Just Like Humans, Lonely Fruit Flies Eat More, Sleep Less

The insects are hardwired to consume lots of food and avoid rest as a way of coping with loneliness

Lonely Fruit Flies
Fruit flies are social creatures. But when isolated, they begin to act differently—not unlike a human in quarantine. Wahne Li/The Rockefeller University

We’ve all heard the joke: What does the “19” in Covid-19 stand for? The number of pounds you gain when you’re lonely in lockdown. Clever enough, but the fact is, many people do put on pounds in isolation. Not only that, people tend to sleep less when deprived of social interaction.

Now, a new study published in the peer-reviewed journal Nature reveals that fruit flies cope the same way as humans when isolated from their kin: they gain weight and sleep irregularly.

Researchers at Rockefeller University discovered that Drosophila melanogaster, a socially inclined fruit fly, altered its eating and sleep behaviors when quarantined in a test tube for a week, reports Margaret Davis of the Science Times.

“Flies are wired to have a specific response to social isolation,” lead author Michael W. Young, a geneticist at Rockefeller University, says in a statement. “We found that loneliness has pathological consequences, connected to changes in a small group of neurons, and we’ve begun to understand what those neurons are doing.”

Fruit flies normally sleep 16 hours a day in the wild and exhibit complex social interactions with others while searching for food. When isolated, though, they experience changes in brain cells known as P2 neurons that influence the insects' eating and sleeping behaviors, reports Shane McGlaun of SlashGear.

As a control, researchers also isolated two fruit flies together. No significant changes were detected in the pairs. When P2 neurons were shut down in isolated fruit flies, the flies stopped eating more and sleeping less.

The researchers conclude that loneliness can have profound pathological consequences for the flies—and for humans, too. Their study cited 2002 findings by neuroscientist Bruce McEwen, who found that stress is the foremost public-health issue of modern times, and that “when activated chronically, it can cause damage and accelerate disease.”

Other research has shown that many stressors are social in nature. When combined with certain social pressures, such as poverty, inadequate education and violent crime, they can contribute to the development of illnesses such as cancer, diabetes and depression.

“Clinically oriented studies suggest that a large number of adults in the United States experienced significant weight gains and loss of sleep throughout the past year of isolation precautions due to Covid-19,” Young says in the statement.

“It may well be that our little flies are mimicking the behaviors of humans living under pandemic conditions for shared biological reasons.”