Jellyfish learning abilities: challenging neuroscientific concepts
Even without a central brain, jellyfish can learn from past experiences like humans, mice and flies, scientists first reported Sept. 22 in the journal. Current biology. They trained Caribbean jellyfish (Tripidalia cestophora) to learn how to detect obstacles and avoid them. The study challenges previous notions that advanced learning requires a central brain and sheds light on the evolutionary roots of learning and memory.
Complex vision in a simple creature
These seemingly simple jellyfish are no larger than a fingernail and have a complex visual system with 24 eyes embedded in their bell-like body. This animal lives in mangrove swamps, and uses its vision to navigate through murky water and swerve around underwater tree roots to hunt prey. Scientists have demonstrated that jellies can acquire the ability to avoid obstacles through associative learning, a process by which organisms form mental associations between sensory stimuli and behaviors.
“Learning is the ultimate functioning of the nervous system,” says first author Jan Bielecki of Kiel University in Germany. In order to successfully teach a jellyfish a new trick, he says, “it’s best to take advantage of its natural behaviors, which is what makes sense for the animal, until it reaches its full potential.”
Simulated learning environment
In an attempt to recreate the jellyfish’s natural habitat, the researchers decorated a circular tank with gray and white stripes, with the gray stripes mimicking the roots of distant mangrove trees. They observed the jellyfish in the tank for 7.5 minutes. At first, the jelly swam near these seemingly distant lines, bumping into them repeatedly. But by the end of the experiment, the gel had increased its average distance to the wall by about 50%, quadrupled the number of successful pivots to avoid a collision, and cut its contact with the wall by half. The results suggest that jellyfish can learn from experience through visual and mechanical stimuli.
Caribbean jellyfish live and feed among the underwater roots of mangrove trees. Credit: Anders Gram
“If you want to understand complex structures, it’s always a good idea to start as simple as possible,” says lead researcher Anders Jarm of the University of Copenhagen in Denmark. “Looking at these relatively simple nervous systems in jellyfish, we have a much greater opportunity to understand all the details and how they come together to perform behaviors.”
Decipher the learning center
The scientists then sought to determine the basic process of jellyfish associative learning by isolating the animal’s visual sensory centers called rupalia. Each of these structures has six eyes, and generates pacemaker signals that control the jellyfish’s pulsating movement, the frequency of which rises as the animal veers away from obstacles.
The researchers showed that the stationary rubalium moves with gray bars to mimic the animal’s approach to objects. The structure did not respond to the light gray bars, interpreting them as being far away. However, after the researchers trained the robalium with weak electrical stimulation as the bars approached, it began generating obstacle avoidance signals in response to the light gray bars. These electrical stimulations mimic the mechanical stimuli of a collision. The results also showed that a combination of visual and mechanical stimuli is required for associative learning in jellyfish and that the rubalium functions as a learning center.
Next, the research team plans to delve deeper into the cellular interactions of the jellyfish’s nervous system to disentangle the process of memory formation. They also plan to understand how the mechanical sensor in the bell works to paint a complete picture of the animal’s associative learning.
“It’s amazing how quickly these animals learn; “It’s about the same speed as advanced animals,” Garm says. “Even the simplest nervous system appears to be capable of advanced learning, and this may turn out to be a very basic cellular mechanism invented at the dawn of the evolutionary nervous system.”
For more information about this study, see Jellyfish’s Surprising Thought Changes Our Basic Understanding of the Brain.
Reference: “Cooperative Learning in the Box Jellyfish Tripedalia Cystophora” 22 September 2023, Current biology.
This work was supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), the Danish Research Council (DFF), and the Villum Foundation.
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