Although these jellyfish only have a thousand neurons, they learn as quickly as advanced animals like fruit flies and mice.
For a long time, scientists believed that jellyfish were simple animals that could learn little. But perhaps we’ve been underestimating these animals all this time. Recent research has shown that Tripidalia cestophora (Tropical box jellyfish) can learn at a more advanced level than we previously thought. This is even better when you take into account that they only have a thousand neurons and no central nervous system.
The prevailing opinion is that animals with more developed nervous systems are better able to learn. Jellyfish and their relatives are among the first evolved animals to develop nervous systems, but their nervous systems are relatively simple and they lack a central brain. “Jellyfish were thought to be capable of only the simplest forms of learning,” says researcher Anders Jarm. “Think about getting used to repeated stimuli, such as continuous sound or constant touch. But we have now discovered that jellyfish can learn more complexly than we first thought. They can even learn from their mistakes. And they modify their behavior based on those experiences.”
The researchers made this discovery after… Tripidalia cestophora (See box) They are trained to recognize and avoid obstacles. The research team placed the jellyfish in a circular tank with gray and white stripes to mimic its natural environment. The gray lines were reminiscent of the roots of mangrove trees that seemed far away. The researchers then observed the jellyfish in the tank for 7.5 minutes. At first, the jellyfish approached these seemingly distant lines, and often collided with them. But by the end of the experiment, the researchers noted that the jellyfish increased the average distance from the wall by about 50 percent, made more successful collision-avoidance maneuvers and reduced the amount of contact with the wall by half. These results suggest that jellyfish can learn from their experiences through visual and mechanical stimuli.
The Tripedalia Cystophora, as mentioned earlier, is a box jellyfish. The box jellyfish belongs to a class of jellyfish that is known to be among the most venomous animals in the world. They use their venom to catch large fish and shrimp. However, the Tripadalia cestophora has a less potent venom and feeds on small crustaceans. Its body is only about a centimeter in diameter – making it no larger than a fingernail – and it is one of the smallest species of box jellyfish. They have a complex visual system with 24 eyes in their bell-shaped body. Jellyfish inhabit mangrove swamps and rely on their vision to navigate murky water and avoid obstacles—such as underwater tree roots—as they hunt for prey. Jellyfish live in the Caribbean Sea and the Central Indo-Pacific region.
The results show that jellyfish can learn from previous experiences, just like humans, mice and flies. This is interesting. It shows that even the simplest nervous system is capable of advanced learning.
Smarter than thought
Jellyfish, despite lacking a central brain, are much more intelligent than thought. The research therefore challenges previous theories that suggested that advanced learning depends on the presence of a central brain. “Although jellyfish only have a thousand neurons — by comparison, humans have about 100 billion neurons — they are able to temporarily collect different impressions and make connections, which we call associative learning,” Garm says. “Surprisingly, they learn just as quickly as more advanced animals like fruit flies and mice.”
The research results were published in the journal Current biology, breaking existing scientific views about what animals with simple nervous systems can achieve. “This is very big news in neuroscience,” Garm asserts. “This gives us new insight into what is possible with a relatively simple nervous system. It suggests that advanced learning may have been one of the most important evolutionary advantages of the nervous system, even since the beginning of evolution.”
This discovery changes our basic understanding of the brain, of which there is still much to discover. “We hope that this research will serve as a model for studying cellular processes associated with advanced learning in different animals,” Garm said. “We are currently working to precisely identify the cells involved in learning and memory formation. Once we are certain of this, we can investigate the structural and physiological changes that occur in those cells during the learning process. If researchers can pinpoint the exact mechanisms in jellyfish that are involved in learning “The next step is to investigate whether this phenomenon is specific to jellyfish or if it occurs in all animals. We will eventually investigate the same mechanisms in other animals to see if this is how memory works in general,” he said.
This knowledge can also provide us with insight into our mysterious brains. “Better understanding something as mysterious and complex as the brain is amazing in itself,” Jarm says. “But there are countless possible practical applications. An important challenge in the future is likely to relate to different forms of dementia. I am not claiming that we have found a cure for dementia, but if we can get a deeper understanding of what memory is involved in, which is a fundamental problem in dementia… We may be able to lay the groundwork for better understanding and treating the disease, and perhaps acting more effectively against it.
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