Genetic population structure of the polkadot skate (Dipturus chinensis) around Japan, based on mitochondrial DNA sequences and polymorphic microsatellite loci

The genetic population structure of the polkadot skate (Dipturus chinensis) around Japan was examined by using mitochondrial (mt) cytochrome (cyt) b gene sequences and polymorphic microsatellite (simple sequence repeat [SSR]) loci. Results of phylogenetic analysis based on mt cyt b gene sequences reveal 2 major lineages, clades A and B. Clade A consists of populations in the Sea of Japan and the East China Sea. Clade B contains populations in the Pacific Ocean and is divided into 2 subclades, clades B1 and B2, which correspond to the populations along the southern and northern coasts of Japan, respectively. This genetic differentiation is also supported by results from SSR analysis. The divergence of clades A and B may reflect isolation of the East China Sea from the Pacific Ocean in the Early Pleistocene. After diverging from clade A, clade B might have extended its distribution northward along the Pacific coast of Japan and divided into clades B1 and B2 in the Middle Pleistocene. The polkadot skate is clearly structured into 3 genetically discrete populations around Japan that should be treated as independent management units for management of this species in the future.