Male flies produce a chemical that makes females sleep in after mating

A “sex peptide” transferred from male to female fruit flies during mating interferes with the female’s biological clock, reducing her chances of mating again

By Christa Lesté-Lasserre

During sex, male fruit flies transfer a chemical that makes females sleep later, missing the chance to mate with other males.

This “sex peptide”, which gets passed along with sperm through the male’s sex organ into the female’s body, is already known to make females less receptive to other males. But a new study reveals that it also interferes with the biological clock mechanism that usually wakes up fruit flies before sunrise, which is when mating often occurs, says Lorena Franco at the National Scientific and Technical Research Council (CONICET) in Argentina.

“The loss of anticipation [of the dawn] could further reduce receptivity by putting females to sleep when males are most active,” she says.

Previous studies have found that fruit flies (Drosophila melanogaster) generally wake up an hour or two before the sun rises or the lights in a laboratory are switched on. But Franco and her colleagues realised that those studies were focused on male flies.

Because females are often overlooked in fruit fly research in general, they decided to use webcams to monitor the activity of virgin and just-mated female fruit flies in their light-controlled laboratory for four days. They also studied a group of males for comparison.

To their surprise, the researchers found that the only females that could still anticipate the morning were the virgins, whereas the mated females continued to sleep until they awoke with a startle at the first light of day. “In mated females, this [morning anticipation] feature is completely suppressed,” says Sebastian Risau Gusman, also at CONICET.

The researchers suspected that the sex peptide might be involved, so they silenced certain groups of neurons with sex peptide receptors in mated females’ reproductive tracts. Those females recovered the ability to wake up before dawn, says Franco.

Fluorescent tracers were then used to track the effects of the peptide on the females’ nervous systems. This revealed that the sex peptide appears to set off a chain of events from the reproductive system to the brain, affecting structures that control the insects’ internal clock.

Female flies can mate with many males and store their sperm inside their bodies. Producing behaviour-altering chemicals is a way for males to improve the chances of their sperm being successful. “This is a ‘strategy’ of the male to keep other sperm from competing with his own inside the female,” says Risau Gusman.

Journal reference: PLOS Genetics, DOI: 10.1371/journal.pgen.1010258