Meeting Abstract
Extreme temperatures fundamentally constrain ectotherm physiology and have both acute and chronic effects. Both hormone-modulated stress response pathways and energetic trade-offs are important drivers of variation in life-history strategies. This study employs an integrative approach to quantify the physiological response to high temperatures in divergent life-history ecotypes of the Western Terrestrial Garter Snake (Thamnophis elegans). Using wild-caught animals, we measured oxygen consumption rate and physiological markers in plasma across five ecologically relevant temperatures (24, 28, 32, 35, and 38° C). We discovered that corticosterone, insulin, and glucose all increased with temperature. This indicates that, as seen in mammals, high temperatures can decouple the glucose regulatory mechanism of insulin, a pathway that has not been well-categorized in reptiles. We also determined that oxygen consumption increased without plateau with advancing temperature, but that lactate concentrations were not temperature responsive, challenging the recent hypothesis that oxygen limitation sets upper thermal tolerance levels. We did not find differences between life-history ecotypes in oxygen consumption rates, hormone concentrations, or glucose levels, perhaps indicating convergence of reaction norms in individuals maintained under long-term common garden conditions. The identification of hormonal-mediated response pathways is especially important given uncertainty around the mechanisms that set thermal limits in vertebrates which may soon experience increased frequencies of stressfully high temperatures in the wild.
