Structure of the hybrid zone between allied species of the common vole, Microtus arvalis and M. obscurus: Influence of genetic factors and landscape-geographic conditions

Patterns of introgression of several genetic markers across the hybrid zone between allied species of the common vole Microtus arvalis s. str. и M. obscurus were studied in four its sections: in northwest Nizhny Novgorod region, east Vladimir and southwest of Nizhny Novgorod regions, south Lipetsk region, and northwest Voronezh region. 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 maximal width was shown for the cytb cline, the minimal width – for the SMCY11 cline; the tp53 cline and chromosomal cline occupy intermediate position for this parameter. Furthermore, in these transects the centre of the cline for the cytb is shifted southeastward (into the distribution range of M. obscurus) from the centres 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 three above-mentioned transects by very narrow clines with nearly coinciding centres. Such characteristics of the “Lipetsk” transect are obviously caused by localization of the hybrid zone in this section along river Voronezh. The obtained results led us to suppose that the structure of the studied hybrid zone is determined mainly by coinciding (or non-coinciding) of its centre with local physical barriers.