Nested Effects of Climate and Substrate in Functional Trait Investment: Insights from Chemical Communication in Geckos

Abstract

Chemical communication is a crucial signalling mode in lizards, yet its ecological and evolutionary drivers remain poorly understood. In geckos, chemical cues are secreted by follicular glands, whose numbers vary widely across species. To test whether this variation reflects phylogenetic conservatism or ecological adaptation, we assembled trait and ecological data for 659 species (Infraorder: Gekkota) and analysed three predictors--substrate use, diel activity, and climatic regime--using phylogenetic comparative models and path analysis. We detected partial phylogenetic conservatism, but ecological factors explained substantial additional variation within the trait. Substrate exerted the strongest direct effect: terrestrial species consistently had fewer glands than arboreal or rupicolus species, likely reflecting differences in signal persistence across habitats. Climatic factors predominantly exerted an indirect effect, by influencing substrate availability and modulating its influence. Arid conditions selected for reduced chemical investment, whereas mesic, structurally complex forests favoured elevated gland numbers, likely to compensate for faster chemical degradation. These results demonstrate that chemical signalling in geckos evolves under a nested hierarchy of constraints, with climate setting broad ecological limits and substrate imposing the strongest immediate selection. This multiscale framework refines sensory evolution theory and clarifies how communication traits respond to ecological and climatic contexts.