Revised Karyotypes of the Japanese Northern Red-backed Vole, Clethrionomys rutilus mikado

Abstract

The karyotypes of the Japanese northern red-backed vole Clethrionomys rutilus mikado and the Japanese gray red-backed vole C. rufocanus bedfordiae were reexamined using chromosome banding techniques. Both mikado and bedfordiae were confirmed to have 2n=56 and FNa =56, and no chromosomal variation could be detected between them so far as the conventionally stained material was concerned. Detailed G-banding analysis, however, revealed distinct interspecific variations in two pairs of acrocentrics (Nos. 1 and 9). These chromosomal variations could be explained by a reciprocal translocation, t(1; 9)(q21; q16), which was regarded to be the same as the 1-9 translocation described from C. glareolus by Gamperl (1982a). Both of the chromosomes concerned (I and 9) were homomorphic in all of the 44 specimens collected from five different localities in Hokkaido, Japan, as revealed by either G-or Q-banding pattern. Therefore, C. rutilus mikado is considered to have been genetically fixed as stable homozygotes throughout their whole population. Furthermore, the G-banded karyotype of C. rutilus mikado was found to be identical with that of the Alaskan northern red-backed vole C. rutilus. It is concluded, therefore, that northern red-backed voles, irrespective of their locality or subspecies, carry the 1-9 translocation as a specific karyotypic character.