Experimental evidence of aposematic signal in black tadpoles

Aposematism is a widespread defense mechanism in animals. Anuran amphibians are known for their extensive repertoire of defenses, especially in the adult stage. Color-based mechanisms are particularly common in this group, although their use during the larval stage is still understudied. The hypothesis of aposematism in tadpoles has been suggested for several species that present conspicuous coloration and unpalatability. Tadpoles of some bufonid toads have been considered aposematic for decades, as they have a conspicuous black color, are unpalatable, and form aggregations that make them even more visible. However, few empirical studies have tested aposematism in these larvae against visually oriented predators, such as birds. In this paper, we tested whether the uniform black coloration acts as an aposematic signal in anuran larvae. The research was conducted through field predation experiments using artificial replicas of tadpoles of different colors (brown, gray, and black). The survival of black replicas was significantly higher than that of control groups, supporting the aposematism hypothesis. Given that the replicas varied only in color, we conclude that the differential attacks among treatments were carried out by visually oriented predators, probably birds, that had learned to recognize and avoid black tadpoles.