Climatic niche evolution and desert colonization in a South American lizard radiation

Organisms in adaptive radiations are able to diversify and colonize multiple environments. Frequently, the evolution of key adaptations enables organisms to confront novel environmental challenges, promoting diversification. Here, we studied desert colonization in the Liolaemus radiation. We assessed the patterns of climatic niche evolution in the L. nigromaculatus section, one Liolaemus clade inhabiting the Atacama Desert. We found that evolution toward arid conditions occurred in two clades independently: one clade colonized the desert through warm coastal environments, and the other through cold highland environments on the Andes Mountains. The precipitation climatic niche evolved fast and early during this clade’s evolutionary history, following an early burst (EB) model of evolution, whereas the thermal climatic niche evolved under Brownian motion (BM) and at a lower rate. Additionally, we explored some features that could have facilitated desert colonization: a higher chromosome number was associated with warmer temperatures, lower selected body temperatures were associated with higher environmental temperatures and drier climates, larger and more elongated bodies with colder environments, and longer limbs and tails were associated with higher thermal variation. Our results highlight that organisms can confront challenging environments in multiple ways such that some niche axes may evolve faster during the colonization of novel environments, and that radiated groups may have the evolutionary potential to rapidly evolve these adaptations.