Two genetically divergent groups in the Japanese spined loach, Cobitis takatsuensis, and their phylogenetic relationships among Japanese Cobitis inferred from mitochondrial DNA analyses

Abstract

The Japanese spined loach, Cobitis takatsuensis, has some unique morphological and ecological features among Japanese Cobitis species. Mitochondrial DNA analyses were conducted to investigate the magnitude of intraspecific differentiation and phylogenetic relationships among Japanese congeners of C. takatsuensis. PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) analysis of the ND1 region with 16 restriction enzymes was carried out for thirteen C. takatsuensis populations throughout the species' distributional range. Populations in each river system possessed their own haplotypes, with marked genetic differentiation between the populations from Chugoku and Kyushu (Chugoku-Kyushu group) and those from Shikoku (Shikoku group). The two allopatric groups also showed different color pattern. Subsequently, sequencing analysis of part (725 bp) of the cytochrome b gene was carried out for C. takatsuensis and six other closely-related Japanese species. The phylogenetic tree indicated the presence of two major mtDNA lineages within Japanese Cobitis. It was noteworthy that the Chugoku-Kyushu and Shikoku groups of C. takatsuensis were included in separate mtDNA major lineages, and each group was closely related to other species. It is inferred that the distinct mtDNA relationship between the two allopatric C. takatsuensis groups is a result of the parallel evolution or mtDNA introgression, rather than divergence by geographic isolations.