Pollinator Movement Research Articles

Machine learning-based bee recognition and tracking for advancing insect behavior research

The study of insect behavior, particularly that of honey bees, has a broad scope and significance. Tracking bee flying patterns grants much helpful information about bee behavior. However, tracking a small yet fast-moving object, such as a bee, is difficult. Hence, we present artificial intelligence, machine-learning-based bee recognition, and tracking systems to assist the researcher in studying the bee’s behavior. To develop a machine learning system, a labeled database is required for model training. To address this, we implemented an automated system for analyzing and labeling bee videos. This labeled database served as the foundation for two distinct bee-tracking solutions. The first solution (planar bee tracking system) tracked individual bees in closed mazes using a neural network. The second solution (spatial bee tracking system) utilized a neural network and a tracking algorithm to identify and track flying bees in open environments. Both systems tackle the challenge of tracking small-bodied creatures with rapid and diverse movement patterns. Although we applied these systems to entomological cognition research in this paper, their relevance extends to general insect research and developing tracking solutions for small organisms with swift movements. We present the complete architecture and detailed methodologies to facilitate the utilization of these models in future research endeavors. Our approach is a simple and inexpensive method that contributes to the growing number of image-analysis tools used for tracking animal movement, with future potential applications under less sterile field conditions. The tools presented in this paper could assist the study of movement ecology, specifically in insects, by providing accurate movement specifications. Following the movement of pollinators or natural enemies, for example, greatly contributes to the study of pollination or biological control, respectively, in natural and agro-ecosystems.

Bumblebees mediate landscape effects on a forest herb's population genetic structure in European agricultural landscapes.

Spatially isolated plant populations in agricultural landscapes exhibit genetic responses not only to habitat fragmentation per se but also to the composition of the landscape matrix between habitat patches. These responses can only be understood by examining how the landscape matrix influences among-habitat movements of pollinators and seed vectors, which act as genetic linkers among populations. We studied the forest herb Polygonatum multiflorum and its associated pollinator and genetic linker, the bumblebee Bombus pascuorum, in three European agricultural landscapes. We aimed to identify which landscape features affect the movement activity of B. pascuorum between forest patches and to assess the relative importance of these features in explaining the forest herb's population genetic structure. We applied microsatellite markers to estimate the movement activity of the bumblebee as well as the population genetic structure of the forest herb. We modelled the movement activity as a function of various landscape metrics. Those metrics found to explain the movement activity best were then used to explain the population genetic structure of the forest herb. The bumblebee movement activity was affected by the cover of maize fields and semi-natural grasslands on a larger spatial scale and by landscape heterogeneity on a smaller spatial scale. For some measures of the forest herb's population genetic structure, that is, allelic richness, observed heterozygosity and the F-value, the combinations of landscape metrics, which explained the linker movement activity best, yielded lower AICc values than 95% of the models including all possible combinations of landscape metrics. Synthesis: The genetic linker, B. pascuorum, mediates landscape effects on the population genetic structure of the forest herb P. multiflorum. Our study indicates, that the movement of the genetic linker among forest patches, and thus the pollen driven gene flow of the herb, depends on the relative value of floral resources in the specific landscape setting. Noteworthy, the population genetic structure of the long-lived, clonal forest herb species correlated with recent land-use types such as maize, which have been existing for not more than a few decades within these landscapes. This underscores the short time in which land-use changes can influence the evolutionary potential of long-lived wild plants.

Pollinator-mediated connectivity in fragmented urban green spaces—tracking pollen grain movements in the city center

Cities are expanding rapidly and emerging as complex ecosystems. This expansion of urbanized areas has resulted in the alteration and fragmentation of several natural habitats. Recent studies have shown that cities support a significant level of biodiversity. This unexpected role of cities holds promise for advancing knowledge of urban ecosystems and promoting their conservation. In particular, the connectivity of plant populations through pollen transfer is crucial for the long-term persistence of insect-pollinated plant species. In this study, we tracked pollen movement areas in four isolated patches of urban greenery in urbanized area using quantum dots. We studied Fritillaria imperialis (spring) and Hemerocallis sp. (mid-summer). Our research revealed frequent pollen transfer between small, isolated flowering patches, even when these locations were not connected by green corridors. Common elements found in urban ecosystems, such as streets, trails, and pavements, do not stop the dispersion of pollen grains. Moreover, the migration pathways of pollen grains vary for each species according to different factors. For F. imperialis, we identified the proportion of green areas in proximity to the study location as a key factor in shaping pollen transfer. For Hemerocallis, we discovered that the proportion of green areas, the distance between study sites, and the frequency of pollinator visits are influential factors. Our study demonstrates that small isolated plant populations exchange pollen due to pollinator movement, indicating that these small populations may serve as stepping stones for pollinators among larger populations.

Where are volatiles produced in the highly synorganised inflorescence of Arum maculatum L.?

Floral scents vary spatially within flowers and inflorescences, with effects on pollinator behaviour. Here, we restudied the spatial scent pattern of Arum maculatum, an Araceae, with a higher spatial resolution than previously. The inflorescence of this species consists of a spadix, whose distal part is a sterile osmophore called the appendix, whereas its basal part bears sterile and fertile male and female flowers. This spadix is surrounded by a spathe, which forms a floral chamber around the flowers. So far, it was known that the appendix is responsible for the emission of most of the volatiles, but some volatiles were specifically found within the floral chamber, with the organ(s) responsible for their emission being unclear. By repeatedly collecting (dynamic headspace) and analysing (gas chromatography/mass spectrometry) the scent of whole inflorescences and of inflorescences with the spathe and the various zones of the spadix sequentially removed, we determined and quantified all scent compounds of the major units of the inflorescence of A. maculatum. We confirm that the inflorescence scent is mainly composed of scents released by the appendix, and we for the first time provide evidence that the male flower zone of the spadix also contributes to the inflorescence scent. Future studies are needed to test whether, and if, how, this spatial scent pattern in A. maculatum affects the movement of pollinators within the inflorescence and their pollination effectiveness.

Citizen science data reveal altitudinal movement and seasonal ecosystem use by hummingbirds in the Andes Mountains

Ensuring connectivity is crucial to protect landscapes but it requires knowledge about how animals use ecosystems throughout the year. However, animal movements remain largely unknown in biodiversity hotspots, even for species that fulfill key ecological roles, as is the case of hummingbirds in the Andes. In the complex topography of mountain slopes, movement of these avian pollinators may occur either between habitat patches with asynchronous plant blooms or across ecosystems that are located within the same elevation bands or along altitudinal gradients. Here, we used two decades (2000–2020) of records from citizen science data and boosted regression trees to predict monthly distributions for 55 hummingbird species in the Andes. We identified shifts in altitudinal distribution between contiguous months and calculated changes in the proportion of predicted distributions occupied by ecosystem types. Our findings reveal substantial altitudinal movement and differences in the proportion of ecosystem types utilized throughout the year that had not been previously reported for several species. Yet the magnitude of altitudinal and ecosystem shifts varies between hummingbird clades, and in some cases changes in the proportion of ecosystem types within estimated distributions occurs with little variation in altitude. All ecosystems across the Andes show temporal changes in hummingbird occurrence, but these are higher in natural landscapes compared to croplands or urban areas. Finally, we used phylogenetic logistic regression to test whether altitudinal and ecosystem shifts affect population trends. We found that higher ecosystem seasonality is more strongly associated with decreasing populations in comparison to altitudinal shifts. Altogether, our study reveals complex patterns of movement in hummingbirds and highlights the importance of ecological connectivity across different ecosystem types. More generally, it demonstrates the opportunity of using citizen science data to increase understanding about species' seasonal occurrences, so that landscapes can be better managed to protect animal movement.Keywords: boosted regression trees, eBird, ecological connectivity, species distribution models

Pollen carryover, pollinator movement, and spatial context impact the delivery of pollination services in apple orchards.

Assessing the relative contributions of different pollinator taxa to pollination services is a central task in both basic eco-evolutionary research and applied conservation and agriculture. To that end, many studies have quantified single-visit pollen deposition and visitation frequency, which together determine a pollinator species' rate of conspecific pollen delivery. However, for plant species that require or benefit from outcrossing, pollination service quality further depends upon the ratio of outcross to self-pollen deposited, which is determined by two additional pollinator traits: pollen carryover and movement patterns among genetically compatible plant individuals. Here, we compare the pollination capacities of managed honey bees, native bumble bees, and native mining bees in apple-a varietally self-incompatible commercial crop-when pollen carryover and pollinator movement patterns are considered. We constructed simulation models of outcross pollen deposition parameterized using empirically measured single-visit pollen deposition, visitation frequency, and probabilities of intertree movement exhibited by each pollinator type, as well as pollen carryover patterns simulated based on parameters reported in the literature. In these models, we also explicitly specified the spatial relationships among cross-compatible trees based on field-realistic orchard layout schemes. We found that estimated pollination service delivery was considerably reduced for all pollinator types when pollen carryover and pollinator movement patterns were considered, as compared to when only single-visit pollen deposition and visitation frequency were considered. We also found that the performance of different pollinator types varied greatly across simulated orchard layout schemes and pollen carryover scenarios, including one instance where bumble and mining bees reversed their relative rankings. In all simulations, native bumble and mining bees outperformed managed honey bees in terms of both outcross pollen delivery per unit time and per flower visited, with disparities being greatest under scenarios of low pollen carryover. We demonstrate the degree to which pollination studies may reach inaccurate conclusions regarding pollination service delivery when pollen carryover and pollinator movement patterns are ignored. Our finding of the strong context dependence of pollination efficiency, even within a single plant-pollinator taxon pair, cautions that future studies in both basic and applied pollination biology should explicitly consider the ecological context in which pollination interactions take place.

Heterospecific pollen deposition in understory plants of a forest in central Amazon

In co-flowering plant communities, pollinator movement can lead to the transfer of heterospecific pollen among species. This can affect the reproductive success of individuals, either by preventing conspecific pollen from reaching the stigma or by allelopathy, but little is known about this process in tropical areas. To analyze heterospecific pollen transfer and deposition, we investigated attributes related to pollinator attraction, such as corolla size, number of flowers per individual, floral arrangement, floral asymmetry, and distance from one flowering individual to another in a Central Amazon forest. The study was carried out in riparian plots of the Adolpho Ducke Forest Reserve during the rainy season. Stigmas and anthers were removed from all individual understory plants found in bloom in permanent plots. Slides were mounted with glycerinated gelatin, and all conspecific and heterospecific pollen grains were identified and counted. We then used a generalized linear mixed model framework to determine how the measured variables were related to the proportion of heterospecific pollen deposition (HPD) on stigmas. We found that the mean proportion of HPD in individuals was 4.7%, and 60% of individuals had no heterospecific pollen; from the 14 species studied, two had no heterospecific pollen. Species with wider flowers received less HPD, while species with more flowers per individual and with solitary flowers received more heterospecific pollen. Despite the significant variation in floral types in the Adolpho Ducke Reserve, there was a low percentage of heterospecific pollen deposition, probably due to specialized plant-pollinator interactions.

Landscape composition and pollinator traits interact to influence pollination success in an individual‐based model

Abstract The arrangement of plant species within a landscape influences pollination via changes in pollinator movement trajectories and plant–pollinator encounter rates. Yet the combined effects of landscape composition and pollinator traits (especially specialisation) on pollination success remain hard to quantify empirically. We used an individual‐based model to explore how landscape and pollinator specialisation (degree) interact to influence pollination. We modelled variation in the landscape by generating gradients of plant species intermixing—from no mixing to complete intermixing. Furthermore, we varied the level of pollinator specialisation by simulating plant–pollinator (six to eight species) networks of different connectance. We then compared the impacts of these drivers on three proxies for pollination: visitation rate, number of consecutive visits to the focal plant species and expected number of plants pollinated. We found that the spatial arrangements of plants and pollinator degree interact to determine pollination success, and that the influence of these drivers on pollination depends on how pollination is estimated. For most pollinators, visitation rate increases in more plant mixed landscapes. Compared to the two more functional measures of pollination, visitation rate overestimates pollination service. This is particularly severe in landscapes with high plant intermixing and for generalist pollinators. Interestingly, visitation rate is less influenced by pollinator traits (pollinator degree and body size) than are the two functional metrics, likely because ‘visitation rate’ ignores the order in which pollinators visit plants. However, the visitation sequence order is crucial for the expected number of plants pollinated, since only prior visits to conspecific individuals can contribute to pollination. We show here that this order strongly depends on the spatial arrangements of plants, on pollinator traits and on the interaction between them. Taken together, our findings suggest that visitation rate, the most commonly used proxy for pollination in network studies, should be complemented with more functional metrics which reflect the frequency with which individual pollinators revisit the same plant species. Our findings also suggest that measures of landscape structure such as plant intermixing and density—in combination with pollinators' level of specialism—can improve estimates of the probability of pollination. Read the free Plain Language Summary for this article on the Journal blog.

Floral and genetic divergence across environmental gradients is moderated by inter-population gene flow in Platanthera dilatata (Orchidaceae)

Understanding how natural selection acts on intraspecific variation to bring about phenotypic divergence is critical to understanding processes of evolutionary diversification. The orchid family is well known for pollinator-mediated selection of floral phenotypes operating among species and along environmental or geographic gradients. Its effectiveness at small spatial scales is less understood, making the geographic scale at which intraspecific floral variation is examined important to evaluating causes of phenotypic divergence. In this study, we quantified phenotypic variation in the orchid Platanthera dilatata across 26 populations in coastal Southeast Alaska and compared this to edaphic and genetic variation at microsatellite loci. We sought to determine (1) if flower morphological variation is structured at smaller geographic scales, (2) the extent of genetic divergence in relation to phenotypic divergence, (3) the scale at which inter-population gene flow occurs, and (4) the relative importance of geographic distance and abiotic factors on population genetic structure. Two morphological groups were found to separate based on lip and spur length and are restricted to different habitats. Small-flowered forms occur in muskeg bogs, whereas large-flowered forms occur in fens and meadows, and rarely in sub-alpine habitat. Genetic analyses were concordant with the morphological clusters, except for four small-flowered populations that were genetically indistinguishable from large-flowered populations and considered to be introgressed. In fact, most populations exhibited some admixture, indicating incomplete reproductive isolation between the flower forms. Pollinators may partition phenotypes but also facilitate gene flow because short-tongued Noctuidae moths pollinate both phenotypes, but longer-tongued hawkmoths were only observed pollinating the large-flowered phenotype, which may strengthen phenotypic divergence. Nevertheless, pollinator movement between habitats could have lasting effects on neutral genetic variation. At this small spatial scale, population genetic structure is only associated with environmental distance, likely due to extensive seed and pollinator movement. While this study corroborates previous findings of cryptic genetic lineages and phenotypic divergence in P. dilatata, the small scale of examination provided greater understanding of the factors that may underlie divergence.

Cover Picture and Issue Information

Functional EcologyVolume 37, Issue 3 p. 473-475 COVER PICTURE AND ISSUE INFORMATIONFree Access Cover Picture and Issue Information First published: 02 March 2023 https://doi.org/10.1111/1365-2435.14073AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract Flowering plants need pollinators to transfer pollen, such as those pictured on this Tamarix chinensis (Credit: Le Jiao). The movement behavior and strategy of pollinators significantly affects pollination success and the subsequent seed set, especially for plant populations that are faced with habitat loss. Jiao et al. 2022 (DOI: 10.1111/1365-2435.14252) simulated two key stages of pollinator movement during the pollination process: a foraging response stage towards plant patches mediated by floral scents, and an individual dispersal stage between plant patches mediated by a densitydependent dispersal strategy. Plant reproduction was negatively affected by habitat loss, as the emission amount of floral scents and the foraging success rate of pollinators decreased in the context of habitat loss. However, the pollinator movement strategy (i.e. density-dependent dispersal strategy) can help mitigate adverse impacts by promoting visitation to suboptimal plant patches, thereby improving the persistence of the plant population in fragmented landscapes. Altogether, this simulation result points to the positive role of pollinator movement strategy in alleviating the negative effects of habitat loss on plant reproduction. Volume37, Issue3March 2023Pages 473-475 RelatedInformation

Density‐dependent dispersal strategy of pollinator moderates the adverse effect of habitat loss on plant reproduction: An integrated model based on pollinators' behavioural response

Abstract Major challenges for plant conservation are predicting the effect of habitat loss on pollination success and plant reproduction potential. Most studies report that pollinator movement is affected by quantitative and spatial characteristics of landscapes. However, little is known about the role of pollinator movement, impacted by floral volatiles and intraspecies interaction, on plant reproduction in fragmented landscapes. To clarify the effect of pollinator movement on plant reproduction relative to habitat loss, we developed an integrated model incorporating pollinator's foraging response with its dispersal process mediated by a density‐dependent dispersal (DDD) strategy. This model performed better in capturing behaviour response of pollinators than do current methods. The integrated model was verified with field results of pollinator visitation and plant reproduction of saltcedar Tamarix chinensis inhabiting the Yellow River Delta, and then was compared against a dispersal strategy called density‐independent dispersal (DID). The model was applied to landscapes with various non‐habitat percentage (NHP) to explore the effect of habitat loss on plant reproduction. Results suggested that saltcedar populations differ in their responses to habitat loss, which depended on the spatial scales considered. At landscape scale, increasing NHP significantly inhibited dispersion extent of floral volatiles and therefore reduced pollinator visitation and subsequent seed production, especially when NHP exceeded the critical threshold of 0.6. However, at patch scale, comparing with DID strategy, the DDD strategy enabled pollinators to increase their utilization of flowers by 43.42% and 6.79% in low‐density and distant plant patches, whereas their utilization was reduced by 7.75% and 2.24% in high‐density and central patches, respectively. Plant reproduction was improved correspondingly in low‐density and distant patches under different NHPs. Consequently, habitat loss inhibits the volatile dispersion and interferes the foraging success of pollinators, a major factor influencing plant reproduction at landscape scale. At patch scale, adaptive utilization of pollinators exhibiting DDD strategy alleviates the negative effect of habitat loss on plant production, and maintain plant population persistence. Since pollinator behavioural response is critical to plant reproduction, we recommend the use of the here presented integrated model to assess the impact of habitat loss on plant reproduction. Read the free Plain Language Summary for this article on the Journal blog.

A negative association between nectar standing crop and pollen transfer suggests nectar functions as a manipulator of pollinating bats.

Nectar standing crop has a fundamental role in controlling pollinator movements between flowers and individuals within a population. In bat pollination systems, plants take advantage of the cognitive abilities of nectarivorous bats, which integrate complex perceptions of the quality and spatial distribution of resources. Here, we propose that associations between standing crop and pollen transfer help to reveal the role of nectar as a manipulator of pollinator behaviour. We used Harpochilus neesianus Ness (Acanthaceae), a bat-pollinated shrub from the Brazilian Caatinga, as a model system to assess nectar removal effects and standing crop, respectively, over the night and to test associations between the amount of nectar available to pollinators, and pollen import and export. Harpochilus neesianus showed continuous nectar secretion throughout the flower lifespan. Flowers subjected to successive nectar removals produced less nectar than flowers sampled just once, and showed, despite a higher sugar concentration, a lower absolute amount of sugar. Under these conditions, bats may realize that nectar production is decreasing after repeated visits to the same flower and could be manipulated to avoid such already pollinated flowers with little nectar, thus increasing the probability of visits to flowers with a high amount of nectar, and a still high pollen availability on anthers and low pollen deposition on stigmas. We found that during most of the period of anthesis, nectar standing crop volume was positively correlated with the number of pollen grains remaining in the anthers, and negatively with the number of pollen grains deposited on the stigma. Nectar secretion patterns can function as a manipulator of pollinating bats in H. neesianus. We propose that the assessment of variability in nectar secretion in response to removal, and the correlation between nectar standing crop and relative pollen transfer throughout anthesis should be considered in order to understand the role of nectar in the manipulation of pollinators.

Insect Pollinator Monitoring in and around a Netted Plot of Apple Trees—Biosafety Implications for Genetically Engineered Fruit Trees

The complete netting of orchards is one strategy to protect fruit trees from pest and pathogen damage by reducing insect movement. When the cultivated trees were derived from genetic engineering (GE), reduced pollinator movement may also reduce outcrossing to cultivated or wild non-GE trees. We report on a field study over four years in a plot of apple tress supplied with insect side nets and covered with hail nets that were closed from shortly before flowering to harvest. A reduced number of arthropods in general, and large bees in particular, were recorded inside the netted plot compared with outside. However, wild bees colonized the plot before the net was closed and built up populations inside. An additional experiment demonstrated that small bees were able to cross the hail net. While the nets were effective in excluding large bees as active pollen vectors, the proportion of small bees acting as such remained unquantified. Furthermore, a companion study showed occasional cross-pollination events through the netting. For the field release of GE apple trees, acceptable levels of outcrossing thus need to be defined.

Pollinator movement activity influences genetic diversity and differentiation of spatially isolated populations of clonal forest herbs

In agricultural landscapes, forest herbs live in small, spatially isolated forest patches. For their long-term survival, their populations depend on animals as genetic linkers that provide pollen- or seed-mediated gene flow among different forest patches. However, whether insect pollinators serve as genetic linkers among spatially isolated forest herb populations in agricultural landscapes remains to be shown. Here, we used population genetic methods to analyze: (A) the genetic diversity and genetic differentiation of populations of two common, slow-colonizing temperate forest herb species [Polygonatum multiflorum (L.) All. and Anemone nemorosa L.] in spatially isolated populations within three agricultural landscapes in Germany and Sweden and (B) the movement activity of their most relevant associated pollinator species, i.e., the bumblebee Bombus pascuorum (Scopoli, 1,763) and the hoverfly Melanostoma scalare (Fabricus, 1,794), respectively, which differ in their mobility. We tested whether the indicated pollinator movement activity affected the genetic diversity and genetic differentiation of the forest herb populations. Bumblebee movement indicators that solely indicated movement activity between the forest patches affected both genetic diversity and genetic differentiation of the associated forest herb P. multiflorum in a way that can be explained by pollen-mediated gene flow among the forest herb populations. In contrast, movement indicators reflecting the total movement activity at a forest patch (including within-forest patch movement activity) showed unexpected effects for both plant-pollinator pairs that might be explained by accelerated genetic drift due to enhanced sexual reproduction. Our integrated approach revealed that bumblebees serve as genetic linkers of associated forest herb populations, even if they are more than 2 km apart from each other. No such evidence was found for the forest associated hoverfly species which showed significant genetic differentiation among forest patches itself. Our approach also indicated that a higher within-forest patch movement activity of both pollinator species might enhance sexual recruitment and thus diminishes the temporal buffer that clonal growth provides against habitat fragmentation effects.

Floral volatiles may influence honey bee visitations in oilseed Brassica species

ABSTRACT Understanding foraging preferences of honey bees (Apis mellifera L.) is essential to maneuver pollinator movement to enhance outcrossing and hence the crop yields. In this communication, we report the role of floral volatile organic compounds (VOCs) in structuring foraging decisions of honey bees. Supercritical fluid extraction of VOCs, coupled with gas chromatography-mass spectrometry, revealed 75 VOCs. Of these, 19 were strong attractants and 8 were strong repellants. Moreover, we detected significant, but variable, species- or genome-level differences in floral scents. Honey bees avoided Brassica juncea cv. PBR357 (0.81 bee visits/sq m/min) and B. carinata cv. PC5 (0.77 bee visits/sq m/min), which possessed peak concentrations of antifeedants or repellents (dibutyl phthalate and 9-octadecenoic acid) in their floral volatiles. B. napus cvs. GSC6 and GSC7 attracted the highest number of bee visitations (1.07 and 0.99 bee visits/sq m/min, respectively), as these possessed VOCs with honey-fruity odor in high amounts and negligible levels of antifeedants. Our results highlight that variability in floral reward chemistry should be considered when breeding crops that are frequently visited upon by bee pollinators to support bee pollinators, in general, and honey industry, in particular.

High flower richness and abundance decrease pollen transfer on individual plants in road verges but increase it in adjacent fields in intensively managed agroecosystems

Road verges can facilitate the movement of pollinators and pollen in intensively managed agroecosystems, reducing the negative impacts of fragmentation (i.e., isolation of wild pollinator communities) and enhancing the pollination service provided to wild plants. To assess the role of road verges in sustaining the pollination service to wild plants, we studied gardens consisting of two plant species arranged within sixteen road verges and their adjacent fields during two consecutive seasons in the Argentine Pampas. We assessed the influence of attributes of road verges on pollination service at different scales: road verges width, species richness of flowering plant, and flower abundance (patch scale), crops and successional pastures (adjacent land use scale), and landscape heterogeneity (landscape scale). We measured the pollination service provided to two species of potted plants (Hirschfeldia incana and Lobularia maritima) in three different ways: visitation rate, conspecific and heterospecific pollen transfer to stigmas, and distance of pollen transfer from a fixed source. The number of conspecific and heterospecific pollen grains deposited on stigmas decreased with an increased abundance of floral units in associated road verges, which is caused by a dilution effect on individual plant pollination. Also, the pollen transfer into adjacent fields decreased with an increased abundance of floral units in the nearby road verges, which is caused by a decrease of pollen spillover into adjacent crop fields. The visitation rate within adjacent fields increased with higher flowering plant species richness in associated road verges. Also, the number of conspecific pollen grains in the road verges adjacent to successional pastures increased with higher flowering plant species richness in road verges, which results in a concentration effect of pollinator visits and pollen transfer into road verges. We conclude that managing flower abundance and increasing flowering plant species richness in road verges are crucial practices for maintaining the pollination service of entomophilous plants in intensively managed agroecosystems.

Strongly unbalanced gender attractiveness in a dioecious mass flowering tropical tree pollinated by stingless bees.

In dioecious, bee-pollinated tree species, male and female flowers offer different resources. It is unclear how this unbalanced quantity and quality of floral resources affects flower visits and pollen transfer to female flowers. We asked, what characteristics of flowering and dynamics of resource production by trees favour flights of bees between male and female trees. We quantified the floral resources produced by individual flowers and entire trees of Myracrodruon urundeuva (Anacardiaceae), measured pollen flow to female flowers, fruit set of naturally pollinated flowers and determined the effective pollinators. Crown volume of male trees was four-fold, flower number 15-fold and nectar volume 60 times higher than in female trees. While ~70% of male flowers opened in the morning, ~70% of female flowers opened in the afternoon. Fruit set was 27%. Stingless bee species were the main pollinators, while honeybees were common only on male flowers. Strongly unbalanced production of floral resources, high potential lifespan of female flowers and anticipated opening of male flowers favour pollinator movement and pollen deposition on female flowers, albeit low (0.003% of pollen that reached stigmas), but sufficient to produce thousands of fruits per tree. Besides being an astonishing pollen and nectar source for numerous social bee species, only a few of them were effective pollinators. Our quantitative approach to floral resource production of each gender provides new insights, such as the proportion of resources allocated to each gender and the corresponding behaviour of flower visitors, for understanding the reproductive strategy of dioecious tropical mass-flowering trees.

Highlighted articles for January 2022.

Highlighted articles for January 2022.

No Evidence of Low Genetic Diversity Despite High Levels of Inbreeding and Poor Genetic Connectivity AmongTetrastigma loheri(Vitaceae) Populations in Remaining Forest Areas in Cebu, Philippines

Abstract—Little is known about the effects of habitat fragmentation on the patterns of genetic diversity and genetic connectivity of species in the remaining tropical forests of Southeast Asia. This is particularly evident in Cebu, a Philippine island that has a long history of deforestation and has lost nearly all of its forest cover. To begin filling this gap, data from 13 microsatellite loci developed forTetrastigma loheri(Vitaceae), a common vine species in Philippine forests, were used to study patterns of genetic diversity and genetic connectivity for the four largest of the remaining forest areas in Cebu. Evidence of relatively high levels of inbreeding was found in all four areas, despite no evidence of low genetic diversity. The four areas are genetically differentiated, suggesting low genetic connectivity. The presence of inbreeding and low genetic connectivity in a commonly encountered species such asT. loheriin Cebu suggests that the impact of habitat fragmentation is likely greater on rare plant species with more restricted distributions in Cebu. Conservation recommendations for the remaining forest areas in Cebu include the establishment of steppingstone corridors between nearby areas to improve the movement of pollinators and seed dispersers among them.

Outcrossing rates in an experimentally admixed population of self-compatible and self-incompatible Arabidopsis lyrata

The transition to self-compatibility from self-incompatibility is often associated with high rates of self-fertilization, which can restrict gene flow among populations and cause reproductive isolation of self-compatible (SC) lineages. Secondary contact between SC and self-incompatible (SI) lineages might re-establish gene flow if SC lineages remain capable of outcrossing. By contrast, intrinsic features of SC plants that reinforce high rates of self-fertilization could maintain evolutionary divergence between lineages. Arabidopsis lyrata subsp. lyrata is characterized by multiple origins of self-compatibility and high rates of self-fertilization in SC-dominated populations. It is unclear whether these high rates of selfing by SC plants have intrinsic or extrinsic causes. We estimated outcrossing rates and examined patterns of pollinator movement for 38 SC and 40 SI maternal parents sampled from an admixed array of 1509 plants sourced from six SC and six SI populations grown under uniform density. Although plants from SI populations had higher outcrossing rates (mean tm = 0.78 ± 0.05 SE) than plants from SC populations (mean tm = 0.56 ± 0.06 SE), outcrossing rates among SC plants were substantially higher than previous estimates from natural populations. Patterns of pollinator movement appeared to contribute to lower outcrossing rates for SC plants; we estimated that 40% of floral visits were geitonogamous (between flowers of the same plant). The relatively high rates of outcrossing for SC plants under standardized conditions indicate that selfing rates in natural SC populations of A. lyrata are facultative and driven by extrinsic features of A. lyrata, including patterns of pollinator movement.