The coupled dual-oscillator model of wing and haltere motion in flies

The mechanics of Dipteran thorax is dictated by a network of exoskeletal linkages which, when deformed by flight muscles, generate coordinated wing movements. In Diptera, forewings power flight, whereas hindwings have evolved into specialized halteres which provide rapid mechanosensory feedback for flight stabilization. Although actuated by independent muscles, wing-haltere motion is precisely phase-coordinated at high frequencies. Because wingbeat frequency is a product of wing-thorax resonance, wear-and-tear of wings or thorax should impair flight ability. Here, we show that wings and halteres are independently-driven, linked, coupled oscillators. We systematically reduced wing length in flies and observed how wing-haltere synchronization was affected. The wing-wing system is a strongly-coupled oscillator, whereas wing-haltere system is weakly-coupled through mechanical linkages which synchronize phase and frequency. Wing-haltere link is unidirectional; altering wingbeat frequency affects haltere frequency, but not vice-versa. Exoskeletal linkages are thus key morphological features of Dipteran thorax, ensuring robust wing-haltere synchrony despite wing damage.