Jellyfish Have No Brain But Are Able To Learn From Experience

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Jellyfish are very strange animals that have existed since ancient times. They have been flying around our oceans and waterways for about 500 million years. Jellyfish evolved so quickly that they have a structure that bears little resemblance to that of other animals. It also includes the nervous system. A new study shows for the first time that jellyfish can learn from their environment and change their behavior accordingly, despite lacking a central brain. This study Current Biology.

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Anders Garm, associate professor of marine biology at the University of Copenhagen and lead author of the new study, says that by spending time floating in empty oceans, jellyfish evolved into the body structures we recognize. He says that there is almost no pressure to evolve. “They have a habit of distributing everything along the edges,” Garm says. The main umbrella-like part of Jelly’s body, the “bell,” contains his 24 or more “eyes,” distributed among his four sensory centers around its edges. These sensory centers are called rhopalia.

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Garm’s research looked at box jellyfish. Tripedaria cystophorapart of the same evolutionary class of jellyfish as the prohibitively toxic sea wasp jellyfish, which can kill humans with its venom. T. cystophora It is less lethal and is about the size of a fingernail. Home in the Caribbean T. cystophora They float around the roots of mangrove trees and hunt for prey like plankton in the murky water. In collaboration with group leader Jan Bielecki from Kiel University, Garm: T. cystophora It was able to learn by responding to signals from the environment. To assess how smart the jellies are, the team designed an experiment closely inspired by the animals’ natural habitats.

The jelly was placed in a circular tank with white and gray stripes, the gray stripes looking like distant mangrove roots. At first, when I put the jelly in the tank, it swam towards the wall of the tank where the gray “roots” were. However, by the end of the experiment after only 7 minutes, the jelly had learned to avoid the gray roots, the number of collisions with the wall had been cut in half, the distance from the wall had increased by 50%, and the chance of turning was increased by 4 It’s doubled. She keeps away from possible conflicts.

Prepare to avoid jellyfish

Next, the researchers placed one of the jellyfish’s rhopalia in a Petri dish and recorded its response to the moving bar, similar to what they showed to an intact jellyfish. These structures did not respond to the gray bars and were recognized as distant structures. But when they looked at the bar and stimulated the ropalium with an electrical signal that mimicked the signal sent during a collision, the ropalium began to produce an “avoid” signal. This suggests that jellyfish can learn to avoid objects through a combination of visual and electrical stimulation.

Galm and Bielicki note that the jellyfish appeared to forget what they had learned about 20 minutes after the experiment ended, suggesting that the type of learning involved was not as long-lasting and permanent as in humans. Rather, it suggests that it is a more temporary function. The exact mechanism is T. cystophora The content of the study remains unclear.

More natural experiments

T. cystophora Their nervous system has about 1,000 neurons, and their exotic body structure is probably the only thing preventing them from becoming a more widely used model organism. Garm and Bielicki agree that an experimental approach has been key to maximizing the benefits. T. cystophora As laboratory animals: “The strength of our story is that we need to understand animals well enough to identify the precise behaviors that are meaningful for them to learn, and to the point where we can reproduce them as naturally as possible in the lab.” , waiting during an experiment.” The pair cite experiments on mice, which are nocturnal animals, conducted during the day as an example of non-naturalistic research. Perhaps a deeper look at what brings animals (even strange and ancient animals) into their natural habitats can further enhance their valuable contributions to science. “You have to ask your animal,” Garm concludes. “You can’t judge a fish by its ability to climb trees.”

reference: Bielecki J, Nielsen SKD, Nachman G, Garm A. Associative learning in the box jellyfish Tripedalia cystophora. current biology. 2023.doi:10.1016/j.cub.2023.08.056

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