Ontogeny of hearing in the plainfin midshipman, <italic>Porichthys notatus</italic>

Abstract

The plainfin midshipman, <italic>Porichthys notatus</italic>, has become a model for vocal communication and auditory reception because acoustic communication plays an important role in spawning behavior in this fish species. The auditory system of the teleost fish,<italic> P. notatus</italic>, is an important sensory receiver system used to encode intraspecific social communication signals in adults, but the response properties and function of this receiver system in pre-adult stages are less known. I describe what is known about the ontogeny of auditory sensitivity in juvenile and larval stages as well as other important background information in chapter one. In chapter two, I examine the response properties of auditory evoked potentials from the midshipman saccule, the main organ of hearing in this species, to determine whether the frequency response and auditory threshold of saccular hair cells to behaviorally relevant single tone stimuli change during ontogeny. I address the question of auditory sensitivity during larval development in chapter three and discuss when in the larval stage audition begins using the innate acoustically evoked behavioral response (AEBR) as a hearing assay. Specifically, I demonstrate that auditory reception develops early in larval development and that auditory sensitivity is similar throughout all larval stages. Additionally, during ontogeny, the saccule undergoes profound growth. I examine the saccular epithelia of larval, juvenile, and adult plainfin midshipman in order to describe the morphological changes that occur in saccular ultrastructure during development. These results are described in greater detail in chapter four. The results from chapters two through four are summarized and placed into broader contexts and I suggest future studies in chapter five.