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.