Jellyfish’s surprising intelligence changes our basic understanding of the brain

Jellyfish are more advanced than previously thought. A new study from the University of Copenhagen shows that Caribbean jellyfish can learn at a more complex level than ever imagined, despite having only about a thousand neurons and the absence of a central brain. This discovery changes our basic understanding of the brain and could shed light on our mysterious brains.

After more than 500 million years on Earth, the enormous evolutionary success of jellyfish is undeniable. However, we always consider them as simple creatures with very limited learning abilities.

The prevailing view is that a more advanced nervous system equates to a more advanced learning potential in animals. Jellyfish and their relatives, known collectively as cnidarians, are the first living animals to develop a nervous system and have a fairly simple nervous system and no central brain.

For more than a decade, neurobiologist Anders Jarm has studied box jellyfish, a group of jellyfish known to be one of the most venomous creatures in the world. But these deadly frosts are interesting for another reason: they turn out to be not as simple as we once thought. It shakes our entire understanding of what simple nervous systems are capable of.

“It was previously thought that jellyfish could only handle the simplest forms of learning, including habituation, that is, the ability to become accustomed to a particular stimulus, such as sound or firm touch. We now see that jellyfish have a more subtle learning capacity and can actually learn “It changes its behavior, and in doing so it changes its behavior,” says Anders Jarm, an associate professor in the Department of Biology at the University of Copenhagen.

One of the most advanced features of the nervous system is the ability to change behavior as a result of experience – remembering and learning. The research team, led by Jan Bilecki from Kiel University and Anders Jarm, decided to test this ability in box jellyfish. The results have just been published in the journal Current biology.

on Tripidalia cestophora

• The box jellyfish is a type of jellyfish known to be one of the most venomous animals in the world. They use their venom to catch large fish and shrimp. Tripidalia cestophora It has a somewhat milder venom and feeds on small copepods.
• Box jellyfish do not have a central brain like most animals. Instead, they have four parallel brain-like structures, each containing about a thousand neurons. The human brain contains approximately 100 billion neurons.
• The box jellyfish has twenty-four eyes distributed among its four brain-like structures. Some of these eyes form an image, giving the box jellyfish more complex vision than other types of jellyfish.
• Making their way through the dark mangroves, four of them Tripidalia cestophora The eyes look up through the water’s surface and navigate using the mangrove canopies.
• Tripidalia cestophora It is one of the smallest square jellyfish ClassifyIts body diameter is only about one centimeter. It lives in the Caribbean Sea and the central Indian and Pacific Oceans.
• Unlike many types of jellyfish, Tripidalia cestophora In fact, they mate when the male grabs the female with his claws. The female’s eggs are then fertilized in her intestinal tract, where they also develop into larvae.

There are a thousand neurons more capable than previously thought

Scientists have studied the Caribbean box jellyfish, Tripidalia cestophoraA fingernail-sized jellyfish that lives in mangroves in the Caribbean. Here, they use their impressive visual system including 24 eyes to search for tiny copepods among the roots of mangrove trees. Although they provide a good hunting ground, the root network is also a dangerous place for soft-bodied jellies.

So when the little box jellyfish approaches the roots of mangrove trees, it turns and walks away. If they shift too early, they won’t have enough time to catch the copepods. But if they turn too late, they risk hitting the root and damaging their gelatinous bodies. So, evaluating distances is crucial for them. Here, variation is key, as the researchers discovered:

“We have many experiences in contrast, the obstacles of the race are covered by water, it is used by the méduses to value the distances of the races, which allows the driver to adjust. right on time. What is even more interesting is that the relationship between distance and contrast changes daily due to rainwater, algae and wave action,” explains Anders Jarm, who continues:

“We can see that with the start of each new hunting day, box jellyfish learn from current discrepancies by combining visual impressions with sensations during unsuccessful avoidance maneuvers. So, even though they only have a thousand neurons – our brain has about 100 billion.” – However, they can correlate the temporal proximity of different impressions and learn associations – or what we call associative learning. And they learn at the same speed as advanced animals like fruit flies and mice.

The new research findings contradict previous scientific perceptions about the ability of animals with simple nervous systems to:

“For basic neuroscience, this is very big news. It offers a new perspective on what can be done with a simple nervous system. “This suggests that advanced learning may have been one of the most important evolutionary advantages of the nervous system from the beginning,” explains Anders Jarm.

Caribbean jellyfish live and feed among the underwater roots of mangrove trees. Credit: Anders Gram

How did they do it?

The researchers replicated mangrove conditions in the laboratory, where box jellyfish were placed in a behavioral arena. Here, the researchers manipulated the jellyfish’s behavior by changing the contrast conditions to see what effect this had on their behavior.

They learned that jellyfish learn through failed escapes. In other words, they learn by misinterpreting contradictions and hitting roots. Here, they combined the visual impression with the mechanical shock they felt every time they hit a root—and in doing so, they learned when to walk away.

“Our behavioral experiments show that three to five failed avoidance maneuvers are enough to modify the jellyfish’s behavior so that it no longer touches the roots. Interestingly, this is the same repetition rate that a fruit fly or mouse needs to learn.

The learning was then verified through electrophysiology and classical conditioning experiments, which also showed where learning occurs in the jellyfish’s nervous system.

In search of brain cells where memory is located

The scientists also showed where learning occurs in these box jellyfish. This gave them unique opportunities to study the subtle changes that occur in a neuron when it is involved in advanced learning.

“We hope that this will become a model system for studying cellular processes in advanced learning in all animal species.” We are currently trying to identify which cells are involved in learning and memory formation. By doing this, we will be able to observe the structural and physiological changes that occur in cells while learning occurs,” explains Anders Jarm.

If the research team can identify the precise mechanisms involved in learning in jellyfish, the next step will be to see if this applies to jellyfish specifically or if it can be found in all animals.

“Eventually, we will look for the same mechanisms in other animals, to see if this is how memory works in general,” the researcher explains.

This kind of revolutionary knowledge can be used for many purposes, according to Anders Jarm:

“Understanding something so mysterious and complex as the brain is in itself absolutely incredible. But there are an unimaginable number of useful possibilities. There is no doubt that various forms of dementia will be a huge problem in the future. I am not claiming that we have found a cure for dementia, but If we can better understand what memory is, which is a central problem in dementia, we may be able to lay the foundations for a better understanding of the disease and perhaps even combat it,” the researcher concludes.

The study will be published today (September 22) in the scientific journal Current biology.

The study was led by Jan Bilecki from the University of Kiel, Anders Jarm, Sophie Katrin Dam Nielsen, and Gösta Nachman from the Department of Biology at the University of Copenhagen.