Geographic distributions and specific relationship of Japanese Tetraclita

Abstract

Three “subspecies” of Tetraclita squamosa, “T, s. squamosa”, “T. s. formosana” and “T. s. japonica”, live in intertidal rocky shore of Japan. It is easy to distinguish them from color of shell and other morphologies. Their geographic distributions overlap with each other in areas of south of central Japan and west Kyushu. In open coast of those areas, it is found a microgeographic sympatric relationship among three “subspecies”. The segregation of ecological niche among them is not present in open coast. These evidences indicate that they are not different subspecies of same species, but they are either different species or different phena of same species. Their reproductive seasons coincide with each other and are from summer to autumn in Kii Peninsula. In electrophoretic analysis of an isozyme (Malate dehydrogeneses), it is found the different gene frequencies among three “subspecies”. Namely, it is distinct that gene flow among them is not present. They are not subspecies, but different species. Tetraclita squamosa widely distributes in Indo-Pacific region. The lther two species narrowly distribute in northeastern periphery of the distribution of T. squamosa. Characteristics of their distributions suggest that T. squamosa is a parental species of them, and that T. formosana and T. japonica had derived from ancester of T. squamosa. T. formosana and T. japonica had differentiated from the common ancester by peripheral speciation.