How Thermal Tolerance Shapes Species Distributions: An Integrative Perspective on the Most Diverse Lizard Family from...

AbstractUnderstanding how thermal tolerance determines species distributions is key to predicting species persistence in changing climates. However, thermal tolerance evolution is likely associated with multiple interacting abiotic and biotic factors, which are rarely explored in combination. Using an integrative framework, we examine how thermal tolerance breadth (TTB) relates to environmental variability, life history traits, and geography in a diverse lizard radiation (family: Phrynosomatidae). We test whether TTB evolution is primarily associated with shifts in cold tolerance (CT_min) or heat tolerance (CT_max) and assess its relationship with temperature variability, vegetation cover, range size, elevational range, reproduction mode, thermal preference, and body size. We found that, contrary to expectations, CT_max exhibits more macroevolutionary shifts than CT_min. Moreover, TTB shows no association with intrinsic traits such as body size and parity mode, suggesting that the evolution of TTB is primarily relevant in the context of environmental pressures rather than intrinsic biological constraints. Finally, causal models revealed that species with broader TTB tend to occupy more thermally heterogeneous regions, which in turn facilitates range expansion. A broader TTB may facilitate species persistence under changing climates, and incorporating physiological traits into conservation assessments could help identify species most vulnerable to climate change, particularly when thermal limits are evaluated in relation to environmental temperatures.