Specialization of control strategies in terrestrial slithering snakes.

Limbless locomotors like snakes use environmental heterogeneities for propulsion. We tested two snake species adapted to different habitats, the desert specialist C. occipitalis and the multi-terrain generalist P. guttatus, in a model terrestrial terrain–rigid arrays of posts on a low-friction whiteboard substrate. Principal component analysis (PCA) revealed the specialist maintained its stereotyped sand-swimming wave in the arrays, while results for the generalist were inconclusive, indicating either a periodic gait was higher dimensional, or the motion was aperiodic. Persistent homology, a mathematical technique which can identify cycles without reducing dimension, suggested the generalist used aperiodic kinematics. We hypothesized that the generalists instead controlled reaction forces and tested this using a simplified terrain, a single force-sensitive post on whiteboard. The generalist was more effective at using the post, maintaining longer contacts and more consistent force vectors. Our study suggests control specialization; the specialist targets beneficial sand swimming kinematics while the generalist controls for advantageous force generation in accord with early studies of generalist snakes in lattices [e.g. Gray 1955].