Why tiny tardigrade animals walk like insects 500,000 times their size

Chunky Tardigrade One of the smallest legged animals on the planet, these tiny water bear worms move around awkwardly like a toddler with chubby thighs. But most creatures as small as tardigrades do not even have legs, so scientists have recently analyzed tardigrades in motion to better understand how they use their limbs.

Tardigrades, also known as mossy piglets, have a segmented body and four pairs of legs.They pass through deep sea sediments and sandy river bottoms, passing quickly Lichen And the moss on the land, running towards future mates and food or away from predators.

Shots of scuttling tardigrades in this species Hypsibius example It is revealed that their movement is very similar to that of insects about 500,000 times their size, even though they have evolved about 20 million years apart and belong to different phyla. The new study found that when the animal speeds up, the pace pattern of insects and other arthropods (invertebrates with segmented bodies and articulated legs) changes, and the pace of tardigrade animals also follows when they walk faster Similar pattern.

There are about 1,300 species of tardigrades known, and they are notorious for being difficult to kill; they can survive extreme temperatures, Sun radiation with The vacuum of spaceJasmine Nirody, a researcher and independent researcher at the Rockefeller University Research Center, said that few studies have examined these hardy creatures in a more ordinary environment. Before this new study, scientists had almost nothing about the way tardigrade animals walk. Know. Physics and Biology in New York City.

Most tiny mollusks have no legs, so it is difficult to observe exactly how these tiny animals move. Nirody told Live Science that by analyzing walking tardigrade animals, it is actually one step at a time, and the researchers also hope to find clues to general movement in a very, very small area.

“We think that tardigrades provide us with portholes into these two things we don’t know much about,” Nirody said.

Nirody’s team studied the adults of this species H. Examples, The longest can reach 0.02 inches (0.5 mm). Their eight legs are structurally similar, but the leg closest to their back has fewer muscles than the other legs.Scientists reported in the journal on August 31 that although these legs play a role in exercise, most of the effort is shared by the other six legs. Proceedings of the National Academy of Sciences (PNAS).

At first, the researchers tested tardigrade animals on a smooth glass slide, but they found that water bear worms had difficulty pushing themselves on the smooth surface. When tardigrades can dig in and push away with their claws, their walking will be easier. Therefore, according to this study, in the rest of the experiment, tardigrade animals trot on gels that succumbed to the pressure of their paws.

Nirody says that unlike large animals that can be stimulated to walk or run, tardigrades are too small for researchers to make them move. So the scientists set up microscopes and cameras in the laboratory to let the tardigrade loose… and wait.

“You can get hours of footage,” Nirodi said. “And I watched them all.”

Slow step

The phylum name Tardigrada (tardigrada is the only member) comes from the Latin “tardigradus” or “slow stepping”, and the tardigrada in the study also fits this name. When moving at a leisurely speed, they move about half of their body length per second—about 0.01 inches (0.25 mm)—and at faster speeds, they move about two body lengths per second.

When tardigrades change gears between slow walking and brisk walking, they will smoothly transition to a new gait like many arthropods, instead of transforming into a new gait as commonly seen in animals—physical The center of gravity will also change. backbone.

When arthropods (and tardigrades) walk slowly, they lift one foot at a time. As they accelerated, they lifted two diagonally across the body’s feet. The faster speed transforms the animal into a new model in which three feet are off the ground at the same time: the front and back feet are on one side of the body, and the other foot is in the middle.

Nirody said: “These modes are strictly controlled by speed. They transition well between five legs on the ground, four legs on the ground, and three legs on the ground, as the speed increases.” In experiments, tardigrade animals proved them. Follow the same pattern, that is, which leg is in the air when the other leg is on the ground.

But why do tardigrades walk like arthropods? It may be that these groups have a common ancestor, and they are born to walk like this. However, according to this study, arthropods and tardigrades may also independently evolve this stepping pattern after their pedigrees diverged.

“This means that although their body structure, body shape and environment are completely different, this special coordination scheme is effective under all these conditions,” Nirodi said.