干旱区生态环境知识资源中心

New data are presented on the distribution of two chromosome races of the common shrew (Sorex araneus L.), namely, at Nerussa and near Penza, in the Oka and Tsna interfluve where loesses were accumulated during the Late Glacial Maximum (LGM, 24-17 Kyr. B.P.). A zone of contact and hybridization between the Nerussa and Penza races has been revealed off the left bank of Tsna River. In the study part of the contact zone, the populations of these races are isolated by the small river Aza, a tributary of the Tsna, 10-15 m in width, and their distribution across the river appears to be close to parapatric. Rivers fail to hamper the spread of common shrew populations, but even a small river may serve as an important isolation barrier in the area of contact between the populations of different races. It seems quite probable that even an insignificant barrier affects the dispersal mode of the populations and prevents the migration of individuals of either race into the territory of the other race. The influence of loess accumulation and wind-deposited sands (in the LGM) on the formation of present-day distributions of the chromosome races is discussed. The distribution area of the ancestral populations of the identical Mologa and Penza races could have become disjunct in such an arid territory during the LGM, and populations of the Moscow race might have colonized this territory during the postglacial period.