ON GENE POOL DIVERGENCE OF THE 2 KARYOTYPICALLY DISTINCT SIBLING VOLESPECIES MICROTUS-ARVALIS AND MICROTUS-ROSSIAEMERIDIONALIS (ARVICOLIDAE, RODENTIA)

Gene-pool divergence between the two sibling vc,le species, Microtus a rvalis (2n=46) and M. rossiaemeridionalis (2n=56) was studied by horiz ontal starch gel electrophoresis of 23 enzyme-systems encoded by 29 st ructural gene loci. Five local samples of M. arvalis, encompassing thr ee nominal subspecies and one sample of M. rossiaemeridionalis, were s tudied. M. guentheri (2n=56), a closely related species, was used for comparison. Genetic distances between the two sibling species (N e i's 1978 unbiased D: mean=0.070, range=0.037-0.137) were generally rather low as compared to the values of intra-specific comparisons of M. arv alis (mean=0.039, range=0.005-0.094), the values calculated between M. arvalis and M. guentheri (mean=0.243, range 0.225-0.284) and those be tween M. rossiaemeridionalis and M, guentheri (0.184). Also, the degre e of partitioning of genetic variability was lower between the two sib ling species (F-ST=0.342) than within M. arvalis (F-ST=0.425 for the l ocal samples, and F-ST=0.450 for the three subspecies studied). This c ontrasts the pattern of karyotypic differences (particularly the diplo id chromosome numbers) encountered earlier in the three species. This suggests independence of genic and chromosome evolution in the studied species.