Sleep — that absurd, amazing habit of losing consciousness for hours on end — is so universal across the animal kingdom that we usually assume it is essential to survival. Now, however, scientists who repeatedly disturbed the sleep of more than a thousand fruit flies are reporting that less slumber may be necessary for sustaining life than previously thought, at least in one species.
A handful of studies involving dogs and cockroaches going back to the late 19th century suggest that being deprived of sleep can result in a shortened life span. But the methods behind some of these studies can make it difficult to say whether the test subjects were harmed by sleep deprivation itself, or by the stress of the treatment they were given — such as being shaken constantly.
The new study took a milder approach, in hope of seeing the true effects of sleep deprivation. The automated system the researchers developed for monitoring the flies kept track of their movements with cameras, scoring any extended period without movement as sleep. When they were not being awakened repeatedly, the males slept about 10 hours a day, females about five on average.
To keep the flies awake, the researchers equipped the system with tiny motors that would gently tip the flies any time they went still for at least 20 seconds. With this method, researchers deprived flies of rest over the course of their entire lifetimes, tipping them hundreds of times a day such that if they were snoozing during those periods of stillness, they might have been able to sleep around 2.5 hours a day on average.
“When the results came from that experiment, it was very surprising,” said Giorgio Gilestro, a professor at Imperial College London who is a co-author of the study, which was published Wednesday in Science Advances.
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While female flies in the experiment died about ten days sooner than other flies, male flies had completely normal life spans of about 50 days. Dr. Gilestro suggests that perhaps whatever sleep is doing in the way of essential maintenance can happen in a very, very short period of time, such that little sleep is required to keep an organism alive.
The study has limitations. It looked at only a single strain of fruit fly, said Dragana Rogulja, a professor at Harvard who studies sleep using fruit flies. “In principle, I think it would be have been awesome to test multiple strains,” she said, to understand whether other flies, some of which can live much longer, respond similarly.
Additionally, not everyone agrees that the scientists have succeeded in accurately recording when the flies are awake or asleep. Some periods in which flies made tiny movements were scored as waking time, for instance.
“I’m not convinced that the micro-movements they report are not part of sleep behavior,” said Amita Sehgal, a professor at the University of Pennsylvania who pioneered the study of sleep in flies. If that is the case, the flies may have been able to sleep more than researchers realized.
Dr. Gilestro countered that these movements are not the same as the twitches that occur while animals are asleep. The flies walked around in between the recorded small movements, and they appeared to be feeding or grooming at those times. “We looked at that and we feel we can exclude this possibility,” he said.
The work touches on an interesting question: how much does the length of time spent asleep connect to sleep’s beneficial effects? For most of us, knowing exactly how much sleep you need to be healthy is likely to remain of academic interest. The unpleasant effects of missing even a couple hours, or being awakened even a couple times during the night, tend to discourage experimentation. But it’s intriguing to think that perhaps some of that time spent asleep matters less than the rest of it.
