UC Davis

Understanding the variations that exist between organisms, populations, and species can provide valuable insight into the evolutionary and environmental drivers relevant to organism fitness. Developing this understanding is critical in an era of rapid environmental change, where effective conservation and management efforts must predict the response of organisms to future, novel environmental conditions.Pacific salmonids are widely considered at-risk from anthropogenic and climatic changes. Additionally, Pacific salmonids exhibit a semelparous anadromous life-history strategy which limits gene-flow and promotes the formation of distinct populations. My first chapter reviews the literature on the thermal physiology of Chinook salmon (Oncorhynchus tshawytscha) from the Central Valley of California, which are the southernmost native populations in the world. I found very little prior research studying interpopulation in thermal physiology among Chinook salmon, despite a vast literature demonstrating the capacity for interaction between thermal physiology and a salmonid’s local environment. I propose a place-based management paradigm which combines both and organisms fundamental and ecological thermal physiology. My second and third chapters employed a common-garden experimental design and several physiological metrics to assess the thermal physiology and acclimation capacity of eight hatchery populations of Chinook salmon from the west coast of North America. All eight populations were reared at the same suite of acclimation temperatures (11, 16 and 20°C) and assessed using five physiological metrics, (growth rate, critical thermal maximum, routine and maximum metabolic rate and aerobic scope). The second chapter aimed to determine whether the thermal physiology and acclimation capacity of three seasonal runs of Chinook salmon in the Sacramento River watershed (CA) differed. I identified quantifiable population differences in CTM, growth, and metabolism among the studied populations and found compelling evidence that the critically endangered Sacramento River winter-run exhibits growth and metabolic capacities indicative of mal-adaptive physiological plasticity to warm temperatures. The final chapter studied six populations of fall-run Chinook salmon and assessed statistical associations between the five physiological traits and 15 environmental predictors to test hypotheses of local adaptation and countergradient variation. My results support local adaptation, wherein populations from warmer habitats exhibit higher critical thermal maxima and faster growth when acclimated to warm temperatures. Among metabolic traits I also found positive associations between migration distance and metabolic capability, indicating that populations with longer migrations may have higher metabolic capacity. Collectively, my research demonstrates that populations of Chinook salmon differ in their thermal physiology and that these differences can be associated with aspects of their environment consistent with hypotheses of local adaptation. With this understanding, one-size-fits-all management frameworks are poised to underserve unique or unusual populations. Instead, place-based population-specific strategies would best serve at-risk populations like the Sacramento River winter-run Chinook salmon.