Pollen Rewards Research Articles

Land use influences the nutrient concentration and composition of pollen and nectar rewards of wildflowers in human-dominated landscapes

Plant biodiversity is crucial to satisfy the trophic needs of pollinators, mainly through nectar and pollen rewards. However, a few studies have been directed to ascertain the intraspecific variation of chemical features and the nutritional value of nectar and pollen floral rewards in relation to the alteration of landscapes due to human activities. In this study, by using an existing scenario of land use gradients as an open air laboratory, we tested the variation in pollen and nectar nutrient profiles along gradients of urbanization and agriculture intensity, by focusing on sugar, aminoacids of nectar and phytochemicals of pollen from local wild plants. We also highlighted bioactive compounds from plants primary and secondary metabolism due to their importance for insect wellbeing and pollinator health. We surveyed 7 different meadow species foraged by pollinators and common in the main land uses studied. The results indicated that significant variations of nutritional components occur in relation to different land uses, and specifically that the agricultural intensification decreases the sugars and increases the antioxidant content of flower rewards, while the urbanization is positively associated with the total flavonoid content in pollen. These effects are more evident in some species than in others, such as Lotus corniculatus L. (Fabaceae) and Malva sylvestris L. (Malvaceae), as shown by the untargeted metabolomic investigation. This study is crucial for understanding the nutritional landscape quality for pollinators in association to different land uses and sets a base for landscape management and planning of pollinator-friendly strategies by improving the quality of plant rewards to provide benefits to pollinator health in various environmental contexts.

Divergent responses of generalist and specialist pollinators to experimental drought: Outcomes for plant reproduction.

Drought is an increasingly important consequence of climate change. Drought often causes plants to alter patterns of resource allocation, which in turn can affect how plants interact with other species. How these altered interactions subsequently influence plant reproductive success remains incompletely understood and may depend on the degree of specialization exhibited by antagonists and mutualists. Specialist pollinators, for example, are dependent on floral resources from their obligate hosts and under drought conditions may thus indiscriminately visit these hosts (at least in certain circumstances). Generalist pollinators, in contrast, may only forage on host plants in good condition, given that they can forage on other plant species. We tested this hypothesis and its consequences for plant reproduction in squash (Cucurbita pepo) grown along an experimental moisture gradient ranging from dry (growth and flowering compromised) to wet conditions. Floral visitation increased with plant soil moisture for generalist honey bees but was independent of plant soil moisture for specialist squash bees. Pollen production increased with plant soil moisture, and fluorescent pigments placed on flowers revealed that pollinators primarily moved pollen from male flowers on well-watered plants to the stigmas of female flowers on well-watered plants. Seed set increased with increasing plant soil moisture but, notably, was higher in bee-pollinated plants compared to plants pollinated by hand with an even mix of pollen from plants grown at either end of the experimental moisture gradient. These results suggest that superior pollen rewards, perhaps combined with selective foraging by generalists, enhanced reproductive success in C. pepo when plant soil moisture was high and more generally illustrate that pollinator behavior may contribute to how drought conditions affect plant reproduction.

Reproductive challenges related to a complex sexual system in Euphorbia rosescens, a rare endemic herb

AbstractWhen the sexual system of a rare plant species is complex, characterizing floral development, plant morphology, and subpopulation structure is essential for assessing reproductive potential. Availability of pollinator rewards and positioning of sexual morphs within inflorescences relates to outcrossing potential. We studied the complex sexual system of the recently discovered Euphorbia rosescens E.L. Bridges & Orzell, a rare species occurring in a single Florida county. Euphorbia rosescens has both monomorphic subpopulations of female plants and mixed subpopulations with male and andromonoecious plants. Most data on cyathia sex, inflorescence architecture, floral visitors, and fruit set came from one female subpopulation and one mixed subpopulation. Cyathia longevity, flowering phase, nectar secretion, pollen production, and viability were measured in female, male, and hermaphrodite cyathia. Female plants had fewer inflorescence levels and cyathia and significantly smaller cyathia than male and andromonoecious plants. Andromonoecious plants were larger and produced more cyathia relative to male plants. Within mixed populations, sex switching occurred in both directions between male and andromonoecious plants. Female plants did not switch sexes. Proximal to distal inflorescence levels transitioned from hermaphrodite to male cyathia on andromonoecious plants. Nectar secretion corresponded to initiation of staminate flowering, but in female cyathia stigmas were receptive approximately a day before nectar secretion. Pollen production and viability were similar in male and hermaphrodite cyathia. Fruit maturation was minimal, primarily observed on andromonoecious plants. Nectar availability, pollen rewards, trimorphic inequalities in inflorescence display, and low fruit set suggest high geitonogamy, thus limiting outcrossing potential for this species.

Genotype and environment effects on sunflower nectar and their relationships to crop pollination

Whether caused by genotype (G) or environment (E), floral trait variation has consequences for plants and their pollinators. Cultivated sunflower is a model system to explore floral trait variation; though sunflowers are bred to self-pollinate, benefits of pollination by bees remain substantial. To better understand sunflower-pollinator interactions, experiments were conducted to: (i) examine genotype and environment effects on nectar quantity and quality under controlled conditions, and (ii) assess effects of bags used for pollinator exclusion on nectar quantity, quality and bee foraging in a field environment. Contrasting temperature treatments (28°C, 21°C, 28°C / 16°C) reveal environment effects or G × E interactions for nectar volume (µl / floret), concentration (°Brix), and sugar composition (% sucrose). Bags used to exclude sunflower pollinators resulted in nectar volumes greater than plants with unrestricted access for bees (= open-pollination), and in ≈ 5-fold increased visitation by wild bees after bags were removed. Differences in bee visits to plants that were previously bagged versus plants never bagged decreased over the 2 h following bag removal. Though genetic variation in sunflower nectar is affected by the environment and G × E interactions, improving pollination via plant breeding still appears feasible. Future research on intraspecific variation in pollen rewards could be helpful, especially because pollen has received little research compared to nectar. For research with nectar or pollen, it seems desirable to measure floral rewards with methods that don’t rely on pollinator exclusion (bags or cages), which should provide more realistic data on what pollinators experience while foraging.

Fertilizers disrupt the electric feel of flowers

Electricity is literally all around us. As humans, we generate weak electric fields whenever we move our muscles; spiders use static electricity in the air to fly across great distances; and geckos use static in their sticky feet to scale vertical walls with ease. Since everything has an electric field, we can imagine that this fundamental force of nature plays an important role in many ecological interactions. Among insects, bumblebees are known to alter the static electricity of flowers to communicate with members of their hive; the positive charge that collects on their tiny hairs alters the electric field around a visited flower for ∼100 s, communicating to the next bee that buzzes by that the nectar and pollen rewards from that flower have already been exhausted. Ellard Hunting and colleagues from University of Bristol, UK, and the Woods Hole Oceanographic Institution, USA, set out to test whether the application of agricultural sprays alters the electric field of flowers and whether bumblebees can detect these disruptions.The pervasive use of chemicals in agriculture is a substantial source of pollution. But besides chemical toxicity, little is known about how agrochemicals otherwise affect plant–pollinator interactions. Hunting and colleagues observed that bumblebees tend to hover around chemically treated flowers and decide not to land. To investigate the cause of this avoidance behaviour, the researchers developed a computational model for how the application of agricultural sprays may alter floral electric fields up to 4 cm from the flower. Their model considered how the presence of droplets on the flower's surface and localized increases in humidity from a spray application might impact the flower's electric field.Next, the researchers studied the effect of common agricultural fertilizers on flower features that bees recognize. To see if fertilizer sprays change the way bees see flowers, the researchers determined what wavelengths of light are reflected from droplets with and without fertilizers added. To study whether fertilizer sprays change the way flowers smell, they measured how much effort the bees put into feeding when offered sugar water laced with fertilizer compared with just sugar water. Lastly, to visualize the electric fields surrounding various blooms, the scientists sprayed charged coloured powder particles onto the centre of ragwort flowers and observed how the powder distributed across the surfaces. Although the fertilizers did not affect how bees see or smell flowers, the chemicals did alter the electric field around each bloom for several minutes.Next, Hunting and colleagues tested whether the adverse effects of spray applications persist over time. To do this, they planted electrodes into the cut stems of potted lavender and Texas bluebell plants and recorded the electrical current streaming down the stems in response to different spray applications. While a water spray caused a change in current that only lasted 30–60 s, a spray containing the fertilizer caused a consistent change in current that lasted up to 16 min. A spray with another common agricultural chemical – the pesticide Imidacloprid – induced a change in current that lasted up to 25 mins. Even subsequent water sprays, simulating rain, produced prolonged changes in the plant stem's electrical signature, suggesting that this effect can endure even after a single application of fertilizer.Finally, the researchers observed wild bumblebees foraging on cut flowers with artificially applied electric fields to mimic the effect of fertilizers. They pierced lavender stems with metal electrodes, placed them in glass jars of tap water, and attached a 13 V battery to produce an electric current in the plant. By recording 2 h videos and counting the number of bumblebees that approached versus those that landed on the lavender, the team showed that bumblebees somehow sense weird electricity as they approach a flower and land less as a result, serving as a healthy reminder that as humans we affect our environments in ways we can't even sense.

Impacts of soil nutrition on floral traits, pollinator attraction, and fitness in cucumbers (Cucumis sativus L.)

Annual plants allocate soil nutrients to floral display and pollinator rewards to ensure pollination success in a single season. Nitrogen and phosphorus are critical soil nutrients whose levels are altered by intensive land use that may affect plants’ fitness via pollinator attractiveness through floral display and rewards. In a controlled greenhouse study, we studied in cucumbers (Cucumis sativus) how changes in soil nitrogen and phosphorus influence floral traits, including nectar and pollen reward composition. We evaluated how these traits affect bumble bee (Bombus impatiens, an important cucumber pollinator) visitation and ultimately fruit yield. While increasing nitrogen and phosphorus increased growth and floral display, excess nitrogen created an asymptotic or negative effect, which was mitigated by increasing phosphorus. Male floral traits exhibited higher plasticity in responses to changes in soil nutrients than female flowers. At 4:1 nitrogen:phosphorus ratios, male flowers presented increased nectar volume and pollen number resulting in increased bumble bee visitation. Interestingly, other pollinator rewards remained consistent across all soil treatments: male and female nectar sugar composition, female nectar volume, and pollen protein and lipid concentrations. Therefore, although cucumber pollination success was buffered in conditions of nutrient stress, highly skewed nitrogen:phosphorus soil ratios reduced plant fitness via reduced numbers of flowers and reward quantity, pollinator attraction, and ultimately yield.

Pollination system and reproductive failure in an endangered semi-evergreen tree, Syzygium myhendrae (Bedd. ex Brandis) Gamble

• The relationship between the phenology of Syzygium myhendrae and climatic factors was studied. • Visitation frequency and visitor activity index were calculated for each floral visitor to confirm its pollination efficiency. • The flowers were exclusively visited by honeybees, rockbee, wasps, psyllids and beetles. • Eulophid and pteromalid parasitic wasps were limited the fruit set rate and induced premature fruit drop. • Higher bud drop, flower wastage and insect infestation on fruits decreased the fruit production. The present investigation has attempted to analyze the phenology, floral biology, pollination biology, fruit set and insect infestation on Syzygium myhendrae , an endemic and endangered semievergreen tree in the Western Ghats, India. This tree exhibited a bi-annual mode of flowering and fruiting behavior. The flowers lack strong fragrance, colorful and attractive petals, or sepals; however, the dense stamens functioned as a major floral advertisement. The flowers were exclusively visited by insects ( Apis dorsata, A. mellifera, A. cerana, A. florea, Tetragonula iridipennis , wasps, psyllids and beetles). Among these, A. dorsata was the most frequent and effective pollinator. The infestation by Eulophid and Pteromalid wasps has limited the fruit set rate and induced premature fruit drop in S. myhendrae. The damage incidence has ranged from 82% to 100%. Higher bud drop, flower wastage and insect infestation on fruits have resulted in lower fruit production in S. myhendrae . This endangered tree has reproduced via outcrossing using stamen advertisement and pollen rewards. Eventually, higher flower wastage and fruits infestation have resulted in lesser fruit production, seed maturation and seedling establishment. These factors might have jointly resulted in the reproductive failure and limited distribution of this endemic and endangered species.

Nectar Abundance and Nectar Composition in Selected Rubus idaeus L. Varieties

The increasing commercial production of R. idaeus offers insects nectar and pollen rewards, thus increasing the chance of cross-pollination, which enhances fruit yields. The knowledge of nectar characteristics may help farmers/beekeepers to improve the quality of their products. Therefore, we determined and compared nectar weight, sugar concentration and weight, and the qualitative and quantitative composition of sugars and amino acids in the nectar of six raspberry cultivars: three biennial and three repeated fruiting cultivars. The nectary abundance in these cultivars ranged between 20.2 ± 3.84 mg (‘Polka’) and 26.4 ± 7.3 mg (‘Glen Ample’) of nectar per flower with a sugar concentration of 34.6 ± 5.61–47.3 ± 9.33%. The contents of glucose and fructose (g/100 g) were in the range from 42.96 ± 0.71 (‘Glen Ample’) to 46.94 ± 0.55 (‘Laszka’) and from 50.7 ± 1.43 (‘Polka’) to 54.2 ± 0.72 (‘Radziejowa’). Sucrose was detected only in ‘Glen Ample’ (5.6 ± 1.12 g/100 g) and ‘Polka’ (6.2 ± 0.95 g/100 g). Taking into account the increasing sugar weight in the nectar, the cultivars were ranked as follows: ‘Polka’ < ‘Polana’ < ‘Radziejowa’ < ‘Pokusa’ < ‘Laszka’ < ‘Glen Ample’. The nectar of the analyzed raspberry cultivars was classified as a hexose-dominant type. Aspartic acid, glutamic acid, and proline were the most dominant endogenous amino acids, whereas exogenous acids were dominated by lysine and leucine. The present results provide valuable information about the nutritious value of R. idaeus nectar for pollinators.

Diversity of Insect Visitor’s on Blossom of Capparis decidua (Forssk.) Edgew (Kair) in Northwest Rajasthan

Capparis decidua flowers are cross-pollinated and favored by number of insect for collecting nectar and pollen rewards. It has for low fruit set ratio due to a high degree of self-incompatibility and it largely depends on cross pollination by insects for fruit setting. Present study focuses on studying diversity of insect visitors of C. decidua to enlist the dominant and most abundant insect pollinator of C. decidua. The data collected revealed that the most predominantly insects visiting the blossom belongs to insect order Hymenoptera, Coleoptera & Diptera. Among Hymenopteran insects different species of honey bees are the most abundant flower visiting insects.

Pollinators adjust their behavior to presence of pollinator-transmitted pathogen in plant population

Abstract Interactions between pollinators and plants can be affected by presence of plant pathogens that substitute their infectious propagules for pollen in flowers and rely on pollinators for transmission to new hosts. However, it is largely unknown how pollinators integrate cues from diseased plants such as altered floral rewards and floral traits, and how their behavior changes afterwards. Understanding pollinator responses to diseased plants is crucial for predicting both pathogen transmission and pollen dispersal in diseased plant populations. In this study, we investigated pollinator responses to contact with plants of Dianthus carthusianorum diseased with anther smut (Microbotryum carthusianorum). We combined three approaches: 1) observation of individual pollinators foraging in experimental arrays of pre-grown potted plants; 2) measurements of floral rewards and floral traits of healthy and diseased plants; and 3) quantification of pollen/spore loads of pollinator functional groups. We found that pollinators showed only weak preferences for visiting healthy over diseased plants, but after landing on plants, they probed fewer flowers on the diseased ones. Since diseased flowers offered lower nectar and no pollen rewards, this behavior is consistent with the prediction of optimal foraging models that pollinators should spend less time exploring less rewarding patches or plants. Furthermore, pollen-foraging solitary bees and hoverflies responded to diseased plants more negatively than nectar-feeding butterflies did. Lastly, based on group-specific behavior and typical pollen/spore loads, we suggest that solitary bees and hoverflies contribute to both pollen and pathogen spore dispersal mainly over short distances, while butterfly visits are most important for long-distance dispersal.

Association of flower color with pollen reward may explain increased bumblebee visitation to the Scotch broom yellow morph

Given that pollinators usually visit flowers for hidden rewards, they need to rely on floral traits that indicate reward status (“honest signals”). However, the relationship between pollination, honest signals, and floral rewards is little documented in natural conditions. The Scotch broom (Cytisus scoparius) is an invasive shrub with polymorphism in the color of its flowers that can be yellow, orange, or red. In three areas dominated by the Scotch broom, we described the abundance of the floral morphs and estimated bumblebee (Bombus terrestris) visitation rate. We examined whether bumblebee visitation to the floral morphs was related to pollen reward. We collected flowers and classified their stamens according to their function: reward or pollen export. Then, we measured anther size and estimated pollen quantity. The yellow morph was more abundant and more visited by bumblebees than the orange and red morphs. The yellow flowers did indeed offer more pollen than the other morphs and this occurred only for rewarding anthers, suggesting that bumblebees could use yellow color as an honest signal to visit the most rewarding flowers. We discuss whether innate and/or learned preferences of bumblebees can explain why the yellow morph is more visited, pollinated, and abundant, while the other morphs are maintained at a lower frequency. This is one of the few field works that shows that variation in intra-specific floral traits is associated with variation in floral reward and pollinator visitation rate, helping to understand the foraging preferences of pollinators and the coexistence of floral morphs in nature. Clinical trials registration: Not applicable.

The Size of it: Scant Evidence That Flower Size Variation Affects Deception in Intersexual Floral Mimicry

Mutualisms involve cooperation, but also frequently involve conflict. Plant-pollinator mutualisms are no exception. To facilitate animal pollination, flowering plants often offer pollen (their male gametes) as a food reward. Since plants benefit by maximizing pollen export to conspecific flowers, we might expect plants to cheat on pollen rewards. In intersexual floral mimicry, rewarding pollen-bearing male flowers (models) are mimicked by rewardless female flowers (mimics) on the same plant. Pollinators should therefore learn to avoid the unrewarding mimics. Plants might impede such learning by producing phenotypically variable flowers that cause bees to generalize among models and mimics during learning. In this laboratory study, we used partially artificial flowers (artificial petals, live reproductive parts) modeled after Begonia odorata to test whether variation in the size of rewarding male flowers (models) and unrewarding female flowers (mimics) affected how quickly bees learned both to recognize models and to reject mimics. Live unrewarding female flowers have 33% longer petals and have 31% greater surface area than live rewarding male flowers, which bees should easily discriminate. Yet while bees rapidly learned to reduce foraging effort on mimics, learning was not significantly affected by the degree to which flower size varied. Additionally, we found scant evidence that this was a result of bees altering response speed to maintain decision accuracy. Our study failed to provide evidence that flower size variation in intersexual floral mimicry systems exploits pollinator cognition, though we cannot rule out that other floral traits that are variable may be important. Furthermore, we propose that contrary to expectation, phenotypic variability in a Batesian mimicry system may not necessarily have significant effects on whether receivers effectively learn to discriminate models and mimics.

Differences in the flower visitor behaviour on female and hermaphroditic flowers of Cimicifuga simplex

ABSTRACT The behavioural patterns of flower-visiting insects are influenced by floral display size, floral reward, etc. We tested whether insects of various taxa visiting Cimicifuga simplex would change their behaviour between hermaphroditic and female flowers. Male-phase flowers of hermaphroditic ramets provide flower visitors with nectar and pollen as rewards, whereas female flowers of female ramets provide flower visitors with only nectar. The appearance of the both sexes in C. simplex is different with hermaphrodite being relatively large and female ramet being relatively small. Therefore, to investigate how sexual differences in floral rewards and conspicuousness affect flower visitor behaviour, we compared flower visitor behaviour between male-phase hermaphroditic ramets and female ramets. C. simplex was visited by the bumblebee Bombus beaticola beaticola (Hymenoptera), Vespula flaviceps (Hymenoptera), Anthomyiidae spp. (Diptera), Episyrphus balteatus (Diptera), and Pidonia aegrota (Coleoptera). The visitation frequency of all visitors, especially of bumblebees and dipteran insects, to male-phase hermaphroditic ramets was higher than that to female ramets. The number of flowers contacted per single visit to an inflorescence was significantly higher for hermaphroditic ramets than for female ramets in bumblebees, but no difference was found in other insect groups. These results suggest that bumblebees visit the low-reward female ramets less often than male-phase hermaphroditic ramets, and they stay on female ramets for a shorter time. In contrast, insects other than bumblebees seem to decide which flowers to visit according to how conspicuous the flowers are, but once they visit a ramet they continue to visit flowers on the ramet even if no pollen rewards there are.

A sensory bias overrides learned preferences of bumblebees for honest signals in Mimulus guttatus.

Insect pollinators readily learn olfactory cues, and this is expected to select for 'honest signals' that provide reliable information about floral rewards. However, plants might alternatively produce signals that exploit pollinators' sensory biases, thereby relaxing selection for signal honesty. We examined the innate and learned preferences of Bombus impatiens for Mimulus guttatus floral scent phenotypes corresponding to different levels of pollen rewards in the presence and absence of the innately attractive floral volatile compound β-trans-bergamotene. Bees learned to prefer honest signals after foraging on live M. guttatus flowers, but only exhibited this preference when presented floral scent phenotypes that did not include β-trans-bergamotene. Our results suggest that a sensory bias for β-trans-bergamotene overrides the ability of B. impatiens to use honest signals when foraging on M. guttatus. This may represent a deceptive pollination strategy that allows plants to minimize investment in costly rewards without incurring reduced rates of pollinator visitation.

Bee (Apoidea) community response to perennial grass treatments managed for livestock production and conservation

Most grasslands world-wide have been converted into various row crops for agriculture and pasture for livestock foraging. This conversion has likely disrupted arthropod communities, including pollinating bee communities. Pollinating native bees have been in decline in recent decades and much of this decline has been attributed to intensive agricultural practices. Native warm-season grasses have been promoted as alternatives to non-native grasses [e.g., bermudagrass (Cynodon dactylon)] in beef production systems. Reestablishing native grasses may provide an opportunity for land-sharing where agricultural production can enable conservation practices that potentially enhance bee biodiversity. Therefore, agricultural practices such as growing native perennial grasses for livestock forage that may minimize pollinating bee community disruption should be considered. We used colored pan traps to collect bees in four treatments of perennial grass plantings associated with operational livestock pastures during 2011−2012. The four treatments were: (1) mix of Bermuda and tall fescue (Schedonorus arundinaceus) grass grazed with cattle; (2) monocultures of Indiangrass (Sorghastrum nutans) grazed with cattle; (3) native grass polyculture [(Indiangrass, little bluestem (Schizachyrium scoparium), and big bluestem (Andropogon gerardii)] grazed with cattle; and (4) native grass polyculture without cattle. We generally documented greater abundances and richness of bees in native grass treatments compared to exotic grass treatments; however, treatment-level differences were bee genera- or species-dependent. Lack of grazing in the native grass mixture treatment did result in higher bee abundance and taxa richness compared to the native grass mixture treatment with cattle. Our results support the conception that perennial native grasses have the potential to attract numerous, beneficial bee species and may provide some pollen rewards and suitable nesting substrate for bees. Therefore, using native perennial grasses as livestock forage may be a more ecologically friendly surrogate to non-native forage used for livestock production to promote pollination services and native bee diversity in agricultural lands.

Pollinator Behavior Drives Sexual Specializations in the Hermaphrodite Flowers of a Heterodichogamous Tree.

Dioecy, the specialization of individuals into either male-only or female-only sexual function, has multiple evolutionary origins in plants. One proposed ancestral mating system is heterodichogamy, two morphs of cross-fertilizing hermaphrodite flowers that differ in their timing of flowering. Previous research suggested that small specializations in these morphs’ functional genders could facilitate their evolution into separate sexes. We tested the possible role of pollinators in driving such specializations. Ziziphus spina-christi is an insect-pollinated heterodichogamous tree with self-incompatible flowers and two sympatric flowering morphs. We compared the flower development patterns, floral food rewards, pollinator visits, and fruit production between the two morphs. Male-phase flowers of Z. spina-christi’s “Early” and “Late” morphs open before dawn and around noon, respectively, and transition into female-phase 7–8 h later. Flowers of both morphs contain similar nectar and pollen rewards, and receive visits by flies (their ancestral pollinators) at similar rates, mostly during the morning. Consequently, the Early morph functions largely as pollen donor. The Late morph, functioning as female in the morning, produces more fruit. We developed an evolutionary probabilistic model, inspired by Z. spina-christi’s reproductive system, to test whether pollinator visit patterns could potentially play a role in an evolutionary transition from heterodichogamy towards dioecy. The model predicts that reproductive incompatibility within flowering morphs promotes their evolution into different sexes. Furthermore, the pollinators’ morning activity drives the Early and Late morphs’ specialization into male and female functions, respectively. Thus, while not required for transitioning from heterodichogamy to dioecy, pollinator-mediated selection is expected to influence which sexual specialization evolves in each of the flowering morphs.

Sonicating bees demonstrate flexible pollen extraction without instrumental learning.

Pollen collection is necessary for bee survival and important for flowering plant reproduction, yet if and how pollen extraction motor routines are modified with experience is largely unknown. Here, we used an automated reward and monitoring system to evaluate modification in a common pollen-extraction routine, floral sonication. Through a series of laboratory experiments with the bumblebee, Bombus impatiens, we examined whether variation in sonication frequency and acceleration is due to instrumental learning based on rewards, a fixed behavioral response to rewards, and/or a mechanical constraint. We first investigated whether bees could learn to adjust their sonication frequency in response to pollen rewards given only for specified frequency ranges and found no evidence of instrumental learning. However, we found that absence versus receipt of a pollen reward did lead to a predictable behavioral response, which depended on bee size. Finally, we found some evidence of mechanical constraints, in that flower mass affected sonication acceleration (but not frequency) through an interaction with bee size. In general, larger bees showed more flexibility in sonication frequency and acceleration, potentially reflecting a size-based constraint on the range over which smaller bees can modify frequency and acceleration. Overall, our results show that although bees did not display instrumental learning of sonication frequency, their sonication motor routine is nevertheless flexible.

A key floral scent component (β‐trans‐bergamotene) drives pollinator preferences independently of pollen rewards in seep monkeyflower

AbstractFloral odours play an important role in attracting insect pollinators. Because pollinators visit flowers to obtain pollen and nectar rewards, they should prefer floral odour profiles associated with the highest‐rewarding flowers (honest signals). In previous work, bumblebees exhibited a preference for flowers from outbred over inbredMimulus guttatusplants. Pollen is the only floral reward inM. guttatus, and pollen viability (a reliable indicator of protein content) is reduced in inbred plants. Yet, differences in pollen viability did not explain the observed preferences.In this study, we examined the floral volatile profiles of inbred and outbredM. guttatusto identify inbreeding effects and associations between volatile compounds and the number of viable pollen grains per flower, designated “PRQ” (pollen reward quality). We also conducted pairwise choice tests withBombus impatiensto evaluate the ability of bees to discriminate between odours of rewarding and non‐rewarding flowers and to determine whether bumblebee preferences are explained by differences in the floral odours of inbred and outbred plants.Inbred plants exhibited reduced emission of β‐trans‐bergamotene, the second‐most abundant compound in the volatile blend of outbred plants. Furthermore, pollen and fertile anthers emitted nonadecane. Six other compounds in the floral blend were positively correlated withPRQ. There was no overlap between compounds affected by inbreeding and compounds associated withPRQ.Even when given prior experience foraging onM. guttatus, bumblebees did not distinguish between the floral odours of rewarding and non‐rewarding outbred plants. However, they preferred floral odours from non‐rewarding outbred plants over rewarding inbred plants. Bumblebees without prior experience of flowers preferred volatile blends with higher versus lower amounts of β‐trans‐bergamotene.Taken together, these results suggest that the volatile emissions ofM. guttatusprovide reliable indicators of pollen rewards (potential honest signals), but that the preference of bumblebees for outbred plants is not driven by these cues but rather by a sensory bias for β‐trans‐bergamotene. This may represent a subtle form of deceit‐pollination that allows plants to attract pollinators while minimizing investment in costly rewards.Aplain language summaryis available for this article.

Intersexual mimicry and flowering phenology facilitate pollination in a dioecious habitat specialist species, Myristica fatua (Myristicaceae)

Myristica fatua is a dioecious specialist species restricted to the endangered, freshwater Myristica swamp forests in the Western Ghats, India. Earlier studies have alluded to pollination by deception in members of the Myristica genus, and thus we examined the pollination ecology comprising floral biology, flower production, flower visitors, and reproductive success in M. fatua and inferred the potential strategies that could permit such deception in this habitat specialist tree. Male flowers provide pollen rewards for an extended period of time while female flowers are rewardless and both sexes are visited by generalist insects, mainly by honeybees and stingless bees. Bee visits were significantly more frequent and longer on male than on female flowers as bees collected pollen from male flowers. We found that flower production patterns create a preponderance of males compared to females in the swamp populations. Using a model of honeybee color vision, we found the distance between the color loci of male and female flowers and based on minimum visual angle subtended by these flowers, we suggest that the two floral sexes cannot be discriminated by bees. Bees are likely deceived by the perceptual similarity of rewardless female flowers to pollen-offering male flowers and pollination is the consequence of foraging errors made by pollinators that encounter largely male–rarely female flower mosaics as they forage among clump-distributed M. fatua trees in the swamp habitat.

The Roles of Bees and Hoverflies in the Pollination of Jacquemontia evolvuloides (Moric.) Meisn. (Convolvulaceae) in a Semiarid Region

Jacquemontia species are often found in disturbed areas, and their flowers are ephemeral and very attractive to insects. We investigated the interaction between the flowers of Jacquemontia evolvuloides and its visitors, with emphasis on potential pollinators, considering morphological, temporal, and behavioral aspects, between September/2009 and August/2010 in an anthropized area in Bahia State, Northeastern Brazil. Jacquemontia evolvuloides flowers are diurnal, ephemeral (approximately five to six hours duration), are present throughout the year, and offer nectar and pollen rewards. Because of the floral morphology of J. evolvuloides insect visitors have easy access to its resources, and its pollination could be considered generalized. While J. evolvuloides flowers are visited by several insects, only small bees (Augochlora spp.) and syrphids (Toxomerus spp.) appear to play a role in pollination of flowers. Although bees have been considered efficient pollinators of that plant, the significant presence of syrphids (considered occasional pollinators but showing high frequency visitation), may indicate their role as potential pollinators, especially when bees are not abundant in the fall/winter. As such, even in pollination systems that are considered generalized (with flowers allowing easy access to various visitor groups), visitor size may be an important factor for efficient pollination, especially when associated with high visitation frequencies.