Meeting Abstract
The Weberian apparatus is a novel hearing adaptation found in otophysan fishes, a large group of freshwater fishes comprised of approximately 8000 species. Cypriniform fishes, the largest otophysan order, are abundant in the freshwaters of Asia, Europe, North America, and Africa. Such environmental variability has led to modification of skeletal structures in non-auditory portions of the apparatus (lesser so in the auditory elements), likely due to heavy constraint for the maintenance of functionality (Bird and Hernandez 2007). Within Cypriniformes, four distinct morphologies have been identified: Open (typical of Cyprinidae), Anterior Shield (typical of Gyrinocheilidae, Catostomidae, and Botiidae), Single-Capsule (typical of Cobitidae), and Double-Capsule (typical of Nemacheilidae and Balitoridae). Little information exists detailing the construction and integration of these morphologies at the tissue level. We used HBQ quad-stained paraffin histology and whole-mount clearing and staining to document and analyze the hard and soft tissue of the Weberian apparatus in species representing six genera (Danio, Gyrinocheilus, Ambastia, Pangio, Schistura, and Sewellia) that characterize all morphologies. We found minimal changes to the Weberian ossicles, swim bladder, and otic sensory structures across morphologies (typically relative changes in size, not shape). Several differences in the non-auditory structures were found among the species of the same morphotype, such as size and shape of lateral openings in the swim bladder capsule, and communication zones between right and left capsules. These results reveal unrecognized variability in the integration of the Weberian apparatus across different morphotypes.
