TO THE PROBLEM ON STABILITY AND VARIABILITY OF THE ROOT VOLE (MICROTUS OECONOMUS, RODENTIA, ARVICOLINAE), KARYOTYPE: AN ANALYSIS OF NEW RECORDS FROM EASTERN EUROPE

摘要

Karyotypes of 29 specimens of Microtus oeconomus from nine localities of its Holarctic area in Eastern Europe (Novgorod, Nizhny Novgorod, Kaluga, Moscow and Ryazan regions) were investigated using methods of differential staining of chromosomes (G-, AgNOR-banding). In Valdai district of Novgorod region, at the edge of the main massif of this species range in the Western Palaearctic, a polymorphic population (2n = 31, n = 2; 2n = 30, n = 6) was revealed. This polymorphic population is similar to that from isolates in Fennoscandia, but differs from the studied by the authors karyologically stable populations (2n = 30) in central parts of Eastern Europe (Nizhny Novgorod (n = 14), Kaluga (n = 1), Moscow (n = 3), Ryazan (n = 3) regions), as well as from the majority of other stable populations from Lapland to Alaska (2n = 30) investigated earlier. Using G-banding, the nature of the chromosomal rearrangement revealed in the M. oeconomus population at the edge of the main part of this species range in the Western Palaearctic (the centric fission of chromosome pair No 8 registered only in the heterozygotic state unlike isolated populations from Fennoscandia) was specified. In the Valdai Upland, in the peripheral root vole populations, as well as in the isolated populations in Fennoscandia, NOR-bearing pairs (AgNOR-banding) were shown not to participate in the formation and maintenance of the chromosomal polymorphism found. The revealed chromosomal polymorphism, which is responsible for the features of the population-genetic structure of this species, does not agree with the traditional view on the M. oeconomus intraspecific system. The obtained and generalized data on the stability and variability of the M. oeconomus karyotype in Eastern Europe that specify the mechanism and limits of distribution of the found chromosomal mutation in the species range are considered in the light of historical reconstructions, although some other hypotheses (the hypothesis of genome instability on the periphery of species area and the mutagen hypothesis) are also attracted to discuss the results.