Female Flies Put Up a Fight to Keep Sex Short

Maggie Koerth-Baker
for National Geographic News
August 21, 2009

Even flies engage in the battle of the sexes, a new study says.

Female fruit flies prefer to keep sex short and sweet, while males like it to last longer. Naturally, a fight ensues.

"After about a minute and a half [of mating], the female begins kicking and struggling," said study co-author Kirsten Klappert of the Swiss Federal Institute of Aquatic Science and Technology.

That's because females get a reproductive boost from shorter sex: When mating lasts longer, female flies have less time to mate again with a different male, if they do so at all.

(Related: "Females Seek Multiple "Valentines" in Some Species.")

That's good for the guy, because it means his sperm have less competition. But it can be disastrous for females, which want to increase genetic variability of their offspring.

What's more, "many male Drosophila montana are infertile, so if you only mate with one you have a high risk of no offspring at all," Klappert said.

Making Babies

To see how much control female flies have over mating length, Klappert, Dominique Mazzi of the University of Jyväskylä, and colleagues paired live males with dead females.

The team propped up the dead insectsWeekend at Bernie's-style—to convince the males that they were still alive and ready for sex.

The males obliged, and this "stiff sex" lasted 1.5 times longer than it did with live females, the researchers found.

The females' control over sex is impressive, Klappert said, since male D. montana are thought to have adaptations such as pinchers that help them latch on to their mates and thwart females' escape plans.

Klappert's research suggests that this conflict has shaped the evolution of the sexes—for fruit flies, at least.

Even so, both genders want the same thing—baby flies, Klappert said. They just have very different ideas of the best way to get there.

All About Foreplay

While many women might balk at the idea of sex that lasts less than two minutes, scientists say that humans might actually relate to the female fruit fly's desires.

Rhonda Snook, a senior lecturer at the University of Sheffield in England, studies sexual selection and reproductive behavior in fruit flies.

"I don't know you could say human females want longer copulation, per se," said Snook, who was not involved in the new research.

"It's really the foreplay, not the actual act of copulation. In the insects, prior to that, there's courtship going on, and that's like foreplay in humans."

Study published June 12 in the journal BMC Evolutionary Biology.




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