Brainless jellyfish demonstrate learning ability | ET REALITY


In the sunlit, dappled waters of the Caribbean mangrove forests, tiny jellyfish dart in and out of the shade. Box jellyfish are distinguished from true jellyfish in part by their complex visual system: The grape-sized predators have 24 eyes. But like other jellyfish, they have no brain and control their cube-shaped bodies with a distributed network of neurons.

It turns out that this network is more sophisticated than one might assume. On Friday, investigators released a report. in the magazine Current Biology indicating that the box jellyfish species Tripedalia cistophora has the ability to learn. Because box jellyfish diverged from our part of the animal kingdom long ago, understanding their cognitive abilities could help scientists track the evolution of learning.

The tricky part about studying learning in jellyfish was finding an everyday behavior that scientists could train the creatures to perform in the lab.

Anders Garm, a biologist at the University of Copenhagen and author of the new paper, said his team decided to focus on a rapid spin that jellyfish perform when they are about to touch a mangrove root. These roots rise through the water like black towers, while the water around them appears pale in comparison. But the contrast between the two can change from day to day, as silt clouds the water and makes it harder to tell how far away a root is. How do jellyfish know when they are getting too close?

“The hypothesis was that they needed to learn this,” Dr. Garm said. “When they return to these habitats, they will have to learn what the current water quality is like. How is the contrast changing today?

In the lab, the researchers produced images of alternating light and dark stripes, representing mangrove roots and water, and used them to line the inside of cubes about six inches wide. When the stripes were a vivid black and white, representing optimal water clarity, the jellyfish never approached the walls of the cube. However, with less contrast between the stripes, the box jellies immediately began to bump into them. This was the opportunity for scientists to see if they would learn.

After a few collisions, the jellyfish changed their behavior. Less than eight minutes after reaching the cube, they were swimming 50 percent farther from the pattern on the walls and had nearly quadrupled the number of times they performed their turn maneuver. They seemed to have made a connection between the stripes in front of them and the sensation of collision.

Going further, the researchers extracted visual neurons from the box jellyfish and studied them in a dish. The cells were shown striped images while receiving a small electrical pulse to represent the collision. Within about five minutes, the cells began sending the signal that would make an entire jellyfish spin.

“It’s surprising to see how quickly they learn,” said Jan Bielecki, a postdoctoral researcher at the Institute of Physiology at Kiel University in Germany, also an author of the paper.

Researchers who were not involved in the study called the results an important step forward in understanding the origins of learning. “This is only the third time that associative learning has been convincingly demonstrated in cnidarians,” a group that includes sea anemones, hydras and jellyfish, said Ken Cheng, a professor at Macquarie University in Sydney, Australia, who studies to the animals. “And this is the coolest demonstration, packed with physiological data.”

The results also suggest that box jellyfish possess some level of short-term memory, because they can change their behavior based on past experiences, said Michael Abrams, a postdoctoral researcher at the University of California, Berkeley, who studies the neuroscience of jellyfish sleep. jellyfish. He wonders how long jellyfish remember what they have learned. If they are taken out of the tank for an hour and then put back in, do they have to learn what to do again?

In future work, the researchers hope to identify which specific cells control the jellyfish’s ability to learn from experience. Dr. Garm and his colleagues are curious about the molecular changes that occur in these cells as the animals incorporate new information into their behavior.

They also wonder if the ability to learn is universal among nerve cells, regardless of whether they are part of the brain. It could explain its peculiar persistence on the tree of life.

“There are organ systems that come and go all the time,” Dr. Garm said. “But nervous systems… once they’re there, they rarely go away again.”

Perhaps the ability to learn is one of the reasons they are still here.

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