Genetic variability in reaction norms between farmed and wild backcrosses of Atlantic salmon (Salmo salar)

Adaptive responses to environmental heterogeneity may vary among populations. Genetic variability in reaction norms might account for population differences in the ability to respond to environmental change and may reflect local adaptation. Reaction norms for early life history traits were compared among three population crosses of Atlantic salmon ( Salmo salar ). Two comprised second-generation backcrosses introgressed with either farmed or wild genes; the third comprised individuals from a second-generation, pure wild cross. Using a common-garden experimental protocol, each cross was exposed to three temperature regimes. Plasticity in embryonic development, growth, survival, and body size was measured from fertilization up to 24 weeks of exogenous feeding. Reaction norms differed markedly among crosses, irrespective of whether individuals interbred with those whose genes originated from another wild population or from a cultured population. We find that introgression involving individuals with comparatively few genetic differences can change reaction norms. If plasticity represents an adaptive response to local environments, then changes to reaction norms resulting from interbreeding between populations are unlikely to have a beneficial effect on fitness.