P3.20 Saturday, Jan. 5 Differential growth and the evolution of novel vertebral morphology: lessons from the cypriniform Weberian apparatus BIRD, NC*; HERNANDEZ, LP; George Washington University; George Washington University email@example.com
The Weberian apparatus, a complex assemblage of vertebral elements linking the inner ear to the swimbladder, significantly enhances hearing within Otophysi. We are interested in the genetic mechanisms responsible for the development and morphological diversification of these vertebral elements within the Weberian apparatus of cypriniform fishes. We have identified changes in growth of these elements as compared with the thoracic vertebrae from which these modified elements purportedly derive. We collected ontogenetic data for specific elements within the Weberian apparatus, including neural arches, ribs, and parapophyses. These data are compared to both serially homologous structures in posterior thoracic vertebrae (which act as internal controls), as well as to vertebral elements from the same axial levels in three non-Otophysan teleosts. Significant differences in growth rate were found among serially homologous structures at different vertebral levels. Global changes in growth rates (in which all structures derived from a specific somite were equally affected) were not found, suggesting precise targeting of morphological change to specific structures. Such patterns of growth help illuminate the specific heterochronic mechanisms required for the origin and subsequent morphological diversification of the Weberian apparatus, which is exemplified by the multitude of forms seen in the cypriniform Weberian apparatus. Understanding the patterns of growth within elements of the Weberian apparatus allows us to hypothesize specific developmental changes, likely constituting differences in gene expression, responsible for this morphological diversity. Such hypotheses are currently being tested through analysis of in situ hybridization of candidate genes.