Thermal tolerance and cardiac phenotypes

<p>Adaptation to local environments involves the evolution of ecologically important traits and underlying physiological processes. Here, we used low coverage whole-genome resequencing (lcWGR) on individuals to identify genome regions involved in thermal adaptation in wild redband trout <i>Oncorhynchus mykiss gairdneri</i>, a subspecies of rainbow trout that inhabits ecosystems ranging from cold montane forests to high elevation deserts. This study includes allele frequency-based analyses for selective sweeps among populations, followed by multiple association tests for specific sets of phenotypes measured under thermal stress (acute and chronic survival/mortality; high or low cardiac performance groups). Depending on the groups in each set of analyses, sequencing reads covered between 43-75% of the genome at ≥15X and each analysis included millions of SNPs across the genome. In tests for selective sweeps among populations, a total of six chromosomal regions were significant. However, association tests for specific phenotypes revealed that the region on chromosome 4 was consistently the most significant and contains the <i>cerk</i> gene (ceramide kinase). This study provides insight into a potential genetic mechanism of local thermal adaptation and suggests c<i>erk</i> may be an important candidate gene. However, further validation of this <i>cerk</i> gene is necessary to determine if the association with cardiac performance results in a functional role to influence thermal performance when exposed to high water temperatures and hypoxic conditions. </p>