Researchers have recently focused on the locomotion capacities of tardigrades in terrestrial environments. To their surprise, the gait of these animals was very similar to that of insects. Details of the study are published in the journal PNAS.
Tardigrades are often portrayed as the toughest creatures on the planet. And for good reason, these small invertebrates are known to withstand temperatures as low as -272 ° C, when others can survive without water or oxygen for many years. Some species can also withstand overwhelming ocean pressures where others acclimatize to the vacuum of space. More recently, a study revealed that tardigrades were also able to survive impacts at very high speed.
While many studies have therefore focused on their incredible robustness, others focus on more practical subjects. A few years ago, a team from the Senckenberg Natural History Museum in Görlitz, Germany, was able to film the mating of these water bears for the very first time. More recently, researchers at Rockefeller University have asked the question: How do these tiny creatures work?
An approach similar to that of insects
Tardigrades are among the smallest footed animals known. To our knowledge, they are also the only soft-bodied animals that can walk on dry land. The tardigrades thus have a set of particularly versatile locomotor tools allowing them to move in a wide range of environments (freshwater or marine and terrestrial environments).
As part of this work, the researchers examined the kinematics and inter-leg coordination of free walking tardigrades (Hypsibius exemplaris). The team found that the gait of these creatures mimics several key characteristics seen in insects, although the two groups are very different (and the insects are at least 500,000 times their size).
“One of the coolest and most surprising things to start with was how good they were,” writes mechanical biologist Jasmine Nirody. “They have a regular gait and it looks remarkably like those of much, much bigger animals!”. According to the researchers, some tended to wander leisurely on the proposed substrate, while others could run at the sight of a potentially interesting target.
Credits: Nirody et al., PNAS, 2021
The team also looked at tardigrades trying to walk on substrates with different levels of stiffness in an effort to determine how this affected their walking. They found that the cubs adapted their locomotion accordingly. On the other hand, they were more comfortable on the surface of gels (more rigidity) and less on smooth glass (less rigidity). “This strategy has also been observed in arthropods to move efficiently on fluid or granular substrates,” says Dr. Nirody.
A tardigrade walking on a stiffer gel. Credit: Lisset Duran
As to why tardigrades walk so much like insects, the question is still open. Researchers are uncertain whether there might be a potential common ancestor or whether the walking trait evolved separately in these two organisms.