Hidden signals play a vital role in evolution of warning coloration in amphibians

New findings help answer a particularly vexing evolutionary question: how do species that use bright coloration to keep predators away survive long enough for this warning signal coloration to evolve, before predators who can better spot them through their colors learn to avoid them? A study comparing a series of models points to warning color signaling, or aposematism, likely appearing through intermediate steps where coloration is only visible when an organism is fleeing or intentionally displaying a hidden feature. Evolutionary selection to avoid being eaten by predators has driven considerable variation in the diversity of animal color patterns. Some species have developed camouflage coloration, enabling them to blend into the background and avoid detection by other animals. Others evolved to exhibit bright colors – conspicuous warning signals boldly advertising defenses like toxicity, venom, or aggression to would-be predators. This strategy is also known as aposematism, and its evolutionary origin is poorly understood. Karl Loeffler-Henry and colleagues performed a large-scale phylogenetic analysis of more than 1,400 amphibian species with known warning coloration and a series of nine different evolutionary models to assess how aposematism evolves. Loeffler-Henry et al. found that the transition from camouflage coloration to aposematism is rarely direct and instead likely arises through a series of intermediate steps where warning coloration is first hidden and only selectively visible. According to the authors, predators exposed to these hidden warning signals would continue to treat permanently aposematic mutants with caution, providing selective pressure for warning coloration to become a permanent adaptation. “… Macroevolutionary studies on animal coloration should take into account these underappreciated hidden signals, which are both common and widespread across the animal kingdom, to advance our understanding of the evolution of antipredator defenses,” Loeffler-Henry et al. write.