Cytogenetic homeostasis and population density in red-backed voles Clethrionomys glareolus and C.rutilus in central Siberia

Authors examined frequency of chromosome aberration in somatic cells in sympatric growin populations of bank vole Clethrionomys glareolus Schreber, 1780 and ruddy vole C. rutilus Pallas, 1779 in central Siberia (Yenisei river island, 62oN, 89'E) from abnormally high flooding which eliminated the previous island populations of the species. The frequency of chromosome aberration increased parallel to the population density of island populations of both species in 1992-1994. In the mainland population of C. rutilus in 1994, the year of low density for this highly cyclic population, significaantly lower frequency of chromosome aberration was found as compared with an island population characterized by high density in this year. The result are interpreted as a disturbance of cytogenetic homeostasis indicating an alteration in an organis'm condition in the overcrowded populations of both species under study.