Assessment of Vulnerability and Adaptive Capacity of Desert Bighorn Sheep to Climate Change: Evolutionary Adaptations to Variations in Heat and Aridity
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Desert bighorn sheep (Ovis canadensis nelsoni) found in the arid regions of the southwestern U.S. are facing a number of challenges. Recent work has shown that populations may be declining at lower elevations where warmer temperatures and decreased precipitation have affected forage quality and quantity and water availability, resulting in increased rates of population extinction and reduced genetic diversity. Desert bighorn sheep populations are still found in all 3 of the “hot desert” ecosystems (Mojave, Sonoran, and Chihuahuan Deserts), which are characterized by differences in temperature, the amount and timing of precipitation, and vegetation communities. These different climatic regimes result in dramatic differences in vegetation, which in turn influences the quantity, quality, and timing of forage availability for desert bighorn sheep, and may influence the availability of reliable surface water as well. Persistence of bighorn sheep in the hotter, drier ecosystems may demand increased evolutionary pressure for mechanisms to limit heat stress, such as the enhanced capacity to reduce water loss while maintaining temperature balance. Understanding potential adaptations of desert bighorn sheep in the 3 southwestern desert ecosystems with varying temperature and aridity conditions has the potential to inform vulnerability of populations to potential future changes in climate and other stressors. Specifically, identifying certain genes that may be related to the ecology of the different desert environments can provide valuable insights regarding future adaptation actions (e.g., translocations) as the climate continues to change. Our objectives are to: 1) assess whether desert bighorn sheep exhibit local adaptations to the different desert ecosystems with corresponding differences in seasonal climatic conditions; and 2) provide recommendations on how managers can implement adaptation actions to maximize evolutionary potential.