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Relationships between behavioral regulation, environmental temperatures, and physiological tolerance are critical to conservation policy; however, these relationships may not be consistent among sister taxa. A species geographic range is influenced by various factors including physiological tolerance to temperature change. In this study, we investigated the effects of temperature variation on thermal preference and standard metabolic rates (SMR) of two species of larval salamanders, Eurycea cirrigera (Southern Two-Lined Salamander) and Eurycea wilderae (Blue Ridge Two-Lined Salamander). These species share similar life histories, but E. cirrigera is broadly distributed and E. wilderae occupies a smaller range. We measured SMR using volume of oxygen consumption during closed-circuit respirometery trials conducted at 5°C increments between 5°C and 25°C. Standard metabolic rates were influenced by temperature, with a range of temperature-independent SMRs observed at those temperatures above each species laboratory-determined thermal preference. Concordant with their thermal preference (15.70°C) and more-narrow geographic range, E. wilderae exhibited a smaller scope of temperatures at which SMR was temperature-independent, relative to E. cirrigera, and metabolic rates were depressed at 25°C. Therefore, preferred thermal temperatures corresponded with physiological maxima and environmental temperatures in each species. Our results support the importance of behavioral thermoregulation in maintaining optimal physiological function. Further, these findings indicate that the physiological specialization that occurs in species of narrow geographic ranges may preclude favorable responses to changing environmental temperatures caused by land-cover changes, including loss of riparian forest in the Eastern United States.
