Specific features of hybrid zones of chromosomal races of the common shrew, Sorex araneus L., at different levels of karyotypic divergence

Narrow hybrid zones of three monomorphic chromosomal races of the common shrew, Sorex araneus, differing from each other by 3 - 4 diagnostic Robertsonian translocations, were revealed in the north of Tver Region. Localization of these hybrid zones follows marginal formation of the Veps stage glacier. A small width of hybrid zones (0,5 - 2,5 km) is determined by a small area of co-habitation of these karyotypically diverged races, which is caused, probably, by concurrent relations between them. Diagnostic metacentrics of the West Dvina race, which is monomorphic from the Valdai to the Smolensk Heights, were noted in populations of the Borisov race on the territory of Belarus (specific feature of this race is the absence of metacentric ip trait for the West Dvina race). A cline variability of the diagnostic metacentric frequencies, decreasing towards the Dnieper and Pripyat junction, was noted in populations of the Borisov and Bialowieza races on the territory of Belarus. A high acrocentric frequency near the hybrid zone between populations with diagnostic metacentrics of the Bialowieza race and the Kiev race was noted. The specific features of the polymorphic populations at the Dnieper and Pripyat junction can be explained by the existence in the past on the mentioned area the common shrew populations with completely acrocentric karyotype. Karyotype with all the diagnostic chromosomes represented by acrocentrics, regarded as primary in the evolution of S. araneus, was revealed in a number of polymorphic populations in the discussed region