Bioacoustics of loricariid catfishes
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. I am 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 I am interested in understanding the behavioral context of these sounds. My goal is to understand the acoustical significance (in terms of hearing and/or sound production) and evolution of these unique structures.
Amanda Webb, a previous honors student and graduate student, characterized pectoral spine stridulation sounds made by two species of loricariid catfishes, Pterygoplichthys gibbiceps and Macrotocinclus affinis. Then she used scanning electron microscopy to measure the ridges along the dorsal process of the pectoral spines and found a strong inverse relationship between inter-ridge distance and frequency of sound production. Patrick Stewart, also a previous honors student, examined the role of the bi-lobed swim bladder in sound localization of the loricariid catfish Macrotocinclus affinis. He trained these small catfishes, using operant conditioning, to come to an underwater speaker emitting conspecific click sounds. Using a circular array of multiple underwater speakers in a round tank, he found that these catfishes almost always localized to the correct speaker, but failed to localized once the gas was removed from their swim bladders.