Geckos reconfigure control modules to self-right on diverse substrates

Animals synergistically employ multiple appendages and body segments to perform behaviors. We hypothesize that these controllable components can be represented by sets of simple models (templates), recruited in series or parallel to provide multiple strategies for executing a maneuver. As the physics of substrate-body interaction changes, these control modules may be reconfigured for new functions, enabling task completion in new environments. To further define our conjecture, we measured terrestrial self-righting in geckos. On flat, rigid surfaces, geckos self-righted with average righting times of 0.22 ± 0.03 s using dynamic motions including body torsion and tail-ground contact. When placed on a partially excavated surface where the tail could not make ground contact, average righting time increased by 40%. However, righting time decreased to 0.19 ± 0.02 s if the geckos used a new strategy, swinging the tail in a way similar to inertial air righting. Body-level behavior was invariant to the dichotomy in tail control. From our experiments, we begin to develop composable templates for terrestrial righting. Our results suggest that geckos employ the tail as a multifunctional control module in parallel with a body torsion template to increase robustness to challenging substrates.