Fruit fly studies reveal the dangers of loneliness

A fruit fly on a Petri dish. Fruit flies are a common model organism that is often used as a research object to reveal more universal laws of life. (ICphoto/Photo)

Biologists have found that prolonged periods of loneliness can lead to a range of changes in gene expression, behavioral patterns, and more. Most obviously, fruit flies that spend solitude for long periods of time exhibit abnormal behaviors such as sleeping less and eating more.

Fruit flies are a common model organism that is often used as a research object to reveal more universal laws of life. The 2017 Nobel Prize in Physiology or Medicine was based on the discovery of fruit flies. In 1984, three scientists born in the 1940s, Jeffrey C. Hall, Michael Rosbash and Michael W. Young, figured out the molecular mechanisms that control circadian rhythms by studying fruit flies, and the Nobel Committee believed that the laws they discovered later proved to apply equally to other animals and plants, so each of them received a third of the prize.

One of the winners, Michael Young, is currently a professor at Rockefeller University and one of the lead authors of the latest study on loneliness. In the latest study, they found that although isolated and alone fruit flies still have enough food to eat at any time, prolonged social isolation changes the expression of their metabolic genes, causing them to feel hungry, so they eat more and sleep less. The study was published in the journal Nature in September 2021. Fruit flies are social animals, there are collective behaviors and social networks within the group, they will reflect a certain sociality in the foraging and perceptual environment, and in view of the important scientific findings such as previous studies of fruit flies that have revealed the molecular mechanism of circadian rhythms, although fruit flies are only an animal, research on loneliness is also worthy of attention.

Moreover, to study the exact role of loneliness in related behaviors, the researchers actually conducted a series of controlled trials through fruit flies. For example, to determine how loneliness after social isolation affects sleep, the researchers compared the differences between 1 solitary group, 2 co-living groups, and 5, 25, and 100 co-living flies by adjusting the size of fruit flies. It was found that if 2, 5, 25, and 100 males stayed together for 7 days, their sleep conditions were similar, but if 1 was alone, it underwent a qualitative change, showing a significant lack of sleep. That is to say, no matter how small the group size is, as long as it is more than 2, it has little impact, as long as it is not alone.

In order to observe the effect of lonely time on sleep, the researchers also controlled the isolation time, found that 1 or 3 days of short-term isolation, the impact on fruit flies is not large, only 1 day of isolation, and 1 day of gregarious 1 day is almost no difference, isolation of 3 days and 3 days of social living in the law of work and rest will be slightly different, but 5 days or 7 days of isolation can significantly change their work and rest, and reduce their total daily sleep time and daytime sleep time and other indicators, isolation for more than 7 days, the relevant sleep time reduction will become more and more serious.

In terms of diet, experiments have also shown that fruit flies that are isolated for 7 days have significantly more total food intake, daytime food intake, nighttime food intake and other indicators than those of their gregarious counterparts. Comparing the expression of the same gene in long-term isolation with short-term isolation and socialization, the researchers found a large number of genetic-level differences, of which some genes related to hunger and satiety were particularly prominent, and through these analyses, the researchers found that the brains of fruit flies that experienced long-term isolation were similar to the usual state of hunger, even if they had enough food to eat at any time during isolation, and speculated that this state of brain hunger may affect the expression of some genes related to metabolism.

Ultimately, the latest research identified a nerve cell called P2 that plays a key role in this process, after a day of isolation, manipulating P2 in the brain of Drosophila can produce the effect of long-term isolation, but for Fruit flies that have not experienced isolation, simply manipulating P2 can not make them sleep less and eat more behaviors, which suggests that the condition of P2 and the isolation state may jointly cause changes in behavior such as sleeping less and eating more, so the rare use of animal models provides a message about isolation, sleep, Evidence of complex links between metabolism and genes, etc. Michael Young analyzed on the school's official website that social animals sleep much less and eat much less during quarantine, possibly because social isolation itself sends a signal of uncertainty about the future, and in order to cope with these potentially difficult moments, they stay alert and eat as much as possible.

These more far-reaching effects of isolation and loneliness on living organisms, while not yet directly applicable to human behavior, provide some basic references for revealing the impact of loneliness on human health in the future. For humans, the meaning of socialization and isolation is obviously more complex. And different people actually have different feelings about whether they are lonely when they are alone. Some psychologists believe that solitude is not necessarily harmful, whether it is harmful depends on the motivation, for the active choice of solitude, may sometimes bring some benefits to people, and passive acceptance of solitude and uncomfortable loneliness, will bring negative psychological impact.

Unfortunately, however, since the COVID-19 pandemic, too many people around the world have been asked to quarantine and thus fall into solitude and loneliness, and many studies have shown that loneliness is a risk factor for depression. In January 2021, The Lancet Psychiatry published a large 12-year follow-up study that found that for people over the age of 50, the lonelier people in the early days had more severe depressive symptoms more than a decade later, and that about 11 to 18 percent of cases of depression might have been avoidable if loneliness had been eliminated sooner. Since the COVID-19 pandemic, scientists around the world have observed depression and anxiety disorders that are also more prevalent, and found that the more people who restrict the movement of people, the more prevalent the associated mental disorders, in October 2021, a new study by The Lancet estimated that due to the new crown pandemic, there are more than 53 million new cases of depression and more than 76 million cases of anxiety disorders in the world in 2020.

A large amount of scientific evidence has shown that depression is an important risk factor for cognitive impairment such as dementia, and the associated risks are interlinked, and the harm of loneliness may be far more than just bad mood. The latest study provides new and powerful evidence for understanding the dangers of loneliness to life by observing the physiological and behavioral changes of fruit flies in lonely social isolation.

Southern Weekend reporter Wang Jiangtao