Neuromechanical control in highly damped environments

Biological locomotors must contend with environmental complexity and variability; thus control strategies underlying movement need to be flexible, robust, and environmentally adaptive. We investigated this adaptivity in the context of undulatory locomotion using the mm-scale nematode C. elegans, which permits interrogation of neuromuscular dynamics through calcium imaging. We imaged muscle activity in organisms locomoting in diverse settings:  fluids, crawling on agar and burrowing within hydrogels. In each condition, neuromechanical phase lags (delays between waves of muscle activation and body curvature) arise, which depend on the physical properties of the surrounding medium, yielding phase lags which either shift continually down the body (viscous fluids) or remain constant (agar surfaces) These experimental results are captured by Resistive Force Theory model which in turn allows comparisons across taxa (Ding et al., 2013). The muscle activity pattern adopted by the nematode in viscous fluids displays similarities to those of cm-scale sandfish lizards swimming in frictional fluids (e.g. sand, Sharpe et al., 2012) indicating the importance of the environment on neuromechanical control in highly damped locomotion.