Range-wide climate risk and adaptive potential in a cold-water fish species.

Predicting extinction risk from climate change requires understanding adaptive variation and local adaptation across species' ranges. We combine experimental and -omics approaches with climate change modeling to identify molecular mechanisms of local adaptation to heat stress in brook trout, a coldwater species experiencing extirpations due to warming temperatures. We identify genomic variation corresponding with thermal conditions across the native range, suggesting local adaptation, and experimentally identify variants linked with gene expression responses to thermal stress. Using climate projections, we find that southern brook trout populations are the most vulnerable to extirpation from climate warming and mid-range populations are the most promising candidates for receiving assisted gene flow to improve climate resilience. Together, this work highlights the importance of genomic information in managing populations threatened by climate change.