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The mandible shape of the common vole semi-species from the hybrid zone was studied for the first time using the methods of geometric morphometry. The hybrid specimens were found to display high morphological variability being closer to the parental Microtus obscurus than to M. arvalis form. The main trends of changes in the mandible shape were primarily observed in the horizontal plane.

The skulls of shrews of genus Sorex from eight samplings from the European part of Russia and two from the vicinity of Novosibirsk were compared. The characteristics were identified using 22 marks on the axial skull. It was found that the centroid size differs significantly in the common and Laxmann's shrews S. caecutens and the pygmy shrew S. minutus, while for selected marks, the common and Laxmann's, as well as pygmy, shrews were significantly different in form, but the differences were very small between Laxmann's and pygmy shrews. The characteristic features of the biology of the shrews Sorex are discussed, which may contribute to understanding the general laws of the morphological evolution of the genus.

The contact points of four karyotypic races (St. Petersburg, Moscow, Seliger and West Dvina) of the common shrew Sorex araneus L. were studied at the Valdai Hills (European Russia) in an area unimpeded by geographic barriers. The populations of the races are separated by narrow hybrid zones that represent the most complex heterozygous hybrid karyotypes. At these points of contact, the morphometric differentiation of karyotype races was examined in 12 cranial measurements in 190 shrews of a known karyotype. A. comparison of the mean values in studied samples of immature shrews revealed statistically significant differences and the correlation of some measurements in order to describe the level of musculus temporalis. It has been proposed that morphometric differences in the karyotypic races were preserved and accumulated because of a 50% reduction of the frequencies of hybrids. The deviation from the Hardy-Weinberg ration in the frequencies of the genotype and haploid sets of chromosomes in the hybrid zones can be attributed to a number of fatalities of hybrid embryos or the nonrandom mating of karyotypic races. The ethological isolation might arise in the evolution of some karyotypic races from the reduced fitness of the hybrids.

The contact zone between Moscow and Western Dvina chromosomal races of common shrew Sorex araneus L. at the south of the Valdai Hights was traced over a distance of 20 km. Within this, close to parapatric, contact zone of chromosomal races the width of sympatry zone was about 500 m (the narrowest among currently known hybrid zones), and the proportion of hybrids was 24.3%. It was shown that in bimodal hybrid zones between chromosomal races of common shrew the width of sympatry zones varied from 0.5 to 13 km. This width does not correlate with the cytogenetic features of the hybrids, and seems to be determined by competitive relations between the races. The hybrid proportion is determined by the type of hybrid heterozygosity, and decreased in the race sympatry zone from 33-40 to 21.5-25.2%. The decrease of the hybrid proportion can be associated with the abnormal fertility of either the first generation, or the backcross hybrids.