Genetic evidence for the persistence and divergence of native and introduced sockeye salmon (Oncorhynchus nerka) within Lake Washington, Washington

The genetic population structure of Lake Washington sockeye salmon (Oncorhynchus nerka) was investigated using the analysis of variation in allelic frequencies at protein-coding loci. Population subdivision was considerable (average F-ST using the four highly polymorphic loci was 0.057) and two divergent population groups were identified (separated by an average genetic distance of 0.014). One population group (Cedar River, lssaquah Creek, and a Lake Washington beach) showed a genetic affinity to collections of sockeye salmon from Baker Lake, Washington. In contrast, the other population group (Bear Creek and Cottage Creek) was distinct from either of the putative non-native ancestral populations (Cultus Lake, B.C., and Baker Lake). We inferred that the former group was comprised of fish of the Baker Lake lineage (transplanted to Lake Washington in the 1930s and 1940s) and that the latter population group was predominantly of native ancestry. Cultus Lake fish were not closely related to any of the other populations but there was some evidence for introgression among the different ancestral lineages within Lake Washington. Allelic frequency differences among several populations of a common origin provided evidence for two possible types of genetic divergence: between ancestral and derived groups and among different derived populations.