Resolving coiled shapes reveals new reorientation behaviors in C. elegans

We exploit the reduced space of C. elegans postures to develop a novel tracking algorithm which captures both simple shapes and also self-occluding coils, an important, yet unexplored, component of worm behavior. We apply our algorithm to show that visually complex, coiled sequences are a superposition of two simpler patterns: the body wave dynamics and a head-curvature pulse. We demonstrate the precise coiled dynamics of an escape response and uncover new behaviors in spontaneous, large amplitude coils; deep reorientations occur through classical Omega-shaped postures and also through larger, new postural excitations which we label here as delta-turns. We find that omega and delta turns occur independently, the serpentine analog of a random left-right step, suggesting a distinct triggering mechanism. We also show that omega and delta turns display approximately equal rates and adapt to food-free conditions on a similar timescale, a simple strategy to avoid navigational bias.