Differential expression of genes that control respiration contribute to thermal adaptation in redband trout (oncorhynchus mykiss gairdneri)

Organisms can adapt to local environmental conditions as a plastic response or become adapted through natural selection on genetic variation. The ability to adapt to increased water temperatures will be of paramount importance for many fish species as the climate continues to warm and water resources become limited. Because increased water temperatures will reduce the dissolved oxygen available for fish,wehypothesizedthat adaptation tolowoxygenenvironmentswould involveimproved respiration throughoxidative phosphorylation (OXPHOS). To test this hypothesis, we subjected individuals from two ecologically divergent populations of inland (redband) rainbow trout (Oncorhynchus mykiss gairdneri) with historically different temperature regimes (desert and montane) and their F1 progeny to diel cycles of temperature stress and then examined gene expression data for 80 nuclear- and mitochondrialencoded OXPHOS subunits that participate in respiration. Of the 80 transcripts, 7 showed ≥2-fold difference in expression levels in gill tissue fromdesert fish underheat stress whereas themontane fishhadnone and the F1onlyhadone differentially expressedgene. A structural analysis of the proteins encoded by those genes suggests that the response could coordinate the formation of supercomplexes and oligomers. Supercomplexesmay increase the efficiency of respiration because complexes I, III, and IV are brought into close proximity and oligomerization of complex V alters the macrostructure of mitochondria to improve respiration. Significant differences in gene expression patterns in response to heat stress in a common environment indicate that the responsewas not due to plasticity but had a genetic basis.