Meeting Abstract
Thermal acclimation responses, i.e., effects of past temperatures on an organism’s thermal performance curve, have important implications for species responses to increased temperature variability. Adaptive changes in thermal limits (i.e., CTmax) are thought to reflect altered heat-shock protein expression, but we know less about physiological mechanisms driving changes to other parts of the thermal performance curve. Our prior study found higher metabolic performance of the Mexican axolotl (Ambystoma mexicanum) following cold-temperature acclimation (i.e., “cooler is better”). Based on principles from Metabolic Theory of Ecology (MTE) and Dynamic Energy Budget theory (DEB), we postulated that this effect was driven by a mismatch between respiratory and digestive thermal performance curves, resulting in a negative energy budget at warmer temperatures. In the current study, we sought to test further predictions of our MTE/DEB hypothesis and to reconcile past conflicting results by subjecting juvenile axolotls to a combination of thermal-acclimation and food-provisioning treatments. We then measured respiration rates, activity levels, and plasma lipid concentrations at new “performance” temperatures. Our respirometry data confirmed the previously observed “colder is better” pattern and generally indicated higher respiration rates with greater food provisioning, consistent with our hypothesis. However, individuals that were warm acclimated, fasted, and tested at a cold temperature had higher than expected respiration rates and activity levels, possibly reflecting increased foraging activity. Evidence of positive effects of food provisioning and cold-acclimation on triglyceride levels was also consistent with our hypothesis.
