Predation facilitates evolution of sex-specific antipredator defences in a sexually dimorphic beetle

Predation is a powerful driving force leading to the evolution of antipredator defences in prey. The effectiveness of the antipredator defences can depend on various ecological contexts such as predator density and the development stages of the prey species. Males and females often exhibit remarkably different morphologies, behaviours and life histories, and the sexual differences are expected to generate different ecological contexts for males and females, potentially driving the evolution of sex-specific antipredator defences. In the horned beetle Gnatocerus cornutus, males have enlarged mandibles, but females lack this exaggeration. As potential defences against predators, these beetles either become immobile or run away. In this study, we established populations subjected to sex-specific predation. We found that male locomotion was increased in populations subjected to male-specific predation and that female immobility was increased in populations subjected to female-specific predation. We also found that males appeared on the surface of food resources more frequently than females. Given such differences in microhabitat preferences, the males are more likely to be detected by predators than the females. The sexual differences in morphology and microhabitat preferences may generate different predatory environments for males and females, resulting in males using locomotion to escape from predators and females using immobility to hide from them. In this laboratory selection experiment, we did not observe the evolution of the opposite sex's antipredator traits in response to sex-specific predation. We detected no intersexual genetic correlation of immobility and locomotion. The genetic decoupling and different predatory contexts for the two sexes may promote sexually different antipredator defences in G. cornutus.