Mating preference functions of individual female barking treefrogs, Hyla gratiosa, for two properties of male advertisement calls.

A mating preference function describes the relationship between variation in a trait in potential mates and the strength of the preference for that trait. Few studies have measured mating preference functions either at a population level or for individuals. We used two-choice playback experiments to determine the mating preference functions of individual female barking treefrogs for two call characteristics: call-repetition rate and fundamental frequency. We tested each female four times with each pair of stimuli and with three to six pairs of stimuli. Individual females exhibited directional preferences for higher call rates and stabilizing preferences for intermediate fundamental frequency. These individual preference functions were similar to population-level preferences documented in previous studies. Within a stimulus type (call rate or fundamental frequency), nearly all females exhibited the same general preference function. However, females varied in the minimum difference between stimuli necessary to elicit a unanimous choice for the higher call rate, and they differed in both the intermediate fundamental frequency they preferred most and the minimum difference in fundamental frequency that elicited a unanimous choice for one of the two alternatives. The variation we observed among females was not repeatable; repeatabilities were in general low and statistically nonsignificant. The observed variation in the preferences of females, even if unrepeatable, should weaken selection on male traits relative to selection in the absence of such variation.