Starlet sea anemones have been discovered to be capable of associative learning.

A type of Cnidaria has been discovered to be capable of associative learning, according to a trio of biologists—two from the University of Fribourg in Switzerland and the third from the Universitat de Barcelona in Spain. The Proceedings of the National Academy of Sciences published the research by Gaelle Botton-Amiot, Simon Sprecher, and Pedro Martinez.

Ivan Pavlov was the first to describe associative learning in his work with dogs, which demonstrated that when trained with enticing rewards, dogs would sneeze at the sound of a bell. Humans’ aversion to touching a hot stove is an illustration of associative learning in action. Memory and some sort of response processing make up this type of learning. There are many different types of animals that exhibit associative learning, but scientists believe that a brain is the bare minimum.

The scientists questioned whether a brain was actually necessary in this new endeavor. They point out that Cnidaria phylum members lack brains. Despite having a network of nerves, they are not known to have an organ that can process neural activity. The researchers chose to concentrate on starlet sea anemones, sea creatures with organs that respond to light and retractable tentacles that respond to stimuli, to ascertain whether such creatures are capable of associative learning.

A sea anemone’s starlet head. Credit: Galle Botton-Amiot

In order to study the samples, the research team brought several of them into their lab. Each was given an electric shock or a bright light. While some anemones received both the light and the electric shock at once, others did so at different times.

The anemones that simultaneously experienced light and shock eventually came to associate the two as one event and reacted accordingly. This was shown by turning on the light without giving the anemone a shock and then watching to see if it would still retract its tentacles. The research team discovered that 72% of them did, demonstrating that the creature was capable of remembering that shocks come with sudden bursts of light and then responding as it normally would to a shock—by pulling in its tentacles.

More information: Gaelle Botton-Amiot et al, Associative learning in the cnidarian Nematostella vectensis, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2220685120

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