BIRD, NC*; HERNANDEZ, LC; George Washington University; George Washington University: Origin of complex structures: Zebrafish as the new model organism for investigating morphological innovation

For the last decade the zebrafish has played an increasingly important role in biomedical research. Such research, exploiting conserved developmental processes among vertebrates in order to better extrapolate to humans, has by necessity concentrated on embryonic and early larval development. We are interested in morphological evolution, thus are more interested in later developmental events leading to the elaboration of those features that set zebrafish apart from related species. We propose that the zebrafish, long considered the lab rat of the piscine world, is exceptionally well suited as a model organism for investigating the developmental mechanisms underlying morphological novelty. Specifically, we are interested in the generation of morphological novelty in the vertebral column of fishes. The zebrafish, like other otophysan fishes, is characterized by the presence of the Weberian apparatus, a unique adaptation of the first four vertebrae that, when paired with adaptations in the swim bladder and the ear, confer increased hearing abilities to these fishes. These vertebral adaptations include significant morphological changes to neural arches, ribs, and parapophyses leading to increased regional complexity and specialization, something generally associated only with higher vertebrates. Immunohistochemistry, using a number of important markers, has allowed us to characterize differences between the developmental cascades leading to typical fish vertebrae found posteriorly, as compared with the greatly modified anterior vertebrae. Moreover, by examining expression patterns of genes both upstream and downstream of chondrogenic and osteogenic pathways, we have gained a better understanding of when during development morphological innovations become apparent.