ONSET OF VITELLOGENESIS IN FEMALE DROSOPHILA-SILVESTRIS IS ACCELERATED IN THE PRESENCE OF SEXUALLY MATURE MALES

Vitellogenesis is a central event in the reproductive maturation of adult females of Drosophila silvestris; it is a necessary precursor to the onset of sexual receptivity. The developmental processes of vitellogenin synthesis and uptake by the maturing ovaries occur in response to intrinsic cues, primarily hormonal, independently of the presence of conspecific males. By scoring the stage of ovarian development of females at 15, 17 and 19 days after eclosion, when reared in all-female groups, with males the same age, or with older sexually mature males, we have found that mature males significantly accelerate the onset of vitellogenesis, and thus ovarian maturation overall, by about 4 days. We infer that extrinsic behavioural cues in the form of social and sexual stimuli from the courtship attempts of males can precociously induce the physiological events of ovarian maturation prior to 15 days of age. Although the proximate stimulus is unknown, it is conceivable that social signals from the males elicit changes in the hormonal levels of the females, thereby initiating the events leading to vitellogenesis. This effect of male behaviour on female reproductive physiology is similar to that reported in vertebrates, but Drosophila may provide a more tractable system for analysis.