Matched filters in insect audition: Tuning curves and beyond

Abstract

The sense of hearing evolved in insects many times independently, and different groups use sound for intraspecific communication, predator detection, and host finding. Although it can be generally assumed that ears and associated auditory pathways are matched to the relevant properties of acoustic signals and cues, the behavioral contexts, environmental conditions, and selection pressures for hearing may differ strongly between insects. Given the diversity in ear structure, active range of hearing, and the behavioral and ecological context under which hearing evolved, it is probably not surprising to find cases of sensory systems apparently mismatched to relevant parameters of the physical world. Indeed, such cases may be equally instructive for the principle of matching as the perfectly matched ones, since they may tell us something about the conflicting selection pressures and trade-offs associated with a given solution. The examples I have chosen cover the most traditional aspect of matching in the acoustic domain, namely, how the carrier frequency of the relevant sound is matched to the tuning of receivers and how central nervous processing allows species-specific responses to the temporal parameters of song. However, economical filtering also occurs in the intensity domain, starting as early as in the receptors and continuing at the first synapse of central processing. All examples serve to illustrate the similarities and differences between the sensory systems; both may help to define the conditions under which matching operates and may have evolved.