Ryoko Segawa

Phylogenetic relationships among species of Calyptogena (Bivalvia: Vesicomyidae) collected around Japan revealed by nucleotide sequences of mitochondrial genes

Phylogenetic relationships among the seven species of deep-sea giant clams Calyptogena (Bivalvia: Vesicomyidae) collected around Japan were examined using parts of nucleotide sequences of mitochondrial genes for cytochrome oxidase I (COI) and cytochrome oxidase III (COIII) and the encoded amino acid sequences. The seven species were C. soyoae (Sagami Bay), C. fausta (Suruga Bay), C. kaikoi (Nankai Trough), C. nautilei (Nankai Trough), C. phaseoliformis (Japan Trench), C. solidissima (Minami-Ensei Knoll, Okinawa Trough) and Calyptogena sp. (Iheya Ridge, Okinawa Trough). A clear phylogenetic split was observed between one group of three species (C. kaikoi, C. phaseoliformis and C. fausta) and the remaining species. This clustering corresponds to the two previously described subgenera within the genus Calyptogena (Calyptogean and Ectenagena) with the exception of the placement of C. nautilei, which had been placed in the subgenus Ectenagena. Genetic distances between two haplotypes of C. soyoae were 0.043 for the COI region and 0.055 for the COIII region, and three amino acid substitutions were detected with the COIII region. Calyptogena sp. from the Iheya Ridge could be distinguished from one of the two haplotypes (type A) of C. soyoae by only a single nucleotide substitution, a result that suggests that Calyptogena sp. of the Iheya Ridge diverged from C. soyoae after the two haplotypes had diverged, and it is now isolated from C. soyoae in Sagami Bay.

Genetic Differentiation of Populations of a Hydrothermal Vent-Endemic Gastropod, Ifremeria nautilei, between the North Fiji Basin and the Manus Basin revealed by Nucleotide Sequences of Mitochondrial DNA.

Abstract The genetic differentiation of populations of a hydrothermal vent-endemic gastropod, Ifremeria nautilei, between two back-arc basins in the south Western Pacific, namely the Manus Basin and the North Fiji Basin, was analyzed on the basis of nucleotide sequences of the mitochondrial gene for cytochrome oxidase I. The two populations of I. nautilei had no common haplotypes and appeared, therefore, to be isolated from one another. All haplotypes obtained from the North Fiji Basin formed a monophyletic group supported by a high bootstrap probability and the genetic diversity of the population in the North Fiji Basin was much smaller than that of the population in the Manus Basin. The population in the North Fiji Basin might have been founded by relatively recent migrants from the Manus Basin. The present results suggest that the larval dispersal ability of I. nautilei might be lower than that of an undescribed species in the closely related genus Alviniconchay.

Stability of the Courses of the Warm Coastal Currents along the Kyushu Island Suggested by the Population Structure of the Japanese Turban Shell, Turbo (Batillus) Cornutus

The genetic structure of a population of the Japanese turban shell, Turbo (Batillus) cornutus at Sata-Misaki Point, on the southern coast of Kyushu Island, was determined on the basis of nucleotide sequences of mitochondrial DNA and compared with that of a population of the western coast of Kyushu Island. The significant genetic differentiation between these two populations suggests that the courses of the warm currents along the coast of the Kyushu Island have been relatively stable after the divergence between the two genetically distant groups of the Japanese turban shell, which was estimated to have occurred during some period in Pleistocene.

Limited Overwater Dispersal and Genetic Differentiation of the Snake-Eyed Skink (Cryptoblepharus nigropunctatus) in the Oceanic Ogasawara Islands, Japan

The genetic differentiation and speciation of lizards on oceanic islands may be affected by their rate of overwater dispersal. Cryptoblepharus is one of the most geographically widespread scincid lizards throughout the Indo-Pacific and Australian regions. Cryptoblepharus nigropunctatus is the northernmost species of the genus, dwelling on several small Pacific islands. To examine the colonization history of this lizard, mitochondrial 16S rDNA and D-loop sequences were compared among populations of the Ogasawara Islands consisting of four island groups (the Muko-jima, Chichijima, Haha-jima, and Kazan groups), and an isolated island, Minamitori-shima (Marcus Island). These four groups and Minamitori-shima have not been connected to each other because each is surrounded by deep sea (>100 m). DNA analyses showed that the lizard populations on individual islands had each representative haplotypes. The ancestors of C. nigropunctatus probably arrived on the islands from the southern Pacific Ocean via wave dispersal and differentiated to produce the present state. They appear to have dispersed from their origin along two independent pathways: one between Kitaiwo-to (Kazan group) and the Muko-jima and Chichi-jima groups, and the other among the Minamitori-shima, Minamiiwo-to (Kazan group), and Haha-jima groups. Limited long-distance overwater dispersal may be responsible for the genetic structure of the C. nigropunctatus populations on these oceanic islands. However, among the small islands within the same island group, D-loop haplotypes were shared and the local genetic diversity was usually high, suggesting frequent gene flow across the same group of islands.

Two new species of freshwater crab (Crustacea: Decapoda: Potamidae) from Tokashiki Island, central Ryukyu Islands, Japan

Abstract Two new species of freshwater crabs are described from Tokashiki Island, the central Ryukyu Islands, Japan. Candidiopotamon tokashikense sp. nov. can be distinguished from the closest congener, C. kumejimense, by the shape of the terminal segment of the male first gonopod and the armature of the outer dorsal margin of the second ambulatory propodus. Amamiku occulta, sp. nov. is differentiated from its only congener, A. amamensis, by the shape of the terminal segment of the male first gonopod and the form of the supraorbital margin of the carapace. Candidiopotamon tokashikense and A. occulta are superficially very similar, but they can be differentiated from each other by the relative length of the antenna, the shape of the male first gonopod, and the relative width of female abdominal segments. A key to the species of Candidiopotamon and Amamiku is provided.