Urbanization is a global phenomenon with major effects on species, the structure of community functional traits and ecological interactions. Body size is a key species trait linked to metabolism, ...life‐history and dispersal as well as a major determinant of ecological networks. Here, using a well‐replicated urban–rural sampling design in Central Europe, we investigate the direction of change of body size in response to urbanization in three common bumblebee species, Bombus lapidarius, Bombus pascuorum and Bombus terrestris, and potential knock‐on effects on pollination service provision. We found foragers of B. terrestris to be larger in cities and the body size of all species to be positively correlated with road density (albeit at different, species‐specific scales); these are expected consequences of habitat fragmentation resulting from urbanization. High ambient temperature at sampling was associated with both a small body size and an increase in variation of body size in all three species. At the community level, the community‐weighted mean body size and its variation increased with urbanization. Urbanization had an indirect positive effect on pollination services through its effects not only on flower visitation rate but also on community‐weighted mean body size and its variation. We discuss the eco‐evolutionary implications of the effect of urbanization on body size, and the relevance of these findings for the key ecosystem service of pollination.
The origin of eusociality is often regarded as a change of macroevolutionary proportions 1, 2. Its hallmark is a reproductive division of labor between the members of a society: some individuals ...(“helpers” or “workers”) forfeit their own reproduction to rear offspring of others (“queens”). In the Hymenoptera (ants, bees, wasps), there have been many transitions in both directions between solitary nesting and sociality 2–5. How have such transitions occurred? One possibility is that multiple transitions represent repeated evolutionary gains and losses of the traits underpinning sociality. A second possibility, however, is that once sociality has evolved, subsequent transitions represent selection at just one or a small number of loci controlling developmental switches between preexisting alternative phenotypes 2, 6. We might then expect transitional populations that can express either sociality or solitary nesting, depending on environmental conditions. Here, we use field transplants to directly induce transitions in British and Irish populations of the sweat bee Halictus rubicundus. Individual variation in social phenotype was linked to time available for offspring production, and to the genetic benefits of sociality, suggesting that helping was not simply misplaced parental care 7. We thereby demonstrate that sociality itself can be truly plastic in a hymenopteran.
► Transplanting sweat bees between field sites reveals cryptic social plasticity ► Social phenotype responds adaptively to environmental conditions ► Switching between phenotypes could help some sweat bees to accommodate global warming
Adaptation to local host plants may impact a pollinator's population genetic structure by reducing gene flow and driving population genetic differentiation, representing an early stage of ecological ...speciation. South African Rediviva longimanus bees exhibit elongated forelegs, a bizarre adaptation for collecting oil from floral spurs of their Diascia hosts. Furthermore, R. longimanus foreleg length (FLL) differs significantly among populations, which has been hypothesised to result from selection imposed by inter-population variation in Diascia floral spur length. Here, we used a pooled restriction site-associated DNA sequencing (pooled RAD-seq) approach to investigate the population genetic structure of R. longimanus and to test if phenotypic differences in FLL translate into increased genetic differentiation (i) between R. longimanus populations and (ii) between phenotypes across populations. We also inferred the effects of demographic processes on population genetic structure and tested for genetic markers underpinning local adaptation. RESULTS: Populations showed marked genetic differentiation (average F
= 0.165), though differentiation was not statistically associated with differences between populations in FLL. All populations exhibited very low genetic diversity and were inferred to have gone through recent bottleneck events, suggesting extremely low effective population sizes. Genetic differentiation between samples pooled by leg length (short versus long) rather than by population of origin was even higher (F
= 0.260) than between populations, suggesting reduced interbreeding between long and short-legged individuals. Signatures of selection were detected in 1119 (3.8%) of a total of 29,721 SNP markers, CONCLUSIONS: Populations of R. longimanus appear to be small, bottlenecked and isolated. Though we could not detect the effect of local adaptation (FLL in response to floral spurs of host plants) on population genetic differentiation, short and long legged bees appeared to be partially differentiated, suggesting incipient ecological speciation. To test this hypothesis, greater resolution through the use of individual-based whole-genome analyses is now needed to quantify the degree of reproductive isolation between long and short legged bees between and even within populations.
Abstract
To accommodate an ever-increasing human population, agriculture is rapidly intensifying at the expense of natural habitat, with negative and widely reported effects on biodiversity in ...general and on wild bee abundance and diversity in particular. Cities are similarly increasing in area, though the impact of urbanisation on wild bees is more equivocal and potentially positive in northern temperate regions. Yet agriculture and urbanisation both lead to the loss and alteration of natural habitat, its fragmentation, a potential reduction in floral availability, and warmer temperatures, factors thought to be drivers of wild bee decline. They have also been shown to be factors to which wild bee populations respond through morphological change. Body size is one such trait that, because of its relation to individual fitness, has received growing attention as a morphological feature that responds to human induced modification in land use. Here, we investigated the change in body size of two sympatric orchid bee species on the Yucatan Peninsula of Mexico in response to urbanization and agricultural intensification. By measuring 540 male individuals sampled from overall 24 sites, we found that
Euglossa dilemma
and
Euglossa viridissima
were on average smaller in urban and agricultural habitats than in natural ones. We discuss the potential role of reduced availability of resources in driving the observed body size shifts. Agricultural and urban land management in tropical regions might benefit wild bees if it encompassed the planting of flowering herbs and trees to enhance their conservation.
The sweat bees (Family Halictidae) are a socially diverse taxon in which eusociality has arisen independently numerous times. The obligate, primitively eusocial Lasioglossum malachurum, distributed ...widely throughout Europe, has been considered the zenith of sociality within halictids. A single queen heads a colony of smaller daughter workers which, by mid‐summer, produce new sexuals (males and gynes), of which only the mated gynes overwinter to found new colonies the following spring. We excavated successfully 18 nests during the worker‐ and gyne‐producing phases of the colony cycle and analysed each nest's queen and either all workers or all gynes using highly variable microsatellite loci developed specifically for this species. Three important points arise from our analyses. First, queens are facultatively polyandrous (queen effective mating frequency: range 1–3, harmonic mean 1.13). Second, queens may head colonies containing unrelated individuals (n= 6 of 18 nests), most probably a consequence of colony usurpation during the early phase of the colony cycle before worker emergence. Third, nonqueen's workers may, but the queen's own workers do not, lay fertilized eggs in the presence of the queen that successfully develop into gynes, in agreement with so‐called ‘concession’ models of reproductive skew.
Understanding population genetic structure is key to developing predictions about species susceptibility to environmental change, such as habitat fragmentation and climate change. It has been ...theorized that life‐history traits may constrain some species in their dispersal and lead to greater signatures of population genetic structure. In this study, we use a quantitative comparative approach to assess if patterns of population genetic structure in bees are driven by three key species‐level life‐history traits: body size, sociality, and diet breadth. Specifically, we reviewed the current literature on bee population genetic structure, as measured by the differentiation indices Nei's GST, Hedrick's G′ST, and Jost's D. We then used phylogenetic generalised linear models to estimate the correlation between the evolution of these traits and patterns of genetic differentiation. Our analyses revealed a negative and significant effect of body size on genetic structure, regardless of differentiation index utilized. For Hedrick's G′ST and Jost's D, we also found a significant impact of sociality, where social species exhibited lower levels of differentiation than solitary species. We did not find an effect of diet specialization on population genetic structure. Overall, our results suggest that physical dispersal or other functions related to body size are among the most critical for mediating population structure for bees. We further highlight the importance of standardizing population genetic measures to more easily compare studies and to identify the most susceptible species to landscape and climatic changes.
Urbanization is considered a global threat to biodiversity; the growth of cities results in an increase in impervious surfaces, soil and air pollution, fragmentation of natural vegetation and ...invasion of non-native species, along with numerous environmental changes, including the heat island phenomenon. The combination of these effects constitutes a challenge for both the survival and persistence of many native species, while also imposing altered selective regimes. Here, using 110 314 single nucleotide polymorphisms generated by restriction-site-associated DNA sequencing, we investigated the genomewide effects of urbanization on putative neutral and adaptive genomic diversity in a major insect pollinator, Bombus lapidarius, collected from nine German cities and nine paired rural sites. Overall, genetic differentiation among siteswas lowand therewas no obvious genome-wide genetic structuring, suggesting the absence of strong effects of urbanization on gene flow. We nevertheless identified several loci under directional selection, a subset of which was associated with urban land use, including the percentage of impervious surface surrounding each sampling site. Overall, our results provide evidence of local adaptation to urbanization in the face of gene flow in a highly mobile insect pollinator.
There is concern about the worldwide decline of bees, in which genetic factors may play a role. As populations of these haplodiploid insects suffer habitat fragmentation and subsequent isolation, ...theory predicts an increase in inbreeding and a concomitant increase in inviable or sterile diploid males, a product of reduced allelic diversity at the sex determining locus, which could lead to a diploid male extinction vortex. To test this idea, we genotyped 1,245 males of one orchid bee, Euglossa cordata, a species with low diploid male production on the mainland. We genotyped bees from the Brazilian mainland and three islands using five highly variable microsatellite loci. Allelic richness was lowest on the most remote island 38 km from the mainland and, though the degree of differentiation across localities was modest (global FST = 0.034; global Formula: see text, both P < 0.001) and isolation by distance was weak (Mantel test, r = 0.614, P = 0.056), sea was revealed to be a significant barrier to inferred historic gene flow (partial Mantel test of distance over sea, r = 0.831, P = 0.003). Only seven males were diploid (mean diploid male production, DMP, 0.6 %). Though the proportion of diploid males was highest on the most remote island (1.3 %), differences in DMP across study areas were statistically non-significant. Thus island isolation leads to reduced genetic variation at putatively neutral microsatellite loci, but E. cordata nevertheless seems to maintain allelic diversity at the sex locus, possibly because of sufficient gene flow, or because it is a locus under balancing selection, or because of the joint action of these two evolutionary forces: migration and selection. These and other bee species may be able to maintain sufficient variability at the sex locus to avoid entering the DM extinction vortex, even on relatively isolated islands or habitat fragments.
Phenotypic plasticity may evolve when conditions vary temporally or spatially on a small enough scale. Plasticity is thought to play a central role in the early stages of evolutionary transitions, ...including major transitions such as those between non-sociality and sociality. The sweat bee Halictus rubicundus is of special interest in this respect, because it is socially plastic in the British Isles: Nests are social or non-social depending on the environment. However, sociality comprises a complex suite of interrelated traits. To further investigate social plasticity in H. rubicundus, we measured traits that are potentially integral to social phenotype at a northern site, where nests are nonsocial, and a southern site where nests can be social. We found that foundresses at non-social sites were smaller, produced offspring of a size more similar to themselves, initiated nesting later, and took longer to produce their first female offspring. They began provisioning earlier in the day, finished earlier, and collected more pollen loads. Common garden experiments suggested that these differences represent mainly plasticity, as expected for traits involved in the overall plastic social phenotype, with only limited evidence for fixed genetic differences in foraging. Conditions during overwintering did not have major effects on a foundress' subsequent behaviour.
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