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What got you interested in how mating affects female behaviour?

For decades, my mum told me stories about how when she was pregnant with me she used to feel bursts of irrational rage towards everyone around her. Yet she didn鈥檛 blame the woman who stole her taxi while she was going into labour, nor the colleague who鈥檇 forgotten about the time difference and called her up at 4 am. She blamed me, her unborn child. After 26 years of hearing these stories and taking the blame, I am researching female aggression after mating.

So was your mum on to something?

She is actually backed up by a fair bit of science. Female aggression rises after mating in a lot of species: you find it in mammals, birds, fish鈥� I even found that in fruit flies, mated females will spend twice as long fighting over food as virgin females.

That鈥檚 understandable enough, surely?

On the surface, yes. The theory is that once you鈥檙e producing eggs, you get this signal from your body saying 鈥淚 need more nutrients鈥�, and so you go out and get more food. Just because you need more doesn鈥檛 mean more food is available, so you may need to get aggressive to get a bigger share of limited resources. But what I wanted to find out was whether the flies actually needed to be making eggs for this aggression to appear.

How did you go about finding out?

I mated sterile female fruit flies, which cannot produce any eggs, with normal males. And I found exactly the same increased aggression: mated females will fight for twice as long as virgin females, regardless of whether they are producing eggs. That鈥檚 counter-intuitive.

So what is causing the aggressive behaviour?

There seems to be a male influence on female aggression, possibly transmitted through the ejaculate itself. There is a whole lot of stuff in ejaculate besides sperm. Molecules called seminal fluid proteins (SFPs) may be having a big effect. We know they can do things like increase female egg production, reduce receptivity to re-mating, and alter sleep patterns. SFPs can find their way into the brains of the females. It looks as if they are serious manipulators of female behaviour.

Could there be parallels in humans?

That would be wildly speculative. What I can say is that the ejaculate of humans and other mammals does contain SFPs. There鈥檚 one called ovulation-inducing factor, which does exactly what it says on the tin. For example, camels and llamas need to mate before an egg is released. Humans, on the other hand, are spontaneous ovulators 鈥� once a month an egg is released regardless of everything else that鈥檚 happening 鈥� so we cannot say if this particular SFP has any impact on human female fertilisation or behaviour. But work is being done to see whether SFPs might improve the success rate of IVF, for example.

What does your mum think of your findings?

She鈥檚 certainly less likely to blame me now! I just feel sorry for my dad.

This article appeared in print under the headline 鈥淪perm with added aggro鈥�