New research from UEA was recently published in the journal Proceedings of the Royal Society B, and reveals that sex can trigger substantial responses in females by activating a wide range of genes.

The changes, observed at different points during studies of female fruit flies, included altered fertility, immunity, libido, and eating and sleep patterns.

Although still not proven, the same reaction is thought to occur in many other animals, and humans, provided semen is released into the female’s body during sex.

Lead researcher Prof. Tracey Chapman from UEA’s School of Biological Sciences said: “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.”

Instead, their research focused on one particular seminal fluid protein called the enigmatic “sex peptide”, which had previously been ignored.

She explained: “There were significant alterations to genes linked to egg development, early embryogenesis, immunity, nutrient sensing, behavior and, unexpectedly, phototransduction [the pathways by which they see].”

This shows that the semen protein works as a “master regulator”. Therefore, the males effectively have direct influence on the general and reproductive behaviour of female fruit flies.

Prof. Chapman commented: “An additional and intriguing twist is that the effects of semen proteins can favour the interests of males while generating costs in females, resulting in sexual conflict.

“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.”

Read the research in full.