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Fig. 1. Oscillatory release of CO2 during tethered flight in a single
fruit fly Drosophila, flying in a flow-through respirometic chamber
of a virtual-reality flight arena and exhibiting only small fluctuations in
metabolic rate. (A) Location of spiracle openings on one side of
Drosophila: sp1, mesothoracic spiracle; sp2, metathoracic spiracle;
sp39, abdominal spiracles. (B) Muscle mass-specific mechanical power
output of the asynchronous indirect flight muscles (IFM) in vivo was
calculated from simultaneous measurements of aerodynamic production, flight
force production, wing stroke amplitude and frequency (left scale, top trace).
Bottom trace shows muscle mass-specific CO2 release rate (right
scale). In the bar below, blue indicates the oscillatory phase of gas release;
gray, non-cyclic gas release. (C) Temporal distributions of oscillatory
CO2 release patterns (blue) of 12 fruit flies flown under three
different experimental conditions (shown in the pictograms): (I) fruit flies
vary metabolic rate in response to visual stimulation by external open-loop
vertical motion of horizontal stripe patterns while simultaneously themselves
stabilizing the azimuth position of a closed-loop vertical stripe using the
relative difference in wing stroke amplitude (dark gray, left; see Materials
and methods); (II) flight under visual-closed-loop conditions but in the
absence of lift stimuli (yellow, middle); and (III) flight in absence of any
moving visual objects (gray, right). Data show that oscillatory releases of
CO2 occur randomly and are essentially restricted to flight
sequences without any visual stimulation of the surrounding panorama
(stationary patterns).