Genetic diversity in natural populations of Japanese Potamoid crabs

日本溪蟹包括15种，分为3属（Geotholphusa，Atodiopotamon和Ryukyum）。在所有种中，只有G. dehaani广泛分布于本州岛至鹿儿岛一带，其他种类仅分布于琉球群岛。我们主要通过mtDNA序列测定来研究各种天然居群内的遗传变异或种间的遗传分化。Dehaani，观察到广泛的遗传分化。遗传分化群体通常呈近界分布，在相互接触处形成很窄的杂交带。研究了杂交区的详细遗传结构与遗传分化的亲本群体之间生殖隔离的发展的关系。根据线粒体ND 2基因（1，008 - 1，011 bp）的核苷酸序列变异，对日本溪蟹属15种的系统发育关系进行了初步探讨。我们的研究结果支持一些以前的分类方面的形态学研究。然而，在分子树中，该属并没有显示为一个强大的组合。此外，Geothelphusa种间的系统发育关系与形态学或生态学研究的结果不一致。本研究揭示的系统发育关系表明，日本溪蟹类的主要进化谱系发生在200-250百万年时，琉球地区被认为是分离成一些陆地块。

Japanese Potamoid consists of 15 species divided into 3 genea (Geotholphusa, Candidiopotamon and Ryukyum). Among the species, only G. dehaani inhabits widely through Honsyu to Kagoshima and the distributions of the other species are restricted in the Ryukyu Islands. We studied genetic variation in natural populations for each species or genetic differentiation among species mainly by using mtDNA sequence determination.In natural populations of G. dehaani, extensive genetic divergence was observed. The genetically differentiated populations are usually distributed parapatrically and very narrow hybrid zones are formed at where they come into contact with each other. Detailed genetic structure at the hybrid zones were investigated in relation to the development of reproductive isolation between genetically differentiated parental populations. From the results we discussed the factors that are responsible to maintain the very narrow hybrid zones.Based on nucleotide sequence variation in ND2 gene of mtDNA (1,008-1,011 bp) phylogenetic relationships were inferred for 15 species of Japanese Potamoid. Our results supported some previous taxonomic aspects from morphological studies. The genus Candidiopotamon, however, was not shown as a robust assemblage in the molecular tree. Moreover, phylogenetic relationships among species of Geothelphusa were not consistent with that of deduced from morphological or ecological studies. Phylogenetic relationships revealed in the present study suggests that the major evolutionary lineages of Japanese Potamoid have occurred at 200-250 mya when the Ryukyu region was thought to be separated into some land blocks.