An Evolutionary Game Model of Sex-Dependent Antipredator Signaling

Various prey animals behave conspicuously to approaching predators. The conspicuous behavior is considered to be an antipredator signal, and the frequency of signaling individuals in a population differs between males and females in many species. We theoretically assessed the evolution of the inter- and intrasexual dimorphism in antipredator signaling by developing an evolutionary game model. We particularly focused on the Chinese grasshopper, Acrida cinerea, in which only a proportion of males and no females escape conspicuously. In our model, the antipredator signal was assumed to be costly and affect the probabilities of predation of both the signaling individual (individual effect) and the signaling or nonsignaling conspecifics around it (collective effect). The model indicates that (1) a positive individual effect is essential for the evolution of antipredator signaling; (2) sexual dimorphism in fecundity cost for signaling individuals or natural predation probability can produce intersexual dimorphism in the signaling where all individuals of one sex and no individuals of the other sex emit signal; and (3) a positive collective effect can explain the intrasexual dimorphism where only some individuals of one sex signal. This study provides the first model of intrasexual dimorphism in antipredator signaling and brings new testable predictions.