Clinging strength, but not sprint speed, underlies morphological divergence between ecologically distinct Liolaemus...

Biomechanical theory suggests a strong link between an organism's physical structure and its ability to perform specific functions. Animals specialized for a particular type of movement, such as running or climbing, are expected to have different anatomical features. Importantly, these specializations often involve trade-offs, where an adaptation that benefits one type of movement may hinder another. Here, we used phylogenetic comparative methods to study the relationships between habitat use, external and muscular morphology, and experimentally obtained performance metrics among a set of Liolaemus species, and tested for performance-based morphological trade-offs between habitat specialists. We found that terrestrial and scansorial species display distinct multivariate phenotypes. Specifically, scansorial species exhibit relatively longer forelimbs, but relatively smaller hindlimb muscles when compared to terrestrial ones. Moreover, morphological proportions associated with scansoriality were found to enhance clinging strength, suggesting that the characteristic morphology exhibited by scansorial species might have evolved due to its positive effect on climbing performance. On the contrary, sprinting performance was not enhanced by morphological proportions associated with terrestriality. In fact, sprint speed was not significantly correlated with morphology, given the traits considered in our study. Overall, our results do not support the existence of a performance-related morphological trade-off between scansorial and terrestrial species in Liolaemus. Instead, they demonstrate how particular ecologies can have a strong impact on morphological evolution even in groups with otherwise conserved body plans.