Geographic variation in the thermal biology of a widespread Sonoran Desert arachnid, Centruroides sculpturatus (Arachnida: Scorpiones)

Abstract

Environmental temperatures can significantly influence the behavior and physiology of terrestrial ectotherms. Small-bodied terrestrial ectotherms can moderate their body temperatures behaviorally via thermoregulation; however, favorable thermal refuges may be limited across heterogeneous landscapes. In such cases, differences in the thermal environment may generate variation in preferred body temperatures among disparate populations. We tested whether geographic variation in preferred body temperatures existed for the Arizona bark scorpion Centruroides sculpturatus, an arachnid widely distributed across the Sonoran Desert. We predicted that geographic variation in thermal preference would exist between populations from a xeric, low-elevation site in western Arizona (Quartzsite) and a cooler, high-elevation site in eastern Arizona (Pinaleño Mountains). We found that scorpions from the Pinaleño Mountains were smaller in body size and exhibited significantly warmer diurnal body temperatures compared to scorpions from Quartzsite. However, no significant difference was detected in the preferred nocturnal temperatures of scorpions from either locality. Scorpions from the Pinaleño Mountains may have shifted their thermoregulatory patterns and selected warmer temperatures during the day as a way to maximize their exposure to favorable temperatures. Less time with mean temperatures within the preferred range of body temperatures may have also lowered metabolic rates of C. sculpturatus in the Pinaleño Mountains, resulting in their smaller female body sizes. The ability of C. sculpturatus to adapt to different thermal regimes may reflect variation in a life history trait which has allowed them to thrive and expand their distribution across the American Southwest.