Use of non-arbitrary acoustic criteria in mate choice by female gray tree frogs

The evolutionary significance of female choice is controversial1. Central to the issue are the mechanisms and criteria used by females to choose among potential sexual partners. For example, females merely responding to conspicuous displays that are uncorrelated with male condition or quality would neither incur costs of assessment nor gain benefits over and above random mating2. Here we show that selective phonotaxis by female gray tree frogs depends on non-arbitrary acoustic cues that indicate the male's species and energetic costs of signal production. Furthermore, some female preferences cannot be explained by differences in signal conspicuousness (acoustic energy) alone. Females obviously benefit by rejecting genetically incompatible, heterospecific males, which can be identified solely by pulse rate. Females also select among conspecific males on the basis of call duration, which is correlated with a male's energetic investment in courtship and probably indicates his physical condition and fitness.