Eavesdropping micropredators as dynamic limiters of sexual signal elaboration and intrasexual competition

To thoroughly understand the drivers of dynamic signal elaboration requires assessing the direct and indirect effects of naturally interacting factors. Here, we use structural equation modeling (SEM) to test multivariate data from in situ observations of sexual signal production against a model of causal processes hypothesized to drive signal elaboration. We assess direct and indirect effects, and relative impacts, of male-male competition and attacks by eavesdropping frog-biting midges (Diptera: Corethrellidae) on call elaboration of male túngara frogs (Engystomops pustulosus). We find that the intensity of attacks by these micropredator flies drives the extent to which frogs elaborate their calls, likely due to a temporal trade-off between signaling and anti-micropredator defense. Micropredator attacks appear to dynamically limit a male’s call rate and complexity and consequently dampen the effects of intrasexual competition. In accounting for naturally interacting drivers of signal elaboration, this study presents a counterpoint to the mechanisms traditionally thought to drive sexual selection in this system. Moreover, the results shed light on the relatively unexamined and potentially influential role of eavesdropping micropredators in the evolution of sexual communication systems.