Sex may not always make the earth move, but there is evidence that it can shake up a woman's genes.
Scientists have found that a single sperm molecule has wide-ranging impacts on female fertility, immunity, behaviour, eating and sleep patterns. And although the effects were seen in fruit flies, the researchers believe many may occur in higher animals including humans.
The sperm peptide, a piece of a protein, triggered a complex pattern of changes in gene activity. These led to responses which became apparent at different times and in different parts of the female body.
Some appeared to advantage the male at the expense of the female. For instance, after mating the female became less receptive to other males, and invested a lot of energy into ensuring the survival of her offspring.
Lead scientist Professor Tracey Chapman, from the University of East Anglia, said: "We tested the effects of one enigmatic seminal fluid protein, known as the 'sex peptide', and found it to change the expression of a remarkable array of many genes in females - both across time and in different parts of the body.
"There were significant alterations to genes linked to egg development, early embryogenesis, immunity, nutrient sensing, behaviour and, unexpectedly, phototransduction - or the pathways by which they see.
"It showed that the semen protein is a 'master regulator' - which ultimately means that males effectively have a direct and global influence on the behaviour and reproductive system of the female. Such effects may well occur across many species. The bottom line is that it's possible these sorts of processes could occur in humans.
"We don't know much about it yet, but over the last few years a number of people working in this area have been looking at interactions between human sperm and what happens in the female reproductive tract. It's well known that a lot of changes occur following mating, but I think it's true that they could be more far-reaching than anyone has imagined."
Effects on immune system genes may help prevent infection of the reproductive tract, or even act as a barrier against sperm from a different male, she said.
The research is published in the journal Proceedings of the Royal Society B.
One of the behavioural changes seen involved female flies being driven to eat more - and more selectively - in preparation for egg laying.
But the responses triggered by sperm proteins were highly costly to the female, even to the extent of shortening lifespan, the research suggested.
"There can be a tug-of-war, where males employ semen proteins to ensure that females make a large investment in the current brood, even if that doesn't suit the longer term interests of females," said Prof Chapman.
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