Meeting Abstract
While traditionally viewed as obstacles to in locomotion, limbless locomotors must use heterogeneities for propulsion. We challenged snakes to traverse a model heterogeneous terrestrial terrain—rigid arrays of posts on a whiteboard substrate. We studied two species adapted to different habitats, the desert specialist shovel-nosed snake C. occipitalis, which we previously found used open-loop control supplemented by passive mechanics to negotiate the sparse obstacles in its sand-dominated environment [Schiebel et al. PNAS 2019], and the generalist corn snake P. guttatus whose natural range includes a variety of terrains. Principal component analysis (PCA) revealed the specialist’s stereotyped sand-swimming wave was omnipresent during motion through the arrays, while results for the generalist were inconclusive, suggesting either the snakes did not have a preferred waveform or two dimensions were not adequate to describe the kinematics. We applied persistent homology, a mathematical technique to search for periodic data without reducing dimension, and found the specialist had long cycles consistent with PCA. The generalist, however, had fewer and shorter cycles, indicating the kinematics were aperiodic. We hypothesized that the generalists were instead targeting a desired pattern of reaction forces and tested this using a simplified terrain, a single force-sensitive post on the whiteboard. Generalists maintained contact with the post for longer durations and had less variation in the direction of the resulting force vector than the desert snake. 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].
