CYTOGENETIC HOMEOSTASIS AND POPULATION-DENSITY IN RED-BACKED VOLES CLETHRIONOMYS-GLAREOLUS AND CHROOGOMPHUS-RUTILUS IN CENTRAL SIBERIA

We examined frequency of chromosome aberration in somatic cells in sym patric growing populations of bank vole Clethrionomys glareolus Schreb er, 1780 and ruddy vole C. rutilus Pallas, 1779 in central Siberia (Ye nisei river island, 62 degrees N, 89 degrees E) from 1992 to 1994. The island was reinhabited from the mainland populations in 1992 after ab normally high flooding which eliminated the previous island population s of the species. The frequency of chromosome aberration increased par allel to the population density of island populations of both species in 1992-1994. In the mainland population of C. rutilus in 1994, the ye ar of low density for this highly cyclic population, significantly low er frequency of chromosome aberration was found as compared with an is land population characterized by high density in this year. These resu lts are interpreted as a disturbance of cytogenetic homeostasis indica ting an alteration in an organism's condition in the overcrowded popul ations of both species under study.