Physiology at near-critical temperatures, but not critical limits, varies between two lizard species that partition the thermal environment

The mechanisms that mediate the interaction between the thermal environment and species’ ranges are generally uncertain. Thermal environments may directly restrict species when environments exceed tolerance limits (i.e. the fundamental niche). However, thermal environments might also differentially affect relative performance among species prior to fundamental tolerances being met (i.e. the realized niche).
We examined stress physiology (plasma glucose and corticosterone), mitochondrial performance, and the muscle metabolome of congeneric lizards that naturally partition the thermal niche, Elgaria multicarinata (southern alligator lizards; SAL) and E. coerulea (northern alligator lizards; NAL), in response to a thermal challenge to quantify variation in physiological performance and tolerance.
Both NAL and SAL displayed physiological stress in response to high temperature, but neither showed signs of irreversible damage. NAL displayed a higher baseline mitochondrial respiration rate t...