No sleep, no problem, but keep the grub coming

Fruit flies thrive without slumber, until food gets low

Some people can forgo sleep and still stay sharp. But a new experiment with fruit flies suggests even those gifted people may be making an evolutionary trade-off that ensures sleep is here to stay.

A variation in a single gene enables a strain of fruit flies to miss 12 hours of sleep without building up a sleep debt. The flies, nicknamed “rovers” for their active behavior, can also learn and remember things after a sleepless night, scientists report online January 30 in the Proceedings of the National Academy of Sciences. But, scientists say, the flies that cope well with sleep deprivation appear more vulnerable to vagaries in food supply.

The findings may eventually help scientists answer one of the most “fundamental questions in the sleep field, that is ‘what is the core function of sleep?’ ” says David Raizen, a neuroscientist at the University of Pennsylvania who was not involved in the study.

In the study, Marla Sokolowski, a behavioral geneticist at the University of Toronto Mississauga, and her colleagues describe how fruit flies with naturally differing versions of the foraging gene behave differently. Flies with the rover version of the gene make more of a protein called protein kinase G or PKG. Rovers also move around more in search of food than flies with the “sitter” version of the gene, which produces lower levels of PKG.

With the advantage of being able to learn and remember in the face of sleep disruption, rovers ought to have completely taken over the fruit fly population. Instead, sitters make up about 30 percent of the fruit fly population in the orchards where Sokolowski first discovered the two types of flies. Now the researchers think they know why the rovers don’t have an evolutionary monopoly: Flies that can defy sleep deprivation are more sensitive to starvation.

Sitter flies, like most people, had trouble learning after being kept up all night, but the flies’ short-term memories improved when food was withheld for 12 hours. The rovers, which seemed like “über-duper super flies” when sleep deprived, had impaired memories when starved, says neuroscientist and study coauthor Paul Shaw of Washington University in St. Louis.

The rover flies also dropped, well, like flies, if starved for days. While sitters could survive several days without food, most rovers died within 41 hours of starvation. Such poor performance when food is scarce, as it often is in the wild, may explain what keeps the rovers from dominating the orchard populations.

Humans who need a full night of sleep to feel sharp can take heart from the results, Shaw suggests.

“All of us ‘weak’ people who need eight hours a night might take comfort in the fact that those who claim not to need as much won’t be as resilient to everything,” Shaw says.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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