Acoustic strategy for avoiding same-sex amplexus in male concave-eared torrent frogs.

In sexually reproducing animals, accurate sex recognition is fundamental for successful mating. Bidirectional signals are a sexually selected mechanism of mate recognition1, involving different, sex-specific cues to signal identity and reduce recognition errors. However, when these signals are insufficiently divergent or become obscured by environmental noise, the probability of misidentification can increase dramatically2. Among frogs, same-sex sexual behavior is widespread and is frequently attributed to sex-recognition errors, ambiguous signals, male-biased sex ratios or the instinct to indiscriminately clasp (amplexus) any suitably sized object they encounter3. Commonly, the male that has been erroneously clasped will emit 'release calls'4. It has been unclear whether frogs have evolved specific mechanisms to avoid such mistakes during acoustic interactions. Here, we report evidence for an acoustic mechanism in concave-eared torrent frogs (Odorrana tormota), through which males reduce such amplexus errors.