A boost for hearing in mosquitoes

It is hard to imagine ears more different from a human's than a mosquito's. Look at a mosquito head-on, and you'll see a pair of large, wraparound eyes, and projecting from the front of its face is a pair of long, hairy antennae—its ears. Each antenna arises from a large, spheroidal base, the Johnston's organ (JO). Function follows form. Whereas human ears are pressure detectors, a mosquito's detects the particle velocity component of a sound field, which is restricted to the immediate vicinity of the sound source in acoustic near field. The mosquito's ears are insensitive to pressure fluctuations in the acoustic far field. The antenna, with its fine, interlacing network of flagellar hairs, senses movements of air particles as they are swept to and fro by impinging acoustic waves. The antennal movements excite the sensory receptors contained within the JOs to generate action potentials that flood into the insect's brain. The bottom line of functional hearing is acuity—maximize sensitivity and sharpen the tuning of each receptor cell. This tuning goes on at the level of cell and molecular biophysics—and when it comes down to fundamentals, functional similarities are often more apparent than differences, even in animals as diverse as humans and mosquitoes. As Jackson and Robert (1) cleverly demonstrate in this issue of PNAS, nonlinearities dominate the biomechanics of hearing that enhance acuity. Similar nonlinearities have been known in mammalian ears for several decades, where they also enhance acuity.

The functional imperatives of any hearing organ—of mice and men or mosquito—are to detect nanoscale movements of air particles at threshold and retain sensitivity over a millionfold dynamic range of intensity. We know a lot about the macroscopic workings of hearing from more than a half-century of inquiry into the workings of the mammalian ear, as we delve down from …

*E-mail: rrh3{at}cornell.edu