Flowering plants under global pollinator decline

Uncovering genes involved in pollinator-driven mating system shifts and selfing syndrome evolution in Brassica rapa

Shifts in pollinator occurrence and their pollen transport effectiveness drive the evolution of mating systems in flowering plants. Understanding the genomic basis of these changes is essential for predicting the persistence of a species under environmental changes. We investigated the genomic changes in Brassica rapa over nine generations of pollination by hoverflies associated with rapid morphological evolution toward the selfing syndrome. We combined a genotyping-by-sequencing (GBS) approach with a genome-wide association study (GWAS) to identify candidate genes, and assessed their functional role in the observed morphological changes by studying mutations of orthologous genes in the model plant Arabidopsis thaliana. We found 31 candidate genes involved in a wide range of functions from DNA/RNA binding to transport. Our functional assessment of orthologous genes in A. thaliana revealed that two of the identified genes in B. rapa are involved in regulating the size of floral organs. We found a protein kinase superfamily protein involved in petal width, an important trait in plant attractiveness to pollinators. Moreover, we found a histone lysine methyltransferase (HKMT) associated with stamen length. Altogether, our study shows that hoverfly pollination leads to rapid evolution toward the selfing syndrome mediated by polygenic changes.

Pollinator-mediated effects of landscape-scale land use on grassland plant community composition and ecosystem functioning - seven hypotheses

Environmental change is disrupting mutualisms between organisms worldwide. Reported declines in insect populations and changes in pollinator community compositions in response to land use and other environmental drivers have put the spotlight on the need to conserve pollinators. While this is often motivated by their role in supporting crop yields, the role of pollinators for reproduction and resulting taxonomic and functional assembly in wild plant communities has received less attention. Recent findings suggest that observed and experimental gradients in pollinator availability can affect plant community composition, but we know little about when such shifts are to be expected, or the impact they have on ecosystem functioning. Correlations between plant traits related to pollination and plant traits related to other important ecosystem functions, such as productivity, nitrogen uptake or palatability to herbivores, lead us to expect non-random shifts in ecosystem functioning in response to changes in pollinator communities. At the same time, ecological and evolutionary processes may counteract these effects of pollinator declines, limiting changes in plant community composition, and in ecosystem functioning. Despite calls to investigate community- and ecosystem-level impacts of reduced pollination, the study of pollinator effects on plants has largely been confined to impacts on plant individuals or single-species populations. With this review we aim to break new ground by bringing together aspects of landscape ecology, ecological and evolutionary plant-insect interactions, and biodiversity-ecosystem functioning research, to generate new ideas and hypotheses about the ecosystem-level consequences of pollinator declines in response to land-use change, using grasslands as a focal system. Based on an integrated set of seven hypotheses, we call for more research investigating the putative pollinator-mediated links between landscape-scale land use and ecosystem functioning. In particular, future research should use combinations of experimental and observational approaches to assess the effects of changes in pollinator communities over multiple years and across species on plant communities and on trait distributions both within and among species.

Ongoing convergent evolution of a selfing syndrome threatens plant-pollinator interactions

Plant-pollinator interactions evolved early in the angiosperm radiation. Ongoing environmental changes are however leading to pollinator declines that may cause pollen limitation to plants and change the evolutionary pressures shaping plant mating systems. We used resurrection ecology methodology to contrast ancestors and contemporary descendants in four natural populations of the field pansy (Viola arvensis) in the Paris region (France), a depauperate pollinator environment. We combine population genetics analysis, phenotypic measurements and behavioural tests on a common garden experiment. Population genetics analysis reveals 27% increase in realized selfing rates in the field during this period. We documented trait evolution towards smaller and less conspicuous corollas, reduced nectar production and reduced attractiveness to bumblebees, with these trait shifts convergent across the four studied populations. We demonstrate the rapid evolution of a selfing syndrome in the four studied plant populations, associated with a weakening of the interactions with pollinators over the last three decades. This study demonstrates that plant mating systems can evolve rapidly in natural populations in the face of ongoing environmental changes. The rapid evolution towards a selfing syndrome may in turn further accelerate pollinator declines, in an eco-evolutionary feedback loop with broader implications to natural ecosystems.

The effect of experimental pollinator decline on pollinator-mediated selection on floral traits

Human-mediated environmental change, by reducing mean fitness, is hypothesized to strengthen selection on traits that mediate interactions among species. For example, human-mediated declines in pollinator populations are hypothesized to reduce mean seed production by increasing the magnitude of pollen limitation and thus strengthen pollinator-mediated selection on floral traits that increase pollinator attraction or pollen transfer efficiency. To test this hypothesis, we measured two female fitness components and six floral traits of Lobelia siphilitica plants exposed to supplemental hand-pollination, ambient open-pollination, or reduced open-pollination treatments. The reduced treatment simulated pollinator decline, while the supplemental treatment was used to estimate pollen limitation and pollinator-mediated selection. We found that plants in the reduced pollination treatment were significantly pollen limited, resulting in pollinator-mediated selection for taller inflorescences and more vibrant petals, both traits that could increase pollinator attraction. This contrasts with plants in the ambient pollination treatment, where reproduction was not pollen limited and there was not significant pollinator-mediated selection on any floral trait. Our results support the hypothesis that human-mediated environmental change can strengthen selection on traits of interacting species and suggest that these traits have the potential to evolve in response to changing environments.

Water deficit changes patterns of selection on floral signals and nectar rewards in the common morning glory

Understanding whether and how resource limitation alters phenotypic selection on floral traits is key to predict the evolution of plant-pollinator interactions under climate change. Two important resources predicted to decline with our changing climate are pollinators and water in the form of increased droughts. Most work, however, has studied these selective agents separately and in the case of water deficit, studies are rare. Here, we use the common morning glory (Ipomoea purpurea) to investigate the effects of experimental reduction in pollinator access and water availability on floral signals and nectar rewards and their effects on phenotypic selection on these traits. We conducted a manipulative experiment in a common garden, where we grew plants in three treatments: (1) pollinator restriction, (2) water reduction and (3) unmanipulated control. Plants in pollinator restriction and control treatments were well-watered compared to water deficit. We found that in contrast to pollinator restriction, water deficit had strong effects altering floral signals and nectar rewards but also differed in the direction and strength of selection on these traits compared to control plants. Water deficit increased the opportunity for selection, and selection in this treatment favoured lower nectar volumes and larger floral sizes, which might further alter pollinator visitation. In addition, well-watered plants, both in control and pollinator deficit, showed similar patterns of selection to increase nectar volume suggesting non-pollinator-mediated selection on nectar. Our study shows that floral traits may evolve in response to reduction in water access faster than to declines in pollinators and reinforces that abiotic factors can be important agents of selection for floral traits. Although only few experimental selection studies have manipulated access to biotic and abiotic resources, our results suggest that this approach is key for understanding how pollination systems may evolve under climate change.

The impact of heavy metal pollution on wild bee communities in smallholder farmlands

Wild bees provide important pollination services, but they face numerous stressors that threaten them and their ecosystem services. Wild bees can be exposed to heavy metal pollution through the consumption of nectar, pollen, and water, which might cause bee decline. While some studies have measured heavy metal concentrations in honeybees, few studies have monitored heavy metal concentrations in wild bees or explored their potential effects on wild bee communities. To investigate the impact of heavy metal pollution on wild bee communities, heavy metal concentrations, including vanadium (V), chromium (Cr), nickel (Ni), cadmium (Cd), Zinc (Zn) and lead (Pb) in multiple wild bee species were measured. Multiple wild bee species, including: Xylocopa tranquabaroroum, Eucera floralia, Apis cerana, and small bee mixtures (representing multiple small wild bee species) were sampled from 18 sites in Quzhou, Zhejiang Province, China. The findings demonstrated that there were significant differences in heavy metal concentrations among different bee species. The concentrations of V, Zn, Cd, and Pb in X. tranquabaroroum, the largest bee species in this study, were lower than that in the other three sample groups. Furthermore, there were significant negative correlations between heavy metal pollution and wild bee diversity and species richness, but not with abundance. Particularly, there was no significant relationship between heavy metal pollution and the abundance of small bees. Given these worrying findings, monitoring multiple heavy metals in wild bees should be conducted for protecting wild bee diversity and securing their pollination services.

Population Rescue through an Increase in the Selfing Rate under Pollen Limitation: Plasticity versus Evolution

AbstractIncreased rates of self-fertilization offer reproductive assurance when plant populations experience pollen limitation, but self-fertilization may reduce fitness by exposing deleterious mutations. If an environmental change responsible for pollen limitation also induces plastic mating system shifts toward self-pollination, the reproductive assurance benefit and inbreeding depression cost of increased self-fertilization occur immediately, while the benefit and cost happen more gradually when increased self-fertilization occur through evolution. I built eco-evolutionary models to explore the demographic and genetic conditions in which higher self-fertilization by plasticity and/or evolution rescues populations, following deficits due to a sudden onset of pollen limitation. Rescue is most likely under an intermediate level of selfing rate increase, either through plasticity or evolution, and this critical level of selfing rate increase is higher under stronger pollen limitation. Generally, rescue is more likely through plasticity than through evolution. Under weak pollen limitation, rescue by enhanced self-fertilization may mainly occur through purging of deleterious mutations rather than reproductive assurance. The selfing rate increase conferring the highest rescue probability is lower when the initial population size is smaller. This article shows the importance of plasticity during plant population rescue and offers insights for future studies of the evolution of mating system plasticity.

Does pollinator dependence decrease along elevational gradients?

Plants have long been thought to be less dependent on pollinators for seed production at higher elevations due to adverse pollination environments. However, recent research has yet to consistently support the generality of this expectation. In this study, we asked whether pollinator dependence decreases along an elevational gradient and how it varies with various reproductive traits. To answer these questions, we quantified pollinator-plant associations and various reproductive traits for 112 flowering plants spanning a large elevational gradient (990-4260 m a.s.l.) in the Qinghai-Tibet Plateau. We found that flowering plants in the Qinghai-Tibet Plateau region are highly dependent on pollinators for seed production (76.2% of seed production was contributed by animal pollinators and 44.6% of plants would produce no seed without pollinator visitation). Contrary to our expectation, there was no significant elevational gradient in pollinator dependence index. Although the pollinator dependence index was not significantly correlated with pollen limitation, flower size, floral longevity, or reward type, it was correlated with compatibility status and flowering time. These findings indicate that pollinator dependence does not decrease along an elevational gradient in the Qinghai-Tibet Plateau. Our study also highlights the severe vulnerability of flowering plant seed production to pollinator declines under global change in the Qinghai-Tibet Plateau region, particularly for early-flowering or self-incompatible plants growing at higher elevations (e.g., subnival belt).

Phenotypic clines in herbivore resistance and reproductive traits in wild plants along an agricultural gradient

The conversion of natural landscapes to agriculture is a leading cause of biodiversity loss worldwide. While many studies examine how landscape modification affects species diversity, a trait-based approach can provide new insights into species responses to environmental change. Wild plants persisting in heavily modified landscapes provide a unique opportunity to examine species' responses to land use change. Trait expression within a community plays an important role in structuring species interactions, highlighting the potential implications of landscape mediated trait changes on ecosystem functioning. Here we test the effect of increasing agricultural landscape modification on defensive and reproductive traits in three commonly occurring Brassicaceae species to evaluate plant responses to landscape change. We collected seeds from populations at spatially separated sites with variation in surrounding agricultural land cover and grew them in a greenhouse common garden, measuring defensive traits through an herbivore no-choice bioassay as well as reproductive traits such as flower size and seed set. In two of the three species, plants originating from agriculturally dominant landscapes expressed a consistent reduction in flower size and herbivore leaf consumption. One species also showed reduced fitness associated with increasingly agricultural landscapes. These findings demonstrate that wild plants are responding to landscape modification, suggesting that the conversion of natural landscapes to agriculture has consequences for wild plant evolution.

Effects of Flupyradifurone and Two Reference Insecticides Commonly Used in Toxicological Studies on the Larval Proteome of the Honey bee Apis mellifera

The western honey bee Apis mellifera is globally distributed due to its beekeeping advantages and plays an important role in the global ecology and economy. In recent decades, several studies have raised concerns about bee decline. Discussed are multiple reasons such as increased pathogen pressure, malnutrition or pesticide use. Insecticides are considered to be one of the major factors. In 2013, the use of three neonicotinoids in the field was prohibited in the EU. Flupyradifurone was introduced as a potential successor; it has a comparable mode of action as the banned neonicotinoids. However, there is a limited number of studies on the effects of sublethal concentrations of flupyradifurone on honey bees. Particularly, the larval physiological response by means of protein expression has not yet been studied. Hence, the larval protein expression was investigated via 2D gel electrophoresis after following a standardised protocol to apply sublethal concentrations of the active substance (flupyradifurone 10 mg/kg diet) to larval food. The treated larvae did not show increased mortality or an aberrant development. Proteome comparisons showed clear differences concerning the larval metabolism, immune response and energy supply. Further field studies are needed to validate the in vitro results at a colony level.

Simulated pollinator decline has similar effects on seed production of female and hermaphrodite Lobelia siphilitica, but different effects on selection on floral traits

PREMISE

Pollinator decline, by reducing seed production, is predicted to strengthen natural selection on floral traits. However, the effect of pollinator decline on gender dimorphic species (such as gynodioecious species, where plants produce female or hermaphrodite flowers) may differ between the sex morphs: if pollinator decline reduces the seed production of females more than hermaphrodites, then it should also have a larger effect on selection on floral traits in females than in hermaphrodites.

METHODS

To simulate pollinator decline, we experimentally reduced pollinator access to female and hermaphrodite Lobelia siphilitica plants. We compared the seed production of plants in the reduced pollination treatment to plants that were exposed to ambient pollination conditions. Within each treatment, we also measured directional selection on four floral traits of females and hermaphrodites.

RESULTS

Experimentally reducing pollination decreased seed production of both females and hermaphrodites by ~21%. Reducing pollination also strengthened selection on floral traits, but this effect was not larger in females than in hermaphrodites. Instead, reducing pollination intensified selection for taller inflorescences in hermaphrodites, but did not intensify selection on any floral trait in females.

CONCLUSIONS

Our results suggest that pollinator decline will not have a larger effect on either seed production or selection on floral traits of female plants. As such, any effect of pollinator decline on seed production may be similar for gender dimorphic and monomorphic species. However, the potential for floral traits of females (and thus of gender dimorphic species) to evolve in response to pollinator decline may be limited.

Spatio-Temporal Variations in Pollen Limitation and Floral Traits of an Alpine Lousewort (Pedicularis rhinanthoides) in Relation to Pollinator Availability

Populations of the same plant species living in different locations but flowering at different times may vary in pollinator availability and floral traits. However, the spatial and temporal links between floral traits and pollination are rarely included in single studies. In this study, three populations of an alpine lousewort, Pedicularis rhinanthoides Schrenk subsp. tibetica (Bonati) Tsoong, were surveyed to detect the variations in floral traits and pollinator activity. We hypothesized that floral divergence was spatio-temporally correlated with pollen limitation (PL) in relation to pollinators. Sampled plants from each population were divided into three groups, according to flowering stage: early, peak, and late. Pollen-supplementation experiments and investigations into pollinators, reproductive success, and floral traits were conducted on the plants from the different flowering stages and across the populations. Our results showed that the extent of PL varies across populations and among flowering stages. Populations in which more pollinators were recorded displayed a lower extent of PL. Furthermore, the temporal differences in PL showed a similar pattern for the three populations; the plants from the peak flowering stage suffered slighter PL than those from the other two stages. Nevertheless, some of the floral traits displayed similar spatial and temporal patterns to the PL, while the others only varied among the populations spatially. The results indicated that the performance of floral traits in a particular spatial-temporal situation shows they are well adapted to the corresponding pollination environment, which might help plants to optimize their reproductive fitness under different abiotic factors.

The potential for floral evolution in response to competing selection pressures following the loss of hawkmoth pollination in Ruellia humilis

PREMISE

In the absence of hawkmoth pollinators, chasmogamous (CH) flowers of Ruellia humilis self-pollinate by two secondary mechanisms. Other floral visitors might exert selection on CH floral traits to restore outcrossing, but at the same time preferential predation of CH seeds generates selection to increase the allocation of resources to cleistogamous (CL) flowers.

METHODS

To assess the potential for an evolutionary response to these competing selection pressures, we estimated additive genetic variances ( σ A 2 ${\sigma }_{{\rm{A}}}^{2}$ ) and covariances for 14 reproductive traits and three fitness components in a Missouri population lacking hawkmoth pollinators.

RESULTS

We found significant σ A 2 ${\sigma }_{{\rm{A}}}^{2}$ for all 11 floral traits and two measures of resource allocation to CL flowers, indicating the potential for a short-term response to selection on most reproductive traits. Selection generated by seed predators is predicted to increase the percentage of CL flowers by 0.24% per generation, and mean stigma-anther separation is predicted to decrease as a correlated response, increasing the fraction of plants that engage in prior selfing. However, the initial response to this selection is opposed by strong directional dominance.

CONCLUSIONS

The predicted evolutionary decrease in the number of CH flowers available for potential outcrossing, combined with the apparent preclusion of potential diurnal pollinators by the pollen-harvesting activities of sweat bees, suggest that 100% cleistogamy is the likely outcome of evolution in the absence of hawkmoths. However, rare mutations with large effects, such as delaying budbreak until after sunrise, could provide pathways for the restoration of outcrossing that are not reachable by gradual quantitative-genetic evolution.

Rapid evolution of selfing syndrome traits in Viola arvensis revealed by resurrection ecology

PREMISE

As part of global change, climate warming and pollinator decline are expected to affect plant phenology and plant-pollinator interactions. This paper aims at characterizing rapid evolution of life history traits and floral traits over two decades in the wild pansy (Viola arvensis), a common weed in agrosystems.

METHODS

We used a resurrection ecology approach with genotypes sampled in 1991 and 2012 from a population in Burgundy (France). The species has a mixed mating system (hereafter: mixed selfer) and presents a floral polymorphism. To correct for maternal effects, we measured plant traits in the second generation in a common garden (after a refreshing generation) to characterize plant evolution during the two decades. In addition, historical population selfing rates in 1991 and 2012 were inferred from microsatellites markers through heterozygote deficiency and identity disequilibrium.

RESULTS

Phenotypic data revealed a significant advance in flowering date, reduced flower sizes and a higher propensity of plants to set seed by autonomous selfing. Moreover, we detected a change in color morph frequency with an increase of the pale morph frequency. In accordance with phenotypic data, the neutral genetic data revealed an increase in historical selfing rates from 0.68 in 1991 to 0.86 in 2012.

CONCLUSIONS

Taken together, such data suggest that the wild pansy, a mixed selfer, is evolving a selfing syndrome that may be the consequence of reduced pollinator activity in agrosystems.

Temporal changes in the Swiss flora: implications for flower-visiting insects

Background

Local floristic diversity has massively decreased during the twentieth century in Central Europe even though in the 1990s diversity began increasing again in several regions. However, little is known whether this increase is equally distributed among plant groups with different reproductive traits.

Methods

Our study is based on data of the Swiss Biodiversity Monitoring Program. In this program, plant species occurrence is recorded since 2001 in 450 regularly distributed 1 km2 study sites. For all 1774 plant species registered in the study, we researched data on flower/pseudanthium type and colour, reproductive system, and groups of flower visitors. We then tested whether temporal changes in species frequency were equally distributed among species with different trait states.

Results

Species richness and functional richness significantly increased in the study sites while functional evenness decreased. The frequency of wind-pollinated species increased more strongly than that of insect-pollinated species. Further, the frequency of species with simple, open insect-pollinated flowers and pseudanthia visited by generalist groups of insects increased slightly more strongly than the frequency of species with complex flowers visited by more specialized groups of flower visitors. Additionally, the frequency of self-compatible species increased significantly more than that of self-incompatible species. Thus, the overall increase in local plant species richness in Switzerland is mostly driven by wind- and generalist insect-pollinated, self-compatible species. In contrast, species with complex flowers, which are essential for specialized groups of flower visitors and species with self-incompatible reproductive systems profited less.

Conclusions

Our study thus emphasizes the need to consider functional traits in the planning and monitoring of conservation activities, and calls for a special focus on plant species with specialized reproductive traits.

Pollinator loss causes rapid adaptive evolution of selfing and dramatically reduces genome-wide genetic variability

Although selfing populations harbor little genetic variation limiting evolutionary potential, the causes are unclear. We experimentally evolved large, replicate populations of Mimulus guttatus for nine generations in greenhouses with or without pollinating bees and studied DNA polymorphism in descendants. Populations without bees adapted to produce more selfed seed yet exhibited striking reductions in DNA polymorphism despite large population sizes. Importantly, the genome-wide pattern of variation cannot be explained by a simple reduction in effective population size, but instead reflects the complicated interaction between selection, linkage, and inbreeding. Simulations demonstrate that the spread of favored alleles at few loci depresses neutral variation genome wide in large populations containing fully selfing lineages. It also generates greater heterogeneity among chromosomes than expected with neutral evolution in small populations. Genome-wide deviations from neutrality were documented in populations with bees, suggesting widespread influences of background selection. After applying outlier tests to detect loci under selection, two genome regions were found in populations with bees, yet no adaptive loci were otherwise mapped. Large amounts of stochastic change in selfing populations compromise evolutionary potential and undermine outlier tests for selection. This occurs because genetic draft in highly selfing populations makes even the largest changes in allele frequency unremarkable.

Global analysis of floral longevity reveals latitudinal gradients and biotic and abiotic correlates

The length of time a flower remains open and functional - floral longevity - governs important reproductive processes influencing pollination and mating and varies considerably among angiosperm species. However, little is known about large-scale biogeographic patterns and the correlates of floral longevity. Using published data on floral longevity from 818 angiosperm species in 134 families and 472 locations world-wide, we present the first global quantification of the latitudinal pattern of floral longevity and the relationships between floral longevity and a range of biotic and abiotic factors. Floral longevity exhibited a significant phylogenetic signal and was longer at higher latitudes in both northern and southern hemispheres, even after accounting for elevation. This latitudinal variation was associated with several biotic and abiotic variables. The mean temperature of the flowering season had the highest predictive power for floral longevity, followed by pollen number per flower. Surprisingly, compatibility status, flower size, pollination mode, and growth form had no significant effects on flower longevity. Our results suggest that physiological processes associated with floral maintenance play a key role in explaining latitudinal variation in floral longevity across global ecosystems, with potential implications for floral longevity under global climate change and species distributions.

Competition for pollinators destabilizes plant coexistence

Mounting concern over the global decline of pollinators has fuelled calls for investigating their role in maintaining plant diversity^1,2. Theory predicts that competition for pollinators can stabilize interactions between plant species by providing opportunities for niche differentiation³, while at the same time can drive competitive imbalances that favour exclusion⁴. Here we empirically tested these contrasting effects by manipulating competition for pollinators in a way that predicts its long-term implications for plant coexistence. We subjected annual plant individuals situated across experimentally imposed gradients in neighbour density to either ambient insect pollination or a pollen supplementation treatment alleviating competition for pollinators. The vital rates of these individuals informed plant population dynamic models predicting the key theoretical metrics of species coexistence. Competition for pollinators generally destabilized the interactions between plant species, reducing the proportion of pairs expected to coexist. Interactions with pollinators also influenced the competitive imbalances between plant species, effects that are expected to strengthen with pollinator decline, potentially disrupting plant coexistence. Indeed, results from an experiment simulating pollinator decline showed that plant species experiencing greater reductions in floral visitation also suffered greater declines in population growth rate. Our results reveal that competition for pollinators may weaken plant coexistence by destabilizing interactions and contributing to competitive imbalances, information critical for interpreting the impacts of pollinator decline.

Phenotypic Selection in Halenia elliptica D. Don (Gentianaceae), an Alpine Biennial with Mixed Mating System

The transition from outcrossing to selfing is a common evolutionary trend in flowering plants, and floral traits change significantly with the evolution of selfing. Whether or not plant traits are subjected to selection remains an open question in species with mixed mating systems. We examined phenotypic selection in two populations of Halenia elliptica with different selfing rates. We found that the pollen–ovule ratio, seed size, plant height, spur length, and pollinator visitation rate in the population with the higher selfing rate were lower than those in the population with the lower selfing rate. Selfing provides reproductive assurance for populations when pollinator service is low, and the floral traits that are associated with selfing syndrome are evident in populations with a higher selfing rate but are subjected to weak selection in each of the two populations with different selfing rates. Directional selection for an early flowering time indicated that late blooming flowers could experience a risk of seed development in alpine environments, and for large plants, selection indicated that seed production could be limited by the available resources. The floral traits that are associated with pollinator attraction and specialization could be subjected to weak selection at the plant level as selfing evolves, and the selective pressures that are independent of pollinators might not change significantly; highlighting the selective biotic and abiotic pressures that shape the morphological traits of plant species and their independence from the mating system.

The genetic basis of selfing rate evolution

Evolution of selfing is common in plant populations, but the genetic basis of selfing rate evolution remains unclear. Although the effects of genetic properties on fixation for mating-unrelated alleles have been investigated, loci that modify the selfing rate (selfing modifiers) differ from mating-unrelated loci in several aspects. Using population genetic models, I investigate the genetic basis of selfing rate evolution. For mating-unrelated alleles, selfing promotes fixation only for recessive mutations, but for selfing modifiers, because the selection coefficient depends on the background selfing rate, selfing can promote fixation even for dominant modifiers. For mating-unrelated alleles, the fixation probability from standing variation is independent of dominance and decreases with an increased background selfing rate. However, for selfing modifiers, the fixation probability peaks at an intermediate selfing rate and when alleles are recessive, because a change of its selection coefficient necessarily involves a change of the inbreeding coefficient, because both depend on the level of inbreeding depression. Furthermore, evolution of selfing involving multiple modifier loci is more likely when selfing is controlled by few large-effect rather than many slight-effect modifiers. I discuss how these characteristics of selfing modifiers have implications for the unidirectional transition from outcrossing to selfing and other empirical patterns.

Plasticity in floral longevity and sex-phase duration of Lobelia siphilitica in response to simulated pollinator declines

PREMISE

Pollinator declines can reduce the quantity and quality of pollination services, resulting in less pollen deposited on flowers and lower seed production by plants. In response to these reductions, plant species that cannot autonomously self-pollinate and thus are dependent on pollinators to set seed could plastically adjust their floral traits. Such plasticity could increase the opportunity for outcross pollination directly, as well as indirectly by affecting inflorescence traits.

METHODS

To test whether plants can respond to pollinator declines by plastically adjusting their floral traits, we simulated declines by experimentally reducing pollinator access to Lobelia siphilitica plants and measuring two traits of early- and late-season flowers: (1) floral longevity; and (2) sex-phase duration. To test whether plasticity in these floral traits affected inflorescence traits, we measured daily display size and phenotypic gender.

RESULTS

We found that experimentally reducing pollination did not affect female-phase duration, but did extend the male-phase duration of early-season flowers by 13% and the longevity of late-season flowers by 12.8%. However, plants with an extended male phase did not have a more male-biased phenotypic gender, and plants with an extended floral longevity did not have a larger daily display.

CONCLUSIONS

Our results suggest that plants can respond to pollinator declines by plastically adjusting both the longevity and sex-phase duration of their flowers. If this plasticity increases the opportunity for outcross pollination, then it could be one mechanism by which pollinator-dependent plant species maintain seed production as pollinators decline.

A comprehensive catalogue of plant-pollinator interactions for Chile

Pollinators and pollination services provide invaluable ecosystem services to agriculture and contribute to the maintenance of biodiversity. In Chile, pollination contributes greatly to the diversity of native ecosystems and provides ecosystem services to crops, but local pollinator abundance and diversity, as well as plant-animal interactions, remain poorly understood. We compiled all available information from the published scientific literature on pollinators, flower visitors, and plant-pollinator interactions in Chile and found 120 publications from which we extracted 2619 records. Those records contain locality, habit type, and establishment means of 357 plant species from 83 families. Thus, we built a database compiling information on their pollinators and flower visitors, including information on 492 pollinator species from 97 families and 13 orders. Our database provides the first systematisation of information about pollinators and pollination in Chile. This country relies heavily on pollinators both for its agricultural industry and its unique and highly endemic biodiversity. This information can be reused in future studies and would contribute significantly to pollinator conservation strategies.

Measurement(s)	pollination
Technology Type(s)	Observation
Factor Type(s)	Pollination
Sample Characteristic - Organism	Aves • Insecta • Mammalia • Magnoliophyta
Sample Characteristic - Environment	habitat
Sample Characteristic - Location	Chile

OUP accepted manuscript

Bee foraging behavior provides a pollination service that has both ecological and economic benefits. However, bee population decline could directly affect the efficiency of this interaction. Among the drivers of this decline, global warming has been implicated as an emerging threat but exactly how increasing temperatures affect bee foraging behavior remains unexplored. Here, we assessed how exposure to elevated temperatures during development affects the foraging behavior and morphology of workers from commercial and wild Bombus terrestris colonies. Workers reared at 33 °C had a higher visiting rate and shorter visiting time than those reared at 27°C. In addition, far fewer workers reared at 33 °C engaged in foraging activities and this is potentially related to the drastic reduction in the number of individuals produced in colonies exposed to 33 °C. The impact of elevated developmental temperature on wild colonies was even stronger as none of the workers from these colonies performed any foraging trips. We also found that rearing temperature affected wing size and shape. Our results provide the first evidence that colony temperature can have striking effects on bumblebee foraging behavior. Of particular importance is the drastic reduction in the number of workers performing foraging trips, and the total number of foraging trips made by workers reared in high temperatures. Further studies should explore if, ultimately, these observed effects of exposure to elevated temperature during development lead to a reduction in pollination efficiency.

Rapid divergent evolution of an annual plant across a latitudinal gradient revealed by seed resurrection

Global change is expected to drive short-term evolution of natural populations. However, it remains unclear whether different populations are changing in unison. Here, we study contemporary evolution of growth-related and reproductive traits of three populations of Cyanus segetum facing warming and pollinator decline across a latitudinal gradient in France. We resurrected stored seeds sampled up to 24 years apart from northern, central-western, and southern populations and conducted an in situ common-garden experiment. To disentangle neutral from selection-driven differentiation, we calculated neutral genetic differentiation (F_ST ) and quantitative trait differentiation (Q_ST ) between temporal samples. We found that phenotypic evolution was divergent across populations exhibiting different trends for rosette size, date of flowering, and capitula size. By measuring seed set as a proxy of fitness, we showed that samples with larger mean capitula size outperformed samples with smaller mean capitula size in the western and southern populations. Regression of traits on seed set showed that flowering date and capitula size are the primary determinants of fitness, and Q_ST -F_ST comparisons indicated that natural selection has likely contributed to the shifts in flowering phenology and rosette size. These findings outline the potential for rescue of natural populations through contemporary evolution and emphasize the complex interplay between spatial and temporal variation in species' responses to global change.

Methylene blue can act as an antidote to pesticide poisoning of bumble bee mitochondria

The population of bumble bees and other pollinators has considerably declined worldwide, probably, due to the toxic effect of pesticides used in agriculture. Inexpensive and available antidotes can be one of the solutions for the problem of pesticide toxicity for pollinators. We studied the properties of the thiazine dye Methylene blue (MB) as an antidote against the toxic action of pesticides in the bumble bee mitochondria and found that MB stimulated mitochondrial respiration mediated by Complex I of the electron transport chain (ETC) and increased respiration of the mitochondria treated with mitochondria-targeted (chlorfenapyr, hydramethylnon, pyridaben, tolfenpyrad, and fenazaquin) and non-mitochondrial (deltamethrin, metribuzin, and penconazole) pesticides. MB also restored the mitochondrial membrane potential dissipated by the pesticides affecting the ETC. The mechanism of MB action is most probably related to its ability to shunt electron flow in the mitochondrial ETC.

Studies on the influence of natural resource utilization by humans on foraging behavior of honey bees at rural ecosystems

Human utilization of natural resources acts as a main driver in altering the ecosystem service and functions. Apart from indirect influence, these human activities also tempt for the behavioral shift in insects especially in honey bees. The foraging behavior of honey bees from the natural floral resources to the man-made food sources eventually degrade the ecosystem's services and cause declining of the honey bee population. Understanding this foraging behavior of bees could help in opting for viable conservation measures for honey bees. In order to understand the influence of human utilization of natural resources on the foraging behavior of bees and its negative impacts on the bee population, the study was carried out in the sites where humans collect palm sap. Palm sap collectors used different containers (mud pots and pet bottles) to collect the palm sap from Borassus flabellifer. The number of containers per tree, volume of palm sap per container/tree, bee visiting frequency, and bee mortality per container/tree were measured at different ecosystems. Palm saps were collected freshly and volatile compounds of samples were identified using FT-IR and GC-MS analysis. The identified volatile compounds were used to study the interaction between volatile compounds and odorant-binding proteins (OBPs) of honey bees for understanding the foraging behavior of bees using in silico approach. Our results clearly showed that bee visitation frequency was directly correlated (0.94) with bee mortality in palm sap in different study sites. The average number of bee mortality was recorded as 491.2 ± 23.48 bees per container/tree/day. GC-MS analyses revealed the presence of 35 volatile compounds in collected palm sap from different study sites. Furthermore, molecular docking studies were performed for all 35 palm volatile compounds OBPs of honey bees to analyze their binding affinities. Docking studies showed that 1-methylbutylmandelate and 6-(hydroxymethyl)-1,4,4-trimethylbicyclo [3.1.0] hexan-2-ol have high binding affinity with OBP residues of bees. These volatile compounds might act as an attractant for bee populations for their foraging behavior. Based on this study, we conclude that human utilization of palm sap has created new ecological niches which highly alters the foraging behavior of bees and results in declining bee populations.

Potential regional declines in species richness of tomato pollinators in North America under climate change

About 70% of the world's main crops depend on insect pollination. Climate change is already affecting the abundance and distribution of insects, which could cause geographical mismatches between crops and their pollinators. Crops that rely primarily on wild pollinators (e.g., crops that cannot be effectively pollinated by commercial colonies of honey bees) could be particularly in jeopardy. However, limited information on plant-pollinator associations and pollinator distributions complicate the assessment of climate change impacts on specific crops. To study the potential impacts of climate change on pollination of a specific crop in North America, we use the case of open-field tomato crops, which rely on buzz pollinators (species that use vibration to release pollen, such as bumble bees) to increase their production. We aimed to (1) assess potential changes in buzz pollinator distribution and richness, and (2) evaluate the overlap between areas with high densities of tomato crops and high potential decrease in richness. We used baseline (1961-1990) climate and future (2050s and 2080s) climatic projections in ecological niche models fitted with occurrences of wild bees, documented in the literature as pollinators of tomatoes, to estimate the baseline and future potential distribution of suitable climatic conditions of targeted species and to create maps of richness change across North America. We obtained reliable models for 15 species and found important potential decreases in the distribution of some pollinators (e.g., Lasioglossum pectorale and Augochlorella aurata). We observed geographical discrepancies in the projected change in species richness across North America, detecting important declines in the eastern United States (up to 11 species decrease for 2050s). After overlapping the maps of species richness change with a tomato crop map for the United States, we found spatial correspondence between richness declines and areas with high concentration of tomato crops. Disparities in the effects of climate change on the potential future distribution of different wild pollinators and geographical variation in richness highlight the importance of crop-specific studies. Our study also emphasizes the challenges of compiling and modeling crop-specific pollinator data and the need to improve our understanding of current distribution of pollinators and their community dynamics under climate change.

Direct and ambient light pollution alters recruitment for a diurnal plant-pollinator system

Artificial light at night (ALAN) functions as a novel environmental stimulus that has the potential to disrupt interactions among species. Despite recent efforts to explain nocturnal pollinators' responses to this stimulus, the likelihood and associated mechanisms of attraction towards artificial light and potential consequences on fitness for diurnal pollinators is still largely unclear. Here, we took advantage of the obligate mutualism between yucca moths (Tegeticula maculata maculata) and yucca plants (Hesperoyucca whipplei) to understand how direct light exposure and skyglow can influence a pairwise plant-pollinator interaction. To surmise whether adult moths exhibit positive phototaxis, we deployed a set of field-placed light towers during the peak of yucca flowering and compared the number of moths caught in traps between dark-controlled and light-treated trials. Adult moth abundance was much higher when light was present, which suggests that ALAN may alter this diurnal moth's activity patterns to expand their temporal niche into the night. To evaluate ALAN effects on yucca fruit set and moth larva recruitment, we measured skyglow exposure above yucca plants and direct light intensity from a second set of light towers. Both larva and fruit recruitment increased with skyglow, and fruit set also increased with direct lighting, but the relationship was weaker. Contrarily, larva recruitment did not change when exposed to a gradient of direct light, which may instead reflect effects of ALAN on moth physiology, such as disrupted female oviposition, or misdirecting behaviors essential to oviposition activity. Our results suggest that ALAN can positively influence the fitness of both plants and moths in this tightly co-evolved mutualism, but the benefits to each species may depend on whether night lighting is direct or indirect. Whether such effects and mechanisms could relate to susceptibility to the presence of ALAN on this or other plant-pollinator relationships will remain an important focus of future research.

Human-Mediated Land Use Change Drives Intraspecific Plant Trait Variation

In the Anthropocene, more than three quarters of ice-free land has experienced some form of human-driven habitat modification, with agriculture dominating 40% of the Earth's surface. This land use change alters the quality, availability, and configuration of habitat resources, affecting the community composition of plants and insects, as well as their interactions with each other. Landscapes dominated by agriculture are known to support a lower abundance and diversity of pollinators and frequently larger populations of key herbivore pests. In turn, insect communities subsidized by agriculture may spill into remaining natural habitats with consequences for wild plants persisting in (semi) natural habitats. Adaptive responses by wild plants may allow them to persist in highly modified landscapes; yet how landscape-mediated variation in insect communities affects wild plant traits related to reproduction and defense remains largely unknown. We synthesize the evidence for plant trait changes across land use gradients and propose potential mechanisms by which landscape-mediated changes in insect communities may be driving these trait changes. Further, we present results from a common garden experiment on three wild Brassica species demonstrating variation in both defensive and reproductive traits along an agricultural land use gradient. Our framework illustrates the potential for plant adaptation under land use change and predicts how defense and reproduction trait expression may shift in low diversity landscapes. We highlight areas of future research into plant population and community effects of land use change.

Towards the flower economics spectrum

Understanding how floral traits affect reproduction is key for understanding genetic diversity, speciation, and trait evolution in the face of global changes and pollinator decline. However, there has not yet been a unified framework to characterize the major trade-offs and axes of floral trait variation. Here, we propose the development of a floral economics spectrum (FES) that incorporates the multiple pathways by which floral traits can be shaped by multiple agents of selection acting on multiple flower functions. For example, while pollinator-mediated selection has been considered the primary factor affecting flower evolution, selection by nonpollinator agents can reinforce or oppose pollinator selection, and, therefore, affect floral trait variation. In addition to pollinators, the FES should consider nonpollinator biotic agents and floral physiological costs, broadening the drivers of floral traits beyond pollinators. We discuss how coordinated evolution and trade-offs among floral traits and between floral and vegetative traits may influence the distribution of floral traits across biomes and lineages, thereby influencing organismal evolution and community assembly.

How rapidly do self-compatible populations evolve selfing? Mating system estimation within recently evolved self-compatible populations of Azorean Tolpis succulenta (Asteraceae)

Genome-wide genotyping and Bayesian inference method (BORICE) were employed to estimate outcrossing rates and paternity in two small plant populations of Tolpis succulenta (Asteraceae) on Graciosa island in the Azores. These two known extant populations of T. succulenta on Graciosa have recently evolved self-compatibility. Despite the expectation that selfing would occur at an appreciable rate (self-incompatible populations of the same species show low but nonzero selfing), high outcrossing was found in progeny arrays from maternal plants in both populations. This is inconsistent with an immediate transition to high selfing following the breakdown of a genetic incompatibility system. This finding is surprising given the small population sizes and the recent colonization of an island from self-incompatible colonists of T. succulenta from another island in the Azores, and a potential paucity of pollinators, all factors selecting for selfing through reproductive assurance. The self-compatible lineage(s) likely have high inbreeding depression (ID) that effectively halts the evolution of increased selfing, but this remains to be determined. Like their progeny, all maternal plants in both populations are fully outbred, which is consistent with but not proof of high ID. High multiple paternity was found in both populations, which may be due in part to the abundant pollinators observed during the flowering season.

Method for detection of mtDNA damages for evaluating of pesticides toxicity for bumblebees (Bombus terrestris L.)

Bumblebees are important for crop pollination. Currently, the number of pollinators is decreasing worldwide, which is attributed mostly to the widespread use of pesticides. The aim of this work was to develop a method for assessing the genotoxicity of pesticides for the Bombus terrestris L. bumblebee using long-range PCR of mitochondrial DNA fragments. We have developed a panel of primers and assessed the genotoxicity of the following pesticides: imidacloprid, rotenone, deltamethrin, difenocanozole, malathion, metribuzin, penconazole, esfenvalerate, and dithianon. All pesticides (except imidacloprid) inhibited mitochondrial respiration fueled by pyruvate + malate; the strongest effect was observed for rotenone and difenocanozole. Three pesticides (dithianon, rotenone, and difenocanozole) affected the rate of H₂O₂ production. To study the pesticide-induced DNA damage in vitro and in vivo, we used three different mtDNA. The mtDNA damage was observed for all studied pesticides. Most of the studied pesticides caused significant damage to mtDNA in vitro and in vivo when ingested. Our results indicate that all tested pesticides, including herbicides and fungicides, can have a toxic effect on pollinators. However, the extent of pesticide-induced mtDNA damage in the flight muscles was significantly less upon the contact compared to the oral administration.

A mathematical model of kin selection in floral displays

Plants can adjust their competitive traits for acquiring resources in response to the relatedness of their neighbours. Recently, it has been found that plants can alter their investment in traits of attracting pollinators based on kin-interaction. We build a mathematical model to study the optimal floral display to attract pollinators in a patch with kin structure. We show that when plants can attract pollinators to a whole patch through the magnet effect, the floral display should increase with the increasing relatedness of the plants in the patch. Our model also indicates that increasing investment into attracting pollinators is a form of altruism, reducing a plant's own seed production but increasing the contribution of other plants to its fitness. We also predict that seed production should increase with increasing relatedness in the patch. Our model provides the explicit conditions when resource allocation to attract pollinators in response to neighbour relatedness can be favoured by kin selection, and a possible mechanism for the plants to deal with the consequent loss of pollinator diversity and abundance.

Pollen adaptation to ant pollination: a case study from the Proteaceae

BACKGROUND AND AIMS

Ant-plant associations are widely diverse and distributed throughout the world, leading to antagonistic and/or mutualistic interactions. Ant pollination is a rare mutualistic association and reports of ants as effective pollinators are limited to a few studies. Conospermum (Proteaceae) is an insect-pollinated genus well represented in the south-western Australia biodiversity hotspot, and here we aimed to evaluate the role of ants as pollinators of C. undulatum.

METHODS

Pollen germination after contact with several species of ants and bees was tested for C. undulatum and five co-flowering species for comparison. We then sampled the pollen load of floral visitors of C. undulatum to assess whether ants carried a pollen load sufficient to enable pollination. Lastly, we performed exclusion treatments to assess the relative effect of flying- and non-flying-invertebrate floral visitors on the reproduction of C. undulatum. For this, we measured the seed set under different conditions: ants exclusion, flying-insects exclusion and control.

KEY RESULTS

Pollen of C. undulatum, along with the other Conospermum species, had a germination rate after contact with ants of ~80 % which did not differ from the effect of bees; in contrast, the other plant species tested showed a drop in the germination rate to ~10 % following ant treatments. Although ants were generalist visitors, they carried a pollen load with 68-86 % of suitable grains. Moreover, ants significantly contributed to the seed set of C. undulatum.

CONCLUSIONS

Our study highlights the complexity of ant-flower interactions and suggests that generalizations neglecting the importance of ants as pollinators cannot be made. Conospermum undulatum has evolved pollen with resistance to the negative effect of ant secretions on pollen grains, with ants providing effective pollination services to this threatened species.

Land use and pollinator dependency drives global patterns of pollen limitation in the Anthropocene

Land use change, by disrupting the co-evolved interactions between plants and their pollinators, could be causing plant reproduction to be limited by pollen supply. Using a phylogenetically controlled meta-analysis on over 2200 experimental studies and more than 1200 wild plants, we ask if land use intensification is causing plant reproduction to be pollen limited at global scales. Here we report that plants reliant on pollinators in urban settings are more pollen limited than similarly pollinator-reliant plants in other landscapes. Plants functionally specialized on bee pollinators are more pollen limited in natural than managed vegetation, but the reverse is true for plants pollinated exclusively by a non-bee functional group or those pollinated by multiple functional groups. Plants ecologically specialized on a single pollinator taxon were extremely pollen limited across land use types. These results suggest that while urbanization intensifies pollen limitation, ecologically and functionally specialized plants are at risk of pollen limitation across land use categories.

Cyclic Synthetic Peroxides Inhibit Growth of Entomopathogenic Fungus Ascosphaera apis without Toxic Effect on Bumblebees

In recent years, the number of pollinators in the world has significantly decreased. A possible reason for this is the toxic effects of agrochemicals reducing the immunity of insects that leads to their increased susceptibility to pathogens. Ascosphaera apis is a dangerous entomopathogenic fungus, afflicting both honeybees and bumblebees. We investigated fungicide activity of cyclic synthetic peroxides against A. apis isolated from Bombus terrestris L. The peroxides exhibited high mycelium growth inhibition of A. apis up to 94–100% at concentration 30 mg/L. EC₅₀ values were determined for the most active peroxides. Two peroxides showed higher antifungal activity against A. apis than the commercial fungicide Triadimefon. The studied peroxides did not reduce the ability of bumblebees to fly and did not lead to the death of bumblebees. A new field of application for peroxides was disclosed.

Population Genomics Provide Insights into the Evolution and Adaptation of the Eastern Honey Bee (Apis cerana)

The mechanisms by which organisms adapt to variable environments are a fundamental question in evolutionary biology and are important to protect important species in response to a changing climate. An interesting candidate to study this question is the honey bee Apis cerana, a keystone pollinator with a wide distribution throughout a large variety of climates, that exhibits rapid dispersal. Here, we resequenced the genome of 180 A. cerana individuals from 18 populations throughout China. Using a population genomics approach, we observed considerable genetic variation in A. cerana. Patterns of genetic differentiation indicate high divergence at the subspecies level, and physical barriers rather than distance are the driving force for population divergence. Estimations of divergence time suggested that the main branches diverged between 300 and 500 Ka. Analyses of the population history revealed a substantial influence of the Earth's climate on the effective population size of A. cerana, as increased population sizes were observed during warmer periods. Further analyses identified candidate genes under natural selection that are potentially related to honey bee cognition, temperature adaptation, and olfactory. Based on our results, A. cerana may have great potential in response to climate change. Our study provides fundamental knowledge of the evolution and adaptation of A. cerana.

Simulated pollinator declines intensify selection on floral traits that facilitate selfing and outcrossing in Impatiens capensis

PREMISE

Anthropogenic environmental change is causing pollinator populations to decline. These declines should intensify selection for floral traits that facilitate outcrossing by making plants more attractive to pollinators and/or for floral traits that facilitate selfing in the absence of pollinators. However, the effect of pollinator declines on selection on floral traits could be modified by other environmental factors such as herbivores.

METHODS

We studied the effect of simulated pollinator declines on selection on floral traits of Impatiens capensis, a mixed-mating species that produces both obligately selfing cleistogamous flowers and primarily outcrossing chasmogamous flowers. We measured directional selection differentials via seeds per plant on two traits that facilitate outcrossing (chasmogamous flower size and number) and one trait that facilitates selfing (cleistogamous flower number) in ambient, reduced pollinator access, and reduced pollinator access combined with increased foliar herbivory treatments.

RESULTS

Reduced pollinator access intensified selection for larger chasmogamous flowers and more cleistogamous flowers. In contrast, increased herbivory did not affect selection on any floral trait.

CONCLUSIONS

Reduced pollinator access intensified selection for a trait that facilitates outcrossing, suggesting that even species such as I. capensis that can autonomously self-pollinate have the potential to respond to pollinator declines by evolving floral traits that reinforce interactions between plants and pollinators. However, reduced pollinator access also intensified selection for a trait that facilitates selfing, suggesting that I. capensis could adapt to pollinator declines by evolving floral traits that maintain the production of both selfed and outcrossed seeds.

Self-compatibility and autonomous selfing of plants in meadow communities

One of the most fundamental, although controversial, questions related to the evolution of plant mating systems is the distribution of outcrossing rates. Self-compatibility, and especially autonomous self-pollination, can become particularly beneficial in anthropogenically degraded habitats with impoverished pollinator assemblages and increased pollen limitation. In a hand-pollination experiment with 46 meadow plants from the Železné hory Mts., Czech Republic, we evaluated the species' ability to adopt different mating systems. For a subset of the species, we also tested seed germination for inbreeding depression. Subsequently, we analysed relationships between the species' mating systems and 12 floral and life-history traits. We found a relatively discrete distribution of the studied species into four groups. Fully and partially self-incompatible species formed the largest group, followed by self-compatible non-selfers and mixed mating species. The germination experiment showed an absence of inbreeding depression in 19 out of 22 examined species. Nectar sugar per flower, nectar sugar per shoot and dichogamy were significant associated with the mating system. Spontaneous selfing ability and self-incompatibility in species of the meadow communities had a discrete distribution, conforming to the general distribution of mating and breeding systems in angiosperms. The low frequency of spontaneous selfers and the lack of inbreeding depression at germination suggest the existence of a selection against selfing at the later ontogenetic stages. Some floral traits, such as the level of dichogamy and amount of nectar reward, may strongly impact the balance between selfing and outcrossing rates in the self-compatible species and thus shape the evolution of mating systems.

A century of pollination success revealed by herbarium specimens of seed pods

A widely observed pollinator decline around the world has led to the prediction that terrestrial ecosystems could be disrupted as plant pollination suffers, but declining pollination success has not been tested rigorously in wild plants, and it still remains unclear how pollination success of plant species responds differently in the context of pollinator decline. By viewing the number of seeds per pod as a quantitative measure of successful pollination, we examined seed pods in 4637 herbarium specimens of 109 obligately outcrossing legumes collected over the past century. We found that only 13 species showed significant temporal change with nine of those as an increase. None of the three subfamilies of legumes showed a consistent trend, and the subfamily Papilionoideae with the most specialized flowers, had increasing seed number per pod more often than decreasing. We conclude that legume pollination in China shows no sign of disruption and the effects of plant-pollinator disruption may be more complicated than simplistic predictions have allowed.

Population genomics and morphological features underlying the adaptive evolution of the eastern honey bee (Apis cerana)

Background

The adaptation of organisms to changing environments is self-evident, with the adaptive evolution of organisms to environmental changes being a fundamental problem in evolutionary biology. Bees can pollinate in various environments and climates and play important roles in maintaining the ecological balance of the earth.

Results

We performed an analysis of 462 Apis cerana (A. cerana) specimens from 31 populations in 11 regions and obtained 39 representative morphological features. We selected 8 A. cerana samples from each population and performed 2b-RAD simplified genome sequencing. A total of 11,506 high-quality single nucleotide polymorphism (SNP) loci were obtained. For these SNPs, the minor allele frequency (MAF) was > 1%, the average number of unique labels for each sample was 49,055, and the average depth was 72.61x. The ratios of the unique labels of all samples were 64.27–86.33%.

Conclusions

Using 39 morphological characteristics as the data set, we proposed a method for the rapid classification of A. cerana. Using genomics to assess population structure and genetic diversity, we found that A. cerana has a large genetic difference at the ecotype level. A comparison of A. cerana in North China revealed that some physical obstacles, especially the overurbanization of the plains, have isolated the populations of this species. We identified several migration events in North China and Central China. By comparing the differences in the environmental changes in different regions, we found that A. cerana has strong potential for climate change and provides a theoretical basis for investigating and protecting A. cerana.

Floral display and habitat fragmentation: Effects on the reproductive success of the threatened mass-flowering Conospermum undulatum (Proteaceae)

Fragmentation of natural vegetation is currently one of the largest threats to plant populations and their interactions with pollinators. Plant reproductive susceptibility to habitat fragmentation has been investigated in many species; however, the response of wild mass-flowering species is poorly known, with research limited to mainly boreal plant species.Here, we studied twelve remnant populations of the threatened mass-flowering shrub Conospermum undulatum in the southwest Australian biodiversity hotspot, each presenting different population size, level of isolation, and floral display. We assessed the impact of fragmentation on (a) fruit and seed production; and (b) seed germination. To gain a deeper understanding of factors influencing the reproductive success of C. undulatum, we performed pollinator exclusion and self-pollination treatments to experimentally assess the mating system of this threatened shrub.We found C. undulatum to be strictly self-incompatible and totally reliant on pollinators visiting with an outcrossed pollen load to complete the reproductive cycle. Further, we found that fruit production dropped from 35% to <20% as a result of decreasing floral display. A reduction in population size from 880 to 5 plants and from ~700 to 0.21 in the floral display index led to a decrease in seed output, while a similar reduction in seed output, from 6% to 3%, was observed as a result of increasing isolation index from -21.41 to -0.04. Overall, seed germination was positively related to population size, and a negative relationship was found between germination and isolation. Synthesis and applications. Our results demonstrate the important relationship between pollinators and floral morphology in plants of southwest Australia that have coevolved with native pollinators and developed characteristic flower morphologies over long time frames. Indeed, due to its characteristic pollination mechanism, the self-incompatible C. undulatum can only rely on specialized native pollinators for pollen flow and cannot rely on its mass-flowering trait to attract generalist pollinators from coflowering species; neither can it compensate for the lack of visitors by promoting geitonogamy. Consequently, fragmentation has a significant effect on the reproductive output of C. undulatum, and size, isolation, and floral display of populations are important factors to be considered when planning conservation actions for the species.

Unique features of flight muscles mitochondria of honey bees (Apis mellifera L.)

Honey bees Apis mellifera L. are one of the most studied insect species due to their economic importance. The interest in studying honey bees chiefly stems from the recent rapid decrease in their world population, which has become a problem of food security. Nevertheless, there are no systemic studies on the properties of the mitochondria of honey bee flight muscles. We conducted a research of the mitochondria of the flight muscles of A. mellifera L. The influence of various organic substrates on mitochondrial respiration in the presence or absence of adenosine diphosphate (ADP) was investigated. We demonstrated that pyruvate is the optimal substrate for the coupled respiration. A combination of pyruvate and glutamate is required for the maximal respiration rate. We also show that succinate oxidation does not support the oxidative phosphorylation and the generation of membrane potential. We also studied the production of reactive oxygen species by isolated mitochondria. The greatest production of H₂ O₂ (as a percentage of the rate of oxygen consumed) in the absence of ADP was observed during the respiration supported by α-glycerophosphate, malate, and a combination of malate with another NAD-linked substrate. We showed that honey bee flight muscle mitochondria are unable to uptake Ca²⁺ -ions. We also show that bee mitochondria are able to oxidize the respiration substrates effectively at the temperature of 50°С compared to Bombus terrestris mitochondria, which were more adapted to lower temperatures.

Pollinator parasites and the evolution of floral traits

The main selective force driving floral evolution and diversity is plant-pollinator interactions. Pollinators use floral signals and indirect cues to assess flower reward, and the ensuing flower choice has major implications for plant fitness. While many pollinator behaviors have been described, the impact of parasites on pollinator foraging decisions and plant-pollinator interactions have been largely overlooked. Growing evidence of the transmission of parasites through the shared-use of flowers by pollinators demonstrate the importance of behavioral immunity (altered behaviors that enhance parasite resistance) to pollinator health. During foraging bouts, pollinators can protect themselves against parasites through self-medication, disease avoidance, and grooming. Recent studies have documented immune behaviors in foraging pollinators, as well as the impacts of such behaviors on flower visitation. Because pollinator parasites can affect flower choice and pollen dispersal, they may ultimately impact flower fitness. Here, we discuss how pollinator immune behaviors and floral traits may affect the presence and transmission of pollinator parasites, as well as how pollinator parasites, through these immune behaviors, can impact plant-pollinator interactions. We further discuss how pollinator immune behaviors can impact plant fitness, and how floral traits may adapt to optimize plant fitness in response to pollinator parasites. We propose future research directions to assess the role of pollinator parasites in plant-pollinator interactions and evolution, and we propose better integration of the role of pollinator parasites into research related to pollinator optimal foraging theory, floral diversity and agricultural practices.

Honey bee colony performance and health are enhanced by apiary proximity to US Conservation Reserve Program (CRP) lands

Honey bee colony performance and health are intimately linked to the foraging environment. Recent evidence suggests that the US Conservation Reserve Program (CRP) has a positive impact on environmental suitability for supporting honey bee apiaries. However, relatively little is known about the influence of habitat conservation efforts on honey bee colony health. Identifying specific factors that influence bee health at the colony level incorporates longitudinal monitoring of physiology across diverse environments. Using a pooled-sampling method to overcome individual variation, we monitored colony-level molecular biomarkers during critical pre- and post-winter time points. Major categories of colony health (nutrition, oxidative stress resistance, and immunity) were impacted by apiary site. In general, apiaries within foraging distance of CRP lands showed improved performance and higher gene expression of vitellogenin (vg), a nutritionally regulated protein with central storage and regulatory functions. Mirroring vg levels, gene transcripts encoding antioxidant enzymes and immune-related proteins were typically higher in colonies exposed to CRP environments. Our study highlights the potential of CRP lands to improve pollinator health and the utility of colony-level molecular diagnostics to assess environmental suitability for honey bees.