Multi-Level Molecular Differentiation of Populations of the Strand’s Birch Mouse Sicista strandi (Rodentia, Dipodoidea)

Previous molecular studies have demonstrated significant differentiation of the Strand’s birch mouse (Sicista strandi) into two groups; differences between them are comparable with those observed between species. However, these studies were based on different, not numerous samples and the small number of individuals. To clarify the differentiation pattern and structure of the Strand’s birch mouse, we analyzed variability of the total mitochondrial cytb gene and the nuclear IRBP gene fragment using additional material on this species. Our results confirmed its division into two main genetically distinct forms: the northern form includes Strand’s birch mice from Belgorod and Kursk regions, while the southern form incorporates specimens from the Greater Caucasus as well as Rostov, Saratov, and Lugansk regions. In turn, within the southern form, moderate differences were first revealed by the cytb gene analysis between individuals from Rostov region and samples from the Greater Caucasus and Saratov region. One specimen from Belgorod region had the IRBP haplotypes, typical of this population, but an ‘alien’ mitotype, close to those of Strand’s birch mice from Rostov region. This result may indicate existence of a modern or ancient hybrid zone between the northern form and the ‘Don’ line of the southern form.