Phylogenetic and Morphological Analysis of Birch Mice (Genus Sicista, Family Sminthidae, Rodentia) in the Kazak Cradle with Description of a New Species

Birch mice (genus Sicista) represent an early diverging lineage of dipodid rodents with a wide geographic distribution and a cryptic lifestyle that makes the genus difficult to study. As a result, reconstructing the evolutionary phylogeny of the group remains incomplete. Here, we report the molecular phylogeny of the genus based on mitochondrial and nuclear markers sampled from 12 of the 14 known living species. Moreover, we discuss morphological character (i.e., fur coloration and glans penis morphology) evolution in the genus. We have found a strong agreement between phylogenetic relationships among species and morphological peculiarities, both supporting a mountainous origin of Sicista, and a recent spread towards lowlands of some lineages. Glans penis structure turned out to be rather simple in the early lineages, but became more complex in phylogenetically later diverging taxa. The presence of dorsal stripes is associated with the colonization of lowland habitats. In addition, we describe here a species new to science from the Tien Shan Mountains, and provide evidence of uncovered cryptic diversity from the region. Additionally, we revise the identification of a specimen collected from China, thus documenting the presence of Sicista pseudonapaea, previously unreported from that country.