Brainless Jellyfish Also Sleeps, Study Finds

Posted: Sep 22 2017, 6:12am CDT | by , Updated: Sep 22 2017, 6:15am CDT, in News | Latest Science News

 

Brainless Jellyfish Also Sleeps, Study Finds
Jellyfish sitting upside down on the bottom of the tank. Credit: Caltech
 

For the first time, researchers have demonstrated that an organism without brain also goes to sleep at night

It is widely believed that sleep is limited to animals with a central nervous system. From humans, to sharks to birds and bees, everyone goes to sleep. But a new research says that brainless creatures like jellyfish also need sleep and feel lazy if they do not get the desired amount.

It represents the first example of sleep in an animal without brain. Moreover, since jellyfish are one of the Earth’s first and most ancient animals, the findings also suggest that the origins of sleep are more primitive than thought. 

“It may not seem surprising that jellyfish sleep -- after all, mammals sleep, and other invertebrates such as worms and fruit flies sleep," said co researcher Ravi Nath from Sternberg laboratory. "But jellyfish are the most evolutionarily ancient animals known to sleep. This finding opens up many more questions: Is sleep the property of neurons? And perhaps a more far-fetched question: Do plants sleep?"

One of the biggest challenges of studying sleep is defining what constitutes “sleep.” Researchers believe that an organism must meet three critical criteria to be considered sleeping. First, it must exhibit a period of reduced activity. Second, it should have a decreased response to otherwise-arousing stimuli during sleep-like state. Third, it should become tired if deprived of sleep. And researchers have observed these telltale signs of sleep in primitive type of jellyfish called Cassiopea. 

Cassiopea or upside-down jellyfish are found in shallow, tropical waters. They usually lie on the bottom of swamps and canals with their tentacles upward and this unique trait has earned them their name.

“When humans sleep, we are inactive, we often can sleep through noises or other disturbances which we might otherwise react to if we were awake, and we're likely to fall asleep during the day if we don't get enough sleep," said co-researcher Claire Bedbrook from Gradinaru laboratory. "We might seem extremely different from jellyfish, but we both exhibit a similar sleep state."

For the study, researchers set up cameras to monitor the activities of more than 20 cassiopea jellyfish for six days and nights. They discovered that the jellyfish go through periods of inactivity at night as they only pulse about 39 times per minute compared to about 58 times per minute during the day. To confirm the less and infrequent pulsation, jellyfish had to undergo several experiments and results eventually showed less activity at night.  

“Sleep is a genetically encoded behavioral state. Genes and neural circuits interact to generate the sleep state,” said Nath. “I think it would be hard to demonstrate a sleep state in an organism that is not an animal, but I think the sleep state that we know may have been co-opted from periods of quiescence in organisms as diverse as plants, bacteria and fungi.”

 

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Hira Bashir covers daily affairs around the world.

 

 

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