Directional cues inDrosophila melanogasteraudition: structure of acoustic flow and inter-antennal velocity differences

Abstract

SUMMARYDrosophila melanogaster have bilateral antisymmetric antennae that receive the particle velocity component of an acoustic stimulus. Acoustic communication is important in their courtship, which takes place in the acoustic near-field. Here, 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 magnitude. Also, male and female D. melanogaster are not usually stationary during courtship, resulting in a variable directionality of the acoustic stimulus. 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 antennae and its directional response. 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±51m (mean ± s.d.), 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 antennae changes as a function of the angle of incidence of the acoustic stimulus, with peak responses along axes at 45 and 315deg relative to the longitudinal body axis. 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 crucial to female sound reception and therefore also perhaps to her decision making.

Sensorimotor Transformations Underlying Variability in Song Intensity during Drosophila Courtship

“…This arises in part from the small size of their wings—each wing maximally generates only ~10 −16 W of power, which is roughly six orders of magnitude below the threshold of human hearing (Bennet-Clark, 1971). In addition, the Drosophila ear (its arista) is most sensitive to the particle velocity component of sound, which is heavily attenuated with increasing distance from a point source (Göpfert and Robert, 2002; Morley et al, 2012). To increase the probability that the female hears his song, the male could continually sing at maximal intensity, but this runs the risk of saturating her auditory system and consequently making his communication signal less effective.…”

Active Mechanisms of Vibration Encoding and Frequency Filtering in Central Mechanosensory Neurons

“…Phase cues can reduce this ambiguity. For example, sound coming from the left or right will cause the antennae to move out of phase, whereas sound coming from the front or back will cause the antennae to move in phase (Morley et al, 2012). The brain could use phase information to reduce ambiguity even further – for example, to determine whether the sound source is in front or in back – because Drosophila courtship song pulses have a stereotyped phase profile (Arthur et al, 2013).…”

The influence of developmental environment on courtship song in cactophilic Drosophila

“…In this sense, Morley et al . () demonstrated that the mechanical sensitivity of the arista changes as a function of the angle of incidence of the acoustic stimulus. Suggestively, males of D. buzzatii produce secondary songs later in courtship and immediately before copulation (Oliveira et al ., ; Iglesias & Hasson, ).…”