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Jellyfish Intelligence: Learning Without A Brain


Fingernail-sized Caribbean box jellyfish use their 24 eyes to spot and dodge mangrove roots that might damage their fragile bodies.


In a fascinating experiment, researchers have made a remarkable discovery regarding Caribbean box jellyfish. These intriguing creatures have demonstrated an ability to learn and adapt their behavior, all while lacking a centralized brain. This groundbreaking finding challenges conventional wisdom about intelligence in the animal kingdom and offers new insights into the evolution of learning processes.


The Caribbean box jellyfish, Tripedalia cystophora, possesses a unique nervous system featuring four rhopalia, each equipped with six eyes and around 1,000 neurons. These jellyfish rely on their vision to navigate the intricate mangrove roots found in tropical lagoons, where they hunt tiny crustaceans. However, this task is far from simple, as the jellyfish must judge the distance of these roots based on their contrast against the surrounding water.


In a controlled experiment, researchers placed 12 jellyfish in a tank encircled by low-contrast, alternating gray and white stripes. Initially, the jellyfish interpreted the gray stripes as distant roots, resulting in collisions with the tank wall. However, these collisions seemed to serve as a form of learning, causing the jellyfish to treat the gray stripes as if they were close roots in murky water. Consequently, the jellyfish adjusted their behavior to avoid these low-contrast obstacles. Their average distance from the tank wall increased from 2.5 centimeters to 3.6 centimeters, while collisions decreased from 1.8 per minute to 0.78 per minute.


This discovery challenges long-held beliefs about the capabilities of jellyfish. Nagayasu Nakanishi, an evolutionary biologist at the University of Arkansas, expressed amazement at the findings, remarking, "I never thought that jellyfish could really learn."


However, some scientists remain cautious, highlighting the need for further experiments with a larger sample size to confirm these intriguing results. Regardless, this research opens up exciting questions about how learning processes evolved in animals.


The Caribbean box jellyfish’s four rhopalia (circled) each have six eyes and about 1,000 neurons to process what they see.

In additional experiments, researchers removed rhopalia from jellyfish and exposed them to low-contrast bars displayed on a screen while delivering a mild electrical pulse, mimicking the sensation of bumping into an obstacle. Remarkably, the isolated rhopalia began responding to these previously ignored obstacles, emitting neural signals associated with avoiding obstacles. This suggests that the rhopalia may serve as the learning centers for Caribbean box jellyfish.


This discovery piques the curiosity of scientists like Ken Cheng, a behavioral biologist at Macquarie University, who remarked, "That gets us one step down into the, you know, wiring of how it works."


Moreover, the revelation that similar learning abilities exist in sea anemones, another cnidarian-like jellyfish, adds depth to this research. Gaëlle Botton-Amiot, a neurobiologist at the University of Fribourg, Switzerland, raises intriguing questions about coordination among the four rhopalia and whether lost rhopalia affects memory.


This groundbreaking study challenges conventional notions of intelligence and learning processes in animals. It opens the door to further exploration into the cellular and chemical mechanisms behind learning in jellyfish and other creatures, shedding light on the potential common ancestry of learning abilities across diverse species.


 

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