High genetic heterogeneity in chum salmon in western Alaska, the contact zone between northern and southern lineages

Genetic relationships among 64 spawning populations of chum salmon Oncorhyn chus kern in western Alaska were studied using allele frequency data from 4 0 protein-encoding loci. Two major lineages of chum salmon inhabiting Alask a were detected using clustering and multidimensional scaling analyses of C avalli-Sforza and Edwards' chord distances. Populations of the northwest Al aska lineage occur in the largely unglaciated areas of Alaska north of the Alaska Peninsula (Beringia, the Beringian Refugium); and the Alaska Peninsu la-Gulf of Alaska lineage occurs in the glaciated and unglaciated areas of the Alaska Peninsula, Kodiak Island, and southcentral Alaska. The two linea ges come into contact in the ISO-km area separating Herendeen Bay and Port Heiden on the northern Alaska Peninsula; this area may represent a major zo ogeographic contact zone. Genetic data also suggest the lineages come in co ntact in upper Cook Inlet; the population representing the Susitna River dr ainage, which drains into Cook Inlet and the Gulf of Alaska, shows affinity to the northwest Alaska lineage. Genetic variability was higher in the Ala ska Peninsula-Gulf of Alaska lineage than in the northwest Alaska lineage. A comparison of allele frequency data collected in this study with data ava ilable for Pacific Rim populations suggests that populations of the Alaska Peninsula-Gulf of Alaska lineage were derived from Cascadia (the Pacific Re fugium) and belong to a larger southern lineage, which includes populations from southeast Alaska, British Columbia, and the Pacific Northwest. In con trast, populations from northwest Alaska appear to be derived from a northe rn lineage with affinities to Asian populations.