Female gray treefrogs maintain mate choice decisions under predation threat, but adjust movements to reduce conspicuousness during mate approach

Abstract

Female mate choice is remarkably complex and has wide-ranging implications for the strength and direction of male trait evolution. Yet mating decisions can be fickle and inconsistent. Here, we explored predation risk as a source of variation in the effort a female is willing to invest in acquiring a preferred mate type (“choosiness”). We did so by comparing phonotaxis behaviors of female eastern gray treefrogs (Hyla versicolor) across trials with and without simulated predators. We tested the behavioral adjustment hypothesis (mate choice is unchanged under predation threat, but mate searching behaviors are modified to reduce conspicuousness) against the mate choice flexibility hypothesis (mate choice becomes indiscriminate under predation threat). Additionally, effectiveness of evasive behaviors may depend on predator attack strategy, so we incorporated two simulated predator cues (bird model vs predatory ranid call). We found support for the behavioral adjustment hypothesis: choosiness was maintained in the presence of predators, but females reduced conspicuousness of mate searching locomotion. Females approached the conspecific male stimuli slower and more cautiously in both predator treatments. In the ranid frog call treatment (stationary cue), females adjusted movements away from predator location. Females also attempted escape more frequently when predator cues were present. We suggest that focusing exclusively on the final mate decision may overlook nuances in mating decisions and hamper our understanding of the remarkable complexity of mate choice.

Significance statement

The presence of predators is an inherent threat to survival. This leads to the general expectation that higher predation risk results in more indiscriminate mate choice decisions and, hence, a weakening of sexual selection. Yet, discriminating mate choice may be maintained if prudent prey change their approach behavior when detecting the presence of a predator. We conducted playback trials with female treefrogs to test whether their willingness to invest in obtaining a more attractive mate (quantified by “choosiness”) differed depending on the presence and type of predation risk. We found that females adjusted their approach behavior in a way that should make them less conspicuous to predators, but that they did not compromise their mate choice decisions. Our results show that strong sexual selection by females’ choice can be maintained in high predation environments.