Purdue University; Smithsonian Tropical Research Institute, United States
Abstract: Sexual selection often favors the evolution of highly conspicuous mating displays. Emitting such overt displays carries the risk of interception by eavesdropping enemies, i.e. predators, parasitoids and parasites that exploit communication systems to find and attack their signaling victims. Yet, many signalers assess and respond to variation in predation risk and can defend themselves through risk-dependent behaviors to mitigate potential costs. We have shown that frog-biting midges (Diptera: Corethrellidae) limit the elaboration of the sexual signals of túngara frogs (Engystomops pustulosus) based on the rate of their attacks. Here, we investigate to what extent defending against midge attack affects the relative calling behavior of competing males. Further, we investigate the relative fitness consequences between rivals of differing calling and defensive strategies. In recording rival responses to multimodal (airborne and vibratory) playbacks, we show that by eliciting anti-midge defenses in calling males, these eavesdroppers indirectly enhance the elaboration of their victim’s rival. Using female choice and predation experiments with eavesdropping, fringe-lipped bats (Trachops cirrhosus), we show that these relative shifts in the call elaboration of competing males impact each male’s relative fitness. Preliminary results suggest that strategies that emphasize defense against frog-biting midge attacks directly and indirectly reduce a male’s attractiveness to females and, to a lesser extent, the predatory bats. Thus, eavesdropping natural enemies appear to dynamically shape the relative fitness of males that compete for mating opportunities. We posit that eavesdropping micropredators likely have an unappreciated impact on the ecology and evolution of communication systems.
