A test of local adaptation in seasonally separate subpopulations of pink salmon (Oncorhynchus gorbuscha)

Abstract

Differences in fitness related traits were observed between first generation (F₁) hybrid and control lines of temporally distinct subpopulations of pink salmon (Oncorhynchus gorbuscha). The lines were cultured in a common freshwater environment, released to sea together, and collected at their natal stream as adults. Early-and late-run pink salmon, which are partially genetically isolated by the time at which they return to Auke Creek in Southeast Alaska to spawn, were crossed to create F₁ and F₂ hybrid groups in the even- and odd-year brood lines. Marine survival of controls exceeded that of F₁ hybrids of the even-year brood line, whereas no difference in marine survival between those experimental groups was detected in the odd-year brood line. First generation hybrids expressed intermediate time of return relative to controls in both brood lines. Second generation hybrids exhibited similar embryonic development rates to controls in both brood lines. These results demonstrate that removal of a genetic barrier as fine as that which occurs within a brood line and location can disrupt local adaptation in a population of pink salmon, which may cause outbreeding depression in hybrids and may potentially reduce the overall biodiversity and productivity of the population.