Temperature has species-specific effects on corticosterone in alligator lizards

In response to conditions that threaten homeostasis and/or life, vertebrates generally increase production of glucocorticoid hormones, such as corticosterone (COAT), which induces an emergency physiological state referred to as the stress response. Given that extreme temperatures pose a threat to performance and survival, glucocorticoid upregulation might be an important component of a vertebrate ectotherm's response to extreme thermal conditions. To address this hypothesis, we experimentally examined the effects of body temperature (10, 20, 28, and 35 degrees C; 5-h exposure) on CURT in two congeneric species of lizard naturally exposed to different thermal environments, northern and southern alligator lizards (Elgaria coerulea and Elgaria multicarinata, respectively). In both species, CURT was similarly elevated at medium and high temperatures (28 and 35 degrees C, respectively), but CURT was only elevated at low temperatures (10 degrees C) in southern alligator lizards. We also examined CURT before and after adrenocorticotrophic hormone (ACTH) challenge. In both species, ACTH induced higher CURT levels than any temperature, suggesting that these animals could respond to further stressors at all experimental temperatures. Finally, we compared our laboratory results to measurements of CURT in field-active southern alligator lizards. Plasma CURT concentrations from our laboratory experiment had the same mean and less variance than the field lizards, suggesting that our laboratory lizards displayed CURT within natural levels. Our results demonstrate that body temperature directly affects CURT in alligator lizards. Moreover, the CURT response of these lizards appears to be adapted to their respective thermal environments. Species-specific differences in the thermal CURT response might be common in vertebrate ectotherms and have implications for species' biogeography and responses to climate change. (C) 2014 Elsevier Inc. All rights reserved.