Effects of Temperature on the Thermal Biology and Locomotor Performance of Two Sympatric Extreme Desert Lizards

Lizards are ideal models for investigating animal adaptations to climate change, given their sensitivity to temperature and their significance in physiological ecology. In this study, the effects of temperature on the thermal biology and locomotor performance of two sympatric desert lizards, Eremias roborowskii and Phrynocephalus axillaris, were examined. We analyzed morphological differences, the relationship between environmental temperatures (T_e) and selected body temperatures (T_sel), and locomotor performance across varying T_e. We also assessed the critical thermal maximum (CT_max) and active body temperature (T_b) to evaluate current thermal conditions. Our results indicate that E. roborowskii's T_sel line intersected isotherm at 27.37 °C is higher than P. axillaris (27.04 °C), and the difference in correlation coefficients between the T_sel line and isotherm indicates that P. axillaris exhibits a superior physiological thermoregulatory capacity, exhibiting less dependence on T_e. Locomotor performance assessments showed P. axillaris and E. roborowskii displayed distinct strengths in sprint speed, number of pauses, and maximum distance movement. Eremias roborowskii demonstrated better endurance with fewer pauses and a more consistent length of continuous movement at higher T_e, while P. axillaris exhibited a faster sprint speed (0.8355 vs. 0.8157 m/s at 30 °C) and greater movement distance (78.53 vs. 89.82 cm at 32 °C). These differences may be attributable to variations in body size and ecological strategies, as E. roborowskii is an ambush lizard, whereas P. axillaris is an active striking type, which suggests that there is a balanced relationship between endurance and speed. Our study provides critical insights into the convergent evolution and ecological adaptation of two sympatric lizard species in extreme desert ecosystems.