Meeting Abstract

94.5  Sunday, Jan. 6  The evolution of fish barbels by the co-option of fin developmental mechanisms HAWKINS, M.B.*; JANDZIK, D.; CRUZ, A.; STOCK, D.W.; Harvard University, Cambridge, MA; University of Colorado, Boulder michaelbrenthawkins@fas.harvard.edu

Barbels are sensory projections from the head that are found in 27 of the 62 orders of fishes, ranging from hagfishes to goatfishes. The phylogenetic distribution of barbels and substantial differences in their structure among groups suggest that they have arisen independently numerous times. The repeated evolution of complex structures may be facilitated by the co-option of existing developmental mechanisms. We tested this hypothesis for barbel origins by examination of gene expression and function during barbel development in the Channel Catfish, Ictalurus punctatus. We found that the maxillary barbels of this species likely deploy two developmental genetic mechanisms that are also used to pattern paired fins: an Fgf/Hh positive feedback loop driving outgrowth, and the Hh-regulated expression of posterior group HoxD genes controlling morphological asymmetry along the anterior-posterior axis. We also compared the development of maxillary barbels to that of the other barbel pairs present in the Channel Catfish, the chin and nasal barbels, which arose in catfish (siluriform) evolution after the appearance of maxillary barbels. While evidence for similar outgrowth and anterior-posterior patterning mechanisms was observed in all barbel pairs, the different pairs are divergent in the expression of Fgf, Dlx, and Hox gene family members. We propose that barbels first arose in catfishes by the co-option of paired fin developmental genetic mechanisms, with the resulting barbel program similarly deployed during the origin of the chin and nasal barbels. In addition to providing insight into the origins of barbels in catfishes, our findings identify candidate mechanisms for the independent origins of these structures in other vertebrate groups.