Meeting Abstract
Periodic steady-state locomotion like flat-ground walking and running typically display high stereotypy of forces and kinematics during limit-cycle behavior. We examined variability in an unsteady maneuver in lizards, Agama agama, during a prey-capture behavior where animals began from a standstill, turned and accelerated to catch prey delivered directly behind it. We expected these high-effort, time sensitive behaviors to exhibit strong stereotypy due to physical constraints (limits on muscle force, range of motion, and ground friction). To our surprise, we found that the sequence of footfalls and the pattern of limb forces varied widely, but resulted in similar task-level behavior (e.g. center-of-mass behavior). On average, agamas used a trot-like timing pattern over the entire behavior, but limbs varied in their functional role. Limbs could provide force to turn or accelerate the body, or both, depending on their location and timing of the step. The inside forelimb contributed least, but the other three limbs varied over similar ranges of linear (-10 to 60 mN*sec) and angular (-0.5 to 1.5 mN*m*sec) impulses, showing trade-offs. To further challenge the animals, we perturbed limb forces by reducing traction under one foot. Despite large slips of the foot, we found no significant difference in average time to complete the turn (350 ms to rotate 150°, even when a foot slipped more than 2 cm), showing that other limbs changed roles to compensate for the reduced effort of the perturbed limb. While steady state behaviors collapse to low dimension, we hypothesize that unsteady prey capture or escape maneuvers possess the capability to exploit a larger solution space to increase the robustness of the behavior.
