Ontogenetic & reproductive state-dependent changes to the auditory inner ear and swim bladder of the plainfin midshipman fish (Porichthys notatus)

Abstract

Fish have become an important model for studying hair cell plasticity and development. Unlike mammals, the inner ears of fish continue to grow and add hair cells throughout their lifespan, and fish can regenerate hair cells after inner ear damage. The plainfin midshipman fish (Porichthys notatus) is a useful model for investigating auditory plasticity because, in addition to these more widely studied contexts of hair cell plasticity, the midshipman auditory system undergoes changes associated with the reproductive state. In chapter 1, I summarize the multiple contexts of hair cell plasticity in fish and the secondary adaptive functions of the gas-filled swim bladder as an auditory and vocal structure. I then discuss the specific questions explored in this dissertation regarding developmental and reproductive state-dependent changes to the auditory inner ear and swim bladder using the plainfin midshipman as a model. In chapter 2, I provide evidence for a reproductive state-dependent change in hair cell density and a possible cellular mechanism in vocal type I male midshipman. In chapter 3, I describe changes in sensory epithelium area, hair cell density, and total hair cell quantity in the auditory inner ear throughout ontogeny in plainfin midshipman fish. In chapter 4, I discuss a change in the morphology of the swim bladder and its proximity to the inner ear in type I males related to reproductive state, indicating a possible change in adaptive use as an auditory structure to a vocal organ. Lastly, in chapter 5, I discuss the implications of the findings in this dissertation and future directions for studying auditory-related questions in the plainfin midshipman fish.