Dramatic changes in the way a female fruit fly behaves after sex have allowed researchers at Oxford University to map the nerve cells responsible.
The fruit fly is an established model for identifying neural elements that direct actions and behaviour. Courtship and reproduction in the fruit fly in particular lend themselves to this.
Yet studies have almost exclusively focused on the male, with the female's role largely ignored or marginalised to a somewhat passive recipient of the male’s attention.
'The male fruit fly is a big show off, always trying to impress the female with his elegant courtship display,' said Dr Stephen Goodwin from the Department of Physiology, Anatomy and Genetics at the University of Oxford.
'During courtship, the female is somewhat "coy" and her behaviours are more enigmatic, so she has tended to be overlooked. But she behaves very differently after mating, and we have exploited this complex behavioural change to explore how chemical signals passed between the sexes can trigger complex behaviours.'
Fruit flies show a range of sophisticated, inter-linked behaviours before sex and afterwards, all of which are focused on producing offspring. But it is after copulating that the female comes into her own, when there is a dramatic shift in her physiology as well as her behaviour.
It was the neural basis for this shift that Dr Goodwin's team at the University of Oxford investigated, in collaboration with scientists from the Harvard Medical School and University of Glasgow. Their research is published in the journal Current Biology.
After mating, a female moves from a highly sexually-receptive state to a non-receptive one, actively rejecting further advances from males while altering her feeding and activity patterns. All these changes have evolved to support the accelerated ovulation and laying of fertilised eggs.
Previous studies have shown that the changes in behaviour are triggered by a protein within the male fly's semen.
Now the Oxford-led team has defined the precise set of neurons in the female genital tract that respond to the male 'sex peptide' protein.
They have also identified the neural circuitry involved in processing this information and generating the female’s behaviour after sex.
This work has allowed the researchers to begin mapping the complete neural circuitry responsible for the female's behaviour during reproduction.
Dr Carolina Rezával of Oxford University added: 'Mating-induced behaviours are important to ensure the propagation and survival of the species. In flies, once the female has mated, something about her demeanour changes to make her less attractive to the male and focus on more maternal activities.
'We have now identified more elements of the fly circuitry that underlie this change in behaviour and shown that it is more sophisticated than was previously thought.'
The work was funded by the Wellcome Trust, the Biotechnology and Biological Sciences Research Council, and an EPA Cephalosporin award.