Meeting Abstract
Snakes can coordinate the interaction of their flexible trunks with environmental heterogeneities to generate propulsion. The complicated relationship between shape and terrain in generalist snakes impedes deduction of neuromechanical controllers. The desert snake C. occipitalis uses a stereotyped travelling wave of body bending. We hypothesized this animal controls for its shape by targeting a pattern of muscle activation beneficial for movement on homogeneous granular matter (GM) [Schiebel et al SICB 2016]. Inspired by previous research probing the neuromechanics of organisms via environmental manipulations, we test the hypothesis by challenging C. occipitalis (N=9, 181 trials) to traverse a model desert terrain—a homogeneous sand-analogue substrate and a single row of posts perpendicular to the direction of travel. Visual feedback was eliminated by covering spectacle scales. After collision, trajectories were re-oriented into preferred directions of either ~0° (continuing straight) or ±21±9°. Since the shape changes of the snake were small during interaction, we posited that the collisional diffraction pattern resulted from a motor program that was largely preserved upon contact. We developed a model whose wave shape was similar to that used by the snake on GM and would passively deform upon interaction with obstacles. Following insights by Astley et al [SICB 2016] based on muscle activation patterns observed by Jayne [1988], we assumed external forces on the body were resisted only where active muscles would be lengthened; thus posts were accommodated by changing curvature so that active muscles would shorten further. The model captured the pattern of preferred trajectories, supporting our hypothesis that the specialist snake uses a motor program that is well-adapted for travel on GM and largely ignores interactions with sparse obstacles.
