Date of Award

Spring 1-1-2011

Document Type

Thesis

Degree Name

Master of Arts (MA)

Department

Ecology & Evolutionary Biology

First Advisor

David W. Stock

Second Advisor

Alexander Cruz

Third Advisor

Daniel M. Medeiros

Abstract

Understanding the origin of morphological novelties is an important goal of evolutionary developmental biology. In pursuit of this goal, we have examined the developmental genetic mechanisms that underlie growth and patterning in a largely overlooked group of morphological novelties: the barbels of fishes. Barbels are appendages that project from the head region in a large and disparate assortment of fish taxa, ranging from hagfishes to gobies. They often bear sensory organs and can be supported by a rod of connective tissue, muscle, cartilage, or bone. Considering the scattered distribution of barbels among fishes, along with the variability of barbel position and composition, it is likely that barbels have originated independently in multiple groups. We investigated the roles of genes known to be involved in the development of other appendages in the developing barbels of the channel catfish, Ictalurus punctatus (Siluriformes: Ictaluridae). Similar to other appendages, the barbels of I. punctatus express members of the Bone morphogenetic protein (Bmp), Distal-less (Dlx), Fibroblast growth factor (Fgf), Hedgehog (Hh), Tumor necrosis factor (Tnf), and Tnf receptor families. Other genes with roles in appendage development were absent from barbels, however, including members of the Dachshund (Dach) and Hox families. Treatment with pharmacological inhibitors of Hh signaling revealed that this pathway is necessary for barbel outgrowth. I conclude that while the barbels of catfishes arose via deployment of a general vertebrate outgrowth mechanism (an Fgf/Hh feedback loop), additional features of the gene regulatory network underlying their development overlap, but are distinct from, those of other appendages.

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