The evolutionary effects of bear predation on salmon life history and morphology

The power of selection to drive evolution has captivated evolutionary biologists since Darwin. It is often noted that conspecific populations differ in phenotypic traits, and divergent selection appears to be a critical force generating this biological diversity. Until recently, most research focused on the role of resource competition in driving divergence but other factors may also be important. The overarching goal of my dissertation research was to examine the role of natural selection in the form of predation in driving adaptive population divergence.; To achieve this goal, I investigated the effects of predation from bears on the evolution of salmon. My research was carried out on sockeye salmon (Oncorhynchus nerka) in the Wood River Lakes system in southwestern Alaska. Previous research in this system has demonstrated that the percent of salmon killed by bears varies among populations, as does the tendency of bears to kill salmon early or late in their reproductive life. This previous research laid the foundation for my research because it allowed me to test whether trait divergence among populations was related to the local predation intensity.; I employed a comparative approach to quantify trait divergence among populations, and then related trait divergence to predation intensity. I focused on salmon life history traits (reproductive lifespan, rates of senescence) as well as morphological traits (body size and shape). My results demonstrate that among population variation in senescence rates, body size and shape is closely associated with the degree of predation experienced. In particular, variation in senescence was related to the extent to which bears killed salmon that exhibited little senescence; populations senesce at slower rates when they have been historically exposed to bear predation that selectively targets fish showing more advanced senescence. Variation in body size and shape was also related to the intensity of bear predation; populations are smaller and more shallow-bodied when they have been exposed to more intense bear predation. In general, my dissertation research contributed to a small but growing body of research demonstrating the importance of divergent selection due to predation in driving adaptive population divergence.