Floral Antagonists Research Articles

Flower visitor networks: Reduced reproductive success driven by antagonists in a hummingbird‐pollinated species

AbstractFlower–animal interactions encompass a continuum of mutualistic to antagonistic behaviors. Although the importance of pollinators in interaction networks has been widely reported, the role of floral antagonists remains overlooked. In Collaea cipoensis, an endemic shrub from southeastern Brazil, we modeled an individual‐based network assessing the flower visitors' functional behavior and tested if plant centrality increases fitness. Centrality indicates how well‐connected a given plant is with the rest of the conspecifics through shared flower visitors. Specifically, we tested if flower visitor interactions are amplified by many‐flowered individuals, and whether the relationship between centrality and plant fitness encompasses the effects of mutualists or antagonists. Subsequently, we quantified each visiting species' effectiveness. Antagonistic interactions were the most frequent in the network (97% of visits), primarily conducted by the nectar‐robbing bee Trigona spinipes (66%), which was also the most central species and detrimental antagonist. The hummingbirds Colibri serrirostris and Eupatomena macroura were the most efficient pollinators, with a high contribution to the quantity—floral visitation—and the quality—viable seeds—components, respectively. Many‐flowered plants showed greater centrality, which boosted the plant's cohesion in the network and increased flower visitation. Accordingly, many‐flowered plants were better connected, mainly due to antagonistic visitors. Thus, centrality increases were not positively translated into more reproductive success. Our results reinforce the dynamic scenarios of flower–animal interactions, with consequences to plant reproductive ecology. We highlight the importance of incorporating distinct types of interactions to unveil the complexity of interacting systems, that when not explored, hide potential evolutionary consequences for plant reproductive success.Abstract in Portuguese is available with online material.

Pollen, anther, stamen, and androecium mimicry.

Floral colours represent a highly diverse communication signal mainly involved in flower visitors' attraction and guidance, but also flower discrimination, filtering non-pollinators and discouraging floral antagonists. The divergent visual systems and colour preferences of flower visitors, as well as the necessity of cues for flower detection and discrimination, foster the diversity of floral colours and colour patterns. Despite the bewildering diversity of floral colour patterns, a recurrent component is a yellow UV-absorbing floral centre, and it is still not clear why this pattern is so frequent inangiosperms. The pollen, anther, stamen, and androecium mimicry (PASAM) hypothesis suggests that the system composed of the flowers possessing such yellow UV-absorbing floral reproductive structures, the flowers displaying central yellow UV-absorbing structures as floral guides, and the pollen-collecting, as well as pollen-eating, flower visitors responding to such signals constitute the world's most speciose mimicry system. In this review, we call the attention of researchers to some hypothetical PASAM systems around the globe, presenting some fascinating examples that illustrate their huge diversity. We will also present new and published data on pollen-eating and pollen-collecting pollinators' responses to PASAM structures supporting the PASAM hypothesis and will discuss how widespread these systems are around the globe. Ultimately, our goal is to promote the idea that PASAM is a plausible first approach to understanding floral colour patterns in angiosperms.

Floral volatiles evoke partially similar responses in both florivores and pollinators and are correlated with non-volatile reward chemicals.

Plants often use floral displays to attract mutualists and prevent antagonist attacks. Chemical displays detectable from a distance include attractive or repellent floral volatile organic compounds (FVOCs). Locally, visitors perceive contact chemicals including nutrients but also deterrent or toxic constituents of pollen and nectar. The FVOC and pollen chemical composition can vary intra- and interspecifically. For certain pollinator and florivore species, responses to these compounds are studied in specific plant systems, yet we lack a synthesis of general patterns comparing these two groups and insights into potential correlations between FVOC and pollen chemodiversity. We reviewed how FVOCs and non-volatile floral chemical displays, i.e. pollen nutrients and toxins, vary in composition and affect the detection by and behaviour of insect visitors. Moreover, we used meta-analyses to evaluate the detection of and responses to FVOCs by pollinators vs. florivores within the same plant genera. We also tested whether the chemodiversity of FVOCs, pollen nutrients and toxins is correlated, hence mutually informative. According to available data, florivores could detect more FVOCs than pollinators. Frequently tested FVOCs were often reported as pollinator-attractive and florivore-repellent. Among FVOCs tested on both visitor groups, there was a higher number of attractive than repellent compounds. FVOC and pollen toxin richness were negatively correlated, indicating trade-offs, whereas a marginal positive correlation between the amount of pollen protein and toxin richness was observed. Plants face critical trade-offs, because floral chemicals mediate similar information to both mutualists and antagonists, particularly through attractive FVOCs, with fewer repellent FVOCs. Furthermore, florivores might detect more FVOCs, whose richness is correlated with the chemical richness of rewards. Chemodiversity of FVOCs is potentially informative of reward traits. To gain a better understanding of the ecological processes shaping floral chemical displays, more research is needed on floral antagonists of diverse plant species and on the role of floral chemodiversity in visitor responses.

Floral trait variation across individual plants within a population enhances defense capability to nectar robbing

Floral trait variation may help pollinators and nectar robbers identify their target plants and, thus, lead to differential selection pressure for defense capability against floral antagonists. However, the effect of floral trait variation among individuals within a population on multi-dimensional plant-animal interactions has been little explored. We investigated floral trait variation, pollination, and nectar robbing among individual plants in a population of the bumble bee-pollinated plant, Caryopteris divaricata, from which flowers are also robbed by bumble bees with varying intensity across individuals. We measured the variation in corolla tube length, nectar volume and sugar concentration among individual plants, and evaluated whether the variation were recognized by pollinators and robbers. We investigated the influence of nectar robbing on legitimate visitation and seed production per fruit. We found that the primary nectar robber (Bombus nobilis) preferred to forage on plants with long-tubed flowers, which produced less nectar and had lower sugar concentration compared to those with shorter corolla tubes. Individuals with shorter corolla tubes had comparatively lower nectar robbing intensity but higher visitation by legitimate visitors (mainly B. picipes) and higher seed production. Nectar robbing significantly reduced seed production because it decreased pollinator visits. However, neither pollination nor seed production differed between plants with long and short corolla tubes when nectar robbers were excluded. This finding suggests that floral trait variation might not be driven by pollinators. Such variation among individual plants thus allows legitimate visitors and nectar robbers to segregate niches and enhances population defense against nectar robbing in unpredictable conditions.

Slippery flowers as a mechanism of defence against nectar-thieving ants.

The great diversity of floral characteristics among animal-pollinated plants is commonly understood to be the result of coevolutionary interactions between plants and pollinators. Floral antagonists, such as nectar thieves, also have the potential to exert an influence upon the selection of floral characteristics, but adaptation against floral antagonists has attracted comparatively little attention. We found that the corollas of hornet-pollinated Codonopsis lanceolata (Campanulaceae) and the tepals of bee-pollinated Fritillaria koidzumiana (Liliaceae) are slippery to nectar-thieving ants living in the plant's habitat; because the flowers of both species have exposed nectaries, slippery perianths may function as a defence against nectar-thieving ants. We conducted a behavioural experiment and observed perianth surface microstructure by scanning electron microscopy to investigate the mechanism of slipperiness. Field experiments were conducted to test whether slippery perianths prevent floral entry by ants, and whether ant presence inside flowers affects pollination. Scanning electron microscopy observations indicated that the slippery surfaces were coated with epicuticular wax crystals. The perianths lost their slipperiness when wiped with hexane. Artificial bridging of the slippery surfaces using non-slippery materials allowed ants to enter flowers more frequently. Experimental introduction of live ants to the Codonopsis flowers evicted hornet pollinators and shortened the duration of pollinator visits. However, no statistical differences were found in the fruit or seed sets of flowers with and without ants. Slippery perianths, most probably based on epicuticular wax crystals, prevent floral entry by ants that negatively affect pollinator behaviour. Experimental evidence of floral defence based on slippery surfaces is rare, but such a mode of defence may be widespread amongst flowering plants.

Light availability influences the intensity of nectar robbery and its effects on reproduction in a tropical shrub via multiple pathways.

The multiple exogenous pathways by which light availability affects plant reproduction (e.g., via influence on attraction of mutualists and antagonists) remain surprisingly understudied. The light environment experienced by a parent can also have transgenerational effects on offspring via these same pathways. We evaluated (a) the influence of light availability on floral traits in Odontonema cuspidatum, (b) the relative importance of the pathways by which light influences nectar robbery and reproductive output, and (c) the role of parental light environment in mediating these relationships. We conducted a reciprocal translocation experiment using clonally propagated ramets and field surveys of naturally occurring plants. Light availability influenced multiple floral traits, including flower number and nectar volume, which in turn influenced nectar robbery. But nectar robbery was also directly influenced by light availability, due to light effects on nectar robber foraging behavior or neighborhood floral context. Parental light environment mediated the link between light availability and nectar robber attraction, suggesting local adaptation to low-light environments in floral visitor attraction. However, we found no transgenerational effect on reproduction. Our findings demonstrate that exogenous pathways by which light influences plants (particularly through effects on floral antagonists) can complicate the positive relationship between light availability and plant reproduction. Our results are among the first to document effects of light on floral antagonists and clonal transgenerational effects on flower visitor attraction traits.

Heavy metals in nectar modify behaviors of pollinators and nectar robbers: Consequences for plant fitness

Plants growing in heavy-metal-rich soils can accumulate metals into their nectar. Nectar chemical composition can alter foraging behavior of floral visitors (including pollinators and floral antagonists) and further affect plant reproductive fitness. The role of nectar heavy metals in deterring pollinators (e.g., shortening foraging time) has been recently studied, but their effects on plant reproduction via changes in behaviors of both pollinators and floral antagonists (e.g., nectar robbers) are less understood. We experimentally manipulated four nectar heavy metals (Zn, Cu, Ni, and Pb) in a native ornamental plant, Hosta ensata F. Maekawa, to investigate the effect of nectar metals on plant reproductive success. We also recorded nectar robbing as well as foraging time and visitation rate of pollinators to assess whether nectar metals could alter the behavior of antagonists and mutualists. Although metals in nectar had no significant direct effects on plant reproduction via hand-pollination, we detected their positive indirect effects on components of female fitness mediated by pollinators and nectar robbers. Matching effects on female plant fitness, nectar robbers responded negatively to the presence of metals in nectar, robbing metal-treated flowers less often. Pollinators spent less time foraging on metal-treated flowers, but their visitation rate to metal-treated flowers was significantly higher than to control flowers. Moreover, pollinators removed less nectar from flowers treated with metals. Our results provide the first direct evidence to date that heavy metals in nectar are capable of deterring nectar robbers and modifying pollinator foraging behavior to enhance plant reproductive fitness.

Floral antagonists counteract pollinator‐mediated selection on attractiveness traits in the hummingbird‐pollinatedCollaea cipoensis(Fabaceae)

AbstractPollinator‐mediated selection toward larger and abundant flowers is common in naturally pollen‐limited populations. However, floral antagonists may counteract this effect, maintaining smaller‐ and few‐flowered individuals within populations. We quantified pollinator and antagonist visit rates and determined a multiplicative female fitness component from attacked and non‐attacked flowers of the Brazilian hummingbird‐pollinated shrubCollaea cipoensisto determine the selective effects of pollinators and floral antagonists on flower size and number. We predicted that floral antagonists reduce the female fitness component and thus exert negative selective pressures on flower size and number, counteracting the positive effects of pollinators. Pollinators, mainly hummingbirds, comprised 4% of total floral visitation, whereas antagonist ants and bees accounted for 90% of visitation. Nectar‐robbers involved about 99% of floral antagonist visit rates, whereas florivores comprised the remaining 1%. Larger and abundant flowers increased both pollinator and antagonist visit rates and the female fitness component significantly decreased in flowers attacked by nectar‐robbers and florivores in comparison to non‐attacked flowers. We detected that pollinators favored larger‐ and many‐flowered individuals, whereas floral antagonists exerted negative selection on flower size and number. This study confirms that floral antagonists reduce female plant fitness and this pattern directly exerts negative selective pressures on flower size and number, counteracting pollinator‐mediated selection on floral attractiveness traits.

Colour as a backup for scent in the presence of olfactory noise: testing the efficacy backup hypothesis using bumblebees (Bombus terrestris).

The majority of floral displays simultaneously broadcast signals from multiple sensory modalities, but these multimodal displays come at both a metabolic cost and an increased conspicuousness to floral antagonists. Why then do plants invest in these costly multimodal displays? The efficacy backup hypothesis suggests that individual signal components act as a backup for others in the presence of environmental variability. Here, we test the efficacy backup hypothesis by investigating the ability of bumblebees to differentiate between sets of artificial flowers in the presence of either chemical interference or high wind speeds, both of which have the potential to impede the transmission of olfactory signals. We found that both chemical interference and high wind speeds negatively affected forager learning times, but these effects were mitigated in the presence of a visual signal component. Our results suggest that visual signals can act as a backup for olfactory signals in the presence of chemical interference and high wind speeds, and support the efficacy backup hypothesis as an explanation for the evolution of multimodal floral displays.

Geographic variation in resistance to nectar robbing and consequences for pollination

Floral evolution is frequently ascribed to selection by pollinators, but may also be shaped by antagonists. However, remarkably few studies have examined geographic mosaics in resistance to floral antagonists or the consequences for other floral interactions. Gelsemium sempervirens experiences frequent nectar robbing in northern Georgia, but rarely in southern Georgia. We conducted common-garden experiments in both locations using genotypes from each region and measured robbing, pollinator attraction, floral attractive and defensive traits, and plant reproduction. Nectar robbing was more than four times higher in the north vs. south, and pollinator visits did not differ between gardens. Across both gardens, northern genotypes were half as likely to be nectar-robbed but received half as many pollinator visits as southern genotypes, suggesting evolution of resistance to robbing at a cost of reduced pollinator attraction. Plant-level traits, such as height and number of flowers, were more closely associated with resistance to robbing than floral size, shape, or chemistry. Northern genotypes had lower female and estimated male reproduction compared to southern genotypes at both locations, which could be due to costs of resistance to nectar robbing, or costs of adaptations to other biotic or abiotic differences between regions. Our study indicates that geographic variation can play a strong role structuring interactions with floral antagonists and mutualists and provides evidence consistent with the hypothesis that local resistance to nectar robbing imposes costs in terms of decreased pollinator attraction and reproduction.

Plant toxin levels in nectar vary spatially across native and introduced populations

Summary Secondary compounds in nectar can function as toxic chemical defences against floral antagonists, but may also mediate plant–pollinator interactions. Despite their ecological importance, few studies have investigated patterns of spatial variation in toxic nectar compounds in plant species, and none outside their native range. Grayanotoxin I (GTX I) occurs in nectar of invasive Rhododendron ponticum where it is toxic to honeybees and some solitary bee species. We examined (i) geographic variation in the composition of nectar GTX I, as well as GTX III (which is not toxic to these species), in the native and introduced range of R. ponticum, (ii) how their expression is structured at patch and landscape scales within ranges, and (iii) whether climatic and environmental factors underpin spatial patterns. While both GTXs varied within ranges, variation in GTX I, but not GTX III, was detected between ranges. GTX I expression was thus markedly lower or (in 18% of cases) absent from nectar in introduced plants. Spatial autocorrelation was apparent at both patch and landscape scales and in part related to heat load interception by plants (a function of latitude, aspect and slope). As expression of nectar GTXs was generally robust to environmental variation, and aggregated in space, this trait has the potential to be spatially discriminated by consumers. Given the specificity of change to GTX I, and its differential toxicity to some bee species, we conclude that its expression was likely to have been influenced during invasion by interaction with herbivores/consumers, either via pollinator‐mediated selection or enemy release from floral antagonists. Synthesis. As the first demonstration of large‐scale geographic variation and spatial structure in toxic nectar compounds, this work deepens our understanding of the chemical ecology of floral interactions in native and introduced species. Spatially explicit studies of nectar secondary compounds are thus required to show how the extent and structure of spatial variation may affect floral ecology. Future development of invasion theory should incorporate a holistic view of plant defence, beyond antagonistic interactions, which integrates the consequences of chemically defended mutualist rewards.

CYP76C1 (Cytochrome P450)-Mediated Linalool Metabolism and the Formation of Volatile and Soluble Linalool Oxides in Arabidopsis Flowers: A Strategy for Defense against Floral Antagonists.

The acyclic monoterpene alcohol linalool is one of the most frequently encountered volatile compounds in floral scents. Various linalool oxides are usually emitted along with linalool, some of which are cyclic, such as the furanoid lilac compounds. Recent work has revealed the coexistence of two flower-expressed linalool synthases that produce the (S)- or (R)-linalool enantiomers and the involvement of two P450 enzymes in the linalool oxidation in the flowers of Arabidopsis thaliana. Partially redundant enzymes may also contribute to floral linalool metabolism. Here, we provide evidence that CYP76C1 is a multifunctional enzyme that catalyzes a cascade of oxidation reactions and is the major linalool metabolizing oxygenase in Arabidopsis flowers. Based on the activity of the recombinant enzyme and mutant analyses, we demonstrate its prominent role in the formation of most of the linalool oxides identified in vivo, both as volatiles and soluble conjugated compounds, including 8-hydroxy, 8-oxo, and 8-COOH-linalool, as well as lilac aldehydes and alcohols. Analysis of insect behavior on CYP76C1 mutants and in response to linalool and its oxygenated derivatives demonstrates that CYP76C1-dependent modulation of linalool emission and production of linalool oxides contribute to reduced floral attraction and favor protection against visitors and pests.

How scent and nectar influence floral antagonists and mutualists.

Many plants attract and reward pollinators with floral scents and nectar, respectively, but these traits can also incur fitness costs as they also attract herbivores. This dilemma, common to most flowering plants, could be solved by not producing nectar and/or scent, thereby cheating pollinators. Both nectar and scent are highly variable in native populations of coyote tobacco, Nicotiana attenuata, with some producing no nectar at all, uncorrelated with the tobacco's main floral attractant, benzylacetone. By silencing benzylacetone biosynthesis and nectar production in all combinations by RNAi, we experimentally uncouple these floral rewards/attractrants and measure their costs/benefits in the plant's native habitat and experimental tents. Both scent and nectar increase outcrossing rates for three, separately tested, pollinators and both traits increase oviposition by a hawkmoth herbivore, with nectar being more influential than scent. These results underscore that it makes little sense to study floral traits as if they only mediated pollination services.

Gloss, colour and grip: multifunctional epidermal cell shapes in bee- and bird-pollinated flowers.

Flowers bear the function of filters supporting the attraction of pollinators as well as the deterrence of floral antagonists. The effect of epidermal cell shape on the visual display and tactile properties of flowers has been evaluated only recently. In this study we quantitatively measured epidermal cell shape, gloss and spectral reflectance of flowers pollinated by either bees or birds testing three hypotheses: The first two hypotheses imply that bee-pollinated flowers might benefit from rough surfaces on visually-active parts produced by conical epidermal cells, as they may enhance the colour signal of flowers as well as the grip on flowers for bees. In contrast, bird-pollinated flowers might benefit from flat surfaces produced by flat epidermal cells, by avoiding frequent visitation from non-pollinating bees due to a reduced colour signal, as birds do not rely on specific colour parameters while foraging. Moreover, flat petal surfaces in bird-pollinated flowers may hamper grip for bees that do not touch anthers and stigmas while consuming nectar and thus, are considered as nectar thieves. Beside this, the third hypothesis implies that those flower parts which are vulnerable to nectar robbing of bee- as well as bird-pollinated flowers benefit from flat epidermal cells, hampering grip for nectar robbing bees. Our comparative data show in fact that conical epidermal cells are restricted to visually-active parts of bee-pollinated flowers, whereas robbing-sensitive parts of bee-pollinated as well as the entire floral surface of bird-pollinated flowers possess on average flat epidermal cells. However, direct correlations between epidermal cell shape and colour parameters have not been found. Our results together with published experimental studies show that epidermal cell shape as a largely neglected flower trait might act as an important feature in pollinator attraction and avoidance of antagonists, and thus may contribute to the partitioning of flower-visitors.

Attracting mutualists and antagonists: plant trait variation explains the distribution of specialist floral herbivores and pollinators on crops and wild gourds.

• Floral traits play important roles in pollinator attraction and defense against floral herbivory. However, plants may experience trade-offs between conspicuousness to pollinators and herbivore attraction. Comparative studies provide an excellent framework to examine the role of multiple traits shaping mutualist and antagonist interactions.• To assess whether putative defensive and attractive traits predict species interactions, we grew 20 different Cucurbitaceae species and varieties in the field to measure interactions with pollinators and herbivores and in the greenhouse to assess trait variation. Cucurbits are characterized by the production of cucurbitacins, bitter nonvolatile terpenoids that are effective against generalist herbivores but can attract specialist beetles. We determined whether plant traits such as cucurbitacins predict herbivore resistance and pollinator attraction using an information-theoretic approach.• Mutualists and floral antagonists were attracted to the same cucurbit varieties once they flowered. However, rather than cucurbitacin concentration, we found that the size of the flower and volatile emissions of floral sesquiterpenoids explained both pollinator and floral herbivore visitation preference across cucurbit taxa. This pattern held across cucurbit taxa and within the Cucurbita genus.• Surprisingly, floral sesquiterpenoid volatiles, which are associated with direct defense, indirect defense, and attraction, rather than defense traits such as cucurbitacins, appeared to drive interactions with both pollinators and floral herbivores across cucurbit taxa. Identifying the relevant plant traits for attraction and deterrence is important in this economically valuable crop, particularly if pollinators and floral herbivores use the same plant traits as cues.

Nectar alkaloids decrease pollination and female reproduction in a native plant

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.

Dosage-Dependent Impacts of a Floral Volatile Compound on Pollinators, Larcenists, and the Potential for Floral Evolution in the Alpine SkypilotPolemonium viscosum

All volatile organic compounds (VOCs) vary quantitatively, yet how such variation affects their ecological roles is unknown. Because floral VOCs are cues for both pollinators and floral antagonists, variation in emission may have major consequences for costs and benefits in plant-pollinator interactions. In Polemonium viscosum, the emission rate for the floral VOC 2-phenylethanol (2PE) spans more than two orders of magnitude. We investigated the ecological and evolutionary impacts of this immense phenotypic variation. The emission rate of 2PE varies independently of nectar rewards and thus is uninformative of profitability. Emission is elevated in flowers that are morphologically vulnerable to ant larcenists, suggesting that chemical deterrence may compensate for weak physical barriers. In nature, plants emitting more 2PE than their neighbors escape ant damage. Flower-damaging ants die when exposed to 2PE in the laboratory, and they avoid high 2PE emitters in the field. High 2PE also reduces bumblebee visitation and pollination, suggesting an ecological cost of defense in pollinator service. However, at more moderate emission rates, 2PE enhances the amount of nectar left in flowers, at no pollination cost. In conclusion, repellency of 2PE is highly sensitive to dosage, giving it a key role in shaping ecological interactions between skypilot plants and their floral visitors.

Pollination ecology in the 21st Century: Key questions for future research

To inspire new ideas in research on pollination ecology, we list the most important unanswered questions in the field. This list was drawn up by contacting 170 scientists from different areas of pollination ecology and asking them to contribute their opinion on the greatest knowledge gaps that need to be addressed. Almost 40% of them took part in our email poll and we received more than 650 questions and comments, which we classified into different categories representing various aspects of pollination research. The original questions were merged and synthesised, and a final vote and ranking led to the resultant list. The categories cover plant sexual reproduction, pollen and stigma biology, abiotic pollination, evolution of animal-mediated pollination, interactions of pollinators and floral antagonists, pollinator behaviour, taxonomy, plant-pollinator assemblages, geographical trends in diversity, drivers of pollinator loss, ecosystem services, management of pollination, and conservation issues such as the implementation of pollinator conservation. We focused on questions that were of a broad scope rather than case-specific; thus, addressing some questions may not be feasible within single research projects but constitute a general guide for future directions. With this compilation we hope to raise awareness of pollination-related topics not only among researchers but also among non-specialists including policy makers, funding agencies and the public at large. download Appendix