Behaviour 2019
Assessing the relative impacts of eavesdropping enemies and male-male competition on signal dynamics
Brian C. Leavell1, Gordon G. McNickle2,3, Ximena E. Bernal1,4. 1Department of Biological Sciences, Purdue University, West Lafayette, IN, United States; 2Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN, United States; 3Center for Plant Biology, Purdue University, West Lafayette, IN, United States; 4Smithsonian Tropical Research Institute, Apartado, Balboa, Ancón, Panama

Sexual selecti­on often favors the evolution of highly conspicuous mating displays. Yet, such overt displays carry the risk of interception by eavesdropping enemies—predators, parasitoids and parasites that exploit communication systems to find their signaling victims. In examining how these opposing forces shape signals, researchers commonly study bivariate relationships between a signal property and a putative modifying force. It remains unclear how signals are affected by the interactions of multivariate, competing forces. Here, we address this gap by integrating multivariate observed data with a hypothesized network of causal processes. Specifically, we determine if the dynamic calling behavior of male túngara frogs (Engystomops pustulosus) fits a structural equation model that is based on the hypothesis that a male’s signaling effort is influenced by midge attack rate, anti-midge defense, bat predation risk, and number of male competitors. We then use this model to assess the direct and indirect effects, and relative impact, of male-male competition and eavesdropping predators on frog calling effort. Our findings highlight the complexity underlying signal dynamics.