Morphometric difference between the Novosibirsk and Tomsk chromosome races of Sorex araneus in a zone of parapatry

A hybrid zone between the Novosibirsk and Tomsk chromosome races of the common shrew Sorex araneus Linnaeus, 1758 was found near Novosibirsk city (West Siberia, Russia) in an area unimpeded by geographic barriers. In this zone, the shrews of both races and their hybrids were trapped and karyotyped and 22 features of their cranial and postcranial skeleton were measured. Canonical discriminant analysis revealed 3 distinct groups of individuals, which corresponded to the 3 karyotypic categories involved in the analysis. The first discriminant function reflected the differences in the size of skeletal elements. The Novosibirsk shrews and the hybrids were significantly smaller than the Tomsk shrews. The second discriminant function was interpreted as a parameter of skeletal proportionality. The hybrids were signifi­cantly less proportional than the parental races. This study revealed one of the clearest examples of morphological differentiation between chromosome races of the common shrew.