Data and code from: Interspecific allometry of sexual shape dimorphism in small-bodied and large-bodied geckos

At macroevolutionary scales and across species, levels of sexual dimorphism often covary with body size, generating allometric trends. While such patterns are most evident for sexual size dimorphism, interspecific trends in sexual shape dimorphism (SShD) remain underexamined. Furthermore, how such patterns are affected by the evolution of small body size (miniaturization) is largely unknown. In this study, we evaluated trends in SShD across 99 gecko species from two families to determine whether small body sizes were associated with increased shape dimorphism in the group. Head shape was characterized using geometric morphometrics from surface scans of nearly 600 individuals, and levels of SShD were quantified for each species. Phylogenetic comparative analyses were then used to evaluate evolutionary patterns of shape dimorphism relative to body size across species. We found considerable variation in the magnitude of SShD across taxa, with some species displaying little dimorphism and others exhibiting large sexual shape differences. Interspecific allometry of SShD differed between the two families, with strong negative allometry observed in Sphaeorodactylidae (a family with many small-bodied species), while in Phyllodactylidae (a family containing few small-bodied species) patterns were more isometric with no discernable trend. Notably, the greater SShD displayed by small-bodied species corresponded with females exhibiting more robust heads, which was consistent with sex-specific foraging strategies and dietary differences observed in this group. Our study reveals that interspecific allometry in traits other than body size can have a pervasive influence on patterns of phenotypic diversity across the tree of life.