Anatomy and biomechanics of interaural coupling in a sarcophagid fly

In flies, the sense of hearing is related to the parasitic life-style. First reported in the parasitoid family Tachinidae, tympanal hearing is used to acoustically locate singing hosts. Here, the auditory anatomy and biomechanics of another family of parasitoid, the Sarcophagidae, is presented. These small auditory organs are located on the ventral prosternum and in several respects conform to the general Bauplan of a dipteran ear. However, the structural organization of their auditory periphery—the tympanal complex—is quite different: it is conspicuously lacking the central pivoting sclerite that constitutes the key element for directional sensitivity by mechanical coupling found in tachinids [Robert et al., J. Comp. Physiol. 179, 29–44 (1996)]. Based on scanning laser vibrometry, deflection shape analysis shows that, in response to sound, the tympana vibrate asymmetrically but with deflection modes clearly different from those observed in tachinids. The tympanal complex does not oscillate about a fixed central fulcrum, but sways about one of its relatively immobile ends. Interaural coupling is proposed to be caused by he anisotropic tympanal structure. This data suggests the presence of an alternative mechanism for directional hearing in this fly. [Work supported by NIH, NSF, and the Swiss Science Foundation.]