2023-09-25 17:46:30
An innovative study on jellyfish, brainless organisms, reveals learning and memory abilities that challenge traditional perceptions of these animals’ cognition. These discoveries, by shedding light on the adaptive capacities of these primitive creatures, might lead to a better understanding of a whole range of marine species.
Jellyfish, often reduced to their translucent appearance and their stinging tentacles, are among the oldest animals on our planet, inhabiting the oceans for at least 500 million years. Their primitive, brainless anatomy has led science to perceive them as beings devoid of cognitive abilities — in other words, as creatures acting solely on reflexes and instinct.
However, a recent study led by the University of Kiel reveals a very different reality, suggesting that these marine organisms may be capable of learning and memorizing. This discovery calls into question the foundations of our understanding of the intelligence and cognition of this type of animal, not to mention that this new knowledge might 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 because of their simple body structure, being no larger than a fingernail, and their rudimentary neural network, containing 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, hunting water fleas and avoiding underwater tree roots. Dr. Jan Bielecki from the Institute of Physiology at Kiel University, lead author of the study, explains in a communiqué
: « Although they are simple animals, they possess an impressive visual ability which they use to adapt their behavior ».
The team’s main goal was to comprehensively examine the cognitive abilities of these jellyfish, particularly their ability to learn and memorize. 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 on which gray and white stripes were painted on the interior wall. The gray stripes represented the mangrove roots that the jellyfish is accustomed to avoiding, while the white stripes represented the aquatic environment. The box jellyfish uses color contrasts to perceive spatial distances. The researchers therefore varied the contrasts during the experiment.
Unexpected results
At the beginning of the experiment, the jellyfish often hit the simulated roots on the tank wall. But following just a few minutes, they had already increased their average distance from the wall by around 50%, hitting them half as often.
Initially, without visual contrast, the jellyfish hit a wall without adjusting their behavior. With a strong visual contrast, they avoid the wall, but do not learn, remaining in the center. Finally, with moderate contrast, following several collisions and receipt of mechanical stimuli, they learn to maintain a distance from the wall, demonstrating true learning ability. © Jan Bielecki/Current Biology
Box jellyfish therefore not only demonstrated an ability to avoid obstacles more effectively over time, but they 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 says: “ 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, incapable of complex adaptive behaviors or learning. However, recent findings indicate 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 fascinating questions regarding the nature of cognition and intelligence. Bielecki explains: “ This is a higher form of learning than one would expect from such a creature “. From an evolutionary perspective, jellyfish are among the first animals to possess a nervous system. He adds : ” If these animals are already capable of learning, this might be a fundamental ability of neurons or neural networks. This suggests that it has existed since the beginning of evolution and therefore earlier than research assumed ».
Reassessing animal cognition
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To better understand the processes underlying associative learning in the 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 moving gray bars to simulate a jellyfish approaching an obstacle. But it was only when he applied weak electrical stimuli to them — simulating impact once morest the wall — that they responded and produced signals, prompting the jellyfish to take evasive action. This allowed Bielecki not only to modify the jellyfish’s behavior, but also to localize their learning processes in their rhopalia, for the first time.
Traditionally, the ability to learn, remember, and adapt behavior has been associated with the presence of an advanced brain and nervous system. Discovering such abilities in an organism as primitive and simple as the jellyfish might lead to a better understanding of the evolution of cognition and intelligence in the animal kingdom.
Source : Current Biology
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