The Morphology and Evolution of the Ear in Actinopterygian Fishes

SYNOPSIS. In this paper we consider various aspects of the anatomy and ultrastructure of the actinopterygian ear and make a number of suggestions on the possible adaptive significance of the structural specializations. The focus of the arguments is based upon the substantial inter-specific variation in teleost auditory systems as measured anatomically, behaviorally, and physiologically. It is potentially of considerable significance that the major points of inter-specific variation in the teleost ear are associated with the gross morphology and ultrastructure of the otolithic organ most often implicated in sound detection, the sacculus. Analysis of patterns of sacculus ultrastructure has led to the conclusion that there are, in effect, only about five different saccular ultrastructural patterns but that these patterns are broadly found throughout the teleost fishes. Based upon patterns of inter-specific variation in the sacculus and in other aspects of the ear and more peripheral auditory structures ( e.g. , swimbladder), it is argued that adaptations encountered in the teleost auditory system cannot be used as reliable taxonomic indicators among fishes. Rather, it is proposed that the teleost auditory system is quite maleable in the evolutionary sense, and that interspecific similarities in many features of the auditory system reflect convergent evoluuon, rather than phylogenetic affinities. The actual selective pressures operating in the evoluuon of the fish auditory system are still essentially unknown. In addition, we cannot be certain that similar ear patterns in different species reflect convergent evolution (or common ancestry), or that conversely, different ear patterns among species reflect differences in auditory function.