Well that seems a bit silly – let’s just start with sleeping jellyfish. First off why do WE need sleep? Most sleep researchers believe that it enables our bodies and brains to recover. Throughout each day as we experience things, our brain cells create new connections. During sleep its believed that these important connections are strengthened, insignificant ones are culled and brain cells are also cleansed of toxins.
Recently a group of Caltech graduate students have observed sleep-like behavior in jellyfish. Why would a jellyfish, an organism lacking a brain, need sleep? Claire Bedbrook, Michael Abrams and Ravi Nath (https://www.youtube.com/watch?v=UPtSlvU6nh8) have the first documented example of sleep in an organism with a diffuse nerve net, a system of neurons dispersed throughout the body, without a centralized brain. Because jellyfish are very low on the evolutionary ladder, it suggests that the ability to sleep evolved very early on.
Birds, bees, fish, even worms sleep. Previous research also found that cnidarian soft corals and box jellyfish experienced periods of quiescence. Considering all of these animals, it begs to ask what constitutes sleep? The three accepted behavioral criteria for sleep are:
One - The animals must undergo a period of diminished activity. However, they must also be able to be aroused from this state. This is differentiates sleep from other states, like comas.
Two - the animals must exhibit decreased responsiveness to stimuli while sleeping.
Three- the animals must show an increased need for sleep if they are kept from it
To prove the Cassiopea, or upside-down jellyfish sleep, the researchers first monitored 23 individual jellyfish over six days and nights. They observed “diminished activity” with the jellyfish pulsing 30% less at night than during the day. If the jellyfish were poked or fed during the middle of the night, the jellyfish would stir temporarily.
Upside-down jellyfish get their name from the fact that they prefer to settle upside-down on the sea-floor, instead of being suspended in the water. So, to test their responsiveness to stimuli while asleep, the researchers placed the jellyfish within small boxes elevated within the tanks which had removal bottoms. If during the day the box bottoms were removed, the jellyfish would immediately swim to the bottom surface of the tank. At night however, they would sluggishly float around at first.
Finally, to assess the need for sleep, the researchers pulsed water through the tanks every 20 minutes at night to prevent the jellyfish from sleeping continuously. The following day the jellyfish showed significantly reduced levels of activity than normal, which suggested sleep deprivation.
The researchers, through a pharmacological study, also found that just like human’s, jellyfish become “sleepy” when exposed to melatonin. Again, this speaks back to their underlying sleep mechanisms may be fundamentally similar to our own. Sleep experts believe that these upside-down jellyfish ““do a good job of demonstrating that jellyfish fulfill the most fundamental criteria for sleep,” William Joiner, a sleep researcher at the University of California, San Diego.
To gain access to this interesting article please Current Biology
http://www.cell.com/action/showMethods?pii=S0960-9822%2817%2931023-0
Nath R.D., Bedbrook C.N., Abrams M.J., Basinger T., Bois J.S. Prober D.A., Sternberg P.W., Gradinaru V., and Goentoro L. (2017) The Jellyfish Cassiopea Exhibits a Sleep-like State. Current Biology. 27: 22984-2990.
