Insect hearing: from physics to ecology.

Abstract

broad range of anatomical variation in both types of hearing organs. As Regen’s experiment with field crickets already indicates, hearing research has strongly benefited from the fact that many species of insects respond so reliably to acoustic playbacks, and that they do so under very different experimental paradigms, from open-loop laboratory conditions on a trackball to the disturbed and noisy conditions in the field. Moreover, with the advent of neurophysiological techniques hearing and sound communication in insects has become one of the classical areas in neuroethology, aiming to understand the proximate mechanisms of behavior in signalers and receivers (Huber et al. 1989; Gerhardt and Huber 2002; Greenfield 2002; Hedwig 2013). Finally, the refinement of methods such as scanning Laser Doppler Vibrometry for measuring sound-induced vibrations down to the nanometer range has greatly improved our understanding of the biophysics of hearing in recent years. This issue of JCP-A presents a synopsis of what is currently known about insect hearing. Its title, Insect hearing: from physics to ecology, reflects its broad thematic scope. We have to keep in mind that natural selection may act on virtually all aspects of hearing, from molecules associated with the transduction and amplification process in receptor cells, to sound guides that provide directionality in the small insect receivers, or to the complex behavior in large choruses of singing insects. The contributions to this issue are guided by four basic themes: (1) ears and receptor mechanisms, (2) pattern recognition and directional hearing, (3) ecology of sound communication, and (4) evolution. Since the first recordings from locust auditory receptor neurons it was established that locusts’ ears are, in principle, able to discriminate different frequencies. However, the biophysical and or physiological basis of this capacity Almost exactly 100 years ago, Johann Regen performed an ingenious simple experiment where he arranged a male cricket calling in one room and transmitted its song via telephone to another room. There a female could be attracted to the earpiece of a second telephone (Regen 1913). Given the poor frequency characteristics of the early (and contemporary) telephones, one could already speculate about the nature of (temporal) cues that guided the female s phonotactic approach. In the meantime a tremendous progress has been made regarding our understanding of insect hearing (Gerhardt and Huber 2002; Hedwig 2013). This is partly due to the bewildering variety of insect ears having evolved independently many times, and virtually anywhere on the insect body such as on the tibia, abdomen, thorax, wing, mouthparts or the base of the neck (reviews: Hoy and Robert 1996; Yack 2004; Straus and Stumpner 2015). Insect hearing organs exist as two basic forms: (1) either as tympanal ears with a thin cuticular membrane, an air-filled cavity behind it and a chordotonal organ directly or indirectly coupled mechanically to the tympanum (Robert and Hoy 1998)—these ears respond to sound pressure changes; or (2) as nontympanal hearing organs which respond to the air particle velocity. These are represented by filiform hairs or antennae, such as those in mosquitoes or fruit flies. The collection of articles in this special issue of JCP-A covers a