Sexual communication in ultrasonic frogs Odorrana tormota involves acoustic and various visual signals

Abstract

Female concave eared torrent frogs are known to produce courtship calls to attract males; yet, like other anurans, they also display positive phonotaxis toward male’s calls. Thus, it is unclear how amplexus is formed and which sex makes the mating decision. We investigated how males and females interact and communicate during the reproductive season and found that females emitted vocalizations during the gravid state only. In playback experiments in the wild, female's courtship calls elicited numerous males to respond. Males’ vocal responses were range dependent and accompanied by staccato calls and phonotaxis toward (but short of reaching) the loudspeaker. In short range encounters, gravid females are highly selective, and males must wait for female’s invitational signal(s) for amplexus. Only a select male showing prominent dominant male’s postures received invitational signal(s), comprising a variety of visual signals (head bob, belly inflation, toe tapping, and eye blink) and an “admission” acoustic signal. Upon receiving one or more of these signals, the male immediately hopped on the female’s back to form amplexus. Our studies revealed that intersexual communication in concave eared torrent frogs is complex, involving both acoustic and visual signaling.