Caribbean Box Jellyfish Found to Learn Rapidly and Retain Information, Surprising Researchers
After years of studying the behavior of Caribbean box jellyfish, researchers have discovered that these creatures are capable of learning at a rapid pace and retaining information. While it was already known that the jellyfish had the ability to learn, the speed at which they learn came as a surprise to the researchers involved in the study.
The study, published in the journal Current Biology, challenges the previously held notion that organisms without a central nervous system cannot engage in associative learning. Led by Anders Garm, an associate professor of marine biology at the University of Copenhagen in Denmark, the research is part of ongoing efforts to understand jellyfish behavior at the Institute of Physiology at Kiel University in Germany.
Jan Bielecki, a postdoctoral fellow in visual neuroethology at Kiel and the study’s first author, explained that their investigations into visual behavior naturally led them to explore learning in the jellyfish. The team had been working with Caribbean box jellyfish for years and anticipated their ability to learn. However, Bielecki emphasized that they were taken aback by how quickly the jellyfish picked up new information.
Caribbean box jellyfish, scientifically known as Tripedalia cystophora, possess 24 eyes, with six in each of their four visual sensory centers called rhopalia. These jellyfish inhabit the Caribbean and navigate through unpredictable areas with mangrove roots. Avoiding these roots is crucial, as colliding with them can cause injuries and infections that may lead to death.
To test the jellyfish’s capacity to learn, the researchers introduced gray and white stripes inside a round tank. The gray stripes resembled the color of a faraway mangrove root, while the white stripes provided contrast. Over the course of 7.5 minutes, the researchers observed whether the jellyfish would bump into the stripes or learn to keep a distance.
Although the jellyfish initially swam into the stripes or bumped into the walls, within five minutes, they started to change their behavior. They effectively learned to associate the visual stimulation from the stripes with the contact of bumping into the obstacles. As a result, they improved their performance in obstacle avoidance.
To further explore the jellyfish’s learning ability, the researchers replaced the stripes with a solid gray field. In this scenario, the jellyfish once again repeatedly collided with the gray surface, indicating that they had not learned anything. This reinforced the idea that the jellyfish rely on visual cues to learn and respond to their environment.
In a neurophysiological experiment, the researchers severed the rhopalia from the jellyfish’s bell and moved the gray lines around. Although the rhopalia’s visual mechanism remained still, the jellyfish’s swim contractions increased in speed as they attempted to navigate around the moving gray lines. This demonstrated that the jellyfish’s visual system had indeed learned to avoid the gray lines.
Bielecki attributes the success of the study to its “behavior relevant” approach. The experiment replicated a situation that the jellyfish would encounter in their natural habitat, combining visual and mechanical stimulation. This allowed the researchers to investigate the jellyfish’s learning capabilities effectively.
Dr. Michael Abrams, a researcher in the department of molecular and cell biology at the University of California, Berkeley, praised the study and its experimental design. Abrams, who has extensively studied jellyfish and sleep, noted that the findings may indicate the presence of short-term memory in the jellyfish. He also expressed curiosity about the duration of their memory.
The study not only adds to our understanding of the complex behaviors of jellyfish but also challenges conventional assumptions about the necessity of a central nervous system for associative learning. Further research in this field may shed light on the cognitive abilities of other organisms without a central brain.