FUNCTIONAL ASPECTS OF DROSOPHILA COURTSHIP

Summary 1. The elements that make up the courtship behaviour of males and of females are briefly described. It is pointed out that some of the terms used, such as female ‘repelling’ behaviour, are misleading as they do not reflect the known functions of the behaviours. 2. Evidence has been presented for a number of distinct pheromones with different functions during courtship. These claims are critically examined as the evidence is incomplete and at times conflicting. It seems unlikely that any pheromones other than those acting over a very short distance are involved in courtship. There is sound evidence for an aphrodisiac pheromone produced by all females which stimulates male courtship. A pheromone, which may be the same one, is produced by males less than 12 h old, which also stimulates male courtship. No function is ascribed to this pheromone. Fertilized females either produce less aphrodisiac pheromone or they may, in addition, produce one that inhibits male courtship. Mature males may also produce an inhibitory pheromone. Females produce a contact pheromone which is species‐specific and involved in sexual isolation. It is not at present clear whether this is different from the aphrodisiac pheromone. 3. There is considerable variability in the importance of vision in courtship. Many species will mate satisfactorily in the dark, suggesting that visual stimuli are not critical. Most species use vision to orient towards one another and for males to track and follow females. Even in light‐independent species such as D. melanogaster , specific visual signals may be used in courtship although they are not obligatory. Thus the red eye of the male is a sexual signal for females. Conversely, some light‐dependent species do not appear to make use of visual signals as a major factor in courtship. Some, however, do perform behaviours that are clearly visual and which may act to emphasize markings on wings, head or body. 4. The majority of Drosophila species perform courtship songs by vibrating one or both wings. The songs produced by males sexually stimulate the females. They are species specific and there is considerable indirect and some direct evidence that the songs are involved in sexual isolation. Males of many species produce two different songs during courtship and it is probable that one is concerned mainly with sexual stimulation and the other with species recognition. Females of certain species of Drosophila and Zaprionus also sing during courtship and these songs may aid species recognition by males. In addition males and unreceptive females perform ‘aggressive’ songs. 5. Almost all studies of Drosophila courtship have been made in very confined conditions in the laboratory. Interpretation of some of the results obtained in this way may require modification in the light of ecological research and observation of courtships under more natural conditions.