The self-oscillation paradox in the flight motor of D. melanogaster

TL;DR

This study investigates the self-oscillation mechanism in Drosophila melanogaster's flight motor, revealing it likely operates without resonance and that muscular elasticity plays a crucial role, challenging previous assumptions about muscle stiffness and resonance.

Contribution

The paper introduces a fundamental condition for motor self-oscillation and demonstrates that D. melanogaster's flight motor defies this condition, providing new insights into insect flight biomechanics.

Findings

D. melanogaster flight motor likely not resonant with exoskeletal elasticity

Muscular elasticity dominates over exoskeletal elasticity in flight

Muscle stiffness may hinder, not facilitate, self-oscillation in insect flight

Abstract

Tiny flying insects, such as Drosophila melanogaster, fly by flapping their wings at frequencies faster than their brains are able to process. To do so, they rely on self-oscillation: dynamic instability, leading to emergent oscillation, arising from muscle stretch-activation. Many questions concerning this vital natural instability remain open. Does flight motor self-oscillation necessarily lead to resonance - a state optimal in efficiency and/or performance? If so, what state? And is self-oscillation even guaranteed in a motor driven by stretch-activated muscle, or are there limiting conditions? In this work, we use data-driven models of wingbeat and muscle behaviour to answer these questions. Developing and leveraging novel analysis techniques, including symbolic computation, we establish a fundamental condition for motor self-oscillation common to a wide range of motor models. Remarkably, D. melanogaster flight apparently defies this condition: a paradox of motor operation. We explore potential resolutions to this paradox, and, within its confines, establish that the D. melanogaster flight motor is likely not resonant with respect to exoskeletal elasticity: instead, the muscular elasticity plays a dominant role. Contrary to common supposition, the stiffness of stretch-activated muscle is an obstacle to, rather than an enabler of, the operation of the D. melanogaster flight motor.