Opportunity for female choice in the wild is frequently curtailed by low male trait variation in Hyla versicolor

To understand the efficacy of female choice in driving the evolution of male displays, we need to not only characterize preferences but examine the opportunity for the expression of such preferences. Mate assessment by females should be constrained if the relative attractiveness of multiple displays is perceived as equal because trait differences between them are indistinguishable. This is expected to result in apparently arbitrary mate choice, and knowledge about the frequency of such mating patterns is crucial in predicting the strength of sexual selection. Here, we examine discrimination abilities of female Hyla versicolor in the context of actual male-male chorus variation. We found that roughly half of mating encounters in the wild do not provide the call variation required for the expression of female preferences (non-arbitrary choice). Interestingly, the trait for which female H. versicolor shows the strongest preference during playback trials (call duration) is not the trait whose difference will most often be detectable to females in the wild (call rate). Furthermore, we document individual variation in discrimination ability, with some females being able to discriminate multiple traits, while others only focus on one trait. This suggests that the relatively high estimate of arbitrary mating is not only due to females struggling to discriminate natural local variation overall but due to an abundance of individuals with limited discrimination abilities that require encounters with males that differ in the specific trait they will discriminate. Lastly, small trait differences between males do not arise from nearest neighbors plastically altering their calls to be more similar. These findings provide insights on the frequently observed mismatch between laboratory phonotaxis and actual mating success in the wild.