BIRD, NC; HERNANDEZ, LP; George Washington University; George Washington University: Development of the Weberian apparatus

The Weberian apparatus is a novel structure providing a direct route of sound and pressure transmission from the swimbladder to the inner ear via drastic morphological modifications to the anterior four vertebrae. Such modifications include changes in the shape of ribs, parapophyses and neural arches. Much of the research into this structure has focused on either functional data, due to marked increase in hearing capabilities, or historical aspects, as this structure yields a considerable amount of phylogenetic information. However, only a small, yet growing literature can be found regarding its morphological development and no published work has examined the molecular mechanisms involved in its formation. We present preliminary data from an ongoing large-scale project focusing on the evolution, ontogeny and developmental genetics of the Weberian apparatus. Using immunohistochemistry on sectioned and whole-mount specimens, we are investigating the underlying hierarchy of genetic regulation in the development of the Weberian apparatus. Particular attention is given to genes important in bone and cartilage pathways, such as collagens, BMPs, FGFs, as well a number of key hox genes thought to play an important role in proper anterior-posterior specification within this complex structure. Changes in gene expression within anterior vertebral elements that compose the Weberian apparatus as compared to other more typical vertebrae will be highlighted. In addition, fate-mapping techniques are being used to help clarify homologies of particular structures which currently have unresolved relationships to structures in other groups, such as the claustrum. This preliminary research will add critical data toward understanding the developmental mechanisms which create morphological novelty.