Satoru N. Chiba

Phylogeography of Blacktip Grouper, Epinephelus fasciatus (Perciformes: Serranidae), and influence of the Kuroshio Current on cryptic lineages and genetic population structure

To investigate the influence of the Kuroshio Current on the high diversity of marine fishes in Japanese waters, the intraspecific phylogeographic structure of Blacktip Grouper, Epinephelus fasciatus, was determined. The genetic analysis of E. fasciatus indicated three intraspecific mtDNA lineages representing different evolutionary histories: the first lineage differentiated in Japanese waters during a long period of fluctuations of the ancient Kuroshio Current, the second lineage, widely distributed in the tropical western Pacific, was transported to Japanese waters by the Kuroshio Current and the third lineage was distributed primarily around the Ogasawara (Bonin) Islands. Present-day sympatric distributions of the three lineages, characterized by different ratios of such individuals at each geographic site, indicated a complex genetic pattern that was classified into three demographic groups, the dispersal and gene flows of which were strongly influenced by the Kuroshio Current and factors such as countercurrent and island arc. Genetic breaks in E. fasciatus populations were congruent with other fish faunal boundaries in Japanese waters.

Geographical distribution and genetic diversity of Gymnogobius sp. “Chokai-endemic species” (Perciformes: Gobiidae)

The geographical distribution and intraspecific genetic diversity of an endangered freshwater goby, Gymnogobius sp. “Chokai-endemic species”, was surveyed based on mitochondrial cytochrome b gene sequences in Yamagata Prefecture and adjacent areas on the island of Honshu, Japan. An extensive field survey showed that the species is distributed in 11 locations from Gosen, Niigata Prefecture to Yuza, Yamagata Prefecture. The species was not collected together with Gymnogobius sp. “widely distributed species” at each location, although the distribution of these two species overlaps. A maximum likelihood phylogenetic analysis showed that Gymnogobius sp. “Chokai-endemic species” is genetically divergent from other Gymnogobius castaneus species complex and the species consists of Niigata and Yamagata sub-clades. The result suggests that the Niigata and Yamagata regional groups can be distinguished from each other by their sequence divergence and the two groups should be treated as provisionally distinct “evolutionarily significant units”. The indices of intra-population genetic diversity were noticeably low, suggesting that each population has probably experienced bottleneck events. The geographical distance between the two populations in the Yamagata group, where the haplotypes are completely different from each other, was within 3 km. This suggests that habitat loss, fragmentation and isolation occurred in the Yamagata area due to some artificial cause. Conservation measures may be needed not only to protect individual habitats but also to promote genetic exchange among habitats in the Yamagata area.

Checklist of marine fishes of the Zunan Islands, located between the Izu and Ogasawara (Bonin) islands, Japan, with zoogeographical comments

The Zunan Islands are located 360–650 km south of Tokyo, and consist of four uninhabited volcanoes: the Bayonnaise Rocks, the Smith Rocks, Torishima Island and the Sofugan Rock. Although all of the elements of the Zunan Islands are tiny islets and rocks, they form a series of stepping stones for shallow water fishes between the Izu Islands in the north and the Ogasawara (Bonin) Islands in the south. We report here the first comprehensive survey of marine fishes in the Zunan Islands. A total of 139 species of fishes (88 genera of 46 families in 11 orders) were recorded on the basis of specimens and/or underwater photographs. Although our survey showed that the fish fauna of the Zunan Islands was more similar to that of the Ogasawara than that of the Izu islands, most of the species from the Zunan Islands occurred in all three island groups.

Genetic Diversity and Evolution of Marine Animals Isolated in Marine Lakes

How do marine organisms genetically differentiate and speciate in illimitable oceans? It is considerably difficult to obtain clear answers to this question due to the following reasons. Marine organisms that reproduce by releasing numerous eggs and larvae are able to disperse over large distances and can therefore be distributed over large geographic areas. Such marine organisms have a large population size, gene flow between distant populations occurs frequently, and interspecies hybridization sometimes occurs (Kuriiwa et al., 2007). Even geographically well-separated populations may be connected genetically, because there are few barriers to prevent gene flow in the oceans (Mayr, 1954; Palumbi, 1994). In contrast to the open ocean environment, the marine lakes of Palau (Western Caroline Islands), which are surrounded entirely by land and isolated from the sea, provide unique local environments for genetic differentiation of marine organisms (Dawson and Hamner, 2005; Gotoh et al., 2009; Goto et al., 2011). We have focused on marine lakes as isolated marine environments and have conducted continuous evolutionary studies of marine organisms in the Palau Islands for the past 13 years.

Review of the Chromis xanthura species group (Perciformes: Pomacentridae), with description of a new species

A taxonomic review of the Chromis xanthura species group, defined here as having 13 dorsal-fin spines, three upper and three lower procurrent caudal-fin rays, two black bands at the preopercular and opercular margins, and a yellow caudal fin when juvenile, resulted in the recognition of three species, Chromis xanthura (Bleeker 1854), Chromis opercularis (Günther 1867), and Chromis anadema sp. nov. Chromis xanthura and C. opercularis, the Pacific and Indian Ocean paired sister species, respectively, are redescribed, with confirmation of two color types of C. xanthura (having a white or black caudal peduncle and fin) as a single species on the basis of morphological and molecular analyses. Chromis anadema sp. nov., described from the oceanic islands of the Pacific Ocean on the basis of 21 specimens, is characterized by having 28–33 gill rakers; longest dorsal-fin soft ray length 20.0–24.7% of standard length (SL); first anal-fin spine length 5.0–6.1% of SL; caudal-fin length 33.4–43.8% of SL; posterior tips of caudal-fin lobes not filamentous in adults; broad black bands along preopercular and opercular margins, sum width of two bands 28.9–38.7% of head length; distal half of soft-rayed portion of dorsal fin transparent in adults; triangular black blotches at upper and lower caudal-fin base in adults; caudal peduncle and fin bluish black in adults; and body grayish, and all fins (except for pectoral fin) bright yellow in juveniles.