Abstract
When threatened by dangerous or harmful stimuli, animals engage in diverse forms of rapid escape behaviors. In Drosophila larvae, one type of escape response involves C-shaped bending and lateral rolling followed by rapid forward crawling. The sensory circuitry that promotes larval escape has been extensively characterized; however, the motor programs underlying rolling are unknown. Here, we characterize the neuromuscular basis of rolling escape behavior. We used high-speed, volumetric, Swept Confocally-Aligned Planar Excitation (SCAPE) microscopy to image muscle activity during larval rolling. Unlike sequential peristaltic muscle contractions that progress from segment to segment during forward and backward crawling, the muscle activity progresses circumferentially during bending and rolling escape behavior. We propose that progression of muscular contraction around the larva’s circumference results in a transient misalignment between weight and the ground support forces, which generates a torque that induces stabilizing body rotation. Therefore, successive cycles of slight misalignment followed by reactive aligning rotation lead to continuous rolling motion. Supporting our biomechanical model, we found that disrupting the activity of muscle groups undergoing circumferential contraction progression lead to rolling defects. We use EM connectome data to identify premotor to motor connectivity patterns that could drive rolling behavior, and perform neural silencing approaches to demonstrate the crucial role of a group of glutamatergic premotor neurons in rolling. Our data reveal body-wide muscle activity patterns and putative premotor circuit organization for execution of the rolling escape response.
Significance Statement To escape from dangerous stimuli, animals execute escape behaviors that are fundamentally different from normal locomotion. The rolling escape behavior of Drosophila larvae consists of C-shaped bending and rolling. However, the muscle contraction patterns that lead to rolling are poorly understood. We find that following the initial body bending, muscles contract in a circumferential wave around the larva as they enter the bend, maintaining unidirectional rolling that resembles cylinder rolling on a surface. We study the structure of motor circuits for rolling, inhibit different motor neurons to determine which muscles are essential for rolling, and propose circuit and biomechanical models for roll generation. Our findings provide insights into how motor circuits produce diverse motor behaviors.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
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Author Contributions: Conceptualization - P.C.C., Y.H., I.S.G., W.B.G., and A.A.Z. Data curation - P.C.C., W.L., Y.H., E.M.C.H., and A.A.Z. Formal Analysis - P.C.C., Y.H., and A.A.Z Funding Acquisition –P.C.C., E.M.C.H., W.B.G., and A.A.Z. Investigation – P.C.C., W.L., Y.H., and A.A.Z. Methodology –P.C.C., W.L., D.M.P., Y.H., R.H., T.T., I.S.G., E.M.C.H., W.B.G., and A.A.Z. Project Administration –P.C.C., W.B.G., E.M.C.H., and A.A.Z. Resources - P.C.C., W.L., Y.H., R.H., T.T., E.M.C.H., W.B.G., andA.A.Z. Software - P.C.C., Y.H., W.L., and E.M.C.H. Supervision – W.B.G., E.M.C.H., and A.A.Z. Validation – P.C.C., W.L., Y.H., E.M.C.H., W.B.G., and A.A.Z. Visualization - P.C.C., Y.H., D.M.P., I.S.G., W.B.G., and A.A.Z. Writing, original draft - P.C.C., W.B.G., and A.A.Z. Writing, review & editing - P.C.C., Y.H., W.L., E.M.C.H., W.B.G., and A.A.Z.
Competing Interest Statement: The authors declare no competing interest.
Classification: BIOLOGICAL SCIENCES-Neuroscience
In this study, we used high-speed volumetric SCAPE microscopy, connectomic analysis, functional manipulation of motor circuits, and biomechanical modeling to uncover how Drosophila larvae execute rapid nocifensive rolling escape behavior. In a significant addition to the revised manuscript, we collaborated with a soft robotics lab to develop a biomechanical model explaining how muscle activity patterns detected by SCAPE microscopy result in rolling behavior. In addition, using a new optogenetic tool, we repeated all the neuronal silencing experiments to ensure the rigor of our findings.
