Risks of multimodal signaling: bat predators attend to dynamic motion in frog sexual displays.

Many sexual displays contain multiple components that are received through a variety of sensory modalities. Primary and secondary signal components can interact to induce novel receiver responses and become targets of sexual selection as complex signals. However, predators can also use these complex signals for prey assessment, which may limit the evolution of elaborate sexual signals. We tested whether a multimodal sexual display of the male túngara frog (Physalaemus pustulosus) increases predation risk from the fringe-lipped bat (Trachops cirrhosus) when compared with a unimodal display. We gave bats a choice to attack one of two frog models: a model with a vocal sac moving in synchrony with a mating call (multisensory cue), or a control model with the call but no vocal sac movement (unimodal cue). Bats preferred to attack the model associated with the multimodal display. Furthermore, we determined that bats perceive the vocal sac using echolocation rather than visual cues. Our data illustrate the costs associated with multimodal signaling and that sexual and natural selection pressures on the same trait are not always mediated through the same sensory modalities. These data are important when considering the role of environmental fluctuations on signal evolution as different sensory modalities will be differentially affected.