Genetic variability of the cold-tolerant Microtus oeconomus subspecies left behind retreating glaciers

The current range of the root vole (Microtus oeconomus) in Europe has been shaped by climate changes, including the last glaciation. In Central Europe there are two isolated subspecies: M. oeconomus mehelyi and M. oeconomus arenicola occurring in the Pannonian lowland and the Netherlands respectively. M. oeconomus stimmingi is present in the northern part of Central Europe in the continuous range of the species distribution. To establish the influence of the postglacial isolation on the subspecies performance, we sampled 192 individuals at seven sites from the three geographic regions. Individuals were genotyped at 14 microsatellite loci highly polymorphic for all subspecies studied. This is the first extensive research presenting the diversity of M. oeconomus mehelyi from Central Europe at the molecular level. Its genetic diversity (Ar = 6.6, SD = 0.4) as well as effective population size (LDNe = 170, SD = 62) were significantly lower than in the other two subspecies, their average Ar = 7.6, SD = 0.2 and LDNe = 504, SD = 134, suggesting M. oeconomus mehelyi is most threatened with extinction. None of the subspecies showed significant genetic bottleneck signatures. The differential analysis of the genetic structure of various subgroups resulting from clustering analysis was performed to reveal the genetic relationships among individuals within and between geographic regions. We found a closer relation of M. oeconomus stimmingi with each of the isolated subspecies than between them. Moreover, we detected a clear substructure in Pannonian M. oeconomus (two subgroups), that could result from more than one colonization episode.