Brainless Jellyfish Demonstrate Learning Ability
        Because box jellyfish are so distantly related to other animals, the research findings could hint at how the ability to learn first evolved.

Article written by Veronique Greenwood for The New York Times, 9-23-23.
(Condensed for this Post by J.X. Mason, 10-1-23)

“In the dappled sunlit waters of Caribbean mangrove forests, tiny box jellyfish (or, box-jellyfish) bob in and out of the shade. Box-jellies are distinguished from true jellyfish in part by their complex visual system — the grape-size predators have 24 eyes. But like other jellyfish, they are brainless, controlling their cube-shaped bodies with a distributed network of neurons…

“That network, it turns out, is more sophisticated than you might assume. On Friday, researchers published a report in the Journal Current Biology indicating that the box jellyfish species (Tripedalia cystophora) have the ability to learn. Because box jellyfish diverged from our part of the animal kingdom long ago, understanding their cognitive abilities could help scientists trace the evolution of learning…

“Anders Garm, a biologist at the University of Copenhagen and an author of the new paper, said his team decided to focus on a swift about-face that box jellies execute when they are about to hit a mangrove root. These roots rise through the water like black towers, while the water around them appears pale by comparison… How do box jellies tell when they are getting too close?…

“In the lab, researchers produced images of alternating dark and light stripes, representing the mangrove roots and water, and used them to line the insides of buckets about six inches wide. When the stripes were a stark black and white, representing optimum water clarity, box jellies never got close to the [striped] bucket walls. With less contrast between the stripes, however, box jellies immediately began to run into them…

“After a handful of collisions, the box jellies changed their behavior. Less than eight minutes after arriving in the bucket, they were swimming 50 percent farther from the pattern on the walls, and they had nearly quadrupled the number of times they performed their about-face maneuver. They seemed to have made a connection between the stripes ahead of them and the sensation of collision.

“Going further, the researchers removed 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 collision. Within about five minutes, the cells started sending the signal that would cause a whole box jellyfish to turn around.

“ ‘It’s amazing to see how fast 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 a significant step forward in understanding the origins of learning…”