Population genetic structure of Sarcocheilichthys variegatus variegatus in the Tokai region, Japan and invasion of a non-indigenous mitochondrial DNA lineage

Abstract

Sarcocheilichthys variegatus variegatus, an endemic Japanese cyprinid fish distributed from western Honshu (Tokai region) to Kyushu, has recently declined due to environmental damage and reduction of host mussels, and has been designated as a near threatened species in the Red List of the Japan Ministry of Environment. In addition, a recent study has noted the artificial introduction of S. v. microoculus from Lake Biwa into the Chubu, Kinki and Kyushu regions, suggesting a threat of genetic introgression. The present study, to investigate the population genetic structure of S. v. variegatus and identify invasions of a non-indigenous mtDNA lineage in the Tokai region, involved phylogeographic and population genetic analyses using cytochrome b gene sequences of 253 individuals of S. variegatus from Gifu, Mie and Shiga Prefectures. In addition, morphological characteristics of S. v. variegatus in the Tokai region, and S. v. microoculus in and around Lake Biwa, were used to identify instances of hybridization between the two subspecies. Phylogeographic analyses revealed greatest genetic divergence between populations of S. v. variegatus in the eastern and western regions of the Suzuka mountain range, and the presence of a non-indigenous mtDNA lineage in S. v. variegatus in the Tokai region. Clearly, the latter is characterized by important endemic genetic features, although already suffering from a loss of genetic identity due to the invasion of non-indigenous individuals. Steps are needed for future conservation of native S. v. variegatus populations in the Tokai region, including risk assessment and protection from invasive non-indigenous forms.