Structure of Baculum of Five Species of Mountain Voles of Subgenus Alticola Blanford, 1881

Mountain voles of genus Alticola (Rodentia) are common in mountainous regions of Central and Northeast Asia are relatively poorly studied, and some of them are included in regional Red Book. Regardless some progress to understand a taxonomic relationships within genus Alticola, some issues remain unexplored. This article presents data on the morphological features of baculum of five species of mountain voles from mountainous regions of southern Siberia (Tuva, Khakassia and Prebaikalia) and Mongolia (Lake Hovsgol). We studied the os penis of 27 vole specimens processed using the differential skeletal staining method. For metric analysis of the shape of the baculum, we applied the baculum index. Two pairs of species can be distinguished among those possessing the most similar baculum shapes: Tuva mountain vole A. tuvinicus tuvinicus and A. tuvinicus khubsugulensis first and A. semicanus and A. strelzowi second. The baculum of A. t. tuvinicus and A. t. khubsugulensis differ only in the shape of the medial process but the baculum of Mongolian mountain vole A. semicanus and flat-headed vole A. strelzowi is very similar and differs only in the shape of the "shoulder". The remaining two species are distinguished from the others by a single element. In Olkhon mountain vole A. olchonensis the baculum bone is similar in shape to A. t. tuvinicus, but differs by a noticeable curvature of the stem in the lateral projection, Gobi Altai mountain vole A. barakshin has a heart-shaped base. Among the studied baculums of mountain voles of the Alticola subgenus, it is difficult to identify any element by which the sexual ossicles differed radically from each other, which showed variability in shape and size in interpopulation variability at the speciesand subspecies-level. The results of our study of baculum morphology are consistent with the data on phylogenetic relationships within the Alticola genus. Species that are morphologically and genetically similar to each other have extremely similar form of baculum (Tuva and Olkhon voles), and species with species independence (Gobi Altai vole) have pronounced differences in this character.