Data from: Thermal plasticity in farmed, wild and hybrid Atlantic salmon during early development: has domestication caused divergence in low temperature tolerance?

Background: In the past three decades, millions of domesticated Atlantic
salmon Salmo salar L. have escaped from farms into the wild. Their
offspring display reduced survival in the natural environment, which
demonstrates that gene-flow is likely to have a negative effect on wild
populations. However, inter-population differences in introgression of
farmed salmon have been observed, and the underlying ecological mechanisms
remain enigmatic. We hypothesised that domestication-driven divergence in
tolerance to low temperatures during early development may contribute to
lower survival of farmed salmon offspring in the wild, which in turn, may
influence patterns of introgression among populations exposed to different
temperature regimes. We reared the offspring of 35 families of wild,
farmed and hybrid origin at three temperatures (3.9, 5.6 and 12 °C) from
the onset of exogenous feeding and throughout their first summer. Thermal
reaction norms for growth and survival were investigated along the
gradient. Results: The main results of this study, which is based upon the
analysis of juvenile salmon from five wild strains, two farmed strains and
two hybrid strains, can be summarised as; (i) salmon of all origins were
able to successfully initiate feeding at all temperatures and similar
survival reaction norms were detected in all strains across the
temperature gradient; (ii) deviating growth reaction norms were detected
between strains, although this result was most likely due to an overall
lack of growth in the lower temperature treatments. Conclusions: This
study revealed no evidence of domesticated-driven divergence in low
temperature tolerance in Atlantic salmon during early development.
Although the potential interaction between low temperature and other
river-specific factors cannot be excluded, our results indicate that the
reduced survival of farmed offspring in the wild is not explained by
farmed salmon displaying impaired abilities to initiate feeding at low
temperatures. We therefore suggest that the observed inter-population
patterns of introgression are not low-temperature driven and that other
ecological or biological factors may explain why detection of farmed
salmon in wild rivers is not synonymous with introgression. In general,
our results support the literature indicating that phenotypic plasticity
instead of thermal adaption has been selected for in Atlantic salmon.