Investigating hearing in sturgeon: Getting closer to the origin of hearing in vertebrates

Abstract

It has been hypothesized that hearing arose early in vertebrate evolution to use sound to glean information about the environment, including the presence of predators and prey. The importance of sound to sense the acoustic scene is especially true underwater where the visual horizon is limited. To create an acoustic scene from sound, an animal needs to localize and identify sound sources. We hypothesize that the sound localization capabilities of primitive bony fishes such as sturgeon are as capable as those of modern bony fishes such as goldfish and, perhaps, many terrestrial vertebrates. We present results from experiments investigating the neural mechanisms of directional hearing and frequency analysis in the auditory periphery of the sturgeon. Extracellular single units were recorded from the eighth nerve during stimulation with a three‐axis shaker system that subjects the fish ear to linear accelerations in known directions at various frequencies. This system enables the characterization of both spatial and frequency tuning of the afferents innervating the ear. The results show that similar neural mechanisms for encoding sound direction and frequency exist in the periphery of modern and primitive bony fish, thereby supporting the hypothesis that basic auditory functions arose very early in vertebrate history.