Smith Lab Research Projects
The primary research interest of the Smith Lab is the sensory biology of fish hearing. Projects in the lab examine the teleost auditory system in biomedical, environmental, and ecological/evolutionary contexts.
The auditory sensory cells of fishes are called hair cells. These cells are similar in form and function to mammalian hair cells, but while mammalian hair cells that are damaged as a result of loud sounds or ototoxic chemicals are not replaced, deafened fish have the capability to regenerate hair cells and recover their hearing. We are studying the process of hair cell death and regeneration following acoustic trauma in goldfish and zebrafish. Such baseline data is needed to begin to understand how hair cell regeneration occurs in fish and why such regeneration does not occur in mammals. Recently, hair cell developing has been shown to be regulated by specific genes (e.g., Atoh1, Rb1, and p27Kip1) in the mammalian auditory system and manipulating gene expression can result in hair cell regeneration. We are currently examining the natural expression of these genes (such as growth hormone) in zebrafish ears that are undergoing hair cell regeneration. For more information: Auditory hair cell regeneration.
High levels of sound are known to have significant effects on the auditory system and overall physiology of humans and other animals. Although there has been recent concern about the effects of anthropogenic sounds, such as those produced by Navy sonar or seismic surveys, on marine mammals, little is known about how such intense underwater sounds affect other marine life such as fishes. Some of my projects focus on how loud sounds damage the ears and hearing capabilities of fishes. We examine damage to the hair cells of fish ears using scanning electron microscopy (SEM) and fluorescent microscopy and the effect on fish hearing using electrophysiological methods (auditory evoked potentials). Loud continuous sounds can cause temporary hearing loss in fishes, with the extent of hearing loss increasing with noise exposure duration and intensity, and recovery of hearing occurring within a few days or weeks. The extent of hearing loss is also species specific- fishes with more sensitive hearing thresholds are more prone to hearing loss, whereas non-sensitive fish are barely affected. The latter was shown in a long term-study on the effects of aquaculture noise in rainbow trout. I have proposed a model termed the Linear Threshold Shift Hypothesis (LINTS) to predict the extent of noise-induced hearing loss in fishes, and this model should be beneficial in mitigating the effects of anthropogenic sound on fishes. Other effects of noise include acoustical masking and physiological and behavioral stress responses, which also depend on species and noise type. For more information: Effects of anthropogenic sound on fishes.
It is generally agreed that the sense of vertebrate hearing first evolved in fishes. Fishes are the most speciose of the vertebrates and exhibit a diverse range of form, function, and ecological niches. Thus they provide a wonderful opportunity to study the evolution of hearing. We are currently examining a family of catfishes (Loricariidae) that have a unique bi-lobed swim bladder and holes in their skull adjacent to their swim bladder. These catfishes also produce sounds by stridulating their pectoral fins and we are interested in understanding the behavioral context of these sounds. Our goal is to understand the acoustical significance (in terms of hearing and/or sound production) and evolution of these unique structures. For more information: Bioacoustics of loricariid catfishes.