of secondary metabolites to serve as tools to cope up with various stress conditions. The exposure of plant cells to abiotic and biotic stresses initiate multilevel reaction cascades that consequently leads to production and accumulation of various secondary metabolites. Various enzymatic and non-enzymatic molecules comprising the antioxidative defense system comes into play to counteract the undesirable effect of ecological stresses. Energy required as fuel in biosynthesis, transport and storage which comprises the costs for the formation of various transcription factors. When plant experiences stress in combination they express various transcription factors that might help the plant to make flexible signaling cascades to increase plant resistance against one of the stress. Based on this limelight, the present review aims to wrap the influence of different abiotic and biotic factors including salt, drought, heavy metals, UV light, herbivory and pathogenesis on secondary metabolites production and their roles in stress tolerance mechanism in plants.
... Other studies suggest that GABA may increase feeding behaviour by stimulating those taste chemoreceptors sensitive to sugars (Nepi 2014). Regarding caffeine, bumblebees have shown preference for artificial flowers with nectar containing low doses of this alkaloid (Thomson et al. 2015). Caffeine content in floral nectar can also elicit feeding preference in honeybees (Singaravelan et al. 2005, Wright et al. 2013) and cause them to increase foraging frequency and persistency to the forage location (Couvillon et al. 2015). ...
Artificial sugar solutions can be used to disrupt the mutualism between aphids and ants. This provides natural enemies with increased access to aphid populations, thus enhancing biocontrol of hemipteran pests. However, research suggests that artificial solutions should be tailored to specific species in order to maximize the desired result. In this study, we test the effect of an alkaloid, caffeine, and a non-protein amino acid, γ-aminobutyric acid (GABA), on preference for sucrose solutions in two ant species, Lasius niger and Oecophylla smaragdina. These secondary metabolites have been shown to have attractive capabilities in other species of insects, who favor nectars from plants containing these compounds. In our first experiment, both species significantly preferred solutions containing GABA over sucrose-only controls, albeit L. niger favored higher concentrations of the amino acid. Caffeine did not significantly increase preference for sugar solutions in either of the tested species, and ants significantly dispreferred the highest concentration of caffeine offered. When the two metabolites were tested simultaneously against sucrose only, L. niger fed equally from all solutions, while O. smaragdina dispreferred caffeine. Thus, while GABA seems to be a promising ant attractant, caffeine is not an adequate choice, at least at the concentrations tested in this experiment.
... In an assay using artificial flowers, bumble bees (B. impatiens) increased pollination at flowers with sucrose plus caffeine versus those without caffeine (Thomson et al. 2015). Taken together, these results suggest that caffeine in nectar may increase foraging by pollinators. ...
As well as sugars to entice pollinators, nectar contains many other chemicals including amino acids and plant secondary compounds such as phenolics, alkaloids, and glycosides. Rather than simply the byproducts of plant metabolism or contamination by compounds meant to deter herbivory, it is clear that these chemicals may have important roles in nectar. Proposed functions of non-sugar components of nectar include pollinator nutrition, reducing nectar robbing, and defense against microbes. Additionally, some of these compounds are able to interact directly with the nervous system via binding to receptor proteins found on the surface of neurons. Thus, these neuroactive components of nectar may be able to manipulate pollinator behavior. To increase our ability to analyze the many functions of nectar, it is important to understand how specific components may interact with neurons. This review examines the neurotransmitter receptors that are targets of some of the chemicals present in nectar. Although these compounds also affect the nervous systems of vertebrates, the focus of this review is on the interactions between nectar and insect pollinators.
... This hypothesis is supported by a previous study, which showed that hummingbirds prefer nectar with a low-nicotine concentration [26]. Similarly, low-toxin nectar preference was also found in other pollinators such as honeybees [27]. As such, the bitter taste may be useful to help the hummingbird recognize specific and toxic nectar which non-pollinators may not be able to detect, thus enforcing plant-pollinator mutualism. ...
Nectar may contain many secondary metabolites that are commonly toxic and bitter-tasting. It has been hypothesized that such bitter-tasting secondary metabolites might keep the nectar exclusive to only a few pollinators. To test this hypothesis, we examined functional changes of bitter taste receptor genes (Tas2rs) in a species of nectar-feeding bird (Anna's hummingbird) by comparing these genes with those from two closely related insect-feeding species (chimney swift and chuck-will's widow). We previously identified a larger number of Tas2rs in the hummingbird than in its close insectivorous relatives. In the present study, we demonstrate higher sensitivity and new functions in the hummingbird Tas2r gene copies generated by a lineage-specific duplication, which has been shaped by positive selection. These results suggest that the bitter taste may lead to increased sensitivities and specialized abilities of the hummingbird to detect bitter-tasting nectar. Moreover, this study potentially supports the hypothesis that bitter-tasting nectar may have been specialized for some pollinators, thus enforcing plant-pollinator mutualism.
... Ecologically relevant concentrations of these substances can deeply impact either positively or negatively various cognitive functions, ultimately affecting pollinators' foraging strategies and feeding preference. Caffeine, nicotine, and cocaine in nectars may serve as a form of floral deception, by manipulating the behavior of pollinators in a way that increases the quantity and quality of pollination services received by the plants (Couvillon et al. 2015;Thomson et al. 2015). ...
... Furthermore, we did not evaluate nectar quality in this study, though it is an attractant and may also contribute to foraging preferences among bees (Heil 2011). Other factors that have been shown to affect the foraging behavior of bees include floral morphology (Harder 1983), competition (Goulson et al. 1998), and even caffeine (Thomson et al. 2015). ...
Non-native plant species reliant on insect pollination must attract novel pollinators in their introduced habitat to reproduce. Indeed, pollination services provided by resident floral visitors may contribute to the spread of non-native species, which may then affect the pollination services received by native plants. To determine the mechanisms by which an invasive thistle attracts pollinators in its introduced range, and whether its presence changes the pollinator visitation to native plant species, we compared bee visitation to native plants in the presence or absence of the invader. We experimentally tested the effect of a thistle invasion into a native plant community. We found that the non-native thistle was the most attractive of the plant species to visiting bee species. However, there was no effect of experimental treatment (presence of thistle) on bee abundance or visitation rate (bees per unit floral area per sample) to native plant species. Across 68 bee and 6 plant species, we found a significant correlation between pollen protein content and bee abundance and visitation rate. Thistle pollen also had a similar protein:lipid ratio to legumes, which correlated with bumble bee visitation. The high protein content of the thistle pollen, as compared to four native asters, may allow it to attract pollinators in novel ecosystems, and potentially contribute to its success as an invader. At the same time, this high protein pollen may act as a novel resource to pollinators in the thistle’s invaded range.
... Floral chemistry is also important for pollinator attraction and visitation [22][23][24] . Secondary metabolites in leaf tissue typically thought to function to deter herbivores are also found in floral rewards, including nectar and pollen [25][26][27] . ...
Floral traits and rewards are important in mediating interactions between plants and pollinators. Agricultural management practices can affect abiotic factors known to influence floral traits; however, our understanding of the links between agricultural practices and floral trait expression is still poorly understood. Variation in floral morphological, nectar, and pollen traits of two important agricultural species, Coffea arabica and C. canephora, was assessed under different agricultural practices (sun and shade). Corolla diameter and corolla tube length were larger and pollen total nitrogen content greater in shade plantations of C. canephora than sun plantations. Corolla tube length and anther filament length were larger in shade plantations of C. arabica. No effect of agricultural practice was found on nectar volume, sugar or caffeine concentrations, or pollen production. Pollen total nitrogen content was lower in sun than shade plantations of C. canephora, but no difference was found between sun and shade for C. arabica. This study provides baseline data on the influence of agronomic practices on C. arabica and C. canephora floral traits and also helps fill a gap in knowledge about the effects of shade trees on floral traits, which can be pertinent to other agroforestry systems.
... At higher concentrations, visitors are most often deterred, while at lower concentrations, nectar may be attractive. This effect translates into higher levels of reproduction (Singaravelan et al. 2005;Manson et al. 2013;Thomson et al. 2015;Baracchi et al. 2017). Moreover, some secondary metabolites (e.g. ...
Main conclusion
Sugars (glucose, fructose and sucrose), as well as proteogenic and non-proteogenic amino acids, are present in the nectar of Platanthera bifolia and P. chlorantha.
Abstract
Nectar quantity and quality are floral traits that are subjected to pollinator-mediated selection. Nectar sugar and amino acid (AA) composition in two sister species, P. bifolia and P. chlorantha, was analysed and the interspecies differences in nectar and the importance of these nectar characteristics for reproductive success were investigated. Nectar was collected from four P. bifolia and three P. chlorantha populations that exist in different habitats in three regions of NE Poland. Nectar from about 30 flowers (from each population) was sampled and analysed using high-performance liquid chromatography. We found the same primary sugars and AA components in the nectar of both species, although their content varied between the populations according to habitat properties. The nectar of P. bifolia and P. chlorantha both had low sugar concentrations (9.04–20.68%) and were dominated by hexoses, with sucrose:hexoses ratios between 0.03 and 0.31 across the different populations (the average for the P. bifolia populations was 0.17 and the average for the P. chlorantha populations was − 0.05). Total sugar content did not influence reproductive success and we found positive selection on fructose content. In general, 23 different AAs were detected in both Platanthera species. Cysteine and γ-aminobutyric acid were present in only one population of P. chlorantha. Sarcosine dominated among the non-proteogenic AAs. To our knowledge, this is the first report that characterizes the sugar and AA profiles in the nectar of P. bifolia and P. chlorantha in natural populations in the context of effectiveness of reproduction. Total AAs negatively influenced male reproductive success (r = − 0.79). Pollinators of the investigated species were found to be sensitive to the AAs’ taste, from taste classes I and IV. Correlation between male reproductive success and the content of AAs from these groups was 0.79 in both cases. In this manuscript, we investigated the characteristics of P. bifolia and P. chlorantha nectar, and compared these characteristics to the available data in the context of their adaptations to the requirements of pollinators and with regard to the importance of nectar quality for reproductive success of the studied species.
... Several studies on the European honeybee (Apis mellifera) show that the presence of caffeine in nectar alters honeybee foraging behaviour: it increases the amount of nectar the bees drink, improves learning performance and increases recruitment and persistence to the nectar sources (Couvillon et al., 2015;Singaravelan et al., 2005;Wright et al., 2013). Similar effects of caffeine on foraging have been found in bumblebees (Thomson et al., 2015). These studies suggest that field-realistic concentrations of caffeine enhance the reward perception of temperate honeybee and bumblebee foragers. ...
Plants and pollinators form beneficial relationships, with plants offering resources in return for pollination services. Some plants, however, add compounds to nectar to manipulate pollinators. Caffeine is a secondary plant metabolite found in some nectars that affects foraging in pollinators. In honeybees, caffeine increases foraging and recruitment to mediocre food sources, which might benefit the plant, but potentially harms the colonies. For the largest group of social bees, the stingless bees, the effect of caffeine on foraging behaviour has not been tested yet, despite their importance for tropical ecosystems. More generally, recruitment and foraging dynamics are not well understood in most species. We examined whether caffeine affects the foraging behaviour of the stingless bee Plebeia droryana, which frequently visits plants that produce caffeinated nectar and pollen. We trained bees to food sources containing field-realistic concentrations of sugar and caffeine. Caffeine did not cause P. droryana to increase foraging frequency and persistence. We observed P. droryana recruiting to food sources; however, this behaviour was also not affected by caffeine. Instead we found that higher sugar concentrations caused bees to increase foraging effort. Thus, unlike in other pollinators, foraging behaviour in this stingless bee is not affected by caffeine. As the Brazilian P. droryana population that we tested has been exposed to coffee over evolutionary time periods, our results raise the possibility that it may have evolved a tolerance towards this central nervous system stimulant. Alternatively, stingless bees may show physiological responses to caffeine that differ from those of other bee groups.
... Also, caffeine present in the nectar of C. arabica has been found to help bees to remember floral scent for a period of times three times longer than they would normally do (Wright et al., 2013). Although it has been proposed that both types of alkaloids have a psychoactive effect, more studies are still required to determine if pollinators are addicted to these compounds, that is, if alkaloids in nectar generate dependency or if pollinators simply prefer them (Thomson et al., 2015). ...
Flowers present visual and chemical signals that mediate the interaction between plants and pollinators, who transfer pollen between flowers of different plants while foraging for nectar and/or pollen. This process favours the sexual reproduction of plants and covers the energy requirements of floral visitors. Colour and floral scent, as well as the chemical composition of nectar and pollen that constitute floral rewards, are among the attraction attributes. The expression of these attributes is the result of the production of a set of secondary metabolites such as pigments, volatile organic compounds and chemical compounds in nectar and pollen. In addition to attracting pollinators, these metabolites can repel natural enemies of plants (florivores, nectar robbers, microorganisms) or pollinators (pathogens), potentially affecting the outcome of pollination, and eventually the production of fruits and seeds.
Key Concepts
• Most flowering plants that depend on pollinators for reproducing sexually have developed visual (colour) and chemical (scent) floral signals, as well as floral rewards (pollen and nectar), to increase the attraction of pollinators.
• Secondary metabolites produced by flowering plants mediate the visual and chemical communication between plants and other organisms. While this communication is essential for pollination, it can also mediate the interaction of plants with florivores, nectar robbers, seed predators, microorganisms and pollinator pathogens that could affect pollination.
• Pollinators are able to perceive variation in visual and chemical attributes of plants from the same or different species, affecting visitation rates and plant fitness.
• Pigments are the secondary metabolites responsible for the synthesis of colour in different floral organs (petals, sepals, sexual organs) and floral rewards (pollen and nectar).
• Floral volatiles are organic compounds emitted by flowers that mediate chemical communication in specialist and generalist plant–pollinators interactions.
• Secondary metabolites in the nectar of various species include alkaloids, phenols and nonessential amino acids that can affect the preferences and foraging behaviour of pollinators, either by attracting or deterring them.
• The impact of secondary metabolites in attracting different pollinators can result in pre‐reproductive isolation between plants and eventually contribute to their divergence.
... In some animals, at (naturally) low doses, caffeine tends to enhance memory retention and cognitive performance (Nehlig, 1999). For instance, when caffeine occurs in floral nectar, pollinator memories of receiving a reward are enhanced (Wright et al., 2013) and thus these flowers tend to receive more bee pollinator visitation (Thomson et al., 2015). Moreover, some insects (e.g., coffee berry borer, Hypothenemus hampei) can metabolize caffeine as a defense (Ceja-Navarro et al., 2015). ...
Addictive “social drugs” that are derived from plants range from reputable stimulants (e.g., coffee and tea) to stigmatized and dangerous preparations (e.g., ephedrine and cocaine). Both legal and illicit global trade has increased the geographic distribution of plants from which the principal social drugs are obtained. In turn, this range expansion increased opportunities to transfer genes controlling production of high levels of secondary chemicals because of increases in overlapping geographic distributions with sexually compatible domesticated, wild, and weedy relatives. We review the literature for evidence that the introduction of these chemicals into ecosystems could occur through gene flow in ten common, addictive, social drug crops: coca, coffee, cola, ephedra, khat, marijuana, opium poppy, tea, tobacco and yerbe maté. From the published literature of the potential evolutionary and environmental consequences of gene flow from popular social drug crops, we also analyse the subsequent unintended ecological or evolutionary consequences, such as increased weediness, loss of genetic diversity in sexually compatible wild relatives, or health and fitness consequences for herbivores of these crops. Given the rapid industrialization of many of these crops, we identify knowledge gaps and call for renewed attention to the study of their ecology and evolution.
... 盗蜜者更加难以忍受, 使得访问者更易成为传粉者而 不是盗蜜者 [71] . 花蜜中的咖啡因可以提升蜜蜂对食物 报酬的气味记忆, 从而提高植物的花粉传递 [72] , 但是 在过高浓度下, 反而降低蜜蜂的访问频率 [73] . 花粉也 是重要的报酬, 花粉中富含蛋白质和脂质, 其蛋白质 与脂质的特定比例受到蜂类传粉者的偏好 [74] . ...
Natural selection is one of the most important components of organic evolution, while the concept of coevolution proposes that reciprocal selection generated by interacting species could also drive their organic evolution. Formally raised in 1964, the concept of coevolution has extensively developed, but been misused or even abused. Although continuously emerging studies have verified that some ecological interactions are indeed coevolution, queries of whether it is an acceptable concept remain. To clarify the precise use of the concept, we list and re-induce mistakes in using or misunderstanding of coevolution. Here a concise principle for correct usage is suggested, i.e. confirming three aspects: species interaction, reciprocal selection as well as co-phylogenesis. Bibliometric methods are applied to quantify the development of the coevolution concept, showing the bursting expansion of the term “coevolution” into study fields beyond evolutionary biology, and revealing that current usage of “coevolution” still remains within a reasonable range. Currently, studies of ecological interactions are commonly considered as in the coevolution field. Differences and commonsense of the other six related terms, namely coadaptation, cooperation, interaction, interplay, mutualism and symbiosis, are briefly discussed. Finally, case studies of frontier topics of coevolution, geographic mosaic theory of coevolution, are introduced. A better understanding of the coevolution concept could be achieved if misuse or abuse is avoided. This paper may provide references for future coevolution studies.
... Estes estimulantes, produzidos como compostos secundários, são substâncias de baixo investi-mento para as plantas, mas com efeitos intensos para os visitantes (Chittka & Peng 2013). Por exemplo, espécies contendo cafeína recebem mais visitantes independente da coloração floral (Thomson et al. 2015), além de gerarem dependência, compromentendo a entrada de recursos na colmeia , Chittka & Peng 2013, Wright et al. 2013. Originalmente, ocorrem em muitos tecidos vegetais (atuando na defesa contra herbívoros), podendo ser adicionados facilmente ao néctar, além de serem encontrados em espécies pertencentes a diferentes famílias como Solanaceae (Nicotiana L.), Tiliaceae (Tilia cordata Mill), Rutaceae (Citrus L.), Rubiaceae (Coffea L.) e Asteraceae (Helianthus annuus). ...
HOW DO BEES PERCEIVE FLOWERS AND WHY IT IS IMPORTANT?
Animal cognition can be defined as the ability of an organism to acquire, retain and subsequently use the sensory information during decision-making processes in different contexts. The understanding of how the signals emitted in the environment interact with the sensory system of animals capable of perceiving them helps to unravel the ecological and evolutionary significance of the interactions between organisms. In the context of pollination, the attraction of visitors to the flower is attributed to a great diversity of signals, especially visuals and olfactory. In addition to acting as attractants, they can also exhibit functions related to the communication of the presence/absence of resources. Nevertheless, other sensory modalities, also play a relevant role on the interaction between flowers and visitors. The central idea of the present study is to present, through relevant examples from the literature, the main signals emitted by the flowers and perceived by the bees, either by a single sensory modality or through multiple modalities. Regardless of the
sensory modality and the complexity of the stimuli, studies of the interactions between plants and their floral visitors can be better understood and detailed if we consider the different aspects related to the signal being emitted and the directionality of the same, or simply the capacity or not to be perceived. Quantifying processes, their causes and consequences reinforce the understanding of volutionary,
ecological and behavioral patterns among interacting organisms, both in mutualistic and antagonistic relationships.
Keywords: cognition; floral attractants; plant-pollinator interaction; pollinators; sensory systems.
... For testing hypotheses in both lab and field conditions, 3D printing may be incredibly useful for making precise, repeatable models. Threedimensional printing has already been used to create precise models of bird eggs to test egg rejection behavior in the context of brood parasitism [27], zebrafish shoals to test the effect of body size on zebrafish shoaling preferences [28], artificial flower corollas to test the effect of floral traits on pollinator visitation [29][30][31], and female turtle decoys to test the effect of body size on mate choice [32] (Table 1). In these studies, 3D printing was chosen for its ability to create identical experimental stimuli because alternative methods, such as constructing models by hand, could introduce unintentional variation that makes it difficult to determine whether study subjects are responding to intentional or unintentional variation in experimental stimuli. ...
Background
Ecological research often involves sampling and manipulating non-model organisms that reside in heterogeneous environments. As such, ecologists often adapt techniques and ideas from industry and other scientific fields to design and build equipment, tools, and experimental contraptions custom-made for the ecological systems under study. Three-dimensional (3D) printing provides a way to rapidly produce identical and novel objects that could be used in ecological studies, yet ecologists have been slow to adopt this new technology. Here, we provide ecologists with an introduction to 3D printing.
Results
First, we give an overview of the ecological research areas in which 3D printing is predicted to be the most impactful and review current studies that have already used 3D printed objects. We then outline a methodological workflow for integrating 3D printing into an ecological research program and give a detailed example of a successful implementation of our 3D printing workflow for 3D printed models of the brown anole, Anolis sagrei, for a field predation study. After testing two print media in the field, we show that the models printed from the less expensive and more sustainable material (blend of 70% plastic and 30% recycled wood fiber) were just as durable and had equal predator attack rates as the more expensive material (100% virgin plastic).
Conclusions
Overall, 3D printing can provide time and cost savings to ecologists, and with recent advances in less toxic, biodegradable, and recyclable print materials, ecologists can choose to minimize social and environmental impacts associated with 3D printing. The main hurdles for implementing 3D printing—availability of resources like printers, scanners, and software, as well as reaching proficiency in using 3D image software—may be easier to overcome at institutions with digital imaging centers run by knowledgeable staff. As with any new technology, the benefits of 3D printing are specific to a particular project, and ecologists must consider the investments of developing usable 3D materials for research versus other methods of generating those materials.
... However, responses to nectar secondary metabolites can be concentration-dependent; at low levels, pollinator responses may be equivocal, while higher concentrations lead to pollinator deterrence (Koehler et al., 2012;Wright et al., 2013;Manson et al., 2013). Some compounds, such as caffeine and nicotine, can even be attractive at low concentrations (Singaravelan et al., 2005;Wright et al., 2013) and may lead to higher rates of pollen transfer (Thomson et al., 2015). Furthermore, pollinator deterrence due to nectar secondary metabolites does not necessarily translate into reduced plant fitness (Kessler et al., 2008), although studies that measure plant reproduction are largely lacking (but see Adler andIrwin, 2005, 2012). ...
Background:
Floral nectar is an important determinant of plant-pollinator interactions and an integral component of pollination syndromes, suggesting it is under pollinator-mediated selection. However, compared to floral display traits, we know little about the evolutionary ecology of nectar. Combining a literature review with a meta-analysis approach, we summarize the evidence for heritable variation in nectar traits and link this variation to pollinator response and plant fitness. We further review associations between nectar traits and floral signals and discuss them in the context of honest signalling and targets of selection.
Scope:
Although nectar is strongly influenced by environmental factors, heritable variation in nectar production rate has been documented in several populations (mean h2 = 0.31). Almost nothing is known about heritability of other nectar traits, such as sugar and amino acid concentrations. Only a handful of studies have quantified selection on nectar traits, and few find statistically significant selection. Pollinator responses to nectar traits indicate they may drive selection, but studies tying pollinator preferences to plant fitness are lacking. So far, only one study conclusively identified pollinators as selective agents on a nectar trait, and the role of microbes, herbivores, nectar robbers and abiotic factors in nectar evolution is largely hypothetical. Finally, there is a trend for positive correlations among floral cues and nectar traits, indicating honest signalling of rewards.
Conclusions:
Important progress can be made by studies that quantify current selection on nectar in natural populations, as well as experimental approaches that identify the target traits and selective agents involved. Signal-reward associations suggest that correlational selection may shape evolution of nectar traits, and studies exploring these more complex forms of natural selection are needed. Many questions about nectar evolution remain unanswered, making this a field ripe for future research.
... Low concentrations of plant defensive compounds in nectar seem to have beneficial effects for bees. For example, honeybees preferentially feed on nectar with a low caffeine concentration, but are deterred by a high concentration [10], a phenomenon known as hormesis [11]. High nectar concentrations of the cyanogenic glucoside amygdalin cause "malaise" symptoms in honeybees [12,13], but the concentrations of amygdalin naturally found in nectar do not deter honeybee feeding or otherwise affect their behavior [14][15][16]. ...
Honeybees (Apis mellifera) pollinate flowers and collect nectar from many important crops. White clover (Trifolium repens) is widely grown as a temperate forage crop, and requires honeybee pollination for seed set. In this study, using a quantitative LC-MS (Liquid Chromatography-Mass Spectrometry) assay, we show that the cyanogenic glucosides linamarin and lotaustralin are present in the leaves, sepals, petals, anthers, and nectar of T. repens. Cyanogenic glucosides are generally thought to be defense compounds, releasing toxic hydrogen cyanide upon degradation. However, increasing evidence indicates that plant secondary metabolites found in nectar may protect pollinators from disease or predators. In a laboratory survival study with chronic feeding of secondary metabolites, we show that honeybees can ingest the cyanogenic glucosides linamarin and amygdalin at naturally occurring concentrations with no ill effects, even though they have enzyme activity towards degradation of cyanogenic glucosides. This suggests that honeybees can ingest and tolerate cyanogenic glucosides from flower nectar. Honeybees retain only a portion of ingested cyanogenic glucosides. Whether they detoxify the rest using rhodanese or deposit them in the hive should be the focus of further research.
... Nectar compounds also influence floral constancythe tendency of pollinators to return to the same floral species (Wright and Schiestl, 2009). Thomson et al. (2015) showed that bumble bees increased visitation to artificial flowers offering caffeinated sugar solution. Determining how such compounds influence pollinator cognition and behaviour will therefore improve our understanding of plantpollinator interactions. ...
The nectar of the thunder god vine, Tripterygium hypoglaucum, contains a terpenoid, triptolide (TRP), that may be toxic to the sympatric Asian honey bee, Apis cerana, because honey produced from this nectar is toxic to bees. However, these bees will forage on, recruit for, and pollinate this plant during a seasonal dearth of preferred food sources. Olfactory learning plays a key role in forager constancy and pollination, and we therefore tested the effects of acute and chronic TRP feeding on forager olfactory learning, using proboscis extension reflex conditioning. At concentrations of 0.5-10 µg TRP/ml, there were no learning effects of acute exposure. However, memory retention (1 h after the last learning trial) significantly decreased by 56% following acute consumption of 0.5 µg TRP/ml. Chronic exposure did not alter learning or memory, except at high concentrations (5 and 10 µg TRP/ml). TRP concentrations in nectar may therefore not significantly harm plant pollination. Surprisingly, TRP slightly increased bee survival, and thus other components in T. hypoglaucum honey may be toxic. Long term exposure to TRP could have colony effects, but these may be ameliorated by the bees' aversion to T. hypoglaucum nectar when other food sources are available and, perhaps, by detoxification mechanisms. The co-evolution of this plant and its reluctant visitor may therefore likely illustrate a classic compromise between the interests of both actors.
... Honey bees do not forage randomly and their behaviour is modulated by learning which plants have an optimum "nutritive value" (Hendriksma and Shafir 2016). Foraging preferences are also influenced by the addictive qualities and visual attractiveness of plants, which are not always linked to nutritional rewards (Nicholls and Hempel de Ibarra 2017;Thomson et al. 2015). As such, it is important to consider both the species composition of these food stores and their nutritional content. ...
Sufficiently diverse and abundant resources are essential for generalist consumers, and form an important part of a suite of conservation strategies for pollinators. Honey bees are generalist foragers and are dependent on diverse forage to adequately meet their nutritional needs. Through analysis of stored pollen (bee bread) samples obtained from 26 honey bee (Apis mellifera L.) hives across NW-England, we quantified bee bread nutritional content and the plant species that produced these stores from pollen. Protein was the most abundant nutrient by mass (63%), followed by carbohydrates (26%). Protein and lipid content (but not carbohydrate) contributed significantly to ordinations of floral diversity, linking dietary quality with forage composition. DNA sequencing of the ITS2 region of the nuclear ribosomal DNA gene identified pollen from 89 distinct plant genera, with each bee bread sample containing between 6 and 35 pollen types. Dominant genera included dandelion (Taraxacum), which was positively correlated with bee bread protein content, and cherry (Prunus), which was negatively correlated with the amount of protein. In addition, proportions of amino acids (e.g. histidine and valine) varied as a function of floral species composition. These results also quantify the effects of individual plant genera on the nutrition of honey bees. We conclude that pollens of different plants act synergistically to influence host nutrition; the pollen diversity of bee bread is linked to its nutrient content. Diverse environments compensate for the loss of individual forage plants, and diversity loss may, therefore, destabilize consumer communities due to restricted access to alternative resources.
Electronic supplementary material
The online version of this article (10.1007/s00442-017-3968-3) contains supplementary material, which is available to authorized users.
... Studying T. tomentosa volatiles and their effects on bees, alongside interactive effects with caffeine on scent-reward association learning [43] using artificial flowers (cf. [44]), could help bring two of the more plausible explanations together to understand this extraordinary natural phenomenon. ...
For decades, linden trees (basswoods or lime trees), and particularly silver linden (Tilia tomentosa), have been linked to mass bee deaths. This phenomenon is often attributed to the purported occurrence of the carbohydrate mannose, which is toxic to bees, in Tilia nectar. In this review, however, we conclude that from existing literature there is no experimental evidence for toxicity to bees in linden nectar. Bee deaths on Tilia probably result from starvation, owing to insufficient nectar resources late in the tree’s flowering period. We recommend ensuring sufficient alternative food sources in cities during late summer to reduce bee deaths on silver linden. Silver linden metabolites such as floral volatiles, pollen chemistry and nectar secondary compounds remain underexplored, particularly their toxic or behavioural effects on bees. Some evidence for the presence of caffeine in linden nectar may mean that linden trees can chemically deceive foraging bees to make sub-optimal foraging decisions, in some cases leading to their starvation. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
... Another determinant of the medicinal value of phytochemicals is whether these compounds are actively sought and consumed by infected hosts. Although high phytochemical concentrations often deter bees [24,25], lower phytochemical concentrations can be attractive [26,27]. Phytochemical preferences can also change across ecological contexts. ...
Background
Floral phytochemicals are ubiquitous in nature, and can function both as antimicrobials and as insecticides. Although many phytochemicals act as toxins and deterrents to consumers, the same chemicals may counteract disease and be preferred by infected individuals. The roles of nectar and pollen phytochemicals in pollinator ecology and conservation are complex, with evidence for both toxicity and medicinal effects against parasites. However, it remains unclear how consistent the effects of phytochemicals are across different parasite lineages and environmental conditions, and whether pollinators actively self-medicate with these compounds when infected.
Approach
Here, we test effects of the nectar alkaloid anabasine, found in Nicotiana, on infection intensity, dietary preference, and survival and performance of bumble bees (Bombus impatiens). We examined variation in the effects of anabasine on infection with different lineages of the intestinal parasite Crithidia under pollen-fed and pollen-starved conditions.
Results
We found that anabasine did not reduce infection intensity in individual bees infected with any of four Crithidia lineages that were tested in parallel, nor did anabasine reduce infection intensity in microcolonies of queenless workers. In addition, neither anabasine nor its isomer, nicotine, was preferred by infected bees in choice experiments, and infected bees consumed less anabasine than did uninfected bees under no-choice conditions. Furthermore, anabasine exacerbated the negative effects of infection on bee survival and microcolony performance. Anabasine reduced infection in only one experiment, in which bees were deprived of pollen and post-pupal contact with nestmates. In this experiment, anabasine had antiparasitic effects in bees from only two of four colonies, and infected bees exhibited reduced—rather than increased—phytochemical consumption relative to uninfected bees.
Conclusions
Variation in the effect of anabasine on infection suggests potential modulation of tritrophic interactions by both host genotype and environmental variables. Overall, our results demonstrate that Bombus impatiens prefer diets without nicotine and anabasine, and suggest that the medicinal effects and toxicity of anabasine may be context dependent. Future research should identify the specific environmental and genotypic factors that determine whether nectar phytochemicals have medicinal or deleterious effects on pollinators.
In recent years, our understanding of the complex chemistry of floral nectar and its ecological implications for plant-pollinator relationships has certainly increased. Nectar is no longer considered merely a reward for pollinators but rather a plant interface for complex interactions with insects and other organisms. A particular class of compounds, i.e., nectar secondary compounds (NSCs), has contributed to this new perspective, framing nectar in a more comprehensive ecological context. The aim of this review is to draft an overview of our current knowledge of NSCs, including emerging aspects such as non-protein amino acids and biogenic amines, whose presence in nectar was highlighted quite recently. After considering the implications of the different classes of NSCs in the pollination scenario, we discuss hypotheses regarding the evolution of such complex nectar profiles and provide cues for future research on plant-pollinator relationships.
Caffeine is a widely occurring plant defense chemical¹,² that occurs in the nectar of some plants, e.g., Coffea or Citrus spp., where it may influence pollinator behavior to enhance pollination.³,⁴ Honey bees fed caffeine form longer lasting olfactory memory associations,⁵ which could give plants with caffeinated nectar an adaptive advantage by inducing more visits to flowers. Caffeinated free-flying bees show enhanced learning performance⁶ and are more likely to revisit a caffeinated target feeder or artificial flower,7, 8, 9 although it is not clear whether improved memory of the target cues or the perception of caffeine as a reward is the cause. Here, we show that inexperienced bumble bees (Bombus terrestris) locate new food sources emitting a learned floral odor more consistently if they have been fed caffeine. In laboratory arena tests, we fed bees a caffeinated food alongside a floral odor blend (priming) and then used robotic experimental flowers¹⁰ to disentangle the effects of caffeine improving memory for learned food-associated cues versus caffeine as a reward. Inexperienced bees primed with caffeine made more initial visits to target robotic flowers emitting the target odor compared to control bees or those primed with odor alone. Caffeine-primed bees tended to improve their floral handling time faster. Although the effects of caffeine were short lived, we show that food-locating behaviors in free-flying bumble bees can be enhanced by caffeine provided in the nest. Consequently, there is potential to redesign commercial colonies to enhance bees’ forage focus or even bias bees to forage on a specific crop.
Stingless bees need different types of resources to rear brood, build nest structures and defend their colony. This has major consequences for tropical ecosystems because the collection of pollen, the main protein source for larvae, and carbohydrates in the form of floral nectars lead to pollination. Worldwide, thousands of plant species are likely to benefit from stingless bee pollination (Chap. 9). Stingless bees differ somewhat from honey bees in that non-floral resources (e.g. resinous materials, fruit juice and carrion; see below) also account for a significant proportion of foraging trips (Roubik 1989; Lorenzon and Matrangolo 2005).
Honey bee viruses are capable of causing a wide variety of devastating effects, but effective treatments have yet to be discovered. Phytochemicals represent a broad range of substances that honey bees frequently encounter and consume, many of which have been shown to improve honey bee health. However, their effect on bee viruses is largely unknown. Here, we tested the therapeutic effectiveness of carvacrol, thymol, p-coumaric acid, quercetin, and caffeine on viral infection by measuring their ability to improve survivorship in honey bees inoculated with Israeli acute paralysis virus (IAPV) using high-throughput cage bioassays. Among these candidates, caffeine was the only phytochemical capable of significantly improving survivorship, with initial screening showing that naturally occurring concentrations of caffeine (25 ppm) were sufficient to produce an ameliorative effect on IAPV infection. Consequently, we measured the scope of caffeine effectiveness in bees inoculated and uninoculated with IAPV by performing the same type of high-throughput bioassay across a wider range of caffeine concentrations. Our results indicate that caffeine may provide benefits that scale with concentration, though the exact mechanism by which caffeine ingestion improves survivorship remains uncertain. Caffeine therefore has the potential to act as an accessible and inexpensive method of treating viral infections, while also serving as a tool to further understanding of honey bee–virus interactions at a physiological and molecular level.
The plant kingdom produces an extraordinary diversity of secondary metabolites and the majority of the literature supports a defensive ecological role for them, particularly against invertebrate herbivores (antagonists). Plants also produce secondary compounds in floral nectar and pollen and these are often similar to those produced for defense against invertebrates elsewhere in the plant. This is largely because the chemical armoury within a single plant species is typically restricted to a few biochemical pathways and limited chemical products but how their occurrence in floral rewards is regulated to mediate both defence and enhanced pollination is not well understood. Several phytochemicals are reviewed here comparing the defensive function alongside their benefit to flower visiting mutualists. These include caffeine, aconitine, nicotine, thymol, linalool, lupa-nine and grayanotoxins comparing the evidence for their defensive function with their impacts on polli-nators, their behaviour and well-being. Drivers of adaptation and the evolution of floral traits are discussed in the context of recent studies. Ultimately more research is required that helps determine the impacts of floral chemicals in free flying bees, and how compounds are metabolized, sequestered or excreted by flower feeding insects to understand how they may then affect the pollinators or their parasites. More work is also required on how plants regulate nectar and pollen chemistry to better understand how secondary metabolites and their defensive and polli-nator supporting functions are controlled, evolve and adapt.
We developed novel artificial flowers that dispense and receive powdered food dyes as pollen analogues while their nectar is replenished by capillary action. Dye receipt, which can be measured colourimetrically, is a direct surrogate for pollen receipt or female reproductive success, but can also serve to compare pollen donation (male reproductive success) from flowers with different colours of dye. By allowing captive bumble bee colonies to visit large arrays of such flowers, we investigated whether total dye receipt depended on the sugar concentration of a flower's nectar. Estimating pollen transfer, rather than simply visitation rate, is appropriate for this question because flowers with more concentrated nectar might accrue more pollen not only through higher visitation rates but also through longer visits that transfer more pollen per visit. Flowers with richer nectar did receive more dye regardless of their spatial arrangement, but the effect was greatest when rich and poor flowers were segregated in large blocks, as opposed to being intermingled.
Background:
Bumblebees use information provided inadvertently by conspecifics when deciding between different flower foraging options. Such social learning might be explained by relatively simple associative learning mechanism: the bee may learn to associate conspecifics with nectar or pollen reward through previous experience of foraging jointly. However, in some studies, observers were guided by choices of 'demonstrators' viewed through a screen, so no reward was given to the observers at the time of seeing other bees' flowers choice and no demonstrator bee was present at the moment of decision. This behaviour, referred to observational conditioning, implies an additional associative step as the positive value of conspecific is transferred to the associated flower. Here we explore the role of demonstrator movement, and the distance between observers and demonstrators that is required for observation conditioning to take place.
Methodology/principal findings:
We identify the conditions under which observational conditioning occurs in the widespread European species Bombus terrestris. The presence of artificial demonstrator bees leads to a significant change in individual colour preference toward the indicated colour if demonstrators were moving and observation distance was limited (15 cm), suggesting that observational conditioning could only influence relatively short-range foraging decisions. In addition, the movement of demonstrators is a crucial factor for observational conditioning, either due to the more life-like appearance of moving artificial bees or an enhanced detectability of moving demonstrators, and an increased efficiency at directing attention to the indicated flower colour.
Conclusion:
Bumblebees possess the capacity to learn the quality of a flower by distal observation of other foragers' choices. This confirms that social learning in bees involves more advanced processes than simple associative learning, and indicates that observational conditioning might be widespread in pollinating insects, raising intriguing questions for the underlying mechanisms as well as the spread of social information in pollinator-plant interactions.
Abstract Ants on flowers can disrupt pollination by consuming rewards or harassing pollinators, but it is difficult to disentangle the effects of these exploitative and interference forms of competition on pollinator behavior. Using highly rewarding and quickly replenishing artificial flowers that simulate male or female function, we allowed bumblebees (Bombus impatiens) to forage (1) on flowers with or without ants (Myrmica rubra) and (2) on flowers with or without ant scent cues. Bumblebees transferred significantly more pollen analogue both to and from ant-free flowers, demonstrating that interference competition with ants is sufficient to modify pollinator foraging behavior. Bees also removed significantly less pollen analogue from ant-scented flowers than from controls, making this the first study to show that bees can use ant scent to avoid harassment at flowers. Ant effects on pollinator behavior, possibly in addition to their effects on pollen viability, may contribute to the evolution of floral traits minimizing ant visitation.
The results of behavioural experiments provide important information about the structure and information-processing abilities of the visual system. Nevertheless, if we want to infer from behavioural data how the visual system operates, it is important to know how different learning protocols affect performance and to devise protocols that minimise noise in the response of experimental subjects. The purpose of this work was to investigate how reinforcement schedule and individual variability affect the learning process in a colour discrimination task. Free-flying bumblebees were trained to discriminate between two perceptually similar colours. The target colour was associated with sucrose solution, and the distractor could be associated with water or quinine solution throughout the experiment, or with one substance during the first half of the experiment and the other during the second half. Both acquisition and final performance of the discrimination task (measured as proportion of correct choices) were determined by the choice of reinforcer during the first half of the experiment: regardless of whether bees were trained with water or quinine during the second half of the experiment, bees trained with quinine during the first half learned the task faster and performed better during the whole experiment. Our results confirm that the choice of stimuli used during training affects the rate at which colour discrimination tasks are acquired and show that early contact with a strongly aversive stimulus can be sufficient to maintain high levels of attention during several hours. On the other hand, bees which took more time to decide on which flower to alight were more likely to make correct choices than bees which made fast decisions. This result supports the existence of a trade-off between foraging speed and accuracy, and highlights the importance of measuring choice latencies during behavioural experiments focusing on cognitive abilities.
Caffeine in floral nectar enhances the memory of bees for the flowers' scent by altering response properties of neurons in the bee brain.
The influence of 63 dietary allelochemicals (alkaloids, terpenes, glycosides,etc.) on the feeding behaviour of bees (Apis mellifera) was tested in terms of deterrency and attraction. For 39 compounds a deterrent (mostly alkaloids, coumarins and saponins) and for 3 compounds an attractive response (mostly terpenes) was obtained in choice tests, which allowed the calculation of respective ED50-values. Under no-choice conditions, 17 out of 29 allelochemicals caused mortality at concentrations between 0.003 and 0.6%. Especially toxic were alkaloids, saponins, cardiac glycosides and cyanogenic glycosides. These data show that bees which are confronted with plant allelochemicals in nectar and pollen, are not especially adapted (i.e. insensitive) to the plants' defence chemistry. GLC and GLS-MS data are given on the alkaloid composition of nectar and pollen ofBrugmansia aurea, Atropa belladonna andLupinus polyphyllus.
Learning and memory in honeybees is analyzed on five levels, using a top-down approach. (a) Observatory learning is applied during navigation and dance communication. (b) Local cues at the feeding site are learned associatively. (c) Classical conditioning of the proboscis extension response to olfactory stimuli provides insight into behavioral, neural, and neuropharmacological mechanisms of associative learning. (d) At the neural level, the pathways coding the conditioned and the unconditioned stimulus are identified. The reinforcing function of the unconditioned stimulus is traced to a particular neuron. (e) At the cellular level, the cAMP pathway is found to be critically involved. Nitric oxide is an essential mediator for the transfer from short- to long-term memory.
The role of secondary compounds (SC) in deterring herbivores and pathogens from vegetative parts of plants is well established, whereas their role in plant reproductive organs such as floral nectar is unclear. The present study aimed to reveal the response of free-flying honeybees to naturally occurring concentrations of four SC in floral nectar. We selected nicotine, anabasine, caffeine, and amygdalin, all of which are found in nectar of various plants. In repeated paired-choice experiments, we offered 20% sucrose solution as control along with test solutions of 20% sucrose with various concentrations of the above SC. Except for anabasine, naturally occurring concentrations of SC did not have a deterring effect. Furthermore, low concentrations of nicotine and caffeine elicited a significant feeding preference. SC can, therefore, be regarded as postingestive stimulants to pollinators, indicating that the psychoactive alkaloids in nectar may be a part of their mutualistic reward. Further studies are needed to test our hypothesis that psychoactive alkaloids in nectar impose dependence or addiction effects on pollinators.
Male-male competition in plants is thought to exert selection on flower morphology and on the temporal presentation of pollen. Theory suggests that a plant's pollen dosing strategy should evolve to match the abundance and pollen transfer efficiency of its pollinators. Simultaneous pollen presentation should be favored when pollinators are infrequent or efficient at delivering the pollen they remove, whereas gradual dosing should optimize delivery by frequent and wasteful pollinators. Among Penstemon and Keckiella species, anthers vary in ways that affect pollen release, and the morphology of dried anthers reliably indicates how they dispense pollen. In these genera, hummingbird pollination has evolved repeatedly from hymenopteran pollination. Pollen production does not change with evolutionary shifts between pollinators. We show that after we control for phylogeny, hymenopteran-adapted species present their pollen more gradually than hummingbird-adapted relatives. In a species pair that seemed to defy the pattern, the rhythm of anther maturation produced an equivalent dosing effect. These results accord with previous findings that hummingbirds can be more efficient than bees at delivering pollen.
Animals exploiting their familiar food items often avoid spatio-temporal aggregation with others by avoiding scents, less rewarding areas or visual contacts, thereby minimizing competition or interference when resources are replenished slowly in patches. When animals are searching or assessing available food sources, however, they may benefit from reducing sampling costs by following others at food sites. Therefore, animals may adjust their responses to others depending on their familiarity with foraging situations. Here, we conducted field experiments to test whether nectar-collecting bumble bees make this adjustment. We allowed free-foraging bees to choose between two inflorescences, one occupied by a conspecific bee and another unoccupied. When bees were presented with flowers of a familiar type, they avoided occupied inflorescences. In contrast, bees visited an occupied inflorescence when the flower type was unfamiliar. To our knowledge, this is the first report suggesting that animals adjust their responses to feeding conspecifics depending on their familiarity with food sources. Such behavioural flexibilities should allow foragers to both explore and exploit their environments efficiently.
Bees visit flowers to collect nectar and pollen that contain nutrients and simultaneously facilitate plant sexual reproduction. Paradoxically, nectar produced to attract pollinators often contains deterrent or toxic plant compounds associated with herbivore defence. The functional significance of these nectar toxins is not fully understood, but they may have a negative impact on pollinator behaviour and health, and ultimately plant pollination. This study investigates whether a generalist bumblebee, Bombus terrestris, can detect naturally occurring concentrations of nectar toxins. Using paired-choice experiments, we identified deterrence thresholds for five compounds found in the nectar of bee-pollinated plants: quinine, caffeine, nicotine, amygdalin, and grayanotoxin. The deterrence threshold was determined when bumblebees significantly preferred a sucrose solution over a sucrose solution containing the compound. Bumblebees had the lowest deterrence threshold for the alkaloid quinine (0.01 mM); all other compounds had higher deterrence thresholds, above the natural concentration range in floral nectar. Our data combined with previous work using honeybees suggest that generalist bee species have poor acuity for the detection of nectar toxins. The fact that bees do not avoid nectar relevant concentrations of these compounds is likely to indicate that it is difficult for them to learn to associate floral traits with the presence of toxins, thus, maintaining this trait in plant populations.
Although secondary metabolites are prevalent in floral nectar, the ecological consequences for pollinators and pollination remain relatively unexplored. While often deterrent to pollinators at high concentrations, secondary metabolite concentrations in nectar tend to be much lower than secondary metabolite concentrations in leaves and flowers; yet, they may still affect the maintenance of pollination mutualisms.Delphinium barbeyi, a common montane herb, contains norditerpene alkaloids in its nectar but at concentrations that are substantially lower than those found in its leaves or flowers. By manipulating nectar alkaloid concentrations in the field and laboratory, we assessed the degree to which varying concentrations of alkaloids in nectar influenced pollinator behaviour and activity and plant reproduction.In the field, nectar alkaloids significantly reduced both the number of flower visits and the time spent per flower by free-flying bumblebee pollinators, but we only observed effects at alkaloid concentrations 50 times that of natural nectar. When we supplemented D. barbeyi nectar with alkaloids at concentrations almost 15 times that of natural nectar, we found no evidence for direct or pollinator-mediated indirect effects on female plant reproduction.In the laboratory, the direct consumptive effects of nectar alkaloids on bumblebee pollinators were also concentration dependent. Bumblebees exhibited reduced mobility and vigour but only at alkaloid concentrations more than 25 times higher than those found in natural nectar.Synthesis. We found that nectar alkaloids have dose-dependent effects on pollinator behaviour and activity. While concentrations of nectar alkaloids rivalling those found in leaves would negatively affect pollinator behaviour and pollination services, the natural concentrations of nectar alkaloids in D. barbeyi have no negative direct or pollinator-mediated indirect effects on plant reproduction. These results provide experimental insight into the dose-dependent ecological consequences of nectar secondary metabolites for pollinators and pollination, suggesting that low nectar alkaloid concentrations incurred no ecological costs for D. barbeyi.
This study considers how a forager moves through its environment when food is patchily distributed and the patches differ in quality. One possibility is to move directionally among patches, staying longer in the best patches (the “Local-Experience Hypothesis”). Additionally, when foragers reuse patches in a regenerating environment, they can potentially benefit from remembering the most profitable patches, and return preferentially to these (the “Memory Hypothesis”). Both hypotheses were tested with foraging bumble bees (Bombus spp.) collecting nectar in the foothills and mountains of southwest Alberta, Canada. Individually marked worker bumble bees were observed visiting flowers on focal plants of five species visited primarily by bumble bees. In three plant species (Epilobium angustifolium, Hedysarum alpinum, and Penstemon confertus), variation in nectar secretion rate was experimentally induced by defoliation and fertilization of individual plants. In the other two species (H. sulphurescens and Oxytropis monticola), bees' responses to natural variation in plant-level nectar secretion were measured. Considering the bee population as a whole, plants with higher nectar production rates attracted more bees (three of five plant species) and had more of their flowers visited (three of five plant species). The Local-Experience Hypothesis was supported in three of the five plant species: individual bees stayed longer by visiting more flowers on plants with higher rates of nectar production. The Memory Hypothesis was supported in four of the five plant species; individual bees were more likely to return to plants with higher rates of nectar secretion. Overall, there was a positive correlation between the extent to which individual plants differed in their rate of nectar secretion (a species-level trait), and the strength of support for the Memory Hypothesis (measured as a standardized effect size). That is, individual bumble bees more strongly adjusted their visitation rate based on plant quality as the magnitude of natural differences in plant quality increased. Support for the Memory Hypothesis may explain why bumble bees often revisit the same plants on successive foraging trips: memory for good plants gives them a fitness advantage over naïve bees using the same area. Bumble bees appear to use a relatively sophisticated spatial memory in resource tracking, which may constrain the evolution of empty-flower strategies of plant nectar secretion.
Although plant-herbivore and plant-pollinator interactions have traditionally been studied separately, many traits are simultaneously under selection by both herbivores and pollinators. For example, secondary compounds commonly associated with herbivore defense have bran found in the nectar of many plant species, and many plants produce nectar that is toxic ol repellent to some floral visitors. Although secondary compounds in nectar and toxic nectar are geographically and phylogenetically widespread, their ecological significance is poorly understood. Several hypotheses have been proposed for the possible functions of toxic nectar, including encouraging specialist pollinators, deterring nectar robbers, preventing microbial degradation of nectar, and altering pollinator behavior. All of these hypotheses rest on the assumption that the benefits of toxic nectar must outweigh possible costs; however, to date no study has demonstrated that toxic nectar provides fitness benefits for any plant. Therefore, in addition to the:se adaptive hypotheses. we should also consider the hypothesis that toxic nectar provides no benefits or is tolerably detrimental to plants, and occurs due to previous selection pressures or pleiotropic constraints. For example, secondary compounds may be transported into nectar as a consequence of their presence in phloem. rather than due to direct selection for toxic nectar. Experimental approaches are necessary to understand the role of toxic nectar in plant-animal interactions.
Bees Get That Caffeine "Buzz"
Caffeine improves memory in humans, millions of whom find that their daily dose enhances clarity, focus, and alertness. The human relationship with caffeine is relatively recent, however, and thus its impact on our brains is likely a by-product of its true ecological role. Caffeine occurs naturally in the floral nectar of Coffea and Citrus plants. Wright et al. (p. 1202 ; see the Perspective by Chittka and Peng ) found that caffeine presented at naturalistic levels significantly improved the ability of bees to remember and locate a learned floral scent and potentiated the responses of neurons involved in olfactory learning and memory.
Summary • Plants that display many open flowers usually receive higher pollinator visitation rates, but it is unclear whether pollinators select plants to visit based on the size of floral display (apparent size) or the value of the floral rewards (reward size). To examine how pollinators respond to apparent size and reward size, we observed bumble bees foraging among arrays of artificial plants. • We constructed two kinds of artificial flower: (i) rewarding flowers that produced nectar constantly; and (ii) unrewarding flowers that produced only water. Thus, we could construct plants that varied both in numbers of flowers (apparent size) and in numbers of rewarding flowers (reward size). • At the beginning of the experiments, bees made more visits to the plants with the most flowers, irrespective of the rewards they contained. However, after several hours of foraging, bees returned selectively to plants with the greater number of rewarding flowers, irrespective of the number of flowers the plant presented. After we replaced rewarding plants with non-rewarding plants, bees continued visiting plants at formerly-profitable locations for a while. • Our results demonstrate that bees initially showed preferences for plants with larger floral displays, but eventually bees were able to discriminate between rewarding and less-rewarding plants of equal display size by associating a plant's location with its reward size. Our results suggest that plants with many flowers can achieve higher visitation rates from pollinators in two ways: (i) by attracting inexperienced pollinators with large displays; and (ii) by encouraging experienced pollinators to return with the promise of greater rewards. Functional Ecology (2007) 21, 854–863 doi: 10.1111/j.1365-2435.2007.01293.x
In the Colorado Rocky Mountains the glacier lily Erythronium grandiflorum exhibits a striking dimorphism in pollen color and is commonly pollinated by the bumble bee Bombus occidentalis. We induced bees to visit sequences of flowers in a flight cage, and compared dispersal of distinctively-colored pollen and fluorescent pigment (dye) that the bee had picked up at a single donor flower. Nonparametric and parametric analyses showed that dispersal properties of pollen and dye differed; consistently less pollen was deposited and it was carried consistently shorter distances than dye. Dye thus does not provide an accurate means of assessing exacty where or how far pollen travels in this plant-pollinator system. On the other hand, both pollen and dye responded similarly to several experimental manipulations of donor and recipient flowers. Hence dye may well be of value for a qualitative investigation of how floral traits influence pollen dispersal.
In field experiments withAralia hispida inflorescences, the following variables were manipulated: number of umbels per inflorescence, number of flowers per umbel, and amounts of pollen and nectar per flower. Visitation rates by bumble bees, the principal pollinators, were then observed. In the reward-variation experiments, bees appeared to learn the positions of nectar-rich shoots, and visited them significantly more often than nectar-poor shoots. They did not respond to similar variation in pollen production. The nectar preferences developed slowly after the treatments were imposed, and bees continued to favor sites that had been occupied by nectar-rich shoots even after the treatments were discontinued. Visitation rate was approximately proportional to flower number, making it unlikely that increases in inflorescence size produced a disproportionate gain in male reproductive success (a necessary condition in certain models for the evolution of dioecy). For a fixed number of flowers per inflorescence, bees preferred inflorescences with more umbels. In pairwise choice tests of male-phase and female-phase umbels of various sizes, bees preferred male-phase umbels and larger umbels; the preference for male-phase umbels is stronger in bees that had previously fed on male-phase umbels.
The types of interactions between learning events can significantly affect the value of learning. Learning one task may enhance the learning of a subsequent task (transfer), but the learning of a new task may also interfere with the memory of a previously learned task. Bumblebees, Bombus occidentalis, were tested for the magnitudes of transfer and interference between two related learning events. On the one hand, bees showed no evidence for positive transfer from one learning task to another. On the other hand, bees showed an initial reduction in performance after switching from task 2 back to task 1. However, after being trained to switch back and forth between two tasks, bees no longer showed an initial reduction in performance after switching. The results suggest first, that bees cannot generalize from one learning incident to another in the manner required in this experiment, and second, that bees can learn to alternate between certain distinct tasks with no reduction in performance.
Pseudoreplication is defined as the use of inferential statistics to test for treatment effects with data from experiments where either treatments are not replicated (though samples may be) or replicates are not statistically independent. In ANOVA terminology, it is the testing for treatment effects with an error term inappropriate to the hypothesis being considered. Scrutiny of 176 experimental studies published between 1960 and the present revealed that pseudoreplication occurred in 27% of them, or 48% of all such studies that applied inferential statistics. The incidence of pseudoreplication is especially high in studies of marine benthos and small mammals. The critical features of controlled experimentation are reviewed. Nondemonic intrusion is defined as the impingement of chance events on an experiment in progress. As a safeguard against both it and preexisting gradients, interspersion of treatments is argued to be an obligatory feature of good design. Especially in small experiments, adequate interspersion can sometimes be assured only by dispensing with strict randomization procedures. Comprehension of this conflict between interspersion and randomization is aided by distinguishing pre-layout (or conventional) and layout-specific alpha (probability of type I error). Suggestions are offered to statisticians and editors of ecological journals as to how ecologists' understanding of experimental design and statistics might be improved.
The evolution of floral traits may be shaped by a community of floral visitors that affect plant fitness, including pollinators and floral antagonists. The role of nectar in attracting pollinators has been extensively studied, but its effects on floral antagonists are less understood. Furthermore, the composition of non-sugar nectar components, such as secondary compounds, may affect plant reproduction via changes in both pollinator and floral antagonist behavior. We manipulated the nectar alkaloid gelsemine in wild plants of the native perennial vine Gelsemium sempervirens. We crossed nectar gelsemine manipulations with a hand-pollination treatment, allowing us to determine the effect of both the trait and the interaction on plant female reproduction. We measured pollen deposition, pollen removal, and nectar robbing to assess whether gelsemine altered the behavior of mutualists and antagonists. High nectar gelsemine reduced conspecific pollen receipt by nearly half and also reduced the proportion of conspecific pollen grains received, but had no effect on nectar robbing. Although high nectar gelsemine reduced pollen removal, an estimate of male reproduction, by one-third, this effect was not statistically significant. Fruit set was limited by pollen receipt. However, this effect varied across sites such that the sites that were most pollen-limited were also the sites where nectar alkaloids had the least effect on pollen receipt, resulting in no significant effect of nectar alkaloids on fruit set. Finally, high nectar gelsemine significantly reduced seed weight; however, this effect was mediated by a mechanism other than pollen limitation. Taken together, our work suggests that nectar alkaloids are more costly than beneficial in our system, and that relatively small-scale spatial variation in trait effects and interactions could determine the selective impacts of traits such as nectar composition.
Secondary compounds may benefit plants by deterring herbivores, but the presence of these defensive chemicals in floral nectar may also deter beneficial pollinators. This trade-off between sexual reproduction and defense has received minimal study. We determined whether the pollinator-deterring effects of a nectar alkaloid found in the perennial vine Gelsemium sempervirens depend on ecological context (i.e. the availability of alternative nectar sources) by monitoring the behavioural response of captive bumblebees (Bombus impatiens, an important pollinator of G. sempervirens in nature) to nectar alkaloids in several ecologically relevant scenarios. Although alkaloids in floral nectar tended to deter visitation by bumblebees, the magnitude of that effect depended greatly on the availability and nectar properties of alternative flowers. Ecological context should thus be considered when assessing ecological costs of plant defense in terms of pollination services. We consider adaptive strategies that would enable plants to minimize pollinator deterrence because of defensive compounds in flowers.
Honey bee (Hymenoptera: Apidae) foraging responses to phenolic-rich nectars Pseudoreplication and the design of ecological field experiments
- J Buchmann
- Sl
J, Buchmann SL (1993) Honey bee (Hymenoptera: Apidae) foraging responses to phenolic-rich nectars. J Kans Entomol Soc 66:223–230 Hurlbert SH (1984) Pseudoreplication and the design of ecological field experiments. Ecol Monogr 54:187–211
Cardenolides in nectar may be more a consequence of allocation to other plant parts: a phylogenetic study
- J S Manson
- S Rasmann
- R Halitsckhe
- J D Thomson
- A A Agrawal
- JS Manson
Manson JS, Rasmann S, Halitsckhe R, Thomson JD, Agrawal AA
(2013b) Cardenolides in nectar may be more a consequence of
allocation to other plant parts: a phylogenetic study. Funct Ecol
26:1100-1110
Estimating pollination success with novel artificial flowers: effects of nectar concentration
- Jd Thomson
- Je Ogilvie
- Tt Makino
- A Arisz
- S Raju
- V Rojas-Luengas
- Mg Tan
Feeding responses of free-flying honeybees to secondary compounds mimicking floral nectars
- N Singaravelan
- G Ne'eman
- M Inbar
- I Izhaki
Singaravelan N, Ne'eman G, Inbar M, Izhaki I (2005) Feeding
responses of free-flying honeybees to secondary compounds
mimicking floral nectars. J Chem Ecol 31:2791-2804