Molecular phylogeny of the species vole genus Microtus (Arvicolinae, Rodentia) inferred from mitochondrial DNA sequences

Voles of the genusMicrotus represent one of the most speciose mammalian genera in the Holarctic. We established a molecularphylogeny for Microtus to resolve contentious issues of systematic relationships and evolutionary history in this genus. A total of 81 specimens representing ten Microtusspecies endemic to Europe as well as eight Eurasian, six Asian and one Holarctic species were sequenced for the entire cytochrome b gene (1140 bp). A further 25 sequences were retrieved from GenBank, providing data on an additional 23, mainly Nearctic, Microtusspecies. Phylogenetic analysis of these 48 species generated four well-supported monophyletic lineages. The genusChionomys, snow voles, formed a distinct and well-supported lineage separate from the genusMicrotus. The subgenus Microtus formed the strongest supported lineage with two sublineages displaying a close relationship between the arvalisspecies group (common voles) and the socialisspecies group (social voles). Monophyly of the Palearctic pitymyid voles, subgenus Terricola, was supported, and this subgenus was also subdivided into two monophyletic species groups. Together, these groupings clarify long-standing taxonomic uncertainties in Microtus. In addition, the "Asian" and the Nearctic lineages reported previously were identified although the latter group was not supported. However, relationships among the main Microtus branches were not resolved, suggesting a rapid and potentially simultaneous radiation of a widespread ancestor early in the history of the genus. This and subsequent radiations discernible in the cytochrome bphylogeny, show the considerable potential of Microtus for analysis of historical and ecological determinants of speciation in small mammals. It is evident that speciation is an ongoing process in the genus and that the molecular data provides a vital insight into current species limits as well as cladogenic events of the past.