Costly traits in a dynamic world: trait responses to fine-scale varying environment differ according to selection pressures in a tropical lizard.

Under current climate change patterns, rapidly changing environments can impose strong selection on traits. Costly traits that require heavy investment and strongly affect fitness may be particularly vulnerable to such changes. Despite organisms experiencing dynamic environments, our knowledge of costly trait response is limited as longitudinal studies across generations are rare. Using a long-term 11-generation dataset, we examined how fine-scale spatial and temporal variation in ecological and demographic conditions modify costly traits, specifically positive allometry in morphological traits under different selection pressures, in Psammophilus dorsalis, a short-lived socially polygynous lizard. We comprehensively measured males and females across non-overlapping generations and space and quantified fine-scale variation in key ecological and demographic parameters. Positive allometry in male head width (under sexual selection) varied dramatically over generations and space. Limited rainfall, harsh temperatures, and greater competition promoted positive allometry in male head width. In stark contrast, positive allometry in female interlimb length (under fecundity selection) only weakly correlated with environmental conditions. We demonstrate that costly traits are sensitive to changing environments depending on the underlying selection pressure, with sexually selected traits showing larger effects in tropical lizards. Future climatic predictions, indicating accelerated warming and altered rainfall, can strongly impact phenotypes in tropical lizards.