Fly naps inspire dreams of sleep genetics

A good night’s sleep is a necessary part of life for all birds and mammals—including people. Scientists had thought, however, that insects don’t need sleep. Now, researchers have found that fruit flies nap, too, and the discovery could help answer some pressing questions about sleep.

It’s hard to tell if an animal as small as a fruit fly is sleeping or not, says Joan C. Hendricks, who led a group of researchers at the University of Pennsylvania that caught fruit flies, Drosophila melanogaster, stealing a few winks. Scientists usually measure an animal’s brainwaves to determine if it’s asleep, but fruit fly brains are too tiny for that.

Instead, the researchers videotaped flies during rest periods to document the insects’ behavior. During the night, the flies crawled off to resting places and settled into what the researchers define as a sleep pose, slumped “face down,” Hendricks says. For about 7 hours every night, the flies stayed still except for a few small twitches of the legs and proboscis. As the evening progressed, it took louder and louder taps on the cages to rouse the insects.

In some sessions, the scientists kept the flies from their rest by tapping whenever the insects stayed still for more than a minute. The rest-deprived animals compensated by sleeping more over the next few days, as sleep-deprived people do.

Some researchers have speculated that a buildup of the chemical adenosine in the brain might cause sleepiness in mammals (SN: 5/24/97, p. 316: https://www.sciencenews.org/sn_arc97/5_24_97/fob2.htm). Hendricks’ team fed the flies caffeine, which disrupts adenosine action in mammals’ brains. The flies slept less after ingesting caffeine and rested more after eating a compound that mimics adenosine.

Although not exactly the same as mammals’ slumber, fruit flies’ resting behavior has many of the characteristics of sleep. “They look sleepy to me,” Hendricks says. “Whatever it is, it has most of the really interesting things that sleep has.”

The researchers describe their discovery of the Drosophila sleeplike state in the January Neuron. Other biologists at the Neurosciences Institute in San Diego have done similar experiments.

Hendricks and her colleagues also tested sleepiness in flies that had disruptions in two genes, period and timeless, that make components of the biological clock (SN: 11/18/95, p. 334). The flies that lacked the period gene didn’t seem to have abnormalities in their sleep behavior.

However, the timeless mutant flies didn’t seem to catch up on sleep after being rest-deprived. Cockroaches and bees have some behaviors that resemble sleep, but those insects are not as attractive for experimentation as fruit flies are, says Irene Tobler of the University of Zurich. “I was delighted that somebody has tackled this,” says Tobler, who studied sleep deprivation in cockroaches in 1982. Although the first evidence of insect sleep appeared nearly 20 years ago, the fruit fly study permits genetic investigation of sleep.

Now, scientists can do experiments that are difficult with more complicated animals such as mice, says Jerry Siegel, a sleep researcher at the Sepulveda VA Medical Center in North Hills, Calif.

Drosophila geneticist Jeff Hall from Brandeis University in Waltham, Mass., says that just as “the little fruit fly cracked the biological clock,” exposing many of its mechanisms, fruit flies will eventually reveal more genetic links between sleep and the biological clock.