Undulatory Locomotion of Caenorhabditis elegans in Disordered Terrain

Animals move through space by deforming their bodies, propelled by reaction forces from the surrounding medium. In homogeneous environments, these self-deformation patterns and the resulting reaction forces are often periodic in space and time. However, natural landscapes contain random obstacles and complex substrate heterogeneity that disrupts purely periodic movement. To discover the effects of disorder on locomotory behaviors, we studied the undulatory gaits of nematodes (Caenorhabditis elegans, ~1mm in length) roaming in a set of 2-dimensional arrays of PDMS pillars within microfluidic devices. Starting with a hexagonal lattice, we introduced disorder by randomly displacing the obstacles from the lattice sites. In the spatially periodic arrays, worms moved in straight-line trajectories along the lattice vectors, interrupted by intermittent turning and reversal events. As the mean random displacement from the lattice sites increased (from 0-10% of the lattice spacing), turning became more frequent, and the overall persistence length of trajectories decreased. Correspondingly, a transition from ballistic to Brownian motion was observed at a shorter time scale (~3-5 seconds) in random lattices relative to periodic obstacle arrays (~7-10s). These results show that the presence of disorder in the terrain affects the statistics of search behaviors in C. elegans, suggesting that structural properties of the environment play a significant role in nematode behavior and ecology.