An innovative study of jellyfish, brainless organisms, reveals learning and memory abilities that challenge traditional perceptions of these animals’ cognition. By shedding light on the adaptive abilities of these primitive creatures, these discoveries could lead to a better understanding of a whole range of marine species.
Jellyfish, often reduced to their translucent appearance and stinging tentacles, are among the oldest animals on our planet, having lived in the oceans for at least 500 million years. Their primitive, brainless anatomy has led science to perceive them as beings without cognitive abilities – in other words, creatures that act solely on reflexes and instincts.
However, a recent study from the University of Kiel shows a very different reality: it suggests that these marine organisms may be slow to learn and strange. This discovery challenges the foundations of our understanding of the intelligence and cognition of this animal species, not to mention that this new knowledge could be transferred from nature to technical fields such as robotics. The article is available in the journal Current Biology.
An exploration of cognitive abilities
The study focuses on a specific species of jellyfish, box jellyfish or box jellyfish (Tripedalia cystophora). They were chosen for their simple build, no larger than a fingernail, and their rudimentary neural network, which contained only a few nerve cells.
However, the box jellyfish has a complex visual system with 24 eyes. She uses them to navigate the murky waters of Caribbean mangroves, hunt water fleas and avoid underwater tree roots. Dr. Jan Bielecki from the Institute of Physiology at the University of Kiel, lead author of the study, explains in a statement: “Although these are simple animals, they have impressive eyesight, which they use to adapt their behavior.”
The team’s main goal was to comprehensively study the cognitive abilities of these jellyfish, particularly their ability to learn and remember. To do this, the researchers confronted the jellyfish with various obstacles in their environment in controlled experiments.
Summary of the experience. © Jan Bielecki / Current Biology
They simulated the jellyfish’s natural habitat with a water tank whose inner wall was painted with gray and white stripes. The gray stripes represented the mangrove roots that the jellyfish normally avoids, while the white stripes represented the aquatic environment. The box jellyfish uses color contrast to perceive spatial distances. Therefore, the researchers varied the contrasts throughout the experiment.
Unexpected results
At the beginning of the experiment, the jellyfish frequently encountered the simulated roots on the tank wall. But after just a few minutes they had increased their average distance from the wall by around 50% and were hitting it half as often.
Without visual contrast, the jellyfish initially crashed into a wall without adjusting their behavior. With a strong visual contrast, they avoid the wall but remain in the center. Finally, with moderate contrast, after several collisions and receiving mechanical stimuli, they learn to keep their distance from the wall, which demonstrates real learning ability. © Jan Bielecki/Current Biology
Box jellyfish therefore not only demonstrated the ability to avoid obstacles more effectively over time, but also showed signs of adapting and changing their behavior in response to their environment. Anders Garm, co-author and professor of marine biology at the University of Copenhagen, Denmark, said: “These results suggest that jellyfish can learn by combining visual and mechanical stimulation experiences.”
The key role of neurons
The lack of a centralized brain in these organisms has long led to the assumption that jellyfish were largely reactive creatures, unable to develop or learn complex adaptive behaviors. However, recent evidence suggests that their simple neural network allows them to make behavioral adjustments in response to changes in their environment, suggesting an ability to learn and adapt.
The crucial role of this rudimentary neural network in adapting and modifying jellyfish behavior raises intriguing questions about the nature of cognition and intelligence. Bielecki explains: “This is a higher form of learning than you would expect from such a creature.” From an evolutionary perspective, jellyfish were among the first animals to have a nervous system. He adds: “If these animals are already capable of learning, this could be a fundamental ability of neurons or neural networks. This suggests that it has been around since the beginning of evolution and therefore earlier than researchers thought.”
Reassessment of animal perception
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To better understand the processes underlying associative learning in box jellyfish, Bielecki next isolated the animals’ visual sensory centers, called rhopalia. Each of the four centers contains six eyes for only 1000 nerve cells.
Bielecki then “showed” the Rhopalia how to move gray bars to simulate a jellyfish approaching an obstacle. But it wasn’t until he applied weak electrical stimuli to them – simulating a collision with the wall – that they responded, producing signals that caused the jellyfish to take evasive maneuvers. This enabled Bielecki not only to change the behavior of jellyfish, but also to localize their learning processes in their rhopalia for the first time.
Traditionally, the ability to learn, remember, and adapt behavior is associated with the presence of an advanced brain and nervous system. The discovery of such abilities in an organism as primitive and simple as the jellyfish could lead to a better understanding of the development of cognition and intelligence in the animal kingdom.
Source: Current Biology