Meeting Abstract

65.3  Wednesday, Jan. 6  Have teleost barbels evolved by the co-option of fin developmental mechanisms? HAWKINS, M.B.*; CRUZ, A.; STOCK, D.W.; University of Colorado, Boulder; University of Colorado, Boulder; University of Colorado, Boulder michael.hawkins@colorado.edu

Understanding how complex structures can emerge repeatedly in distantly-related lineages is an important goal of evolutionary biology. A striking example of such convergent evolution is provided by the barbels of fishes. Barbels are taste bud-covered sensory organs that project from the snout of numerous disparate lineages of fishes, ranging from nurse sharks to minnows. Co-option of pre-existing developmental genetic mechanisms is one possible explanation for the apparent ease of barbel origin, and paired appendage development provides candidate mechanisms. Like paired appendages, barbels are outgrowths from the body that are supported by skeletal elements and, in some cases, associated musculature. In addition, the barbels of some species display anterior-posterior polarization, as is seen in paired appendages. We tested this co-option hypothesis by analyzing the expression and function of paired appendage-associated genes during barbel development in the channel catfish (Ictalurus punctatus). As in limb and fin buds, the developing barbels express shh in a polarized pattern across the anterior-posterior axis, and further similarities were found in the expression of Bmp, Dlx, and Fgf family members. Treatment with chemical inhibitors of hedgehog signaling or with retinoic acid reduced barbel outgrowth, an effect similar to that reported for limbs and fins. In contrast, dach, a transcription factor involved in patterning the proximal-distal axis of limbs and fins, is absent from developing barbels. We conclude that barbel development is regulated by similar, but not identical, mechanisms to that of paired appendages.