Genomic and experimental evidence of rapid evolution in an introduced population of Atlantic salmon (Salmo salar) in Rocky River, Newfoundland

We characterized the presence of recent divergence in a population of Atlantic salmon (Salmo salar) introduced from Little Salmonier River into Rocky River, Newfoundland ~ 5 generations previously, by quantifying genomic divergence and conducting reciprocal transplant experiments. Genomic evidence based on Bayesian clustering and hybrid characterization using genome-wide single nucleotide polymorphisms support the presence of two populations, one at Little Salmonier, and both at Rocky River with hybridization with non-anadromous residents. In conjunction with evidence of adaptive divergence at ~90 loci, this finding supports the hypothesis of rapid evolution. Reciprocal transplants from controlled lab crosses revealed no significant growth differences between rivers, but higher survivorship in Rocky River. Purebreds outperformed hybrids in both rivers and the laboratory, a finding consistent with outbreeding depression. Overall, the results support the hypothesis of rapid evolution of salmon in Rocky River; with both adaptive evolution and introgression with residents as likely causes