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.