Physiology and morphology of clonal Atlantic salmon-influence of incubation temperature, ploidy, and zygosity.

Isogenic (clonal) fish lines are useful experimental models to study effects of environment versus genetics on phenotypic traits, as they can be maintained for generations without change, providing advantages over outbred groups prone to generational change and higher variation. Here we performed experiments on isogenic Atlantic salmon groups that were either heterozygous diploid, homozygous diploid, triploid, or heterozygous diploid incubated at 4 °C instead of 8 °C. We measured metabolic rates, stress response, and hypoxia tolerance to assess whole-animal performance traits. Then we measured the morphology of hearts and otoliths since both are known to be influenced by environmental history. Isogenic, ploidy, and zygosity statuses were confirmed from microsatellite markers. Embryonic development is affected by temperature, hence the 4 °C incubation group was tested 9 months later when it had reached an equivalent size as the other groups. Curiously, a bimodal size distribution emerged in this group. Physiological traits were similar between groups apart from higher standard metabolic rates in the 4 °C incubated fish. Each group had distinct heart morphologies where fish with a slower growth history resembled wild-phenotypes while homozygous fish had the most deviating hearts. Proportions of vaterite deposition in otoliths showed high individual variation and did not differ between groups. Lower coefficients of variation within groups were found when compared to outbred fish, but this was not consistent for all traits assessed. As such, substantial phenotypic variation in physiology and morphology was still observed in isogenic Atlantic salmon, which can be ascribed to random environmental factors.