Thermophysiology and Locomotor Performance of the Andean Lizard Phymaturus williamsi: Vulnerable to Rising...

Ambient temperature strongly influences the physiology and performance of ectotherms, making it essential to understand their responses to thermal variation under climate change. We evaluated locomotor performance and thermal vulnerability in a population of Phymaturus williamsi from the Argentine Andes. Field measurements included body (T_b) and operative temperatures (T_e), while laboratory analyses assessed preferred temperature (T_pref), thermoregulatory effectiveness, critical thermal limits, and thermal sensitivity of locomotion (endurance, sprint, and long runs). P. williamsi exhibited a preferred temperature higher than field body temperatures, together with high thermoregulatory effectiveness (E = 0.83) and a broad thermal tolerance range (TT = 35.41 °C). Optimal temperatures for locomotor performance were lower than T_pref, providing no support for the thermal coadaptation hypothesis. Despite low environmental thermal quality, individuals maintained body temperatures close to performance optima through effective behavioral thermoregulation. Thermal vulnerability indices indicated relatively high tolerance to projected warming scenarios. However, our results suggest that vulnerability to climate change is constrained more by the availability of suitable thermal microhabitats than by intrinsic physiological limits. We conclude that P. williamsi is a eurythermic and effective thermoregulator with thermally sensitive locomotor performance, whose persistence will depend on habitat structure and thermal heterogeneity.