Karyological characterization of the Japanese water shrew, Chimarrogale platycephala (Soricidae, Soricomorpha)

We analyzed the karyological criteria of the Japanese water shrew, Chimarrogale platycephala in central Honshu. Only a few studies on the karyotype of this species for samples from Aomori Prefecture, northernmost Honshu, the Japanese Islands have been published. Our current results indicate that the chromosomal constitutions are fundamentally identical to those of previous studies. In addition, heteromorphism in the largest autosomal pair (no. 1 homologue) was also observed, in agreement with previous data. This heteromorphism of the no. 1 homologue is considered a usual phenomenon in C. platycephala based on previous and current results. In addition, another autosomal heteromorphism on medium-sized subtelocentrics was observed as the first example. The heteromorphic regions were positively stained by C-banding. Moreover, a cline seemed to appear in the degree of the heteromorphic status along south to north in comparison with previous studies. In C. platycephala, there are several kinds of heterochromatinizations; such heteromorphisms would be neutral differentiations karyologically for natural selections from an evolutionary standpoint.