Unveiling the Mind-Blowing Discovery: Jellyfish Break the Bounds of Learning and Memory

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Recent research has unveiled that despite being creatures that seem to drift aimlessly through life without a central brain, Caribbean box jellyfish possess the remarkable capacity to swiftly learn and retain information.

A study published in the journal Current Biology on Friday, has revealed a groundbreaking discovery that challenges the prevailing belief that organisms cannot engage in associative learning without a central nervous system. Led by Anders Garm, an associate professor of marine biology at the University of Copenhagen in Denmark, the study is part of the ongoing research on jellyfish behavior conducted at the Institute of Physiology at Kiel University in Germany.

"We have been conducting extensive research on visual behavior and conducting various experiments. Learning is a natural progression in our study," stated Jan Bielecki, a postdoctoral fellow specializing in visual neuroethology at Kiel.

Jellyfish are found in oceans across the world, in both deep seas as well as surface waters.

Charles Platiau/File/Reuters

A recent study may uncover the mysterious process by which the 'immortal jellyfish' reverts the aging process. The team, having spent years studying the Caribbean box jellyfish, was not taken aback by the creatures' learning capabilities. However, what did come as a surprise was the speed at which they acquired new knowledge, according to Bielecki.

The Caribbean box jellyfish, scientifically known as Tripedalia cystophora, possesses 24 eyes, with six in each of its four visual sensory centers called rhopalia. Its jelly-like body, commonly referred to as a bell due to its shape, is susceptible to bruising, which can prove disadvantageous as the jellyfish navigates through mangrove roots in the Caribbean. Colliding with a root could potentially inflict damage that could lead to bacterial infection and ultimately death, explained Bielecki.

"We were certain that these animals had the ability to learn because avoiding the mangrove roots is a crucial learning process for their survival," he stated.

In order to assess the learning capabilities of jellyfish, the researchers conducted an experiment in which they placed gray and white stripes on the inside of a circular tank. The purpose was to investigate how the jellyfish, with their 24 eyes, perceived the gray stripes, which resembled distant mangrove roots in their natural environment. Over a span of 7.5 minutes, the researchers closely monitored the jellyfish's behavior to determine whether they would collide with the stripes or if they would successfully learn to maintain a distance.

In the initial few minutes, the jellyfish swam in close proximity to or made contact with the walls. However, the situation took a turn within a span of five minutes.

The jellyfish experienced a blend of visual stimulation due to the stripes and mechanical stimulation caused by colliding with the obstacles.

"They discovered the ability to simultaneously receive these stimuli and successfully navigate around obstacles," stated Bielecki. "Their performance in all the metrics we assessed for obstacle avoidance visibly improved."

Caribbean box jellyfish, also known by the scientific name Tripedalia cystophora, have 24 eyessix in each of four visual sensory centers called rhopalia.

Jan Bielecki

The researchers subsequently substituted the stripes with a uniform gray surface, causing the jellyfish to repeatedly collide with it.

"They failed to gain any visual information and remained unresponsive," noted Bielecki. "They continued to encounter obstacles without any proper response."

Christian-McCall

Scientists have made a groundbreaking discovery in the Canadian Rockies - the identification of the earliest recorded species of jellyfish. To further explore this finding, a neurophysiological study was conducted. This study focused on understanding the mechanism behind the electric signal emitted by the rhopalia, which is responsible for the rhythmic propulsion of jellyfish through water. Interestingly, the research unveiled a remarkable increase in the speed of pulsing when these creatures encounter obstacles, suggesting an adaptive and responsive behavior.

The scientists detached the rhopalia from the bell to isolate them, while the mangrove root substitutes were repositioned. As a result, the jellyfish's visual system remained stationary while the lines moved. Was it possible for the visual system to learn to avoid the gray lines?

To address this, the scientists established a system capable of transmitting a weak electric signal to the visual sensory centers. When the rhopalia did not naturally generate the signal that induced swimming contractions, the scientists initiated it on their behalf. Gradually, the rhopalia began producing the signal without any external prompting, even in response to the lighter gray bars that had less contrast with the surrounding environment.

Bielecki attributed their findings to the experiment's relevance to the jellyfish's behavior. The researchers created a scenario that mimicked a natural wild environment for the animals.

"So both visual stimulation and mechanical stimulation is something that (occurs) in their natural habitat," he said. "They know exactly what to do with this."

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According to Dr. Michael Abrams, a researcher at the University of California, Berkeley, who has conducted extensive research on jellyfish and sleep, the study was robust. Although he was not directly involved in the new research, Abrams commended the scientists for developing a compelling experimental approach to measure associative learning in box jellyfish. In an email, he stated that their findings could potentially indicate the presence of short-term memory in these creatures. Moreover, Abrams highlighted that the study unequivocally showcased the animals' aptitude for learning, prompting him to question the duration of their memory retention.

During his doctoral studies at the California Institute of Technology, Abrams conducted research in 2017 on the upside-down jellyfish (Cassiopea) and its "sleep-like state." This state, previously thought to be exclusive to animals with a central nervous system, was a key focus of his study.