Abstract
Chromosomes of Sorex caecutiens shinto, S. c. saevus, S. unguiculatus and S. gracillimus were compared in detail based on the G and C-banding patterns, paying attention to the structural variations of their No. 5 chromosomes. The first three had the diploid number of 42, and carried prominent satellites on the short arms of the pairs Nos. 19 and 20, but the last one (2n=36) only on the short arms of No.17. These satellites seemed to function as active NORs, being differentially stained by the one-step silver-staining method which was applied only to S.c. shinto in the present study. The caecutiens complex and S. unguiculatus were almost identical in their G-banding pattern as well as in their chromosome constitution, except for the No.5 chromosomes slightly differing from one another in the arm ratio and/or G-banding pattern. These chromosomal variations could be explained by two kinds of pericentric inversion rearrangements. S. gracillimus was highly homologous in the G-banding pattern with the caecutiens complex and S. unguiculatus in spite of a marked differentiation in the karyotype, sharing the identical pattern of G-bands with S. unguiculatus in almost 92% of its total chromosome length. The pair No. 5 of S. gracillimus was identical in the G-banding pattern with that of S. unguiculatus. The phylogenetic relationships of these four species and subspecies of Sorex were briefly discussed from a karyosystematic viewpoint.
