A song and a dance: the acoustic geometry of courtship in Drosophila melanogaster
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1
University of Bristol, United Kingdom
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2
University of Tours, France
Drosophila melanogaster have bilateral antisymmetric antennae that receive the particle velocity component of an acoustic stimulus1. Acoustic communication is important in their courtship2, taking place in the acoustic near-field where the small size of the dipole sound source (the male wing) and the rapid attenuation rate of particle velocity produce a spatially divergent sound field with highly variable magnitude3. In addition, male and female D. melanogaster are not usually stationary during courtship, further increasing the variable directionality of acoustic stimuli. The antennal receiver of D. melanogaster is actively tuned by virtue of the contributions from mechanosensory neurons in an amplitude dependent manner4. Amplification occurs at low input amplitudes where the antennae are tuned to frequencies of around 200Hz, but at higher amplitudes there is no amplification and resonant frequency is increased to around 800Hz. The directional sensitivity of particle velocity receivers has drawn little attention with the assumption that directionality is conveyed by the inherently directional particle velocity stimulus5. As the antisymmetric antenna of D. melanogaster rotate about a central axis, the inherent directionality in the stimulus is mechanically removed, therefore cues must be derived by other means. The structure of the acoustic field during courtship is highly variable, raising questions about antennal sensitivity to directional cues and whether active contributions from mechanosensory neurons are involved in providing directionality in this species.
Using both particle image velocimetry and laser Doppler vibrometry, we examined the stimulus flow around the head of D. melanogaster to identify the actual geometry of the acoustic input to the antenna and its directional characteristics. We reveal that the stimulus changes in both magnitude and direction as a function of its angle of incidence. Remarkably, directionality is substantial, with inter-antennal velocity differences of 25 dB at 140 Hz. For an organism whose auditory receivers are separated by only 660 µm ±51µm, this inter-antennal velocity difference is far greater than differences in intensity observed between tympanal ears for organisms of similar scale. Further, the mechanical sensitivity of the antenna changes as a function of the angle of incidence of the acoustic stimulus, with peak responses along axes at 45o and 315o relative to the longitudinal body axis. Interestingly, we show that active contributions from mechanosensory cells produce angle-dependent increases in antennal sensitivity and inter-antennal tuning differences in response to differential velocities at the two antennae. These inter-antennal tuning differences show peak frequencies at angles where the highest antennal velocities are recorded and are a novel directional cue that may be used in sound source localisation. This work indicates not only that the flies are able to detect differential cues in signal direction, but also that the male song structure may not be the sole determinant of mating success; his spatial positioning is also critical.
1 Ewing, A. 1978 Physiol. Entomol. 3, 33-36.
2 von Schilcher, F. 1976 Anim. Behav. 24, 18-26.
3 Bennet-Clark, H. 1971, Nature 234, 255-259.
4 Göpfert, M. & Robert, D. 2003 PNAS 100, 5514-5519.
5 Morley et al in press J. Exp. Biol.
Keywords:
audition,
Courtship,
directional hearing,
Drosophila melanogaster
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for participant symposium and student poster award)
Topic:
Sensory: Audition
Citation:
Morley
E,
Steinmann
T,
Casas
J and
Robert
D
(2012). A song and a dance: the acoustic geometry of courtship in Drosophila melanogaster.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00197
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Received:
29 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Erica Morley, University of Bristol, Bristol, United Kingdom, erica.morley@bristol.ac.uk