Mountain masses as a determinant to genetic structure of char distributed in the Chugoku region, Japan

A mountain mass from which multiple river basins originate is a possible determinant of genetic structure of freshwater fishes. In this study, subspecies composition and genetic structure were examined for Japanese white-spotted char comprising of two subspecies, Salvelinus leucomaenis imbrius (Jordan and McGregor), “Gogi,” and S. l. pluvius (Hilgendorf), “Nikkoiwana,” collected in the 19 river basins originating from 6 mountain masses in the Chugoku Region, Japan, based on mitochondrial DNA sequences. In the western mountain masses, only Gogi was collected, while in the eastern mountain mass, only Nikkoiwana was collected. A total of 27 haplotypes were detected, among which only seven were shared by two subspecies and three were detected only in Nikkoiwana whereas 17 were detected only in Gogi. As many as 11 haplotypes were distributed only in the Oyorogi Mountain mass in the middle region. In the network, one group was exclusively constructed by the samples from the Oyorogi Mountain mass. Furthermore, in a tree of river basins based on average genetic distance of char, the Gono River basin originating from the Asa Mountain mass, situated in the western region, participated in a clade constructed by the rivers originating from the westernmost Sukegatake and the adjacent Asa Mountain masses, whereas the Gono River basin originating from the Oyorogi Mountain mass participated in a different clade constructed by the rivers originating from the Oyorogi to the easternmost Hyonosen Mountain masses. These results suggest that a mountain mass is a determinative factor to subspecies composition and genetic structure of char, with an implication of invasion of fish taking advantage of some geological events or conditions.