Researchers
at the California Institute of Technology have found evidence that at
least one type of jellyfish engages in a very unexpected behavior:
sleep. The study, published by Ph.D. candidate Ravi Nath and his fellow
researchers in Current Biology [1] in September, showed that Cassiopea jellyfish passed several criteria
established in their lab to demonstrate they were engaging in a behavior
that could be considered sleep.
The finding comes as a surprise to the scientific community, as previously sleep was thought to be an activity performed only by more complex organisms with central nervous systems: humans, dogs, fish, even worms. Now, adding to the mystery of why organisms sleep, there is one without a brain that does it too.
To establish that the jellyfish were sleeping rather than engaging in other behavior, the researchers set up three criteria: a regular period of diminished activity, decreased responsiveness to stimuli during this period and an increased need for the hypothesized sleep behavior when it was not getting enough. The jellyfish passed all three.
Sleep - it's a NO-brainer!
Formal testing revealed that the jellyfish pulsed 30% less during this period of diminished activity and could be “awoken” with food or prodding, ruling out other possible states such as coma. The researchers tested responsiveness by removing the floors from under the jellyfish at random times; in the hypothesized sleeping phase, they would float around before swimming to their preferred place on the floor of the tank. A need for sleep was operationalized by shooting water through the tank every 20 minutes, keeping the jellyfish from attaining this restful state; during the wakeful period the following day, the jellyfish engaged in lower levels of activity than usual.
Cassiopea,
the “upside-down jellyfish” have a non-centralized radially symmetric
nerve net, a diffused organization of nerve cells throughout the body
with no large centralized concentration (a brain) [1]. However, like
organisms with central nervous systems, theirs functions using action
potentials, synaptic transmission, neuropeptides and neurotransmitters.
This commonality suggests maintenance of the nervous system at a very
basic level may be a reason organisms need to sleep.
Cnidaria, the phylum of Cassiopea, branched early on from the evolutionary line of human beings. The researchers suggest that this signifies “sleep is rooted in basic requirements that are conserved across the animal kingdom.” [1] More research however, will need to be done to determine whether this behavior evolved in Cnidaria separately, or whether it is truly an early behavior in our evolutionary history.
By Alex Masurovsky, MSc Student Berlin School of Mind and Brain
This article originally appeared December 2017 in CNS Volume 10, Issue 04, Sleep
[1] Nath et al., Curr Biol, 2017;
[2] http://nyti.ms/2fE9JuC
[3] http://bit.ly/2hF7bgC
The finding comes as a surprise to the scientific community, as previously sleep was thought to be an activity performed only by more complex organisms with central nervous systems: humans, dogs, fish, even worms. Now, adding to the mystery of why organisms sleep, there is one without a brain that does it too.
SLEEP: A BASIC REQUIREMENT IN THE ANIMAL KINGDOM
To establish that the jellyfish were sleeping rather than engaging in other behavior, the researchers set up three criteria: a regular period of diminished activity, decreased responsiveness to stimuli during this period and an increased need for the hypothesized sleep behavior when it was not getting enough. The jellyfish passed all three.
Sleep - it's a NO-brainer!
Formal testing revealed that the jellyfish pulsed 30% less during this period of diminished activity and could be “awoken” with food or prodding, ruling out other possible states such as coma. The researchers tested responsiveness by removing the floors from under the jellyfish at random times; in the hypothesized sleeping phase, they would float around before swimming to their preferred place on the floor of the tank. A need for sleep was operationalized by shooting water through the tank every 20 minutes, keeping the jellyfish from attaining this restful state; during the wakeful period the following day, the jellyfish engaged in lower levels of activity than usual.
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| Image source: prilfish via Flickr |
Cnidaria, the phylum of Cassiopea, branched early on from the evolutionary line of human beings. The researchers suggest that this signifies “sleep is rooted in basic requirements that are conserved across the animal kingdom.” [1] More research however, will need to be done to determine whether this behavior evolved in Cnidaria separately, or whether it is truly an early behavior in our evolutionary history.
By Alex Masurovsky, MSc Student Berlin School of Mind and Brain
This article originally appeared December 2017 in CNS Volume 10, Issue 04, Sleep
[1] Nath et al., Curr Biol, 2017;
[2] http://nyti.ms/2fE9JuC
[3] http://bit.ly/2hF7bgC
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