Distortion rules: audibility creation in the mosquito ear

Hearing begins when ears convert sound into neuronal excitation. The hearing organs of male Anopheles mosquitoes rank amongst the most sensitive ears evolved. Males use them to detect faint female flight tones within noisy mating swarms, but female flight tones largely lie above the male's hearing range. We report a mechanism by which inaudible higher-frequency primary tones become audible through intrinsically generated, lower-frequency distortion tones. Distortion-evoked responses show ~10-times greater sensitivity and 45% higher temporal precision than those of same-frequency primary tones. Moreover, self-sustained oscillations of the male's ear dramatically reshape auditory frequency tuning and neuronal recruitment. By one mechanism, mosquito ears thus create audible signals and isolate these from the most salient frequencies of background noise. In audiology, distortions are used for diagnostics; their biological relevance, however, is unknown. Our results suggest that distortions are not mere by-products of the auditory process, but integral to its signaling logic.