Anim. Behav., 1996, 51, 353–366 Recognition of courtship song in the field cricket, Teleogryllus oceanicus ROHINI BALAKRISHNAN & GERALD S. POLLACK Department of Biology, McGill University (Received 4 November 1994; initial acceptance 9 February 1995; final acceptance 9 June 1995; MS. number: 7146) Abstract. 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 and courtship songs are recognized share common with each other. These signals take the form of or similar features. stereotyped, repetitive songs produced by stridu- Studies of song recognition have focused on lating males. Many cricket species, including Tel- calling song. Female crickets recognize and pref- eogryllus oceanicus, have a repertoire that includes erentially orient towards the conspecific calling three structurally distinct songs termed calling, song, which they identify based on its fundamen- courtship and aggression song, respectively tal frequency and species-specific temporal param- (Alexander 1961). The three songs serve distinct eters (reviewed in Elsner & Popov 1978; Doherty functions: calling song serves to attract females & Hoy 1985). The prior identification of song from afar, courtship song induces the female to parameters required for behavioural effectiveness mount the male, and aggression song is produced has been invaluable in studies of the neuronal during aggressive encounters with other males mechanisms for calling song recognition (Alexander 1962). (Schildberger et al. 1989). Little is known about The evolutionary processes that have resulted in the mechanisms, either behavioural or neuronal, this repertoire of three songs are unknown, but it of courtship song recognition in any cricket is generally believed that song in crickets first species. evolved in the context of courtship (Alexander The courtship behaviour of T. oceanicus, first 1962). The use of song for long-range attraction of described in detail by Burk (1983), is very similar females and in interactions with other males prob- to that of other gryllid species (Alexander 1961; ably evolved later. It is therefore interesting to Loher & Dambach 1989; Adamo & Hoy 1994). know whether the mechanisms by which calling 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 sing- ing posture and begins to produce courtship song, Correspondence: G. Pollack: Department of Biology, McGill University, 1205 Dr Penfield Avenue, simultaneously stroking the female with his anten- Montreal, Quebec H3A 1B1, Canada (email: nae. He then turns away from her and presents his [email protected]). abdomen, stridulating all the while. The female 0003–3472/96/020353+14 $12.00/0 ? 1996 The Association for the Study of Animal Behaviour 353 354 Animal Behaviour, 51, 2 0 (a) (b) –20 –40 –60 –80 Relative intensity (dB) 0 6183012 24 0122461830 Frequency (kHz) Chirp Trill 200 ms (c) 30 ms Figure 1. The courtship song of T. oceanicus. (c) The oscillogram shows the amplitude-modulated chirp and long, constant-intensity trill. A portion of the trill is shown on an expanded time scale below. (a) Power spectrum of a single (high-amplitude) chirp pulse. (b) Power spectrum of a single trill pulse. Both chirp and trill pulses have a dominant peak at the fundamental frequency of 4–5 kHz and higher harmonics extending up to at least 30 kHz. Points superimposed on the spectra are mean (&) values of the relative intensity levels and frequencies of the harmonics. Data are based on analysis of at least 67 chirp and trill pulses in recordings from seven males. reacts by following the male, approaching from success in eliciting a mounting response from the behind and touching his abdomen with her anten- females. Mounting can be restored if courtship is nae and palpi, whereupon the male spreads his accompanied by playback of recorded courtship hind wings and flattens his abdomen, allowing her song. to mount him. Mounting of the male by the The courtship song of T. oceanicus (previously female is a prerequisite for copulation. described by Leroy 1966; Hutchings & Lewis The role of courtship song in T. oceanicus was 1984; Libersat et al. 1994) consists of a 7–10 pulse, first examined by Burk (1983). From observations amplitude-modulated chirp (Fig. 1), followed by a of males under semi-natural conditions, he con- long trill (2–4 s) of high pulse rate (33/s). Both cluded that male mating success was correlated chirp and trill are produced at a fundamental with the production of courtship song. Muting frequency of 4.5 kHz and contain higher harmon- and playback experiments in different cricket ics extending up to about 30 kHz. Libersat et al. species support this conclusion (von Hörmann (1994) demonstrated that the fundamental 4.5- Heck 1957; Crankshaw 1979; Libersat et al. 1994). kHz component of courtship song was both Males that have been muted by removing their necessary and sufficient to evoke normal female tegmina perform all the acts of courtship nor- mounting responses in T. oceanicus, and also mally, including ‘singing’ (as seen by move- showed that one of the higher frequency compo- ments of their wing stubs), yet they have little nents, 13.5 kHz, was not sufficient. In the present Balakrishnan & Pollack: Cricket courtship song 355 study, we confirmed and extended their findings Spectral and Temporal Pattern Analysis on the exclusive importance of the fundamental Power spectra were computed from digitized frequency. We also investigated the importance of songs using the Fast Fourier Transform. Tem- the temporal parameters of the song. The goal of poral pattern analysis was performed either by these studies was to provide insight into the manually measuring pulse durations and pulse mechanisms underlying recognition of courtship periods from digitized recordings of songs, or by song. routing tape-recorded songs through a custom- built circuit that converted each sound pulse to a METHODS rectangular voltage signal (details of the circuit can be obtained from the authors). The onsets and Crickets offsets of these rectangular pulses were detected Teleogryllus oceanicus males and females were and stored on computer, and used to calculate reared in the laboratory at 25–30)C in 66-litre pulse durations and periods. The calculated plastic containers on a diet of Purina cat chow spectral and temporal parameters are reported as (Adult Formula) and given water ad libitum. mean values&. Male and female nymphs were separated before the final moult. Adult males and virgin Acoustic Stimuli females were kept separately in plastic boxes (38#20#23 cm) on a 12:12 h light:dark cycle for We delivered digitized sound pulses (12-bit at least 2 weeks before use. Experiments were resolution, 100-kHz update rate), either recorded performed within 3–6 h of the onset of scoto- or synthesized, at computer-controlled intervals. phase. We used 2–3-week-old virgin females and The signals were routed through a calibrated 2–4-week-old males in all experiments. attenuator (either Hewlett Packard 350D or Grason Stadler 1292) before being amplified (Sanken S1-1050G) and broadcast through a Song Recording and Analysis loudspeaker (Realistic 40-1310). Acoustic signals We recorded courtship, calling and aggression were digitized and synthesized with a National songs of 2–4-week-old T. oceanicus males in the Instruments ATMIO16F5 multi-function board, laboratory. To record courtship song, we intro- resident in a 80486-based computer. Signal analy- duced a male and a female into a cylindrical sis and synthesis were done with programs written (14#13 cm) cotton gauze cage. Recordings of with LabWindows software. calling song were obtained in the same manner, but from isolated males. To record aggression The Behavioural Assay song, we placed two males (of which one was muted by cutting off his forewings) in a smaller Courtship assays were performed in a cylindri- cylindrical cage (6#2.5 cm). All recordings were cal, anechoic chamber (13#10 cm) made of min- carried out in an anechoic chamber, in the dark, at eral wool covered with cheesecloth. A ring of a temperature of 24–26)C. cellulose acetate was pinned around the rim and We made recordings using a Brüel and Kjaer projected about 1 cm into the chamber to prevent condenser microphone (type 4135) and measuring the crickets from escaping. Experiments were amplifier (type 2610). The microphone was placed performed in the dark, at 24–26)C. Illumination at a height of 5–6 cm close to the wall of the cage was provided by a 60-W red light bulb suspended (because the male was free to move and turn in about 25 cm above and to one side of the any direction, the reported intensity levels are chamber.