From humans to amoeba, we all shimmy like these electric fish

An electric knifefish won’t carve a roast dinner for you, but it will do a little shimmy to make sense of the world around it.

Researchers studying these peculiar fish have now demonstrated that the behaviour isn’t unique – a wide range of organisms, even microbes, perform the same pattern of movements to sense their surroundings.

The findings, in a new study in the journal Nature Machine Intelligence, have implications for the fields of cognition and robotics.

By figuring out how animals unconsciously move to improve their perception of the world around them scientists could translate that knowledge into robotic control systems to improve the way robots sense their surroundings.

In the wild, electric knifefish cut through the water and emit weak electric discharges to sense their location, locate predators and prey, and find shelter. But for this study, the research team watched electric knifefish in an observation tank.

They noticed that the knifefish shimmied back and forth significantly more often when it was dark, compared to when lights were on. With visibility restored, the fish swayed about gently with only occasional bursts of rapid movement.

Wiggling rapidly allows them to actively sense their surroundings, which becomes more vital in dark water.

An observation tank illuminated by infrared shows electric knifefish behavior with the lights on (top) and lights off (bottom). Credit: Johns Hopkins University

“We found that the best strategy is to briefly switch into ‘explore mode’ when uncertainty is too high, and then switch back to ‘exploit mode’ when uncertainty is back down,” says first author Dr Debojyoti Biswas, a computational cell biologist and neuroethologist at Johns Hopkins.

This is the first time that this mode-switching strategy has been seen in fish, but the team wanted to see if the behaviour could also be linked across species.

They created a model to simulate these key sensing behaviours and looked at previously published data to see whether the same sensory dependent movements occur in other organisms.

And it turns out that they do! The behaviours occur across a wide variety of creatures: from omoeba, to moths, cockroaches, moles, bats, mice, and even humans.

“Not a single study that we found in the literature violated the rules we discovered in the electric fish, not even single-celled organisms like amoeba sensing an electric field,” says co-author Noah Cowan, a professor of mechanical engineering at Johns Hopkins University, US.

“Amoeba don’t even have a nervous system, and yet they adopt behaviour that has a lot in common with a human’s postural balance or fish hiding in a tube.

“These organisms are quite far apart from each other in the tree of life, suggesting that evolution converged on the same solution through very different underlying mechanisms.”

Researchers are only just beginning to understand how animals control sensing movements unconsciously. 

“If you go to a grocery store, you’ll notice people standing in line will change between being stationary and moving around while waiting,” Cowan says.

“We think that’s the same thing going on, that to maintain a stable balance you actually have to occasionally move around and excite your sensors like the knifefish. We found the statistical characteristics of those movements are ubiquitous across a wide range of animals, including humans.”

The next steps? Seeing whether these insights hold true for other living things like plants.

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