Reconstruction of Pleistocene Evolutionary History of the Root Vole <em>Alexandromys oeconomus </em>(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 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. North Asian lineage occurred to be more diverse than the Beringian and both European lineages. Southern Siberia and especially the Altai-Sayan region displayed the highest haplotype and nucleotide diversity, suggesting the region&#039;s role as a genetic diversity hotspot. We suppose that expansion of the North Asian lineage started from Western Transbaikalia. Its representatives colonised the territory from 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 first A. oeconomus records, 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 the subsequent studies.