Genetic diversity in natural populations of Japanese Potamoid crabs

日本金龟子由15个种组成，分成3个属(Geotholphusa、Candiopotamon和Ryukyum)。在这些物种中，只有G.dehaani通过本州到鹿儿岛广泛栖息，其他物种的分布仅限于琉球群岛。我们主要通过线粒体DNA序列测定，研究了不同物种在自然居群中的遗传变异或物种间的遗传分化。遗传分化的种群通常分布在热带附近，在它们相互接触的地方形成非常狭窄的杂交区。研究了杂交区的详细遗传结构与遗传分化亲本群体之间生殖隔离发展的关系。根据mtDNAND2基因(1,008-1,011个碱基)的核苷酸序列变异，推测了15种日本金龟属的系统发育关系。我们的研究结果支持了以前形态研究中的一些分类学方面。然而，假丝酵母属在分子树中并没有显示为一个强大的组合。此外，地藻属物种间的系统发育关系与形态或生态研究所推论的亲缘关系并不一致。本研究揭示的系统发育关系表明，当琉球地区被认为被分成一些陆块时，日本钾盐类的主要进化谱系发生在200-250万年左右。

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.