Karyotypic races of the common shrew (Sorex araneus) with exceptionally large ranges: The Novosibirsk and Tomsk races of Siberia

Altogether 419 common shrews comprising 38 samples from 36 geographically-distinct sites in Siberia have been categorised as belonging to either the Novosibirsk karyotypic race (XX/XY1Y2, af, bc, g/o, hn, ik, j/l, m/p, q/r, tu) or the neighbouring Tomsk karyotypic race (XX/XY1Y2, af, bc, g/k, hi, j/l, mn, o, p, q/r, tu). The most notable Robertsonian polymorphism was that for arm combination qr present in both races that may reflect introgression after contact of the ancestral Novosibirsk race (fixed for metacentric qr) and the ancestral Tomsk race (fixed for acrocentrics q, r) at the end of the last glaciation. The Novosibirsk race occurs over a huge area (estimated at 700,000 km(2)) and is one of the most widespread karyotypic forms in S. araneus. Together with rather less extensive Tomsk race, these two races occupy much of the range of the species to the east of the Ural Mts. We discuss how the distributions of the Novosibirsk and Tomsk races were attained, in the context of the Pleistocene-Holocene transition.