Sex can trigger "remarkable" responses in women, including altered fertility, immunity, libido as well as changes in eating and sleep patterns, according to a new study on fruit flies.
Scientists say the findings could, in principle, be similar to responses in many animals, including humans, when sperm and semen is released inside the female's body during copulation.
The study, published in the journal Proceedings of the Royal Society B, looked at how female Drosophila melanogaster, or fruit flies, respond to mating.
Investigators from the University of East Anglia discovered that a single protein found in semen elicits a wide range of responses in many genes in females, and that these changes become apparent at different times and in different parts of the female's body after mating.
"It's already known that seminal fluid proteins transferred from males during mating cause remarkable effects in females -- including altered egg laying, feeding, immunity, sleep patterns, water balance and sexual receptivity," lead researcher Professor Tracey Chapman, of UEA's school of Biological Sciences, said in a statement.
However, researchers from the current study focused on the effects of only one enigmatic seminal fluid protein called the "sex peptide" and found that it changed the expression of a "remarkable array of many genes in females - both across time and in different parts of the body," Chapman said.
"There were significant alterations to genes linked to egg development, early embryogenesis, immunity, nutrient sensing, behavior and, unexpectedly, photo-transduction - or the pathways by which they see," he added.
He said that the latest findings showed that the semen protein is a "master regulator," meaning that male fruit flies have a direct and global influence on the behavior and reproductive system of the female fruit flies, and that this effect may also occur across many species.
"An additional and intriguing twist is that the effects of semen proteins can favor the interests of males whilst generating costs in females, resulting in sexual conflict," he said. "For example, 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."