Riverine barriers and geographic variation in little ground squirrel Spermophilus pygmaeus (Sciuridae, Rodentia) based on mitochondrial cytochrome b gene sequences

Little ground squirrel (Spermophilus pygmaeus) typically inhabit semi-deserts and dry steppes of the European plains and Kazakhstan. Range-wide latitudinal distribution along with major river separation zones makes this species a proper model for testing the riverine barrier hypothesis. For the first time, we have evaluated genetic variation in little ground squirrel populations throughout its range based on the analysis of cytochrome b gene sequences. A high level of genetic diversity (4.9%) among "western" and "eastern" populations of the little ground squirrel has evidenced the Volga River to be an effective biogeographic barrier. A barrier role of the Ural River is expressed to a lesser extent, and the Don River has neither effect on the restriction to gene flow and phylogeographic structure. The genetic diversity data has confirmed the hypothesis on S. pygmaeus speciation in the long-term Ciscaucasia refugium, and the appearance of the mountain ground squirrel (S. p. musicus) in the Middle Pleistocene.