Comparative Molecular Phylogenetic Study on Speciation and Genetic Differentiation of Marine Organisms between the Pacific Ocean and the Japan Sea

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In order to reveal effects of large enviromnental changes during the Pleistocene on marine organisms in the Japan Sea, population structures of various marine organisms were analyzed using molecular phylogenetic methods.The analysis of the most dominant deep-sea demersal fish of the Japan Sea, Bothricara hollandi, showed that populations of this species consist of the two genetically different groups and it was suggested that no drastic environmental change occurred near the Thushima Strait during the last glacial period.While the clear genetic structure of a population of the Japanese turban shell, Turbo (Batillus) cornutus, whose planktonic period is very short, formed during the Pleistocene and have been kept until now, the genetic structure of an intetidal gastropod wth much longer planktonic period, Omphalinus pfeifferi, was shown to have formed after the end of the last glacial period. Individuals of O.pfeifferi, which were isolated in the Japan Sea, are thought to have become the subspedes, O.pfeifferi carpenteri, in the relatively short period.A direct-developing mud flat snail, Batillaria cumingi, showed more diverged genetic structure than the congeneric planktonic species, B.multiformis as well as the Japanese turban shell. No clear genetic differentiation was detected between the Japan Sea and the Pacific for some shallow water gastropods, namely Sulculus diversicolor, Astralium haematragum, Chlorostoma argyrostoma and Monodonta labio.The present results suggest the importance of larval dispersal ability far the formation of the genetic structures of marine species.