Local Thermal Adaptation occurs via Modulation of Mitochondrial Activity in Chinook Salmon

Freshwater and anadromous fish have been identified as one of the most at-risk groups threatened by climate induced warming given their metabolic dependence on environmental temperature and limited ability to track favorable environmental conditions. The future of these fish will depend on their ability to adapt to new thermal regimes over biologically relevant timescales. However, the mechanistic understanding of temperature responses required to predict if adaption can keep pace with climate change is limited. To address this question, we investigated the mechanistic basis of thermal adaptation across multiple levels of biological organization in the iconic and endangered Chinook Salmon (Oncorhynchus tshawytscha). We uncovered a mechanistic basis of thermal adaptation centered on the thermal responsiveness of mitochondrial function which modulates the extent to which rising temperatures increase metabolic demand on the cardio-respiratory system. These insights demonstrate that the populations studied here are able to maintain high levels of physiological performance at temperatures several degrees above historic averages, indicating that the decline Chinook Salmon and failure to recover despite conservation efforts is unlikely to be due to increased temperatures as a consequence of climate change.