Mechanisms of Thermal Adaptation Among Desert and Montane Populations of Redband Trout

We tested for differential transcriptional response of ecologically divergent populations of redband trout (Oncorhynchus mykiss gairdneri) that have evolved in desert and montane climates.  Gill tissues were collected from three strains of fish (desert, montane, F1 crosses) at the peak of heat stress and tested for mRNA expression differences across the transcriptome with RNA-seq.  Strong differences in transcriptional response to heat stress were observed across strains confirming that fish from desert environments have evolved diverse mechanisms to cope with stressful environments.  Strongly differentiated genes (> 4 fold change and FDR ≤ 0.05) were particularly abundant in the desert strain (824 unique contigs) relative to the other two strains (montane = 58; F1 = 192).  Key stress response genes such as molecular chaperones (i.e., heat shock proteins) had adaptive patterns of gene expression among strains, but also a much higher number of metabolic and cellular process genes were differentially expressed in the desert strain demonstrating these biological pathways are critical for thermal adaptation to warm aquatic climates.  The results of this study further elucidate the molecular basis for thermal adaptation in aquatic ecosystems and extend the potential for identifying genes that may be critical for adaptation to changing climates.