Isoenzyme variation in the common shrew (Sorex araneus) in Britain, in relation to karyotype.

Samples of common shrews with an Aberdeen race, Oxford race and Hermitage race karyotype and from the Oxford-Hermitage hybrid zone were screened for genotype at six polymorphic enzyme loci. The common allele at all loci was the same in all samples suggesting that the degree of genic divergence between the karyotypic races is not great. However, shrews of the Aberdeen race appear to be somewhat distinct. There were differences in allele frequencies, range of alleles and heterozygosities at the Mpi-1, Pgm-2 and Pgm-3 loci between the Aberdeen race samples and samples of other karyotypic categories. The allele frequency variation across the Oxford-Hermitage hybrid zone is not substantially linked with karyotype frequency change, but there is notable allele frequency variation between close sites of similar habitat, particularly at the Pgm-2 and Pgm-3 loci. This suggests that gene flow between close sites may be reduced sufficiently in some instances to allow allele frequency change by genetic drift. This may have implications for the mode of origin of karyotypic races of common shrew.