Even without a brain, this cell blob can not only learn, but also pass on its experiences.

P. polycephalum, a single-celled organism otherwise known as a slime mold, grown on agar in the laboratory.
Credit: Audrey Dussutour (CNRS)

Physarum polycephalum is a strange thing. It isn’t an animal, a plant, or a fungus. It’s a strange slimy mold which inhabits shady, cool, moist areas, such as decaying leaves and logs. Researchers had already known that it can learn, navigate the world around it, and even solve real-life problems — now, they’ve shown that it can also transmit what it has learned to a fellow slime mold when the two combine.

Imagine you could temporarily fuse with someone, learn all that person knows, and then go your own way. That’s pretty much what happens to the slime, ironically giving its name another layer of meaning (Physarum polycephalum literally means “many-headed slime”). Audrey Dussutour and David Vogel had already trained slime molds to move past repellent but harmless substances to reach their food. Now, they’ve shown that a slime which had already learned this behavior can pass it down to another slime which hadn’t – through a process of temporary fusion.

In order to prove this, they cultivated 4,000 slimes and split them into two equal groups. The first group had to pass a bridge covered with salt to reach its food, while the second one had to cross a clean bridge. The first group became habituated with salt, while the second group was the “naive group”. Then, they created another group of fused slimes and had them move over the salty bridge. Much to their surprise, the fused slimes crossed the bridge just as fast as the habituated ones, while the naive ones, when faced with the salt bridge, moved much slower. This held true for slime molds formed from 3 or 4 individuals. No matter how many fused, only 1 habituated slime mold was needed to transfer the information.

In order to check that this was a teaching process and not just some manipulation by the habituated part of the fusion, they then separated the slimes after 1 or 3 hours. The learning process was demonstrated only for slimes which remained fused for 3 hours or more. Subsequent observations showed that a thin channel formed in fused pairs after 3 hours, likely a channel used for passing information (and potentially other things).

It’s truly stunning that even without a brain, the slime can learn and pass information. It undoubtedly forces us to rethink what we understand by ‘intelligence’. Now, researchers want to see just how this information takes place, and how complex it is. If they teach one slime to avoid salt, and another one to avoid something else like quinine, will the fused slime know to avoid both? We’ll have to wait and see.

Journal Reference: David Vogel, Audrey Dussutour. Direct transfer of learned behaviour via cell fusion in non-neural organisms. Proceedings of the Royal Society B: Biological Sciences, 2016; 283 (1845): 20162382 DOI: 10.1098/rspb.2016.2382

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