Molecular genetic evidence of a deep phylogenetic discontinuity between the asian and european races of pygmy wood mouse based on the mitochondrial cytochrome b gene variation

The variation of mitochondrial DNA (mtDNA) cytochrome b gene sequences of pygmy wood mouse Sylvaemus uralensis (Pallas, 1811) from local populations of European Russia, West Siberia, and neighboring countries (Moldova, Kazakhstan, Uzbekistan, and Turkmenistan) has been studied. Phylogenetic analysis based on our results and GenBank data revealed two clusters of haplotypes: the Western clade, which was reliably subdivided into two sequence groups, and the Eastern clade with no significant differentiation. The clusters corresponded exactly to the European and Asian races of pygmy wood mouse recognized previously on the basis of biochemical and karyotypic variation. We suppose that the Asian race can be considered as an independent allopatric species. This concept is supported by the following evidence: the high interrace divergence level suggesting more than 1 Ma of divergent evolution, the absence of common haplotypes and the hiatus between the main peaks of the mismatch distribution, difference in the codon usage frequencies, fixed nucleotide substitutions in cyt b, as well as different amino acid sequences of cytochrome b. Only specimens of the western phylogenetic lineage should be classified as S. uralensis (Pallas, 1811), while S. tokmak, according to its first description (Severtsov, 1873), may be considered as the species uniting specimens of the eastern phylogenetic lineage.