Meeting Abstract
72.2 Tuesday, Jan. 6 Constructing a complex morphological novelty: Insights from growth, development, and genetics of the cypriniform Weberian apparatus BIRD, Nathan C.*; HERNANDEZ, L. Patricia; George Washington University; George Washington University nbird@gwmail.gwu.edu
Vertebrate morphologists have long examined hearing capabilities in fishes, with particular emphasis on so-called hearing specialists. However, less emphasis has been placed on investigating the morphogenetic mechanisms involved in the origin of these specialized morphologies. We present a broad review of the mechanisms responsible for development of the Weberian apparatus, a hearing specialization unique to otophysan fishes, which include minnows, loaches, catfishes, characins, and electric fishes. While thoracic vertebrae in unmodified species serve as protective elements and sources of muscle attachment, otophysan anterior thoracic vertebrae have morphologies uniquely adapted for hearing. Given that otophysan fishes utilize vertebral elements to conduct sound pressure rather than moving the swimbladder into closer proximity to the ear, significant selection must have existed to break the constraints of typical thoracic vertebrae. Such forces may have led to changes in growth rates and gene expression within the context of changing environmental influences. We take advantage of some of the molecular tools used by developmental biologists to describe the early development and growth of the vertebral elements of this novelty in the zebrafish, a cyprinid, with a specific focus on genes involved in early skeletal development. Growth rates are examined to determine broad-scale allometric changes within the thoracic vertebrae. These data are then used to shed light on the morphological variation seen within cypriniform fishes as a proxy for the variation seen within Otophysi. Identifying the developmental mechanisms responsible for the origin of this hearing adaptation will enhance our understanding of how such functional novelties form and evolve.
