London, Nov 28 (IANS) Male fruit fly sperm is coated with a chemical sex peptide which aborts the female’s noon siesta and compels it into an intense period of foraging activity, according to new research.
The surprise discovery was made by Elwyn Isaac, professor at the University of Leeds faculty of biological sciences, when investigating the marked differences in sleeping patterns between virgin and mated females.

Both male and female fruit flies (Drosophila melanogaster) — commonly seen hovering around rotting fruit and vegetables — are active at dawn and dusk, and have deep sleep at night.

They also exhibit a marked ‘resting state’ during the afternoon, which Isaac likens to a siesta that conserves the fly’s energy and reduces damaging exposure to the sun during hot afternoons.

“However, we noted that after mating, females still slept deeply at night, but ditched the usual siesta in favour of extra foraging and searching for places to lay her eggs,” he says.

“This behaviour lasts for around eight days — and our research findings suggest that this change is not by choice. Females who mated with males that produced sperm without the sex peptide continued to take their siesta. So we’re certain that this change of behaviour is chemically induced by the male.”

Previous research studies have shown that the sex peptide encourages females to increase egg production — a mated female will lay up to 100 eggs a day compared with 1-2 eggs laid by a virgin female. It also inhibits her from mating with other males for around a week to 10 days, says a Leeds varsity release.

“It would appear that preventing sleep and inducing extra domestic-type duties to prepare for the birth of offspring in females is a further tactic used by the male to ensure successful paternity after mating,” says Isaac.

“If we can work out exactly how this natural molecular switch can disrupt sleep behaviour, we may be able to apply this knowledge to neurological disorders relating to human sleep such as narcolepsy,” adds Isaac.