Meeting Abstract
Despite vast differences in animals’ size and number of legs, the trajectory of the center of mass (CoM) during locomotion can be described with simple mechanical models. For example, when running, cockroach and human decelerate to the lowest speed at midstance, which can be modeled as a spring-loaded inverted pendulum (SLIP). Here, we investigated the locomotion of Drosophila because a recent study showed that its slow speed imposed a challenge to SLIP, and because we wanted to leverage its versatile genetic toolbox to obtain a deeper insight into control of insect locomotion. Through automated data acquisition and processing, we analyzed >1000 steps at a range of speeds; at all speeds, flies predominantly used a tripod gait. We found that the fly’s CoM was at its highest height and speed at midstance. Since this kinematics was inconsistent with SLIP, we used a new model – angular and radial spring-loaded inverted pendulum (ARSLIP) – which is a modified SLIP with an angular spring ankle. The combination of angular and radial spring could either decelerate or accelerate CoM before midstance, and therefore could model a range of CoM kinematics including those of both cockroach and fly. For each step, we also estimated spring constants of ARSLIP from a spread of tripod legs by assuming a tripod as a point mass supported by three springy legs. The estimated values matched values optimized to fly kinematics. We also examined the role of sensory feedback by silencing sensory neurons in the legs. Interestingly, the sensory deprived flies maintained tripod gait and had similar kinematics to the wild type flies. In sum, the diverse kinematics observed in insects represent different regimes of the ARSLIP model, and the basic characteristics of insect locomotion is created through feedforward signals and mechanics of a tripod.
