According to a study carried out by scientists at the University of Kyushu, in Japan, a small invertebrate called Hydra has characteristics similar to sleep despite not having a central nervous system. This would confirm that the evolution of sleep precedes the development of the brain.
In a release, those responsible for the research concluded that from what was observed in Hydra it can be said that animals in general acquired mechanisms related to sleep before the evolutionary development of the central nervous system. Furthermore, many of these mechanisms were conserved as the brains of each species evolved.
A situation that we have all gone through at some point is the inability to think correctly in the absence of sleep. However, it is a problem that we can easily solve with some simple patterns, behaviors and habits that can be seen in humans and many other species.
With this in mind, scientists have wondered when and why animals begin to need sleep and whether the presence of the brain is a prerequisite or not. Now, new research published in the journal Science Advances sheds light on this phenomenon, thanks to the study carried out on Hydra vulgaris, a small cnidarian with a simple anatomy.
First the dream, then the brain
The work of Japanese specialists could help to understand the evolutionary origin of sleep in animals, since it has shown that tiny hydras show signs of a sleep-like state, even without a central nervous system. According to Taichi Q. Itoh, leader of the research, “we now have strong evidence that animals must have acquired the need to sleep before they have a brain,” he stressed.
The research on Hydra vulgaris adds to other discoveries surrounding sleep behavior in jellyfish, a close relative of hydras. Experts from Kyushu University found in previous studies that both species have reactions to chemicals that cause drowsiness and sleep, substances that even have similar effects in humans.
In terms of hydras, exposure to melatonin, a commonly used sleep-promoting substance, produced a moderate increase in the amount and frequency of sleep. On the other hand, the inhibitory neurotransmitter GABA, another chemical substance related to sleep in different animal species, considerably increased sleep activity.
At the same time, the scientists found that some sleep mechanisms appear to have been preserved during brain evolution, while others have changed function. For example, while dopamine generates excitement in some animals, in hydras it works by promoting sleep.
Mechanisms that remain
In another sense, species with a brain and those that do not have it also show differences in terms of sleep-related behaviors. While in the human being the circadian rhythm and the cycles that repeat every 24 hours are a central arrangement, in the hydras there are four-hour cycles of active states interspersed with others dedicated to sleep-like behaviors.
Another of the conclusions of the Japanese study indicates that lack of sleep leads to changes in the expression of 212 genes, including some present in a wide range of animals, such as rodents, fruit flies and nematodes. In addition, the researchers identified genes in the fruit fly that appear to share a common evolutionary origin with those that are related to sleep in hydras.
To conclude, the scientists indicated that all these data together provide strong evidence that animals acquired mechanisms related to sleep prior to the evolutionary development of the central nervous system. Even a large part of these mechanisms were preserved as the brains of each species evolved.
A sleep-like state in Hydra unravels conserved sleep mechanisms during the evolutionary development of the central nervous systemHiroyuki J. Kanaya, Sungeon Park, Ji-hyung Kim, Junko Kusumi, Sofian Krenenou, Etsuko Sawatari, Aya Sato, Jongbin Lee, Hyunwoo Bang, Yoshitaka Kobayakawa, Chunghun Lim, and Taichi Q. Itoh. Science Advances (2020). DOI: https://doi.org/10.1126/sciadv.abb9415
Hydra. Wikimedia Commons.
Eddie is an Australian news reporter with over 9 years in the industry and has published on Forbes and tech crunch.