Static stability predicts the continuum of interleg coordination patterns inDrosophila

Abstract

statement: 20A simple stability-based modelling approach can explain why walking insects use different 21 leg coordination patterns in a speed-dependent way. 22 23 Abstract 24During walking, insects must coordinate the movements of their six legs for efficient 25 locomotion. This interleg coordination is speed-dependent; fast walking in insects is 26 associated with tripod coordination patterns, while slow walking is associated with more 27 variable, tetrapod-like patterns. To date, however, there has been no comprehensive 28 explanation as to why these speed-dependent shifts in interleg coordination should occur in 29 insects. Tripod coordination would be sufficient at low walking speeds. The fact that insects 30 use a different interleg coordination pattern at lower speeds suggests that it is more optimal 31 or advantageous at these speeds. Furthermore, previous studies focused on discrete tripod 32 and tetrapod coordination patterns. Experimental data, however, suggest that changes 33 observed in interleg coordination are part of a speed-dependent spectrum. Here, we explore 34 these issues in relation to static stability as an important aspect of interleg coordination in 35Drosophila. We created a model that uses basic experimentally measured parameters in fruit 36 flies to find the interleg phase relationships that maximize stability for a given walking speed. 37Based on this measure, the model predicted a continuum of interleg coordination patterns 38 spanning the complete range of walking speeds. Furthermore, for low walking speeds the 39 model predicted tetrapod-like patterns to be most stable, while at high walking speeds tripod 40 coordination emerged as most optimal. Finally, we validated the basic assumption of a 41 continuum of interleg coordination patterns in a large set of experimental data from walking 42 fruit flies and compared these data with the model-based predictions. 43 44 attainable stability but also how robustly such stability can be realized in the presence of 131 locomotor variability. 132 133 Materials and Methods 134 Stability model 135 Based on previous experimental findings (Wosnitza et al., 2013) we created a model that 136 incorporates several key aspects of walking in D. melanogaster and explicitly addresses the 137 speed-dependent nature of inter-leg coordination. The model makes the following 138 assumptions: 139

A size principle for recruitment of Drosophila leg motor neurons

“…To optogenetically manipulate motor neuron activity during walking, we positioned tethered flies on a spherical treadmill ( i.e ., a Styrofoam ball) within a visual arena ( Reiser and Dickinson, 2008 ; Figure 7D ). Previous studies have found that walking speed and gait on the treadmill are similar to freely walking flies ( Szczecinski et al, 2018 ). In our setup, the fly was motivated to walk forward with a wiggling stripe ( Figure 7E ), and we tracked the treadmill and the fly’s behavior with multiple high-speed cameras.…”

Unravelling intra- and intersegmental neuronal connectivity between central pattern generating networks in a multi-legged locomotor system

“…In a recent modelling study, Szczecinski et al [46] demonstrated that interleg coordination patterns in D. melanogaster result from the interplay between static stability of the animal and robustness of the coordination pattern. The authors found that at a large variety of walking speeds (hence coordination patterns), only the ipsilateral phase differences change, whereas contralateral phase differences remain at about 1/2.…”

Fast tuning of posture control by visual feedback underlies gaze stabilization in walking Drosophila

“…Changes in FLx over a step can displace the fly's center of stability away from its center of mass (Figure 5G), thereby momentarily decreasing posture stability. 65,66 To recover stability, posture control systems could either adjust lateral foot placement in the next step, like in humans, 67 or dynamically engage viscoelastic properties of the musculoskeletal system, as observed in the cockroach. 68 Our data are consistent with the first possibility.…”