Comparative phylogeography of five bumblebees: impact of range fragmentation, range size and diet specialization

Abstract

We characterised the phylogeographic patterns displayed by five species of bumblebees with largely overlapping ranges in Eurasia, but different levels of range fragmentation, range size and food specialization. Genetic variation across the range of each species was explored by using sequence variation of a total of 368 specimens at one mitochondrial and two nuclear DNA fragments (total of ~2380 bp). Comparing patterns of genetic variation across species allowed us to investigate whether diet specialization, relative range size and/or fragmentation, impact phylogeographic patterns in bumblebees. As expected, stronger fragmentations of the species range are associated with a stronger overall geographic differentiation. Furthermore, diet specialization appears to increase population structure at the landscape level, presumably due to the less widespread and more heterogeneously distributed food resources. Conversely, no clear association was highlighted between diet specialization or overall range size and genetic diversity. Surprisingly, the two generalist and co-distributed species investigated, B. pratorum and B. hortorum, displayed widely divergent patterns in terms of genetic diversity and population structure. We suggest these differences are best explained by contrasting responses to past climate changes, possibly involving different glacial refuges. Overall, our results are compatible with a combined impact of two interacting parameters on intraspecific genetic variation: environment disturbances (presumably related to past climate changes) and features specific to the organism, such as diet specialization. They thus further highlight the challenge of dissociating both parameters in phylogeographic studies.