Predation risk increases permissiveness for heterospecific advertisement calls in túngara frogs, Physalaemus pustulosus

Factors that influence the strength of sexual selection within a population may have important consequences for the evolution and maintenance of reproductive isolation between populations. Here we examine the role of one such factor, predation risk, in influencing female permissiveness for heterospecific advertisement calls. Specifically, we tested the effect of simulated predation risk on mate choice in female túngara frogs, Physalaemus pustulosus, using variation in ambient light levels, travel time and the presence of auditory cues of local predators. Simulated predation risk increased female permissiveness for advertisement calls along an artificial gradient of calls intermediate between conspecifics and a congener, Physalaemus enesefae. Across the entire gradient, the presence of auditory cues of the predatory frog Leptodactylus pentadactylus in association with the conspecific call dramatically increased the likelihood of females choosing the intermediate call. In addition, higher ambient light levels and simulation of increased travel distances both increased the likelihood that females would choose intermediate calls over conspecific calls. These results suggest that, although mate choice may be important in causing reproductive isolation between allopatric populations, spatial or temporal variation in predation risk may strongly influence the expression of mate choice and thus the outcome of secondary contact.