When the Male Fruit Fly Gets a Headache

An international team of scientists has discovered that when aroused, Drosophila males get frenzied, but female fruit flies manage to sleep just fine.

Ruth Schuster
Ruth Schuster
Photo shows two fruit flies with bright green eyes mating on a bright green leaf stem.
Fruit flies: We know one isn't asleep.
Ruth Schuster
Ruth Schuster

We females always knew we could have sex when asleep, not that we want to, and that men can't. It turns out the same applies to fruit flies.

A vast international study by multiple institutions – one can't have too many studying woo-woo in fruit flies – has concluded that when male Drosophila are sleep-deprived, their interest in courtship disappears.

When the female is bushed, nothing happens to their mating behavior.

One way to deprive a fruit fly of sleep, would seem to be to offer it sex. The team also realized that aroused male Drosophilae got little sleep. Sexually aroused females slept fine.

Given the nature of the beasts, animals have to choose between sex and sleep. At least, the males do — they can't do both at the same time. Now scientists have found how the choice is regulated, at least in the fruit fly.

"An organism can only do one thing at a time," states the team, with Prof. Michael Nitabach of Yale, an expert on molecular physiology and genetics, in Nature Communications. "What we have discovered is a neuronal connection that regulates the interplay between courtship and sleep."

What Nitabach and his colleagues from the Howard Hughes Medical Institute, the Southeast University in China, and the University of San Diego, did is to study the neuronal activity involved in sex and sleep. They found that sleep-deprived male flies lost interest in courtship, but the females' mating behavior was unaffected.

Darwin would be proud

The evolutionary explanation they offer is a trivial one. The males' behavior is easily explained as adaptive: Falling asleep during sex is not a good way to pass on your genes, they stated.

But, they wondered, why are females still receptive to male advances when sleepy? One possibility is that as the recipient, they can afford to be. Another, postulated by Nitabach, is that the females can't afford to pass up an eligible suitor. But there are a lot of fruit flies out there. Ostensibly, the females would seem to be spoiled for choice.

The team also found functional connections between the different nervous centers that mediate sex and sleep, they say. Nitabach's conclusion is that whichever behavior has the highest biological drive at a given moment physiologically suppresses the yen for the other behavior. Thus, when a boy fly wants sleep badly enough, it depresses his sex drive, and vice versa.

So, is the human drive for sex and the human desire for sleep also controlled by our neurons? Probably, at least to some degree. Just like the fruit fly, there are other factors in play.

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