| dc.description.abstract | In recent decades, neuroscience research has become largely dependent on a few “model organisms” (e.g. Drosophila melanogaster, Mus musculus). A holistic understanding of nervous systems requires study of a diversity of species and should consider the ecological context under which behaviors and their neural underpinnings evolved. My dissertation used a multidisciplinary and comparative phylogenetic approach to study signaling and sensory traits in a clade of weakly electric fishes, providing a more robust foundation for a burgeoning model in neuroscience. Gymnotiformes is a speciose and ecologically diverse order of Neotropical fish. These mostly nocturnal fishes generate electric organ discharges (EODs) to communicate with other electric fishes and to navigate and detect objects in dark waters. Previous studies in three species showed that melanocortin hormones can regulate the ion channels in the electrogenic cells (electrocytes) and modify EOD waveform properties such as amplitude and duration.
In the first study, I describe variation in electric signaling behavior in response to adrenocorticotropic hormone (ACTH) in 21 species. Responses to ACTH varied greatly, suggesting there are species-specific differences in how melanocortins regulate electric signaling. Only species from the Hypopomidae and Sternopygidae consistently showed increases in EOD amplitude; however, individuals from species in all five families showed some form of waveform modulation. The second study examined the effects of ACTH at the level of electrocyte membranes, compared ion channel distributions in two representative species, and described the kinetics of a sodium channel in a unique monophasic species, Brachyhypopomus bennetti. B. bennetti showed significantly less EOD plasticity relative to biphasic congeners. Sodium channels in this species were unexpectedly detected on both electrocyte membranes, and I determined that a second action potential reduces the EOD amplitude. The final study describes variation in the dimensions and distributions of electroreceptor pores on the heads of seven species. In some species, I found unique electroreceptor distributions associated with specialized feeding strategies, suggesting species habitat use influences electroreceptor organization. Together, these studies highlight the value of gymnotiforms as excellent models for studying the pleiotropic functions of melanocortin hormones, ion channel evolution, and the role of ecology in shaping specialized sensory systems. | en |
