These guys may be smarter than you think. Photo: Elisha Terada // Unsplash
A new study published in Current Biology shows that, despite lacking a central brain, at least one species of jellyfish can learn from experience. Scientists designed a study to replicate the environment of a species of box jellyfish, and found that the animals quickly learned to avoid obstacles put in their way.
Jellyfish are strange critters. They’ve been around for 500 million years, and in that time have developed structures that are pretty unique in the animal kingdom. “They have this habit of distributing everything all along their edges,” Anders Garm told Technology Networks. Anders is an associate professor of marine biology at the University of Copenhagen and senior author of the new study. He continued to explain that the main section of a jellyfish’s body, called a “bell,” has 24 “eyes,” called rhophalia, distributed among four sensory centers around its rim.
Those “eyes” factored into the study Garm designed around the box jellyfish Tripedalia cystophora. About the size of a fingernail, T. cystophora drifts around the roots of mangrove trees in the Caribbean, hunting plankton-like prey. Working alongside Jan Bielecki, a group leader at Kiel University, Garm wanted to test whether T. cystophora could learn in response to signals from its environment.
The jellyfish were placed in a round tank, which was lined with white and gray stripes. Initially, they would swim towards the gray stripes, colored to resemble distant mangrove roots, and ran into the tank wall in the process. However, the animals quickly learned to avoid the gray “roots.” After seven minutes, they managed to cut the number of collisions with the wall in half, increase their distance from the wall by 50 percent and became four times more likely to pivot away from potential collisions.
The researchers then placed one of the jellies’ rhopalia in a petri dish to observe its response to stimuli more closely. At first the “eyes” did not respond to the gray bars, but then the scientists stimulated them with electrical signals that replicated the ones generated after a collision. This created a sort of pavlovian reaction, where the rhopalium began to generate “dodge” signals whenever it saw the bars.
However, swimmers don’t yet have to live in fear of learning jellyfish, as they were observed to forget what they had learned around 20 minutes after the experiment ended. The exact mechanism by which T. cystophora is able to learn at all is still unclear, but seems to be different from the type of long-term, lasting memories in humans.
Though we still have more to understand about how jellyfish are able to exhibit this behavior with such simple structures, it’s a step towards broadening our knowledge of how not only these types of creatures function, but animal nervous systems in general. “Our work challenges the notion that associative learning requires complex neuronal circuitry,” says the abstract for the study. “It suggests the intriguing possibility that advanced neuronal processes, like operant conditioning, are a fundamental property of all nervous systems.”
