Some humans just need more sleep than others, and it turns out that the same is true in fruit flies. In a new study, published December 14, 2017 in PLOS Genetics, Susan Harbison of the National Heart Lung and Blood Institute (part of the National Institutes of Health) in Bethesda, Maryland, and colleagues, identified numerous genetic variations in wild fruit flies that can contribute to unusually long or short sleep times.
Catching some zzz's is vital for most animal species, but the quality and length of that sleep can vary widely. While researchers in the lab can alter a fruit fly's sleep cycle by introducing new mutations, no one knew if similar variations exist in the wild. To explore the limits of a fruit fly's need to sleep, researchers bred different populations of wild flies to have very long or very short sleep times. After 13 generations, the short-sleepers got a little more than 3 hours of sleep each day, while the long-sleepers slept almost 15 hours more. Neither population experienced any change in lifespan, suggesting that there were no obvious ill effects or benefits from these sleep extremes. When the researchers analyzed the genomes of the short- and long-sleepers, they identified 126 differences in 80 genes. These changes occurred in several important and well-known developmental and signaling pathways, suggesting that many biological processes can potentially affect how long an animal needs to sleep.
The paper's finding that multiple signaling pathways contribute to sleep duration fits into our current understanding of the numerous roles of sleep. Previous studies have shown that sleep flushes out wastes in the brain, solidifies memories and facilitates proper development and cognitive ability, but no one has been able to find a single reason why sleep is so vital. The new study may explain why a single purpose for sleep has been so difficult to pin down.
"We used combinations of wild-derived genes to generate long and short sleep phenotypes that rival those of flies having engineered single-gene mutations," says Harbison. "Intriguingly, sleep increased in the short-sleeper populations after selection was relaxed, suggesting that short sleepers are less fit than their more moderate-sleeping counterparts. In the future we would like to discover why the genetic changes that make the less-fit short sleepers possible are maintained in nature."
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Citation: Harbison ST, Serrano Negron YL, Hansen NF, Lobell AS (2017) Selection for long and short sleep duration in Drosophila melanogaster reveals the complex genetic network underlying natural variation in sleep. PLoS Genet 13(12): e1007098. https://doi.org/10.1371/journal.pgen.1007098
Image Credit: Susan Tracy Harbison and colleagues
Image Caption: The figure depicts allele frequency changes in sleep-associated polymorphisms across generations of artificial selection for short and long sleep in Drosophila. The top set of bars shows how allele frequencies become more extreme, migrating towards 0 (dark blue) or 1 (dark fuschia) for generations 0, 1, 2, 5, 8, 10, and 12 of selection for short sleep. The bottom set of bars show similar changes in allele frequency for flies selected for long sleep.
Funding: This research was supported by the Intramural Research Program of the NIH, The National Heart Lung and Blood Institute. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.