Abstract
Land-use changes have threatened populations of many insect pollinators, including bumble bees. Patterns of dispersal and gene flow are key determinants of species' ability to respond to land-use change, but have been little investigated at a fine scale (<10 km) in bumble bees. Using microsatellite markers, we determined the fine-scale spatial genetic structure of populations of four common Bombus species (B. terrestris, B. lapidarius, B. pascuorum and B. hortorum) and one declining species (B. ruderatus) in an agricultural landscape in Southern England, UK. The study landscape contained sown flower patches representing agri-environment options for pollinators. We found that, as expected, the B. ruderatus population was characterized by relatively low heterozygosity, number of alleles and colony density. Across all species, inbreeding was absent or present but weak (FIS = 0.01–0.02). Using queen genotypes reconstructed from worker sibships and colony locations estimated from the positions of workers within these sibships, we found that significant isolation by distance was absent in B. lapidarius, B. hortorum and B. ruderatus. In B. terrestris and B. pascuorum, it was present but weak; for example, in these two species, expected relatedness of queens founding colonies 1 m apart was 0.02. These results show that bumble bee populations exhibit low levels of spatial genetic structure at fine spatial scales, most likely because of ongoing gene flow via widespread queen dispersal. In addition, the results demonstrate the potential for agri-environment scheme conservation measures to facilitate fine-scale gene flow by creating a more even distribution of suitable habitats across landscapes.
Highlights
Land-use change and the consequent loss and degradation of habitats have fragmented the ranges of many insect pollinator species, leading to significant declines in population size and an increased risk of extinction (Potts et al 2010)
There is a need for analyses of fine-scale population structure in intensively managed environments, to determine to what extent these schemes affect landscape connectivity and gene flow in both common and vulnerable species. We addressed these issues by conducting a genetic study of five social species of bumble bee (B. terrestris, B. lapidarius, B. pascuorum, B. hortorum and B. ruderatus) across an agricultural landscape in Southern England, UK
We tested the hypotheses that (i) the declining species (B. ruderatus) shows reduced genetic diversity and higher levels of inbreeding than the common species; and (ii) related queens do not tend to nest in proximity to one another at fine spatial scales
Summary
Land-use change and the consequent loss and degradation of habitats have fragmented the ranges of many insect pollinator species, leading to significant declines in population size and an increased risk of extinction (Potts et al 2010). Bumble bees (Bombus spp.) are important pollinators of a range of native plant species and commercial crops and contribute significantly to global crop yields and the persistence of plant communities (Potts et al 2010; Garratt et al 2014) Evidence suggests that they have declined in abundance and range size across Europe and North America in recent decades (Cameron et al 2011). As many bumble bees nest under or at ground level, nesting sites are vulnerable to intensive land management practices (Lye et al 2009; Carvell et al 2011)
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