How to train your jellyfish

Jellyfish have been shown to learn from past experience for the first time. This may not seem all that remarkable except for the fact that jellyfish have no centralised brain.

Other animals including crows, mice and flies are capable of learning. Despite the fact that I still try to drink my coffee without waiting for it to cool down, there is also evidence that humans are capable of learning.

But a study published in the journal Current Biology is the first indication that jellyfish are learners.

Time to unlearn what we’ve learned about learning

Researchers from Germany’s Kiel University trained Caribbean box jellyfish (Tripedalia cystophora) to learn to spot and dodge obstacles.

The study challenges the idea that learning requires a centralised brain. It also sheds light on the evolutionary roots of learning and memory.

Caribbean box jellyfish are no bigger than a human fingernail. While simple organisms, they have a complex visual system with 24 eyes on their bell-shaped body. They live in mangrove swamps and use their advanced vision to navigate the murky waters.

The scientists showed that the jellyfish could avoid obstacles using associative learning. This is the process through which organisms form connections between sensory information and behaviour. It is seen in animals as the modification of existing behaviours.

For example, if you put your hand on a hot stove, you may learn to associate hot stoves with pain and therefore be conditioned to not touch them. (Unfortunately I’m still waiting on my associative learning to kick in with those thermonuclear coffees!)

“Learning is the pinnacle performance for nervous systems,” says first author and neuroscientist Dr Jan Bielecki.

How do you teach jellyfish new tricks?

Bielecki says “it’s best to leverage its natural behaviours, something that makes sense to the animal, so it reaches its full potential.”

The researchers filled a round tank with grey and white strips to simulate the animal’s natural habitat. The strips were intended to mimic mangrove roots, with the grey ones meant to fool the jellyfish into thinking they were far away.

After observing the jellyfish for 7.5 minutes, the researchers noted that the creatures initially bumped into the “far” strips frequently. By the experiment’s end, the jellyfish went 50% further and pivoted away from the grey strips 4 times more often.

To understand the underlying processes helping the animal learn, the researchers isolated the rhopalia – the jellyfishes’ visual sensory centres. Each of these structures holds 6 eyes and generates electrical signals which tell the jellyfish how to pulse, to move. These signals spike when the animal swerves from obstacles.

Jellyfish on black background
A Caribbean box jellyfish. Black dots embedded low on the bell are the animal’s visual sensory and learning centre called rhopalia. Credit: Jan Bielecki.

Showing stationary rhopalia the grey strips led to no response, as they were interpreted as far away. By training the rhopalia with weak electric stimulation when the bars approach, the structures started producing obstacle-dodging signals in response to the grey bars.

Jellies learn without thinking

Though we are much more complex organisms, the researchers suggest that the experiment may shed light on learning in humans and other creatures.

“If you want to understand complex structures, it’s always good to start as simple as you can,” says senior author Anders Garm of the University of Copenhagen, Denmark. “Looking at these relatively simple nervous systems in jellyfish, we have a much higher chance of understanding all the details and how it comes together to perform behaviours.”

The team hopes to understand the cellular interactions in the jellyfish which drive memory formation.

Jellyfish are among Earth’s longest-lived multicellular lifeforms, having evolved an estimated 700 million years ago. Understanding how they remember and learn could inform such processes in other creatures like coffee-drinking humans.

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