The clinal variation of metacentric frequency in the populations of the common shrew, Sorex araneusL., in the Dnieper and Pripyat interfluve

The common shrew, Sorex araneus, is characterized by an exclusive polymorphism for Robertsonian translocations. Karyotypes of more than 70 chromosomal races of S. araneusdiffer from each other in composition and number of metacentrics resulting from Rb translocations which involve ten pairs of acrocentric chromosomes. The karyotype with ten pairs of acrocentric chromosomes is regarded as the initial in evolution of this species. Such acrocentric karyotype is characteristic of two chromosomal races in mountain isolates. Shrews with acrocentric karyotype have not been detected in polymorphic populations of Europe. Analysis of the chromosome polymorphism of the S. araneusin the Dnieper–Pripyat interfluve has demonstrated frequency clines for the specific metacentrics of three chromosomal races, namely the Białowieża, Kiev, and West Dvina races. The individuals with ten acrocentric chromosome pairs were revealed for the first time in the polymorphic populations in the terminal cline parts of the Kiev and West Dvina races and in contact zone between the Białowieża and Kiev races. Two hypotheses are being discussed to explain the clinal variation of the frequency of three race metacentrics: (1) “acrocentric peak” in contact zone of metacentric races and (2) hybridization between the metacentric races and the acrocentric race which might exist in the Dnieper basin in the past.