Do Jellyfish Sleep?



If you’re like most people, you sleep. Every so often, your body enters an extended period of little movement and you become less responsive to stimuli. And if you find your sleep regularly disturbed, you become sleepier and sleepier, eventually finding yourself dozing off during the day. Research published this week in the journal Current Biology finds that one species of jellyfish, Cassiopea, has a similar behavior, making it the simplest organism known to nap.An interdisciplinary team of researchers at the California Institute of Technology found that Cassiopea enter a nightly period of quiescence, in which their rhythmic pulsing slows. They become less likely to respond to stimuli, such as squirts of water, and slower to react to changes in their environment. And if the jellyfish are regularly disturbed during this quiescent period, they become more likely to enter a similar state during times when they’re normally active.

[What exactly is sleep, anyway?]

Claire Bedbrook, one of the co-authors of the new study, says that they don’t yet know if there is a genetic component to the sleeplike behavior across species, or what changes might be going on at the neuronal level during the jellies’ quiescent period. However, the presence of a sleeplike behavior in such an evolutionarily ancient species raises questions about what exactly sleep is, and its role in animal life.

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