On Friday, a report was published in Current Biology, revealing that the box jellyfish species Tripedalia cystophora has the ability to learn.

In the sun-dappled waters of Caribbean mangrove forests, tiny box jellyfish gracefully move in and out of the shadows. These creatures, distinct from typical jellyfish, possess a complex visual system with 24 eyes. Surprisingly, despite their lack of a conventional brain, they navigate their bodies through a decentralized network of neurons.

This neural network, as it turns out, is more sophisticated than one might expect. On Friday, researchers released a report in Current Biology indicating that Tripedalia cystophora, a species of box jellyfish, possesses the capacity to learn. Investigating their cognitive abilities could aid scientists in understanding the evolution of learning.

The challenge in studying learning in box jellyfish was identifying a routine behavior that could be trained in a laboratory setting. Anders Garm, a biologist at the University of Copenhagen and a co-author of the study, explained that his team chose to focus on a swift change in direction that box jellies execute when approaching a mangrove root. These roots emerge from the water like dark towers, while the surrounding water appears comparatively pale. However, this contrast can change due to silt clouding the water, making it harder for the box jellies to judge the root's distance. The question was, how do these box jellies discern when they are getting too close? Garm said, "The hypothesis was, they need to learn this. When they return to these habitats, they must learn to gauge today's water quality."

In the laboratory, researchers created images of alternating dark and light stripes, representing mangrove roots and water, which they used to line the inside of six-inch-wide buckets. When the stripes had a strong black-and-white contrast, simulating ideal water clarity, the box jellies consistently avoided the bucket walls. However, when the contrast between the stripes was reduced, the box jellies promptly began colliding with the walls. This presented an opportunity for scientists to observe if they could learn from these collisions.

After a few collisions, the box jellies altered their behavior. In less than eight minutes of being placed in the buckets, they began swimming 50% farther from the pattern on the walls, and they significantly increased the frequency of their about-face maneuvers. It appeared that they had established a connection between the visual stripes ahead of them and the sensation of collision.

Taking their investigation further, researchers extracted visual neurons from the box jellyfish and observed them in a controlled environment. These cells were exposed to striped images while receiving a mild electrical stimulus to simulate collision. Remarkably, within about five minutes, the cells initiated the signal that would prompt an entire box jellyfish to execute a turnaround. Jan Bielecki, a postdoctoral researcher at the Institute of Physiology at Kiel University in Germany and a co-author of the study, marveled at how quickly they learned, saying, "It's amazing to see how fast they learn.