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 with smaller body size. We discuss potential explanations for this association and suggest that prey profitability (related to body size) could be an important force driving the macroevolution of warning signals.

The dataset attached includes colour information for 594 species of frogs, extracted from photographs (from this study). It also contains additional variables employed in the comparative analysis. These variables were extracted from sources described in the methods of the paper, and include the presence of chemical defences and the time of activity (diurnal/nocturnal). 

Each row represents a different species and the names match the phylogeny of Jetz & Pyron (2018). 

Files also contain the links to the photographs (dorsal and ventral) used for each species, and the raw values of colouration extracted (RGB pixel values for each colour extracted). 

The datasets can be accesed using excel.