BPS2026 - Elucidating adaptive locomotion of tardigrades in varied environments through coarse-grained analyses

Tardigrades are an emerging model organism for studying biomechanics due to their robust physiology and distinct crawling locomotion. As the smallest legged animals, tardigrades are soft-bodied walkers with a neural system consisting of only a few hundred neurons arranged into a multi-lobed brain, ventral nerve cord, and segmental ganglia. Despite their simple neuroanatomy, tardigrades display remarkably complex behaviors, including individual limb use, robust interlimb coordination, phototaxis, thermotaxis, chemotaxis and transitions between active and dormant states. Although their resilience to extreme conditions has been well investigated, less is known about their locomotion in changing physical constraints. Here, we examine how tardigrades ( Hypsibius exemplaris ) move across environments with two systematically varied parameters: substrate roughness and medium viscosity. We attain a coarse-grained perspective by quantifying trajectory characteristics and develop a simplified model that captures essential features of their movement patterns without relying on fine-scale kinematic detail. This approach connects tardigrade locomotion to broader principles of animal locomotion in complex environments.