The control of sexual receptivity in female Drosophila

Abstract

Abstract 1. 1. This paper describes various experiments on the integration of reproductive physiology and behaviour in female Drosophila melanogaster and D. simulans. 2. 2. The sexual behaviour of females is ascribed to two distinct processes. One determines the state of receptivity, i.e. whether a female is ‘accessible’ to stimulation from the courtship of a male, the other summates the various stimuli from courtship and eventually leads to the female accepting a male. 3. 3. Females are unreceptive to males on the day of eclosion (day 0) about 25 per cent are receptive on day 1, the rest by day 2. More precise tests place the transition period between 24 and 40 hr from eclosion. In any individual the change is a sudden one; females are either fully receptive or fully unreceptive. Accordingly this change is called ‘switch-on’. 4. 4. The corpus allatum and ovaries show a growth cycle parallel to that of receptivity. Evidence is presented that increase in juvenile hormone titre is responsible for the ‘switch-on’ of receptivity. 5. 5. Virgin females remain receptive for many days, but an increasing proportion become unreceptive after the first week of adult life. ‘Switch-off’ like ‘switch-on’ is a rapid, all-or-nothing process. Females also become unreceptive immediately after mating and this inhibition of receptivity has two components, (a) an effect of copulation itself, probably mechanical, which wears off after 48 hr, (b) an effect due to the presence of live sperm, which wears off once a female has exhausted the sperm by egg laying, after some 8 to 10 days. 6. 6. Old females which have mated and used up their sperm are more often receptive than virgins of the same age. It is suggested that this is so because their corpora allata are more active and the juvenile hormone concentration is kept up above the critical level for longer. 7. 7. The situation revealed in Drosophila is compared with that found in other insects, particularly with regard to the role of the endocrine system.