Report by Prashasti Kulkarni
Tripedalia cystophora, or Caribbean box jellyfish, is a species of jellyfish that only has a thousand nerve cells (lesser than usual) and no central brain. These jellyfish are very tiny, smaller than a fingernail, and are found mostly in mangrove swamps.
For a long time, scientists believed that, due to their lack of central brain, they were not very perceptive and would drift aimlessly, as other species (cnidarians) which have similar features do so.
However, after an extensive experiment on the topic, the scientists found that these jellyfish are quick learners and can identify and respond to stimuli (changes in the environment to which organisms respond) very easily.
The experiment included a tank which had white and gray stripes, resembling the mangrove roots in the jellyfish’s natural habitat. The jellyfish were placed in the tank and observed for approximately 7 minutes at a time. As expected by the scientists, in the initial few takes, the jellyfish swam close to the dark stripes, occasionally ‘colliding’ into them. However, by the end of the experiment, they had swum away from the tank’s wall and were able to avoid bumping into the stripes, or the mangrove roots.
This means that they were able to identify the presence of the supposed “mangrove roots” by noticing the color of the stripes. If the color was dark and clear, it meant they were close to the ‘roots’ and had to turn away, but if it was light, they could keep swimming. This is known as associative learning or being able to realize what to do and what not to do by learning from past experiences, like bumping into the walls, which made the jellyfish realize that they needed to turn away. This is something that scientists did not expect creatures without centralized brains and 200,000 neurons (units of nerve cells) to be able to do.
The experiment closely resembled the jellyfish’s natural habitat and their response to it which replicates their original response to the mangrove roots present in their swampy habitat. The jellyfish use their 24 eye-like parts to identify the appearance of a mangrove root and turn away accordingly.
This discovery has helped scientists get more insight into the way a body works with and without a central brain and could potentially help them understand and counteract various diseases present in animals that directly affect the brain.
Images credit: Current Biology publication