PHYLOGENY OF PACIFIC SALMON AND TROUT BASED ON GROWTH-HORMONE TYPE-2 AND MITOCHONDRIAL NADH DEHYDROGENASE SUBUNIT 3 DNA-SEQUENCES

The phylogeny of Oncorhynchus has previously been studied using a vari ety of morphological and genetic characters, but two unresolved proble ms remain: the position of masu (Oncorhynchus masou) and amago (Oncorh ynchus rhodurus) salmon and the relationships within the group contain ing sockeye (Oncorhynchus nerka), pink (Oncorhynchus gorbuscha), and c hum (Oncorhynchus keta) salmon. We examined relationships among nine O ncorhynchus species, Atlantic salmon (Salmo salar), and lake trout (Sa lvelinus namaycush) using DNA sequence analyses of the mitochondrial N ADH dehydrogenase subunit 3 gene and a portion of the nuclear growth h ormone type-2 gene. Phylogenetic trees inferred using both cladistic a nd distance approaches were highly concordant except in the placement of the outgroup; strong support is provided for the proposition that p ink and chum salmon are sister species, and that masu and amago salmon are closer to the Pacific trout than the other Pacific salmon. The ph ylogeny inferred by total evidence cladistic analysis of our data comb ined with five different morphological, biochemical, and DNA character sets provides evidence that the common ancestor of rainbow (Oncorhync hus mykiss) and cutthroat (Oncorhynchus clarki) trout was the first to diverge from the proto-Oncorhynchus evolutionary line, which then rad iated to form the seven extant Pacific salmon species.