And it turns out that quarantined lone fruit flies sleep too little and eat too much. Recognizable?

For many people, the lockdowns introduced have led to distorted sleep schedules and stretched waists. A culprit may be social isolation itself. Scientists have discovered that solitary fruit flies quarantined in a test tube also sleep too little and eat too much.

fruit flies

You might not say it, but those tiny fruit flies in your kitchen are very social creatures. For example, they forage and eat in groups, serenade each other through complex mating rituals and fight in miniature boxing matches to see who is the strongest. Researchers therefore found the sociable and good-natured fruit fly extremely suitable for studying the consequences of social isolation. “These creatures have put us on the right track time and time again,” explains researcher Michael Young. “Evolution put a lot of complexity into these insects a long time ago. And when we dig into their systems, we often find the rudiments of something that manifests itself in mammals and humans as well.” “If we don’t have a roadmap, the fruit fly becomes our roadmap,” adds study leader Wanhe Li.

“If we don’t have a roadmap, the fruit fly becomes our roadmap”

Lockdown

The researchers studied in the study how fruit flies put in test tubes responded to different lockdown conditions. After seven days, flies housed together in groups of different sizes showed no abnormal behavior. Even two congeners who had been separated from the rest together were perfectly happy with each other. But when a single fruit fly became completely isolated, after a week it started to show remarkable behavior: the lone insect began to sleep less and eat more.

brain cells

The researchers found that a small group of brain cells known as P2 neurons are involved in the observed changes in sleep and feeding behavior. When the researchers switched off the P2 neurons of chronically isolated flies, the flies suddenly stopped eating too much and their sleep patterns were restored. And boosting P2 in flies isolated from the group for just one day caused them to eat and sleep as if they’d been alone for a full week. “We managed to trick the fly into thinking it was in quarantine for a long time,” Li said. “The P2 neurons appear to be related to the perception of the duration of social isolation, or the intensity of loneliness.”

More experiments
In follow-up experiments, the team studied the fruit flies even more closely. For example, they wanted to rule out that just lack of sleep led to overeating (it didn’t). They then examined whether manipulating P2 neurons caused overeating and sleep deprivation (it didn’t). In the end, the researchers could only conclude one thing: an interaction between P2 neurons and social isolation causes fruit flies to sleep too little and eat too much.

By the way, fruit flies are not the only ones who sleep less and eat more when they are lonely. It is a known behavior in many social animals, including humans. For example, many people have arrived during the lockdowns; the well-known corona kilos. And many of us will also recognize what the corona crisis is doing to sleep quality. The reason for this is still somewhat unclear. “One possibility is that social isolation indicates a degree of uncertainty about the future,” Young suggests. “Preparing for difficult times may involve being alert and awake as often as possible and eating when food is available.”

Of course, the researchers cannot directly confirm in their study that people slept more and ate less during the lockdowns because of the same biological mechanisms that make fruit flies hungry and tired. Although the researchers do not rule this out. “It may very well be that our small fruit flies mimic the behavior of humans living under pandemic conditions for shared biological reasons,” Young says. In any case, the team has now discovered neurons and genes that seem to respond to social isolation in fruit flies. And so future studies can look for similar connections between loneliness, overeating and insomnia in laboratory animals and – ultimately – humans.