LAUSR

The initial evolution of warning signals in unprofitable prey, termed aposematism, is often seen as a paradox because any new conspicuous mutant would be easier to detect than its cryptic conspecifics and not readily recognized by naïve predators as defended. One possibility is that permanent aposematism first evolved through species using hidden warning signals, which are only exposed to would-be predators on encounter. Here, we present a large-scale analysis of evolutionary transitions in amphibian antipredation coloration and demonstrate that the evolutionary transition from camouflage to aposematism is rarely direct but tends to involve an intermediary stage, namely cryptic species that facultatively reveal conspicuous coloration. Accounting for this intermediate step can resolve the paradox and thereby advance our understanding of the evolution of aposematism. Description Warning signs Using bright coloration to warn predators off of toxic prey, or aposematism, presents a conundrum in evolution. How do brightly colored organisms survive long enough to warn predators when they are easier to predate than their cryptic peers? Loeffler-Henry et al. used a large phylogeny of amphibians with known warning coloration to assess how such displays evolve. After comparing a series of models, they determined that aposematism likely appears through intermediate steps in which coloration is only visible when an organism is fleeing or intentionally displaying a hidden feature. This work demonstrates how the cost of such a trait may be circumvented through intermediary phenotypes. —CNS Conditionally visible coloration in amphibians may be an important step in the evolution of warning coloration.