The "sexual selection hypothesis" for the origin of aposematism.

The evolution of aposematism, in which prey exhibit conspicuous signals indicating the presence of antipredator defenses, is puzzling. Before predators learn to associate the signal with defense, increased visibility makes the conspicuous prey highly vulnerable to predation. Although several hypotheses have been proposed to explain the evolution of aposematism, they often assume that these signals can only be recognized by predators. Yet, many studies show that aposematic signals can also be involved in mate choice. Here, we demonstrate that some aposematic signals may have originally evolved as mating signals driven by sexual selection. In this study, we analyze a mathematical model to explore how sexual selection can drive the evolution of aposematism. We thereby identify key features of this "sexual selection hypothesis" for the origin of aposematism to be tested with empirical data. Our results show that the evolution of conspicuous signals through sexual selection increases the visibility of prey to predators and thus predation pressure. This, in turn, promotes the evolution of defense mechanisms, ultimately leading to aposematism when predators learn to associate the signal with defense. Additionally, we show that when sexual selection drives the evolution of aposematism, it often results in sexual dimorphism in both signaling and defense traits.