The genetic characteristics of three populations of the tideland snail Cerithidea djadjariensis (Martin) that were recently discovered on the Pacific coast of the eastern Japan were compared with other Japanese conspecific populations of this snail on the basis of the nucleotide sequences of mitochondrial DNA. Two populations from the Pacific coast of northeastern Honshu, the Japanese mainland, showed lower genetic diversity than and no significant differentiation from populations in western Honshu and Kyushu. The foundation of these populations might be attributed to range expansion along the coast, probably due to global warming. On the other hand, the population in Tokyo Bay, which was rediscovered in 2001 on an artificial tideland, was shown to be genetically different from all other Japanese populations whose genetic structures have been analyzed. It is suggested that this population was founded by human-mediated introduction such as transportation with short-necked clams, ballast water, or hull fouling.
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