A new study has found that Caribbean jellyfish, animals that seem to live aimlessly and lack a central brain, still have the ability to learn quickly and retain information.
The findings upend the long-held idea that organisms cannot engage in associative learning without a central nervous system, according to a study published Friday in the journal. Current biology.
Led by Anders Jarm, a professor of marine biology at the University of Copenhagen in Denmark – is part of ongoing research into the behavior of jellyfish outside the ocean. Institute of Physiology at Keele University in Germany.
“We’ve seen 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 the University of Kiele.
After years of working with Caribbean box jellyfish, the team wasn’t surprised to learn that the animals could learn, but “it was surprising how quickly they learned,” Bilecti said.
The Caribbean box jellyfish, also known by its scientific name Tripedalia Cystophora, has 24 eyes – six in each of the four visual sense centers called rhopalia. The jellyfish’s gelatinous body, known as a bell because of its shape, bruises easily, which is a potential weakness when the creature moves among mangrove roots in the Caribbean. Swimming into the roots can cause damage that leads to bacterial infection and eventually death, Bilecti said.
“So we believe these animals can learn because (avoiding mangrove roots) is an important 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 line on the jellyfish’s 24 eyes would look as dark as mangrove roots in its natural habitat. For 7.5 minutes, the researchers monitored the jellyfish to see if the animals collided with the line or learned to keep their distance.
For the first few minutes, the jellyfish swim close to or hit the wall. But within five minutes everything changed.
Jellyfish receive a combination of visual stimulation from lines and mechanical stimulation from hitting obstacles.
“They’ve learned that they get this stimulus simultaneously (and) they avoid obstacles,” Bilekki said. “they Improved performance across the criteria we measure to avoid bottlenecks.
The Caribbean box jellyfish, also known by its scientific name Tripedalia Cystophora, has 24 eyes – six in each of the four visual sense centers called rhopalia.
The researchers then replaced the lines with solid gray areas. The jellyfish hit him repeatedly.
“There are no visual cues, so they don’t learn anything,” Bilecti said. “They kept bumping into each other and didn’t react.”
Finally, the researchers conducted neurophysiological experiments centered on how Rupalia provides electrical signals that induce the pulsating movements, or swimming contractions, that jellyfish make to propel themselves through water. Their pulse rate increases dramatically as they move to avoid obstacles.
Scientists isolated Rupalia by separating it from the bell. However, the replacement mangrove roots were removed. So, the jellyfish’s vision mechanism remains constant as long as the stripes move. Can the visual system know that it should avoid gray lines?
Scientists have connected a system that can send a weak electrical signal to the center of the visual sense. When robalia does not activate the signals that normally stimulate swimming contractions, Scientists do it for them. Rupalia immediately starts emitting signals without any prompting, even for a light gray bar that provides much less contrast with the rest of the environment.
Bilecki said they made this discovery because the experiment was “behaviourally relevant” to the jellyfish. The researchers put the animals in situations similar to those they would encounter in the wild.
“So visual stimulation and mechanical stimulation (occur) in the natural environment,” he said. “They know what to do with this.”
Michael Abrams, a researcher in the Department of Molecular and Cell Biology at the University of California, Berkeley, who has done extensive research on jellyfish and sleep, says the research is powerful. Abrams was not involved in the new research.
“Scientists have created a very interesting experimental model to measure associative learning in this box jellyfish. Their findings may also be evidence of some level of short-term memory,” Abrams said via 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 research in 2017 about upside-down jellyfish (Cassiopea) and “sleep-like states,” which “were previously thought to be behaviors found only in animals with a central nervous system.”