First we were told the composition of semen could possibly help fight depression.

Now, research suggests that male semen can affect the genes and behaviour of females in other ways, too.

British scientists have dubbed the phenomenon seminal signalling - and say it is widespread in the animal world.

The team, from the University of East Anglia, found male fruit flies selectively alter the chemical make-up of their seminal fluid.

And that when around rivals, the males produce more seminal proteins, New Scientist reports.

Furthermore, the scientists found that one of the proteins is a 'master regulator' of genes - and females exposed to it showed a wide range of changes in gene expression.

Semen may alter gene expression in females - affecting factors such as a woman's hormones. Scientists have dubbed the phenomenon seminal signalling - and say it is widespread in animal world

Gene expression is the process by which specific genes are activated to produce a required protein to help the body function.

These proteins go on to perform essential functions as enzymes, hormones and receptors, for example.

'[Our finding] came as a real surprise,' study leader Tracey Chapman, Professor of Evolutionary Genetics, told the magazine.

'It's a sophisticated response to the social and sexual situation.'

The research was presented earlier this month at the Society for Molecular Biology and Evolution conference in Austria.

It adds to a growing body of scientific evidence showing seminal fluid may have both physical and psychological effects on the body.

Previous studies have claimed semen can elevate mood, increase affection, induce sleep and also contain at least three antidepressants.

Another study, published in the journal Clinical & Experimental Obstetrics & Gynecology, found there was a significant increase in pressure inside the uterus once semen arrived there after intercourse.

Previous studies have claimed semen can elevate mood, increase affection, induce sleep and also contain at least three antidepressants

The researchers suggest this increase in pressure may be to help transport the sperm to the oviduct - the tube that links the ovary to the uterus.

Other research in fruit flies has shown that seminal fluid can affect how interested females are in other males and how many eggs they produce.

And semen isn't just vehicle for carrying sperm - it also plays a crucial role in triggering ovulation, according to another study.

Scientists at the University of Saskatchewan discovered the protein in the sexual fluid acts as a hormonal signal on the female brain.

This triggers the release of other hormones that signal the ovaries to release an egg.

One of the most controversial studies, published in 2002 in the Archives of Sexual Behaviour, claimed to examine the studied the effects of semen's 'mood-altering chemicals'.

Previous research has found a change in pressure occurred in the uterus once semen arrived - in order to help conception, scientists believe

The State University of New York study - which scientists carried out via survey - compared the sex lives of 293 females to their mental health.

The researchers claimed that women who had regular unprotected sex were less depressed and performed better on cognitive tests.

Recent sexual activity without condoms was used as an indirect measure of seminal plasma circulating in the woman’s body.

Each participant also completed the Beck Depression Inventory, a commonly used clinical measure of depressive symptoms.

The most significant findings from this study, were that, even after adjusting for frequency of sexual intercourse, women who engaged in sex and 'never' used condoms showed significantly fewer depressive symptoms than did those who 'usually' or 'always' used condoms.

Importantly, these condom-less, sexually active women also evidenced fewer depressive symptoms than those who abstained from sex altogether.

By contrast, sexually active heterosexual women, including self-described 'promiscuous' women, who used condoms were just as depressed as those who totally abstained.

The research suggests it is not just that women who are having sex are simply happier, but that happiness levels might be related to the quantity of semen within their body.

However it is still not clear if any elements of human semen get into the bloodstream - although one theory is it may be possible for small molecules like hormones, New Scientist reports.

Seminal proteins can directly affect the behaviour of flies because they enter the circulation and get to the brain, says Professor Chapman.

This, in turn, helps her to reproduce as soon as possible.