Utricular auditory sensitivity of the vocal plainfin midshipman, Porichthys notatus

Abstract

The detection of behaviorally relevant auditory signals is critical to the reproductive success of many vocal non-mammalian vertebrate species, including songbirds, amphibians, and fishes. Among vocal fishes, the plainfin midshipman (Porichthys notatus) has served as a robust model organism for investigating the behavioral, physiological, and neuroanatomical mechanisms underlying the detection, integration, and localization of behaviorally relevant social and reproductive-related vocal acoustic signals. Many of the previous studies investigating the auditory functions of the midshipman inner ear have focused on the saccule and lagena; however, little is known regarding the auditory sensitivity of the utricle. Here, using a well-characterized electrophysiological approach, I investigate the auditory sensitivity of the midshipman utricle. In chapter 2, I characterize the auditory sensitivity of utricular hair cells in nonreproductive male midshipman and show that the utricle exhibits auditory sensitivity similar to the saccule in response to a broad range of behaviorally relevant auditory stimuli. Next, in chapter 3, I show, using surgical manipulations, that the swim bladder of female plainfin midshipman functions to transduce acoustic sound pressure to the utricle, thus effectively enhancing auditory and frequency sensitivity. Finally, in chapter 4, I ask if seasonal variation in reproductive state modulates the auditory sensitivity of the utricle in female plainfin midshipman. We show that the utricle serves an auditory function that is seasonally plastic and highly adapted in reproductive females to detect the dominant frequencies of conspecific vocalizations. Taken together, the results of these experiments show that the utricle of the plainfin midshipman exhibits robust auditory capabilities, which likely aid in the detection of social and reproductive-related communication. A brief summary, larger implications of the data presented, and future directions are discussed in chapter 5.