Walking or hanging: the role of habitat use for body shape evolution in lacertid lizards.

Differences in habitat use impose ecological constraints which in turn lead to functional and morphological differences through adaptation. In fact, a convergent evolutionary pattern is evident when species exhibit similar responses to similar environments. In this study, we examine how habitat use influences the evolution of body shape in lizards from the family Lacertidae. We divided our species into two categories: ground-dwellers and climbers, which encompasses the verticality and horizontality aspects of the habitat. We performed phylogenetic comparative analyses employing 186 species and seven linear morphological traits. Our results show contrasting patterns between head and limb shapes, which are considered distinct functional blocks. We observed differences in forelimb proportions, but not in hindlimb length, contrary to what was documented in other lizard groups, demonstrating a novel axis in the limb-locomotion-habitat relationship in this family. In addition, a clear effect of habitat use on head shape was detected. We observed that climbing species present on average flatter heads than ground-dwelling species, as well as different evolutionary trajectories. These findings suggest the complex interplay between habitat use and morphological evolution in lizards, highlighting how distinct selective pressures drive divergent adaptations in different functional traits.