Climbing favours the tripod gait over alternative faster insect gaits

Pavan Ramdya,Robin Thandiackal,Dario Floreano,Thibault Asselborn,Richard Benton,Raphael Cherney,Auke Jan Ijspeert

doi:10.1038/ncomms14494

Abstract

To escape danger or catch prey, running vertebrates rely on dynamic gaits with minimal ground contact. By contrast, most insects use a tripod gait that maintains at least three legs on the ground at any given time. One prevailing hypothesis for this difference in fast locomotor strategies is that tripod locomotion allows insects to rapidly navigate three-dimensional terrain. To test this, we computationally discovered fast locomotor gaits for a model based on Drosophila melanogaster. Indeed, the tripod gait emerges to the exclusion of many other possible gaits when optimizing fast upward climbing with leg adhesion. By contrast, novel two-legged bipod gaits are fastest on flat terrain without adhesion in the model and in a hexapod robot. Intriguingly, when adhesive leg structures in real Drosophila are covered, animals exhibit atypical bipod-like leg coordination. We propose that the requirement to climb vertical terrain may drive the prevalence of the tripod gait over faster alternative gaits with minimal ground contact.

Highlights

To escape danger or catch prey, running vertebrates rely on dynamic gaits with minimal ground contact
To investigate factors favouring the prevalence of the insect tripod gait, we discovered fast locomotor gaits for an in silico insect model using an optimization algorithm (Particle Swarm Optimization (PSO)30)
In this study we asked which conditions might have led to the near universality of the tripod gait as a fast locomotor strategy among insects[7,8,12,14,20,21]

Summary

Introduction

To escape danger or catch prey, running vertebrates rely on dynamic gaits with minimal ground contact. Since the pioneering photographic studies of Muybridge[1], it has been widely appreciated that animals use distinct gaits at different locomotor speeds These discontinuous shifts in leg coordination are hypothesized to minimize energy consumption by changing the number and relative timing of legs in motion[2,3]. Drosophila melanogaster, a popular model for studying insect locomotion[11,12,13], transitions from a slow wave gait to a tetrapod gait and to a fast tripod gait[11,12,13,14], always keeping at least five, four or three legs on the ground at a given time, respectively. We focused on footfall patterns, as we were interested in understanding why insects rely on the tripod rather than alternative threelegged or even dynamically stable two-legged gaits during fast locomotion

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Conclusion