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The mechanical basis of Drosophila audition

Martin C. Göpfert^1,* and Daniel Robert¹

Institute of Zoology, University of Zurich, Winterthurerstraße 190, CH-8057 Zurich, Switzerland
¹ Present address: School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK

View larger version (71K): [in a new window]   Fig. 1. The Drosophila melanogaster antenna. Schematic drawing (left) and scanning electronmicrograph (right). Each antenna is composed of three segments, the scape, the pedicel and the funiculus, the latter carrying the feather-like arista. The drawing by P. Bryant was reproduced with permission from FlyBase (1999). Scale bar (right panel), 0.1 mm.

View larger version (18K): [in a new window]   Fig. 2. Apparatus and analysis. (A) Schematic drawing showing the arrangement of the loudspeaker, the animal, the pressure-gradient microphone and the laser Doppler vibrometer (LDV). The vibration velocity vib was assessed via the LDV, the particle velocity air via the microphone. (B) Detail from A depicting the animal's orientation during the measurements (in contrast to the picture shown, the animal's wings and legs were removed for experiments). (C) Comparison between the measured velocity response of an arista (red trace) and the fitted function of a simple harmonic oscillator (blue trace). Magnitude (left panel) and phase (right panel) responses are shown. The fitted function is described by f0=394Hz, Q=1.24 and vib/air at f0=1.13, where f0 is the resonance frequency and Q is the quality factor.

View larger version (81K): [in a new window]   Fig. 3. Antennal anatomy. (A) Longitudinal section through the two distal antennal segments, the pedicel and the funiculus. The pedicel/funiculus joint, the funicular hook and the funicular stalk are depicted. (B) Cross section through the pedicel at the level of the pedicel/funiculus joint. (C) Detail from B showing the medial (Med) and posterior (Post) groups of receptors, their distal threads (T), the `V'-shaped sites to which the threads attach (V) and the membrane (M) that suspends the flagellar hook in the pedicel. (D) Cross section through the funiculus at the level of the insertion of the arista. Connections between the funiculus and the arista (I) and between the three sub-elements that make up the arista (II, III) are depicted. Scale bars, 50 µm (A,B,D) and 25 µm (C).

View larger version (28K): [in a new window]   Fig. 4. The arista tip response in four male and four female flies. (A) Stimuli: superimposed frequency spectra of the acoustic random-noise stimulus at the position of the antenna during vibration measurements in eight animals and a spectrum of the background noise (BN). (B) Data reliability: frequency spectra of the coherence between the laser and the microphone signals during the same eight vibration measurements. Coherence can range between 0 and 1, with a value of 1 indicating the absence of unrelated noise. (C) Superimposed magnitude responses of the eight arista tips examined (males, blue traces; females, red traces). A response magnitude of unity (vib/air=1), where vib is the vibration velocity and air is the particle velocity, means that arista tip and air particles move at the same velocity. (D) Corresponding phase responses. A phase angle of +90° means that vib leads air by a quarter of an oscillation cycle.

View larger version (54K): [in a new window]   Fig. 5. Mechanical responses measured on different parts of a female arista (left panels), funiculus (middle panels) and pedicel (right panels, including one measurement from the compound eye). Measurement points (A), magnitude responses (B) and phase responses (C) are shown. For colour conventions, see A. The drawings by P. Bryant, used to depict the measurement points, were reproduced with permission from FlyBase (1999). vib/air is the response magnitude, where vib is the vibration velocity and air is the particle velocity.

View larger version (23K): [in a new window]   Fig. 6. Intensity characteristics. (A) Frequency spectra of the acoustic random-noise stimuli. Intensity was varied in steps of 3 dB over a total range of 36 dB. `0 dB' (red) depicts the stimulus of lowest intensity, `+36 dB' (green) the stimulus of highest intensity. (B) Superimposed magnitude responses of an individual arista tip to the stimuli depicted in A. (C) Corresponding phase responses. For colour conventions, see A. vib/air is the response magnitude, where vib is the vibration velocity and air is the particle velocity. BN, background noise.

View larger version (19K): [in a new window]   Fig. 7. (A) The frequency f0 of the resonance measured at the arista tips of two males and two females as a function of the relative particle velocity of the random-noise stimuli (for corresponding absolute particle velocities, see Fig. 6A). f0 increases linearly with stimulus intensity. (B) Intensity-dependent response magnitudes of two male and two female arista tips to pure-tone stimulation at different frequencies. The responses exhibit maxima at frequency-specific intensities. vib/air is the response magnitude, where vib is the vibration velocity and air is the particle velocity.

View larger version (28K): [in a new window]   Fig. 8. Courtship songs. (A) Time trace of a song consisting of a series of 20 sound pulses. (B) Superimposed (grey traces) and averaged (black trace) time traces of the pulses shown in A. (C) Frequency spectra calculated on the basis of 20-30 averaged pulses (as shown in B) recorded from five male Drosophila melanogaster.