Recognition of courtship song in the field cricket, Teleogryllus oceanicus

The courtship song of the cricket, Teleogryllus oceanicus plays an important role in inducing the female to mount the male, which is necessary for mating. The song consists of a short, amplitude-modulated chirp, followed by a long trill of constant intensity and high syllable rate. Using playback techniques, it was determined which physical parameters of courtship song are necessary and/or sufficient to evoke normal female mounting of muted, courting males. The higher harmonics of natural courtship song were neither necessary nor sufficient for the effectiveness of the song. The chirp component alone was sufficient to evoke normal levels of mounting, but the trill was only partially effective on its own. The conspicuous amplitude modulation of the chirp was not necessary to evoke normal responses. The results suggest that the high effectiveness of the chirp is due to its characteristic temporal pattern. As in other cricket species, the song repertoire of T. oceanicus also includes distinct calling and aggression songs, which contain chirps that are structurally similar to the courtship chirp. Both calling and aggression songs evoked normal mounting responses when played back in the context of courtship. ? 1996 The Association for the Study of Animal Behaviour Crickets use acoustic signals to communicate with each other. These signals take the form of stereotyped, repetitive songs produced by stridulating males. Many cricket species, including Teleogryllus oceanicus, have a repertoire that includes three structurally distinct songs termed calling, courtship and aggression song, respectively (Alexander 1961). The three songs serve distinct functions: calling song serves to attract females from afar, courtship song induces the female to mount the male, and aggression song is produced during aggressive encounters with other males (Alexander 1962). The evolutionary processes that have resulted in this repertoire of three songs are unknown, but it is generally believed that song in crickets first evolved in the context of courtship (Alexander 1962). The use of song for long-range attraction of females and in interactions with other males probably evolved later. It is therefore interesting to know whether the mechanisms by which calling and courtship songs are recognized share common or similar features. Studies of song recognition have focused on calling song. Female crickets recognize and preferentially orient towards the conspecific calling song, which they identify based on its fundamental frequency and species-specific temporal parameters (reviewed in Elsner & Popov 1978; Doherty & Hoy 1985). The prior identification of song parameters required for behavioural effectiveness has been invaluable in studies of the neuronal mechanisms for calling song recognition (Schildberger et al. 1989). Little is known about the mechanisms, either behavioural or neuronal, of courtship song recognition in any cricket species. The courtship behaviour of T. oceanicus, first described in detail by Burk (1983), is very similar to that of other gryllid species (Alexander 1961; Loher & Dambach 1989; Adamo & Hoy 1994). Briefly, courtship is initiated when the antennae of the male contact the body of the female. The male then vibrates his antennae, adopts a typical singing posture and begins to produce courtship song, simultaneously stroking the female with his antennae. He then turns away from her and presents his abdomen, stridulating all the while. The female Correspondence: G. Pollack: Department of Biology, McGill University, 1205 Dr Penfield Avenue, Montreal, Quebec H3A 1B1, Canada (email: [email protected]). 0003–3472/96/020353+14 $12.00/0 ? 1996 The Association for the Study of Animal Behaviour