Jellyfish Are Brainless, But Still Sleepy

Do jellyfish sleep? Learn more about a new study on the need for sleep in animals, and in jellyfish, in this BrainStuff episode.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain stuff from how stuff works. Hey, brain stuff,
it's Christian saga. You probably don't think you have much
in common with a jellyfish, After all, their species don't
share elemental properties with you, like you know, a spine
or a brain, or even the same interests. The primitive
jellyfish in the genus Cassiopeia spends its time resting upside

(00:24):
down on the ocean floor rather than you know, waiting
for the next season of Game Thrones. Researchers, though, have
now discovered that you and old Cassiopeia are more alike
than anyone might have suspected. You both begin and end
your days with a little shut I yes, jellyfish sleep.
The study was published online in the September edition of

(00:47):
the journal Current Biology. Unlike most jellyfish, Cassiopeia jellyfish often
rest on the floor of mangrove swamps and seagrass beds
and rarely move from their under water spots. By lying
upside down, the jellyfish exposes the algae on its underside
to the sun, allowing it to photosynthesize and live off

(01:10):
the food the algae produces. Ravi Nath, the papers co
first author and a graduate student in cal texts Sternberg Laboratory,
says that it may not seem surprising that jellyfish sleep,
after all, mammals sleep, and other invertebrates such as worms
and fruit flies sleep, but Nath points out that jellyfish

(01:31):
are the most evolutionary 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? To test whether the jellyfish were actually sleeping,
researchers set up cameras and found the jellyfish were largely

(01:52):
inactive at night, and they pulsed less during the day,
about thirty nine times compared to fifty eight times during
sunlight hours. Then the team discovered it was harder to
rouse the jellyfish at night too. They set up a
false bottom within the jellyfish tank and pulled the platform
out from under the jellyfish. When alert during the day,

(02:14):
the jellyfish immediately swam to the bottom of the tank.
At night, however, it took several seconds for the jellyfish
to awake before heading to the tank floor. The researchers
also demonstrated that sleep is essential to jellyfish, just like
it is to people. After keeping the jellyfish awake during
the night with pulses of water, the jellyfish were sluggish

(02:36):
and sleepy the next day, when they otherwise would have
been active. Mondays am I right. The discovery that jellyfish
sleep could be an important next step in sleep research
for all types of species. While the basis and function
of sleep is still a mystery to scientists, it's often
associated with the brain because sleep has a profound impact

(03:00):
on memory and learning. Jellyfish don't need a brain to sleep,
which could be a revolutionary concept for sleep science. Today's
episode was written by Laurie L. Dove, produced by Tristan McNeil,
and For more on this and other topics, please visit

(03:22):
us at how stuff works dot com.