Neuromechanics of Gait Adaptation in the Nematode C. elegans

The mm-scale nematode C. elegans adapts its undulatory gait to changing environmental resistance via a combination of distributed and centralized control mechanisms. We record body kinematics across environments (varying viscosity, and on agar surfaces) using bright field imaging and measure muscle activation patterns using ratiometric calcium imaging to investigate control strategies underlying gait adaptation. Waves of muscle activation display a constant spatial frequency (~0.8 times the body length) across environments while the resulting waves of undulating body curvature shift in response to increasing environmental resistance (from ~0.6 to ~1.5 body lengths). In contrast, undulation frequencies of muscle activation shift in parallel to body wave frequencies as drag increases. This leads to the existence of “neuromechanical phase lags” – phase shifts between muscle activation and body curvature -which depend on the environment. We compare measured phase lags to a resistive force theory model, which allows cross-taxa comparisons to previously studied systems, such as the cm-scale sandfish lizard, which locomotes through granular terrain.