With no central brain, can jellyfish learn from past experiences?

Even without a central brain, jellyfish can learn from past experiences like humans, mice, and flies. The researchers trained Caribbean box jellyfish (Tripedalia cystophora) to learn to spot and dodge obstacles. The study published in Current Biology has challenged previous notions that advanced learning requires a centralised brain and sheds light on the evolutionary roots of learning and memory. No bigger than a fingernail, these seemingly simple jellies have a complex visual system with 24 eyes embedded in their bell-like body. Living in mangrove swamps, the animal uses its vision to steer through murky waters and swerve around underwater tree roots to snare prey. Scientists demonstrated that the jellies could acquire the ability to avoid obstacles through associative learning, a process through which organisms form mental connections between sensory stimulations and behaviours. The researchers dressed a round tank with grey and white stripes to simulate the jellyfish’s natural habitat, with grey stripes mimicking mangrove roots that would appear distant. They observed the jellyfish in the tank for 7.5 minutes. Initially, the jelly swam close to these seemingly far stripes and bumped into them frequently. But by the end of the experiment, the jelly increased its average distance to the wall by about 50%, quadrupled the number of successful pivots to avoid collision and cut its contact with the wall by half. The findings suggest that jellyfish can learn from experience through visual and mechanical stimuli.