Song recognition and song pattern in a shorthorned grasshopper

Abstract

1. Computer generated, artificial songs (Fig. 1) were played to grasshoppers of the gomphocerine speciesOmocestus viridulus L. in a temperature-regulated, echo-reduced chamber (Fig. 2). The animals often responded by singing their response song, and the occurrence of response songs was used to indicate the animals' preference for the artificial songs. At various temperatures, the chirp duration and impulse rate preferred by the animals were determined and compared with the magnitudes of these parameters in the response songs. 2. The duration of the response songs decreases with temperature (Fig. 5), and so does the chirp duration (Fig. 3). The chirp rate (which in this species is the reciprocal of the chirp duration) decreases during a response song (Fig. 6). 3. In the first experiments the chirp duration was varied in the artificial songs, while the ratio chirp rate to impulse rate was kept constant (as in the natural songs). The preferred chirp duration changes more with temperature than does the chirp duration of the response songs (Fig. 3). At all temperatures, songs with chirp durations half or double of the preferred one could also release a response song. The animals even responded to chirp durations outside the natural range (Fig. 3). 4. In the second experiments, the chirp rate (C) and impulse rate (I) at 28 °C (C28 and I28) and 38 °C were combined into four different songs: C28I28, C38I38, C28I38 and C38I28. The former two songs correspond to the natural songs at 28 ° and 38 °C, whereas the latter ones are artificial. The temperature of the listening animals was also varied. The choices made by femal grasshoppers showed that the chirp rate is the major parameter and the impulse rate the minor parameter in determining the acceptance of a song. 5. Four different criteria for measuring the female song discrimination were compared: (a) the behavioural threshold (i.e. the sound level of an artificial song which is just sufficient for response songs to be released in the females), (b) response or no response, (c) the number of response songs in a response, and (d) whether the response was given to the 1st, 2nd or 3rd song presentation. (a) was more sensitive than (b), and both gave rather similar results. In (c) and (d) the responses appeared to be independent of the type of songs presented. 6. The behavioural threshold increased before and decreased after egg deposition (Fig. 7).