A group of investigators from Bar-Ilan University, situated in Israel, conducted a series of experiments, the findings of which were published in the journal Nature Communications. During their work, the scientists discovered that jellyfish, lacking a brain and an anus, also require adequate rest.
It turned out that jellyfish of the species Cassiopea andromeda spend about a third of the day in a sleeping state. This revelation underscores that slumber is an ancient biological process, which emerged long before the advent of humanity, as the common ancestor of people and jellyfish lived roughly a billion years ago.
Despite the absence of a centralized intellect, jellyfish possess a nervous structure comprising decentralized neural networks spread throughout their bodies. However, even such simple beings have a need for repose.
Chronobiologists Ofael Agullon and his associates noted that sleep is associated with certain perils, as it lessens the level of vigilance and can render an organism susceptible to predators. Nevertheless, the majority of jellyfish and humans tend to sleep during the nighttime, while some types, such as the sea anemone Nematostella vectensis, are active during the day.
In the scope of the research, the scientists examined the effect of sleep deprivation on neuronal DNA damage in jellyfish and sea anemones. The outcomes demonstrated that a lack of repose leads to an increase in the extent of DNA damage. This was verified both in controlled laboratory settings and in their natural habitat.
The researchers also observed that when exposed to agents that promote DNA damage, such as ultraviolet radiation and mutagens, the jellyfish and sea anemones prolonged their sleeping period. This suggests that sleep might have evolved as a protective mechanism for cells against such harm.
The administration of melatonin resulted in an extension of sleep duration in the jellyfish and a reduction in the level of DNA damage. This indicates that melatonin plays a vital function in sleep regulation not just in humans but also in cnidarians.
The investigators concluded that insufficient sleep, ultraviolet rays, and mutagens contribute to the deterioration of neuronal DNA. Concurrently, spontaneous and artificially induced sleep help maintain genome integrity.
Hence, even rudimentary neural systems require downtime to lessen the DNA injuries caused by prolonged periods of wakefulness. The study’s results suggest that DNA damage and cellular strain might have been pivotal elements in the evolution of sleep.
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