Model-Based Tracking of Fruit Flies in Free Flight

Abstract

Insect flight is a complex interdisciplinary phenomenon. Understanding its multiple aspects, such as flight control, sensory integration, physiology and genetics, often requires the analysis of large amounts of free flight kinematic data. Yet, one of the main bottlenecks in this field is automatically and accurately extracting such data from multi-view videos. Here, we present a model-based method for the pose estimation of free-flying fruit flies from multi-view high-speed videos. To obtain a faithful representation of the fly with minimum free parameters, our method uses a 3D model that includes two new aspects of wing deformation: a non-fixed wing hinge and a twisting wing surface. The method is demonstrated for free and perturbed flight. Our method does not use prior assumptions on the kinematics apart from the continuity of the wing pitch angle. Hence, this method can be readily adjusted for other insect species.

The self-oscillation paradox in the flight motor ofDrosophila melanogaster

“…To resolve the self-oscillation paradox, D. melanogaster wing flexibility would have to reduce drag forces ( c Ω 2 ) to below half of current estimates, maintaining roughly equivalent lift. The flexibility observed in D. melanogaster wings during flight is not large [32,57]; and existing studies of insectoid flexible flapping wings indicate reductions in drag-per-lift of up to approximately 20% in the very best cases [58–60]. As such, wing flexibility could contribute slightly to resolving the self-oscillation paradox in D. melanogaster , but does not offer a complete resolution.…”

“…The quadratic model (equation (2.2)) requires approximation. If the response, x(t), is simple-harmonic, x ¼ xe iVt , approximating observed D. melanogaster wingbeat kinematics [12,32], then an approximate representation is…”

“…Third, the distribution of elasticity across the flight motor may not be exactly parallel. Series elasticity (equations (2.6) and (2.7)) can arise from the flexibility of the wing hinge [15,33] and local modes of deformation within the exoskeleton [6]; and could act as a first-order approximation of the elastic effects of distributed wing flexibility-though the deformation observed in D. melanogaster wings during flight is relatively minimal [32,57]. We can account for these effects via a hybrid parallel-series model of the flight motor (equation (2.7)).…”

“…The quadratic model (equation (2.2)) requires approximation. If the response, x ( t ), is simple-harmonic, x=xfalse^normaleiΩt, approximating observed D. melanogaster wingbeat kinematics [12,32], then an approximate representation isfalse(−Ω2+icΩ2+ω02false)xfalse^= ffalse^,where the quadratic damping ratio c is dependent on amplitude xfalse^. A derivation is given in the electronic supplementary material (§1), alongside the relations c=βxfalse^ for a peak-damping approximation; c=πβxfalse^/4 for an average-damping approximation.…”

Solving the thoracic inverse problem in the fruit fly

“…Sources of data used in this study are tabulated in table 1; and illustrated in figure 2. Wingbeat kinematics for D. melanogaster are sourced from published results [11,22,62], as well as additional in-house data [67]. Aerodynamic data for D. melanogaster, accounting, e.g.…”