Tardigrades exhibit robust interlimb coordination across walking speeds and terrains

Abstract

Tardigrades must negotiate heterogeneous, fluctuating environments and accordingly utilize locomotive strategies capable of dealing with variable terrain. We analyze the kinematics and interleg coordination of freely walking tardigrades (species: Hypsibius exemplaris). We find that tardigrade walking replicates several key features of walking in insects despite disparities in size, skeleton, and habitat. To test the effect of environmental changes on tardigrade locomotor control circuits we measure kinematics and interleg coordination during walking on two substrates of different stiffnesses. We find that the phase offset between contralateral leg pairs is flexible, while ipsilateral coordination is preserved across environmental conditions. This mirrors similar results in insects and crustaceans. We propose that these functional similarities in walking coordination between tardigrades and arthropods is either due to a generalized locomotor control circuit common to panarthropods or to independent convergence onto an optimal strategy for robust multilegged control in small animals with simple circuitry. Our results highlight the value of tardigrades as a comparative system toward understanding the mechanisms—neural and/or mechanical—underlying coordination in panarthropod locomotion.

Synchronous multi-segmental activity between metachronal waves controls locomotion speed in Drosophila larvae

“…Locomotion speed is a function of the frequency and length of a cycle. We found that, similar to previous findings, the speed of larval crawling is determined more so by stride frequency than stride length (Frigon et al, 2014; Grillner et al, 1979; Jacobson and Hollyday, 1982; Nirody et al, 2021). Furthermore, similar to limbed animals including mammals and other insects, the two constituent phases of a locomotor cycle vary differentially with speed, with the interwave phase varying more than the wave phase.…”

“…On the other hand, limbed animals change the frequency of walking by varying the locomotor cycle differentially: the stance phase is varied, but the swing phase is almost unchanged, even as animals switch to different gaits. This holds true for animals ranging from insects and tardigrades to mammals (Boije and Kullander, 2018;Frigon et al, 2014;Grillner et al, 1979;Jacobson and Hollyday, 1982;Nirody et al, 2021). How the nervous system generates this asymmetry in the variation of stance and swing phases is still an open question (Bidaye et al, 2018;Boije and Kullander, 2018;Kiehn, 2016).…”

Multiresponsive Microactuator for Ultrafast Submillimeter Robots

“…In general, the robots in this work is presently the fastest submillimeter robot that can be actuated remotely and move continuously on nonspecialized surfaces. It is faster than some micro­organisms such as Caenorhabditis elegans ( C. elegans ) and Tardigrade of this size, and even comparable to the speed of Paramecia and some arthropods in the Formicidae family. , …”

“…Similarly, microrobots with fast speed enable them with more application potential for practical scenarios. Figure shows the comparison of relative speeds with respect to body length including several arthropods and microorganisms (green), − the set of most advanced optical actuated microrobots (orange), ,,,− ,− inchworm-type microrobots (blue), ,,− and this work (red stars). Among inchworm-type microrobots, the microrobots in this work have the smallest size and can operate at a relatively fast speed (3.66 BL/s).…”

A lift in snail's gut provides an efficient colonization route for tardigrades

“…Accordingly, most of the tardigrades would be dispersed on the second day post‐ingestion that is, on average 1 m (maximum 10 m) away from their original location. On a smooth, wet, two‐dimensional surface in laboratory conditions, tardigrades were reported to move at speeds between 1.98 and 15.81 mm/min (Li & Wang, 2005 ; Nirody et al, 2021 ). Hence, theoretically, at directed higher speed movement, tardigrades could match, or even exceed, the distance traveled by a snail (e.g., 48 h at 15.81 mm/min = 45.5 m).…”