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The nucleotide sequence (572 bp) of the cytochrome b gene of the common shrew Sorex araneus was analyzed. In total, 92 animals of five chromosome races from 12 localities were studied. The median haplotype network has a pronounced star-like structure. The central haplotype common for all samples, except for the southern island sample of the race Sok, accounts for about 36%. The main characteristics of molecular variation in our work correspond to those obtained in other studies. We revealed the lack of a correlation between the genetic and geographic distances and also population structurization of the species. On the basis of variation of the haplotypes in the samples, a scenario of colonization of the postglacial territories by females of one or several close matrilines with subsequent rapid subdivision of the population into independent populations is discussed.

Variability of the cranial properties of chromosomal races Serov, Manturovo and Pechora of the common shrew were studied. A consistent increase of scull size in the Serov race with moving from the plain to highlands and a skull size decrease from low to high latitudes was detected. Interpopulation variability among different races was shown to be comparable with interracial variability or to exceed it. This suggests microevolution at the level of local populations.

Combination of different dispersal modes may itself, without external obstacles, lead to the appearance of subdivided populations and maintain the existence of independent population systems. The common shrew, a mammal convenient for studying different levels of intraspecific differentiation, was the object of the study. Empirical data have been used for simulation taking into account the change of dispersal modes in the population area. The obtained results agree with empirical data on the distribution of races and hybrids in the hybrid zone of chromosome races Moscow and Seliger. Change of the dispersal mode may maintain independent population dynamics and, in the case of chromosome races, prevent the migration of parental individuals into the territory of the other race.

Two chromosome races of common shrew, Moscow and Seliger, differ in the arm combination in 11 diagnostic chromosomes (Robertsonian metacentrics/acrocentrics). Homozygotes of both pure races, simple Robertsonian heterozygotes of Seliger race, and complex heterozygotes (FI hybrids) were detected in the found earlier between hybrid zone of these races, in the spring before the breeding seasonbreeding season. The g/oheterozygote was first discovered in race Seliger, whose chromosome formula typically contains acrocentrics g and o. The m/q heterozygote was recorded for the second time. Meiosis was studied in 16 males representing five detected karyotypic categories. No abnormal in pairing of homologs in either sex trivalent common for the species (XY1Y2) or autosome trivalents (g/o and m/q) was detected at diakinesis--metaphase I. Two hybrids displayed a theoretically expected and unimpaired meiotic configuration in a form of a very long chain comprising 11 monobrachial homologs (g/gm/mq/qp/pr/rk/ki/ih/hn/no/o). The results are discussed in terms of hypotheses on fertility of complex heterozygotes and limited gene flow in hybrid zone.

A karyological analysis of three species of South American field mice of the genus Akodon from four different localities of the Department of Tarija, Bolivian Republic, was performed. In Akodon simulator, 2n = 40 - 42, NFa = 42. The variation of the diploid number is caused by a polymorphism of the Robertsonian type involving six pairs of acrocentric chromosomes. Five variants of karyotypes were revealed. The chromosome set of A. sp. has 2n = 36, NFa = 40; in A. toba, 2n = 42 - 43, NFa = 44 - 46. The variation of the diploid number and the number of autosomal arms is caused by the polymorphism of the first autosomal pair. A comparative karyological analysis of A. simulator, A. sp., and A. toba revealed a high level of similarity of all karyotypic elements. Fifteen autosomal pairs of these three species have identical G-banding patterns; the others are involved in formation of larger chromosomes, representing one possible combination of the same chromosomal material. The set of rearrangements is limited only to tandem chromosome fusions.