Genetic variation for upper thermal tolerance diminishes within and between populations with increasing acclimation temperature in Atlantic salmon

Populations may counteract lasting temperature changes or recurrent extremes through plasticity or adaptation. However, it remains underexplored how outbreeding, either naturally, unintentionally, or facilitated, may modify a local response potential and whether genotype-by-environment interactions or between-trait correlations can restrict this potential. We quantified population differences and outbreeding effects, within-population genetic variation, and plasticity of these, for thermal performance proxy traits using 32 pedigreed wild, domesticated, and wild-domesticated Atlantic salmon families reared under common-garden conditions. Following exposure to ambient cold (11.6°C) or ~4- and ~8-degree warmer summer temperatures, populations differed notably for body length and critical thermal maximum (CTmax) and for thermal plasticity of length, condition, and CTmax, but not for haematocrit. Line-cross analysis suggested mostly additive and some dominant outbreeding effects on means and..., Described in manuscript
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