|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1995 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1994 : ¥1,200,000 (Direct Cost : ¥1,200,000)
To infer the differentiation processes of karyotypes in three species of the genufusca-group, Nelima nigricoxa, N.sp. (tentatively called Ezonami-zatomushi in Japanese), and N.genufusca, chromosomal survey has been made for more than 100 populations of the group. As a reference, some populations of two additional species (Nelima satoi and N.aokii) belonging to the satoi-group have also been karyotyped. As a result, the numbers of chromosomes were found to be 16 and 22 for two species of the satoi group and Nelima sp. (Ezonami), respectively. On the other hand, Nelima nigricoxa and N.genufusca showed a wide range of variation in the chromosome number : 2n=16-22 and 2n=18-22, respectively. Both the outgroup comparison and geographic patterns of distribution of the karyotypes suggest that the number successively decreased within the ranges of both species.
A hybrid zone found in western part of Tottori Prefecture, Honshu was analyzed in detail. Frequency of the individuals with 2n=19 in the hybridized population (2n=20/19/18a : Kawadoko on the northern slope of Mt.Daisen) was significantly lower than the expected value from Hardy-Weinberg's theorem (p<0.02). This indicates decrease of fitness in hybrids between 2n=20 and 18a and in turn it may partly account for the narrowness of the hybrid zone. However, no evidence of disorder in the spermatogenesis was obtained for the heterozygotes with 2n=19.
To estimate the degree of differentiation at the genic level among races with three different karyotypes (16,18a, and 20), the sequences of bases of the DNA fragments of the Co1 (cytochrome oxidase 1) were determined for six populations of Nelima nigricoxa. In six sites out of 310 bp, substitutions of the bases were found among populations with three different karyotypes. More detailed comparison using restriction endonucreases is now undertaken.