Neuroethology of Acoustic Communication

Insects were among the first terrestrial animals that began to use acoustic signals for communication between conspecifics. Nowadays insects, which rely on acoustic cues in looking for a mate, must have highly specialized sensory systems capable of extracting the conspecific signal from the acoustic environment and for detecting predators. The latter task has become very important for sound producing insects because they demask themselves by their own sound emissions. This chapter concentrates on Orthopterans (gryllids, tettigonioids and acridids) in an attempt to illustrate the basic principles of nervous mechanisms underlying acoustic behavior. Orthopterans are chosen for this neuroethological approach, because their acoustic behavior, the neural mechanisms of sound production and sound reception, their development, genetics and evolution are better known than in all other insects. The long-range goal of the neuroethological approach discussed in this chapter is to understand the functions and interactions of nerve cells, receptors, and effector organs during the performance of acoustic behavior. The connections between neurophysiology and classical ethology have been strengthened in many promising ways. Electromyographic recordings in freely moving animals have provided a detailed description of stridulatory patterns in terms of neurophysiological events at the level of individual motor units. Certainly, the CNS is able to produce the specific patterns of stridulation even after deafferentation, but often only for a limited time. A population of individually tuned neurons performs auditory information processing on the level of thoracic and known brain neuropiles. Each neuron is characterized by definite preferential areas in the intensity-frequency field, certain directional sensitivity and time resolution. It seems probable that the neuronal circuits, which are independent of the recognition networks, perform the sound localization and the measurement of loudness