Warts and all: evolutionary and ecological patterns in frog skin texture

The external appearance of frog skin varies among species and across body regions. Although this variation has long been recognized, it remains an understudied aspect of frog diversity. Further, the evolutionary processes driving this variation are unclear because previous work has been largely qualitative. Here we quantify the skin texture of 187 species spanning 45 of the 57 frog families using standardized gel-based profilometry. Using phylogenetic comparative models we explore the extent to which skin texture differs among body regions, how these differences have evolved across major frog clades, and whether microhabitat, climate, and body size help explain texture patterns. We find that the ventral posterior region, which functions in water uptake and rehydration, tends to be rougher than other body regions, yet skin texture evolves at similar rates across the body. Microhabitat, particularly arboreality, is linked to greater skin texture variation among body regions. Among species occupying more terrestrial microhabitats (e.g., arboreal, burrowing, leaflitter), we find that body size and local climate has little effect on skin texture. By comparing skin texture across a wide range of species and environments worldwide, our study tests hypotheses about external skin diversity in frogs that have previously received limited comparative evaluation and highlights texture as an informative component of amphibian skin biology.