Jellyfish IQ: How a Brainless Wonder Stunned the Scientific World

Scientists found out that box jellyfish, specifically the kind called Tripedalia cystophora, can learn. In an experiment in a lab, they taught these jellyfish to recognize and avoid patterns that look like mangrove roots, which they usually bump into. After a few bumps, the jellyfish changed their behavior and started swimming away from the pattern. This study helps us understand how learning works and makes us wonder if nerve cells, even without a brain, can learn things.

On Friday, researchers wrote a report in Current Biology saying that Tripedalia cystophora box jellyfish can learn.

In the sunny waters of Caribbean mangrove forests, tiny box jellyfish move in and out of the shadows. These jellyfish are different from regular jellyfish because they have a complex visual system – they have 24 eyes, like grapes. But like other jellyfish, they don’t have a brain. They control their bodies with a network of neurons spread throughout their bodies. This network is more advanced than we thought. On Friday, researchers wrote a report in Current Biology showing that Tripedalia cystophora box jellyfish can learn. Understanding how smart they are can help scientists figure out how learning evolved.

Studying learning in box jellyfish was tricky. Scientists needed to find a behavior they could teach them in a lab. Anders Garm, a biologist at the University of Copenhagen and one of the authors of the report, decided to focus on how box jellyfish quickly turn around when they are about to hit a mangrove root. These roots stick up through the water like dark towers, while the water around them looks lighter. But when the water gets muddy, it’s hard to tell how far away a root is. Garm said, “We thought they needed to learn this – how clear the water is when they come back to these places.”

In the lab, researchers put pictures of dark and light stripes, like mangrove roots and water, inside buckets that were about six inches wide. When the stripes were very different, showing clear water, the box jellyfish stayed away from the bucket walls. But when the stripes were less different, the jellyfish immediately bumped into the walls. This was the scientists’ chance to see if they could learn. After a few bumps, the box jellyfish changed what they did. In less than eight minutes, they were swimming 50% farther from the stripe pattern on the walls, and they turned around almost four times more often. They figured out that the stripes meant they were going to bump into something.

Researchers also took out some visual neurons from the box jellyfish and studied them in a dish. They showed the cells striped pictures while giving them a small electric shock to pretend like there was a bump. Within about five minutes, the cells started sending a signal that would make a whole box jellyfish turn around. Jan Bielecki, a scientist at the Institute of Physiology at Kiel University in Germany, who was also part of the study, said, “It’s incredible how fast they learn.” Scientists who weren’t involved in the study said this is a big step in understanding how learning works. Ken Cheng, a professor at Macquarie University in Sydney, Australia, said, “This is only the third time that we’ve seen animals like jellyfish learn in this way.”

In the future, researchers want to find out which specific cells help box jellyfish learn from their experiences. Garm and his colleagues are curious about what happens in these cells when the animals learn new things. They want to know if the ability to learn is something nerve cells can do, even if they’re not part of a brain. This might explain why box jellyfish have been around for so long in the history of life on Earth.

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