Complete mitochondrial genomes of Gritzenko's charr Salvelinus gritzenkoi and Miyabe charr Salvelinus malma miyabei and their interpretation regarding intraspecific taxonomy.

Abstract

Salvelinus is one the most species-rich genera of salmonids (Salmoniformes: Salmonidae), and mitogenomic sequence data have served as a rich source of information for resolving fish phylogenies and identifying new charr species. However, current reference databases contain limited mitochondrial genome information on narrow-ranged, endemic charrs with disputable origin and systematic status. More comprehensive mitochondrial genome-based phylogenetics will help enhance understanding of the relationship and delineate charr species. In the present study, the complete mitochondrial genomes of three taxa (S. gritzenkoi, S malma miyabei, and S. curilus) were sequenced (PCR and Sanger dideoxy sequencing) and compared with those of other charr species whose mitochondrial genomes are already reported. Results indicate that the mitochondrial genomes of the three taxa were similar in length (16,652bp and 16,653bp for S. curilus and S. malma miyabei, to 16,658bp for S. gritzenkoi). Analyses of nucleotide composition showed that the newly sequenced five mitochondrial genomes skewed strongly towards high AT (54.4%) content, which is typical of Salvelinus. No large deletions and insertions were found in the mitochondrial genomes, including samples from isolated populations. Heteroplasmy associated with single-nucleotide substitution in the ND1 gene was found in one case (S. gritzenkoi). In maximum likelihood and Bayesian inference trees, S. gritzenkoi and S malma miyabei were clustered with S. curilus with strong branch support. Our results provide the basis for a possible reclassification of S. gritzenkoi to S. curilus. The results of this study may be useful for future genetic studies on charrs of the genus Salvelinus toward the in-depth phylogenetic study and proper assessment of the conservation status of the disputed taxa.