Courtship in Drosophila Melanogaster: Behaviour of Mixed-Sex Groups in Large Observation Chambers

Abstract 1. Mixed-sex groups of Drosophila melanogaster were observed in chambers sufficiently large to allow females to decamp during courtship. 2. There were two main experimental classes; one OVR, consisting of groups of four males and four virgin females (octet with virgin receptive females) the other, SVR comprising four males and two virgin females (sextet with virgin receptive females). Supplementary information was obtained from a third group, SMU (sextet with mated females) consisting of four males and two mated females. 3. Quantitative information was obtained on a number of courtship parameters which could then be compared with information from single pairs of the same Drosophila stock in the small cells normally used for courtship studies. 4. Courtship in groups was observed to consist of a number of short bouts (OVR: 14 s., SVR: 7 s.) interspersed with longer periods of non-courtship (OVR: 20.9 s., SVR 23.1 s.). Females could be courted by one or more of the available males and could mate with a male initially rejected. The shorter courtship bouts in SVR groups appeared to be related to increased interference between courting males which resulted in females terminating the bout. 5. This general pattern of courtship differed considerably from the pattern in small cells where females received a single continuous bout of courtship, consisting of 41 % vibration and lasting on average, 130 s. until copulation. In the group situation vibration comprised only 24% of each courtship bout and there were a number of gaps in courtship before copulation occurred. The overall mean courtship times including breaks were 399 s. (OVR) and 511 s. (SVR). 6. A detailed analysis of the observations on the groups in the large chambers showed that virgin females terminated the majority of bouts and did so by flying off or moving off. These elements alone of the so-called rejection responses listed by other authors appeared to have a rejection function. No function could be attributed to the other responses which may be in part an artefact of small observation cells. 7. Female decamping was not preceeded by a specific act by the male but could occur anytime during following/orientation and vibration. It rarely occurred after licking or attempted copulation. 8. The courtship of successful males differed from that of unsuccessful males only in that more time was spent courting the female eventually mated; bouts being longer and more numerous.