Auditory sensitivity, spatial dynamics, and amplitude of courtship song in Drosophila melanogaster

Abstract

Acoustic communication is an important component of courtship in It takes the form of courtship song produced by males through the unilateral extension and vibration of a wing. Following the paradigm of sender-receiver matching, song content is assumed to match tuning in the auditory system, however, audition is nonlinear and tuning dependent upon signal amplitude. At low stimulus amplitudes or in the absence of sound the antenna is tuned into song frequency, but as amplitude increases the antenna's resonance is shifted up by hundreds of Hertz. Accurate measurements of song amplitude have been elusive because of the strong dependency of amplitude upon the spatial geometry between sender and receiver. Here, auditory directional sensitivity and the geometric position between the courting flies are quantified. It is shown that singing occurs primarily from positions resulting in direct stimulation of the female antenna. Using this information, it is established that the majority of song is louder than theoretically predicted and at these sound levels the female antenna should not amplify or be tuned into song. The study implies that hearing, and, in particular, its active mechanisms, could function in a broader context than previously surmised.

Sound localization behavior inDrosophila melanogasterdepends on inter-antenna vibration amplitude comparisons

“…Conspecific song is a sound likely to be encountered by both females (which we focused on initially) and males (which we tested in separate experiments described later). The sound intensity was 0.125 cm s −1 (88 dB SVL) at the fly's location, which is comparable to the intensity of natural courtship song according to classic theoretical predictions (80-95 dB SVL; Bennet-Clark, 1971) and recent measurements (88-99 dB SVL, median sound level for sine and pulse song, respectively; Morley et al, 2018).…”

“…This pattern of phonotaxis fits with the antenna's vibration amplitude tuning (Morley et al, 2012(Morley et al, , 2018. Antennal vibration amplitudes should not change when the sound source moves from 45 to −135 deg (Fig.…”

“…We placed two speakers in the back hemifield, at 135 and −135 deg. These are the two positions in the back hemifield where auditory sensitivity is highest (Morley et al, 2012) and they are the two positions predominately occupied by the wing of a singing male in the coordinate frame of a courted female (Morley et al, 2018). For comparison, we also placed two speakers in the front hemifield (at 45 and −45 deg).…”

Anthropogenic noise and the bioacoustics of terrestrial invertebrates

“…This scenario suggests that thin hairs will move in response to a large range of stimuli, even those produced at long distances. Additionally, some invertebrates, such as mosquitoes and flies, employ near-field receptor organs that actively amplify quiet signals and provide directional sensitivity (Göpfert and Robert, 2001;Gopfert et al, 2005;Morley et al, 2018). Together, these pieces of evidence extend the effective range of anthropogenic near-field noise to at least 10 m and potentially much further.…”

“…In these cases, animals may use non-linear tuning to avoid injury to their receptors when noise is loud. Additionally, there is some evidence that this mechanism may be useful for spatial release from masking (see Glossary; Morley et al, 2018). These examples likely represent just a small sample of the potential strategies available to invertebrates for avoiding near-field noise.…”