Abstract
We examined morphological variation in Kunashiri populations of P. sapporensis Shiraki and P. tyatiensis Bugrov using multivariate morphometrics to clarify their taxonomic status in comparison with Hokkaido populations of P. sapporensis. Although P. sapporensis in Kunashiri Island has a unique karyotypic characteristic, the neo-X and neo-Y system, cluster analysis indicated that the morphology is included in the range of variation seen in Hokkaido populations with the XO-male determination system. P. tyatiensis is characterized by having short-armed chromosomes compared with other Podisma species, but the morphology of this species did not differed much from P. sapporensis in Hokkaido, either. These results suggest that chromosomal changes do not contribute to phenotypic diversification. P. sapporensis in Kunashiri Island is probably reproductively isolated from P. tyatiensis on the same island because of conspicuous differences in the karyotype, whereas it is highly probable that P. tyatientsis in Kunashiri Island and P. sapporensis in Hokkaido constitute the same biological species.
