Functional gene diversity and migration timing in reintroduced Chinook salmon

Abstract

Reintroductions are used to reestablish populations to historical habitats from which they were extirpated. The long-term success of these efforts will depend on genetic diversity and the ability of reintroduced individuals to adapt to ecological change. We examined variation at circadian clock (OtsClock1b and OmyFbxw11) and reproductive timing (Ots515NWFSC)—associated genes in two threatened spring-run Chinook salmon (Oncorhynchus tshawytscha) populations that are undergoing restoration to historical habitats above dams. We also tested for an association between the genes and individual variation in arrival time to the spawning grounds. Our findings indicate that levels of genetic diversity in reintroduced individuals are similar to those found in previously studied spring, summer, fall and winter-run Chinook salmon populations. Captive-rearing programs established following dam construction and the more recent reintroduction efforts thus appear to have maintained diversity at these genes. We observed temporal (between run-years) and spatial (between populations) patterns of genetic differentiation, but little evidence that selection underlies these differences. However, there was a relationship between the circadian-associated gene, OmyFbxw11, and arrival time to the spawning grounds, and in one year of the study, “early” and “late” arrivers to the spawning grounds were more differentiated at the gene than at neutral markers. Taken together, these findings suggest that reintroduced salmon may be capable of an evolutionary response to ecological shifts that alter the adaptive landscape between fitness and arrival timing to the spawning grounds.