Meeting Abstract
Identifying the ecological factors that shape the evolution of life histories has been a topic of great interest and research for several decades. Populations of the same species can express important differences in life history traits, often apparent when comparing populations along an elevation gradient, where differences in phenology, reproduction, survival, and growth exist. Higher elevations are typically characterized by a shorter growing season, lower temperatures, and limited resources. High elevation individuals must allocate resources among growth, immunity, and reproduction, shaping a different life history strategy than lower elevation populations. However, such trade-offs between fitness traits and immunity have rarely been studied in the wild. We live-trapped Uinta ground squirrels (UGS, Urocitellus armatus) to examine the relationship between immune function (measured by bacterial killing assay) and body mass dynamics in two populations located 600 m. apart in elevation while accounting for age and sex. Higher elevation yearlings/adults emerged at a lower body mass but gained mass more quickly, entering estivation at the same body mass as lower elevation UGS. This increase in growth came at a cost, as immune response decreased more rapidly in UGS at the higher elevation, indicating a trade-off between growth and immunity. Interestingly, these trade-offs weren’t detected in juveniles, which had similar growth rates and immune response across elevations, with immune function actually increasing over the season. We hope to quantify the consequences of such trade-offs on survival and population growth to predict the ability of UGS to adapt to different climatic conditions and resource phenologies, and understand how UGS and other hibernators may respond to an increasingly variable climate in the future.
