How the tardigrades walk

Tardigrades are renowned for their extreme durability, but new research shows how well they work, despite their small size. size and spongy body.

The tardigrades present an incomparable curriculum vitae. These microscopic extremophiles can endure an absurd amount of stress, like freezing temperatures, intense radiation, dehydration and even be fired from a cannon. But tardigrades “also display remarkable robustness in their daily activities”, according to research published today in Proceedings of the National Academy of Sciences.

Indeed, these eight-legged animals can be found all over Earth, forcing them to explore wet leaves, sandy deserts, Antarctic moss and lichens, and underground soils. As a result, tardigrades, also known as water bears or moss piglets, have developed “a unique set of versatile locomotor tools”, as the biologists write in their study. Jasmine Nirody, fellow of the Center for Studies in Physics and Biology at Rockefeller University, is the lead author of the article.

Tardigrades are among the smallest animals on Earth, and they are also among the smallest animals known to have legs. Typically, animals on this scale move by struggling, wiggling, and sliding, but tardigrades can actually walk.

It’s okay for animals on a macro scale, but physics works a little differently for smaller ones. creatures. Viscous and inertial forces make their navigation much more difficult through substrates.

“An analogy would be if we were to go through a vat of something really thick and viscous, say honey or peanut butter,” Nirody explained in an email. “So we might expect that the ‘ideal’ strategies for tardigrades would be different from those for larger animals,” she said, adding, “I even walk differently submerged in a swimming pool than in the pool. sidewalk.”

In addition, tardigrades, like other microscopic creatures, have a soft body, devoid of an internal or external skeleton. They’re basically gummy bears (uh, gummy water bears, I guess), but gummy bears that need to move around despite the lack of bones.

“When we walk, we tend to push off the ground with our hind legs to throw ourselves forward. [and] it’s possible because we have rigid bones that act a bit like a pole that we “jump” on, ”Nirody explained. “But if this post is a mess, we have to use different strategies.”

Nirody and his colleagues set out to learn more about these strategies.. To this end, the team captured videos of the tardigrade species Hypsibius dujardini, measuring their steps, following their step and carefully watch the placement of their feet as they move from place to place.

As the videos show, tardigrades “use their claws like grappling hooks, so they reach out and grab the substrate and pull their bodies forward,” Nirody said. “It depends a lot on whether the substrate is going to be rigid and not going to give way on them.”

Once the team realized this was how tardigrades moved, they hypothesized that changing the stiffness of the substrate would affect their walk. Subsequent testing proved this to be the case.

The fact that tardigrades even have a steady rate of progression surprised the researchers. Nirody and her colleagues entered the study with the preconceived idea that tardigrades are “clumsy, dumb walkers,” as she put it, but they seem to have regular coordination.

“And that makes sense, if you think about it more carefully, there are thousands of tardigrade species, living and moving in almost any environment imaginable,” Nirody said. “It’s pretty successful, and you don’t get that far being bad at locomotion, which is crucial for finding food, friends, whatever is important for survival!” “

And they walked. During leisurely walks, tardigrades moved half a body length per second, and during sprints this increased to two body lengths per second. Interestingly, the tardigrade gait, or walking style, did not change with speed, and the gait was like that of insects 500,000 times their size.

It is not clear whether tardigrades and insects acquired these abilities from a shared common ancestor. or if they have developed this walking ability independently (an example of convergent evolution). Either way, Nirody said, the answer will be fascinating, as it could provide new insights into the evolution of multi-legged walking and the biological “circuits” responsible for behavior.

EThis research could also have implications for microrobotics and nanotechnology. I imagine tardigrade-type machines capable of moving around the human body, delivering drugs, and performing complex repair work. Similar microscopic machines could also work in synthetic systems, hauling goods to hard-to-reach places and weaving tiny components. It makes sense that we use water bears as models for the microscopic machines. Tardigrades are really awesome, and we’d do well to copy nature job.

Following: Scientists have shot tardigrades with guns to test alien theory.