The genetic architecture of ecotypic differentiation in Chinook salmon of the California Central Valley

This study delves into the genetic architecture underlying the ecotypic differentiation observed in Chinook salmon populations within California's Central Valley. Using genomic and genetic techniques, the researchers identified a key genomic region that contributes to the seasonal shift in adult freshwater migration. They further discovered two functional domains within this locus that independently and additively influence the migration timing, with each allele copy affecting the trait by around two weeks. The findings reveal how the evolution of a distinct ecotype in the Central Valley is partially driven by an allele derived from the more widespread early-migrating haplotype, while the genomic background of the evolutionarily differentiated ecotypes also plays a significant role in shaping the observed phenotypic diversity. This study provides valuable insights into the complex interplay between simple genetic systems and genomic backgrounds in generating remarkable phenotypic variation in this iconic species.