WELCH, A.M.*; REICHERT, M.S.; Univ. of North Carolina, Chapel Hill; Univ. of North Carolina, Chapel Hill: Plasticity in frog calling: sexier rivals elicit costlier calls

In many species, males aggregate and display during the breeding season, while females choose among potential mates based on display attractiveness. Social interactions among males within these groups can affect male signaling and, thereby, patterns of female choice; hence, understanding male interactions within leks is important to understanding how these sexual signaling systems evolve. Male gray tree frogs, H. chrysoscelis, alter their calls in response to playbacks of conspecific signals. We investigated this socially-mediated plasticity in signaling as a function of specific features of the stimulus that could serve as cues to the social context. Using playback experiments in the field, we found that male H. chrysoscelis altered their calls in response to two distinct social cues: stimulus loudness and stimulus attractiveness. In response to louder stimuli, males produced longer calls at slower rate. This result explains the previously documented effect of chorus density on male call length and rate, as loudness should increase in denser choruses. In response to more attractive stimuli (longer calls with higher calling effort), males increased call length and calling effort, resulting in increased energetic expenditure. Hence, it appears that males invest more in signaling when faced with more attractive competitors. The different responses to these two social cues may reflect variation, among social contexts, in the adaptive value of different signal features.