Reconstruction of Pleistocene Evolutionary History of the Root Vole Alexandromys oeconomus (Cricetidae, Rodentia) in Northern Asia

Previous phylogeographic study of the root vole (Alexandromys oeconomus) revealed four mitochondrial cytochrome b lineages—North and Central European, North (=Central) Asian and Beringian. Three of them were studied in detail, while the North Asian lineage, which occupies the most extensive territory and is considered to be the place of origin for the species, was understudied. In the framework of the current study, we obtained 95 new sequences (34 localities) from the wide territory of Northern Asia and in total, examined 940 specimens from 181 localities throughout the species’ distribution range. The North Asian lineage was found to be more diverse than the Beringian and the European lineages. Southern Siberia and especially the Altai–Sayan region displayed the highest haplotype and nucleotide diversity, suggesting the region’s role as a genetic diversity hotspot. We suppose that the expansion of the North Asian lineage started from Western Transbaikalia. Its representatives colonised the territory from the Urals to the northern shore of the Okhotsk Sea, and then spread in the opposite direction, to Southern Siberia. As a result, a mixture of haplogroups is observed in the Altai–Sayan region. According to the BEAST analysis calibrated with the first A. oeconomus records, the MRCA of North Asian and Beringian lineages is dated back to ~0.82 Mya, and the first divergence within the North Asian lineage may have occurred ~0.6 Mya. When compared with colonisation times of other representatives of the Arvicolinae subfamily, our dating seems to be overestimated. In this regard, molecular data for dated fossil remains of the root vole are essential for subsequent studies.