Mitochondrial DNA sequence analysis of the masu salmon--phylogeny in the genus Oncorhynchus.

We determined 2162-bp sequences from the mitochondrial genome of the masu salmon Oncorhynchus masou masou, chum salmon Oncorhynchus keta, and Atlantic salmon Salmo salar by using polymerase chain reactions. These DNA sequences span from the 3' region of the gene for ATPase subunit 6 to the 5' region of the gene for NADH dehydrogenase subunit 4L. With the aid of the sequence data from other Pacific salmonid species (Thomas and Beckenbach, 1989, J. Mol. Evol. 29: 233-245), the evolutionary distances among the masu salmon and other species in the genus Oncorhynchus were calculated. These evolutionary distances were then used to construct a neighbor-joining tree. Further, a maximum parsimony tree was constructed. The evolutionary trees that were obtained suggest that masu salmon first diverged from the common ancestor of the genus Oncorhynchus.