The evolution of conspicuousness in frogs: when to signal toxicity?

Many organisms use conspicuous color patterns to advertise their toxicity or unpalatability, a strategy known as aposematism. Despite the recognized benefits of this antipredator tactic, not all chemically defended species exhibit warning coloration. Here, we use a comparative approach to investigate which factors predict the evolution of conspicuousness in frogs, a group in which conspicuous coloration and toxicity have evolved multiple times. We extracted color information from dorsal and ventral photos of 594 frog species for which chemical defense information was available. Our results show that chemically defended and diurnal species have higher internal chromatic contrast, both ventrally and dorsally, than chemically undefended and/or nocturnal species. Among species that are chemically defended, conspicuous coloration is more likely to occur if species are diurnal. Our results also suggest that the evolution of conspicuous color is more likely to occur in chemically defended prey...