Population genetic structure and gene flow in the Japanese sea cucumber Apostichopus japonicus across Toyama Bay, Japan

The Japanese sea cucumber Apostichopus japonicus has a pelagic-lecithotrophic larva. Here, we clarify larval dispersal among Japanese sea cucumber populations by describing the levels of distinctiveness and gene flow among red and green variant populations of A. japonicus across Toyama Bay using 11 polymorphic microsatellite markers. Samples of Japanese sea cucumber populations were collected from three localities (Noto, Shinminato, and Uozu) around Toyama Bay. Geographically separated populations of red and green variants were determined to be genetically distinct, supported by phylogenetic analysis and the distinctiveness range values of pairwise multilocus estimates of F _ST. Contemporary migration analyses indicated that the majority of estimated migration events occurred within A. japonicus populations comprised of only either red or green variants. In a historical gene flow analysis, two best-fit models (n-island and stepping stone models) showed circulation for the gene migration in Toyama Bay among red variant populations. Our results provide useful information on the genetic structure of Japanese sea cucumber populations and will be helpful for genetic conservation and fisheries management of sea cucumber populations in Toyama Bay.