Hearing

Jayne Yack

Carleton University

Ron Hoy

Cornell University

Among all terrestrial animals, only vertebrates and insects are richly endowed with a sense of hearing. By "hearing," we usually mean the ability to detect minute, time-varying changes in air pressure that we familiarly experience as "sound." Under this restricted definition, we can say that audition has evolved in at least seven orders of insects, including all of the major orders except the Hymenoptera (wasps, ants, bees). However, if we were to include under "hearing" the ability to detect sound waves in water and solids, or the displacement of molecules in a sound's near field, then the number of "auditive" insects would expand enormously to include not only the Hymenoptera, but even small orders such as Plecoptera (stone flies) and Isoptera (termites). Initially, we focus on the form and function of tympanal ears, which are organs that are sensitive to sound signals that are propagated through the air or water as fluctuations in pressure and which come to mind when we (humans) use the term "hearing with ears." Following this, we provide some examples of nontympanal hearing organs.

Using sound, vertebrates and insects are often capable of sensing, identifying, and locating their predators, prey, conspecific rivals, and mates by hearing their intentional or unintentional acoustic signals. As might be expected, natural selection has shaped the form and function of hearing organs ("ears") in insects over evolutionary time. In this respect, the ears of insects show much greater diversity than those of vertebrates, for reasons that will be apparent in our discussion. However, it must be emphasized that despite the scope of morphological diversity among insect ears, there is a morphological "bauplan" (structural design) that underlies their great range in behavioral and physiological function.

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