A surprising jellyfish find challenges what is known about learning and memory

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A new study finds that Caribbean jellyfish, animals that may seem to float through life aimlessly and have no central brain, still have the ability to learn quickly and retain information.

The discovery upends a long-standing idea that organisms cannot engage in associative learning without a central nervous system, according to a study published Friday in the journal. Current biology.

Study-led Anders Jarman associate professor of marine biology at the University of Copenhagen in Denmark — is part of ongoing research into jellyfish behavior outside the ocean. Institute of Physiology at Keele University In Germany.

“We’ve looked at visual behavior and all kinds of experiences, and learning is just a natural progression,” said first author Jan Bilecki, a postdoctoral fellow in visual neuroethics at Kiele University.

After years of working with Caribbean box jellyfish, the team was not shocked to find that the animals could learn, but “it was a surprise how quickly they learned,” Bilecki said.

The Caribbean box jellyfish, also known by the scientific name Tripedalia Cystophora, has 24 eyes — six in each of the four visual sensory centers called rhopalia. The gelatinous body of the jellyfish, known as a bell because of its shape, bruises easily, a potential drawback when the creature moves among mangrove roots in the Caribbean. Swimming into the root can cause damage that leads to bacterial infection and eventually death, Bilecki said.

“So we were pretty sure that these animals were able to learn because (avoiding mangrove roots) is a crucial learning process for them if they want to survive,” he said.

To test the animals’ ability to learn, the researchers lined the inside of a circular tank with gray and white stripes. The gray lines of the jellyfish’s 24 eyes would appear as dark as a distant mangrove root in their natural habitat. Over the course of 7.5 minutes, the researchers monitored the jellyfish to see whether the animals collided with the lines or learned to keep their distance.

For the first several minutes, the jellyfish swam close to or bumped into the walls. But within five minutes things changed.

The jellyfish received a combination of visual stimulation from the lines and mechanical stimulation from bumping into obstacles.

“They’ve learned that they get these stimuli simultaneously (and) they avoid obstacles,” Bilecki said. “they Increased performance across all criteria we measured to avoid bottlenecks.

The researchers then replaced the lines with a solid gray field. The jellyfish hit him again and again.

“There was no visual cue, so they didn’t learn anything,” Bilecki said. “They kept bumping into things and not responding.”

Finally, the researchers conducted a neurophysiological experiment centered on how rupalia gives an electrical signal that drives the pulsating movement, or swimming contractions, that jellyfish make to propel themselves through the water. Their pulse speed increases dramatically as they move to avoid any obstacle.

Scientists isolated the rupalia by separating it from the bell. But mangrove root substitutes have been moved. So, the jellyfish’s vision mechanism remained constant while the lines moved. Can the visual system learn that it should avoid gray lines?

Scientists have connected a system that can send a weak electrical signal to visual sensory centers. When robalia did not activate the signal that would normally stimulate swimming contractions, Scientists did it for them. Soon the rupalia began transmitting the signal without any prompting, even for the light gray bars that provided much less contrast with the rest of the environment.

Bilecki said they achieved their findings because the experiment was “behaviorally relevant” for jellyfish. The researchers put the animals in a situation similar to what they would encounter in the wild.

“So visual stimulation and mechanical stimulation is something that (occurs) in their natural environment,” he said. “They know exactly what to do with this.”

Dr. Michael Abrams, a researcher in the Department of Molecular and Cell Biology at the University of California, Berkeley, who has done extensive work on jellyfish and sleep, said the study was robust. Abrams was not involved in the new research.

“Scientists have created a very compelling experimental model to measure associative learning in this box jellyfish. Their findings may also be evidence of some degree of short-term memory,” Abrams said in an email. He added that the study clearly demonstrated the animal’s ability to learn, Which made him wonder, “How long will his memory last?”

While earning his PhD at Caltech, Abrams worked on a 2017 study of the upside-down jellyfish (Cassiopea) and its “sleep-like state,” which “was also previously considered a behavior found only in animals with a central nervous system.”