Socially mediated plasticity of chorusing behavior in the gladiator frog Hypsiboas rosenbergi

Abstract

Competition for mates often occurs in social set- tings composed of many displaying males. While this poses some special challenges for communication, the proximity of other males may also provide information that chorus partic- ipants may use to adaptively adjust their calling behavior to the local level of competition. Conducting behavioral obser- vations in natural choruses as well as playback experiments with focal males, I investigated socially mediated plasticity in the calling behavior of a neotropical gladiator frog, Hypsiboas rosenbergi. In natural choruses, male call rate was negatively correlated with the distance to the nearest calling neighbor, suggesting that the presence and distance of competing males influences call rate in this species. In a playback experiment thattestedfortheeffectofthepresenceandcompetitivenessof rivals, H. rosenbergi males proved able to quickly notice changes in their acoustic environment and to respond to those changes in a graded fashion. As competition increased (either by increasing the number or attractiveness of the simulated rivals), males raised their calling rate; as competition was reduced, males lowered their calling rate. This indicates that males can perceive changes in their social environment and modify their calling behavior in ways that reflect the level of competition in the chorus. This socially mediated plasticity in calling behavior may help males to economize their energy reserves.