When they were just strolling around, the water bears generally moved at a rate of about half a body length per second, increasing to two body lengths per second when they loped at full throttle. The team was surprised to note that the water bears did not have distinct gaits for each speed, like horses as they transition from a walk to a gallop. Rather, their locomotion closely resembled that of insects and arthropods, scurrying along faster and faster with no change to the basic step pattern.
Specifically, as the tardigrades sped up, they would transition between having five legs on the ground, then four legs on the ground, then three legs on the ground—just like insects and arthropods, despite a 20-million-year evolutionary gap between them. “What that means is that despite having completely different body structures, body sizes, and environments that they’re moving through, there’s something about this particular coordination scheme that’s efficient across all of these conditions,” Nirody told Live Science.
There are two leading hypotheses for why this might be the case. Perhaps water bears, insects and arthropods share common ancestors that had a common neural circuit. Alternatively, the organisms may have evolved this scurrying gait independently through natural selection.
“If there is some ancestral neural system that controls all of panarthropod walking, we have a lot to learn,” said Nirody. “On the other hand, if arthropods and tardigrades converged upon this strategy independently, then there’s much to be said about what makes this strategy so palatable for species in different environments.”Jennifer Ouellette, “Tiny tardigrades walk like insects 500,000 times their size” at Ars Technica (December 28, 2021)