Structure of the Hybrid Zone between Allied Species of the Common Vole, Microtus arvalis and M. obscurus: Influence of Genetic Factors and Landscape-Geographical Conditions

Patterns of introgression of several genetic markers across the hybrid zone between allied species of the common vole Microtus arvalis s. str. and M. obscurus was studied in four of its sections: in northwest Nizhny Novgorod oblast, east Vladimir and southwest Nizhny Novgorod oblasts, south Lipetsk oblast, and northwest Voronezh oblast. Analysis of the clinal variability for three molecular genetic markers (cytb, tp53, SMCY11) and for karyotypes showed a structural similarity between the “Vladimir–Nizhny Novgorod,” “Nizhny Novgorod,” and “Voronezh” sections. The maximum width was shown for the cytb cline; the minimum width was shown for the SMCY11 cline; the tp53 cline and chromosomal cline occupy an intermediate position for this parameter. Furthermore, in these transects, the center of the cline for the cytb is shifted southeastward (into the distribution range of M. obscurus) from the centers of three other clines. The revealed asymmetric introgression of mitochondrial genome from M. arvalis to M. obscurus may be explained by the fact that the hybrid zone was formed as a result of invasion of M. obscurus into the range of M. arvalis. The “Lipetsk” transect differs from the three above-mentioned transects in very narrow clines with nearly coinciding centers. Such characteristics of the “Lipetsk” transect are obviously caused by localization of the hybrid zone in this section along Voronezh River. The obtained results led us to suppose that the structure of the studied hybrid zone is determined mainly by coincidence (or noncoincidence) of its center with local physical barriers.