The Andes are a driver of physiological diversity in <i>Anolis</i> lizards

Abstract The Andes, with its diverse topography and climate, is a renowned cradle for adaptive radiation, particularly for vertebrate ectotherms such as lizards. Yet, the role of temperature in promoting physiological specialization in the Andes remains unclear. Aseasonality in the tropics should favour physiological specialization across elevation in lizards, but empirical data are limited and equivocal. Determining how thermal tolerances are geographically and phylogenetically structured is therefore a priority, particularly as environments continue to change rapidly. However, there is a gap in our knowledge of thermal limits of species from the Andes, one of the planet’s most biodiverse regions. Anoles, a diverse lizard group found across thousands of metres of elevation in the Andes, can offer insights into evolutionary adaptations to temperature. This study focused on 14 anole species from two clades (Dactyloa and Draconura) that independently diversified along elevational gradients in the Andes. We measured critical thermal limits (CTmin and CTmax) and found patterns of thermal tolerance specialization across elevation, both among and within species. Patterns of thermal specialization are similar among anole clades, indicating parallel responses to similar environmental pressures. Specifically, high-elevation anoles are more cold tolerant and less heat tolerant than their low-elevation counterparts, rendering thermal tolerance breadths stable across elevation (thermal specialization). Evolutionary rates of physiological traits were similar, reflecting parallel specialization in heat and cold tolerance across elevation. The adaptive radiation of anole lizards reflects physiological specialization across elevation, and the endemism such specialization favours, probably catalysed their remarkable diversity in the tropical Andes.