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Contact zones and ranges of chromosomal races of the common Shrew, Sorex araneus, in north-eastern European Russia

Abstract. 
 The common shrew is a major evolutionary model for understanding the factors that lead to chromosomal subdivision; it is one of the most chromosomally variable species. We karyotyped 106 common shrews (Sorex araneus) from 24 localities in north-eastern European Russia which we showed to belong to five chromosomal races: Kirillov, Manturovo, Petchora, Serov and Sok. These new data were combined with published results on 146 individuals from 55 localities (with three additional races: Kanin, Yagry and Yuryuzan) to provide a substantive analysis of chromosomal variation in this region. The ranges of the eight races were mapped, the areas of contacts between neighbouring races were determined and new interracial hybrid zones were localised. In total, F1 hybrid karyotypes were found in 22 individuals from 11 localities; including our demonstration of Manturovo-Petchora, Manturovo-Sok, Petchora-Serov, Petchora-Sok and Serov-Sok F1 hybrid karyotypes for the first time. These hybrids would be expected to produce ring-of-four, ring-of-six or ring-of-eight meiotic configurations. The distribution of the races could not readily be related to environmental or geographic features, and in particular major rivers did not appear important in separation of races. This represents one of the most detailed studies of chromosomal variation in the common shrews at a regional geographic scale and is of especial significance because north-eastern European Russia has been little affected by human activity, and therefore the results are likely to represent fully natural processes.