Mate sampling by female barking treefrogs (Hyla gratiosa)

Despite intense interest in mate choice, relatively little is known about how individuals sample prospective mates. Indeed, a key issue is whether females sample males or simply mate with the first male encountered. We investigated mate sampling by female barking treefrogs (Hyla gratiosa). Females choosing mates in natural choruses did not move between males but instead mated with the first male they approached closely. Most females mated with the male closest to them at the start of their mate-choice process, and females were more likely to mate with the closest male when the distance to other males was large. These observations are consistent with the hypothesis that females do not sample potential mates but instead mate with the first male they distinguish from the rest of the chorus. To test this initial detection hypothesis, we conducted a playback experiment in which we offered females a choice between two calls, one of which was detectable above the background chorus sound at the female's release point, and one of which became detectable only as females moved toward the initially detectable call. Females did not prefer the initially detectable call, thus ruling out the initial detection hypothesis and implicating sampling of potential mates by females. Based on the behavior of females in natural choruses, we hypothesize that females approach the Chorus, move to locations where they are able to detect the calls of several males simultaneously, and choose a mate from among these males at some distance from the males. Such simultaneous sampling may be common in lekking and chorusing species, which have been the subjects of many studies of sexual selection.