Meeting Abstract
The Weberian apparatus is a synapomorphy for the diverse (>7,900 spp.) clade of otophysan fishes. This feature involves a chain of three bilateral vertebral elements (Weberian ossicles) that transduce sound pressure oscillations of the swim bladder to fluid motion in the saccule of the ear. The Weberian apparatus and inner ear modifications confer acute hearing and a wider auditory bandwidth that are hypothesized to have facilitated radiation of otophysans. Acute hearing may be an adaption of otophysans used to assess the acoustic environment and locate food, however, this hypothesis remains speculative. Neotropical Serrasalmidae (piranhas, pacus, tambaqui, pirapatinga, silver dollars) include species that feed on falling fruits and seeds, consume small fish, eat scales and fins, and rheophilic species that feed on macrophytes in noisy rapids. We used μCT scans to examine the Weberian ossicles, vertebrae 1-4, neurocranium, otoliths, and swim bladders of 50 specimens from 19 species of serrasalmids. Initial results indicate allometry between volumes of Weberian ossicles and otoliths and body length. On average, rheophilic species displayed the smallest relative Weberian ossicle and otolith sizes and least size variation of the tripus, scaphium, and lagenar and utricular otoliths. Species that feed on whole fish, fins, or scales showed the largest relative tripus and scaphium sizes and were most variable in Weberian ossicle and otolith sizes. Fruit and seed eating species showed the largest intercalarium and otolith sizes. Observed differences are predicted to impact hearing sensitivities and be associated with noise environments and targeted prey sounds. Shape and phylogenetic comparative analyses will be used to examine relationships further.
