Meeting Abstract

P3.71  Wednesday, Jan. 6  Origin and development of the hypertrophied cypriniform pharyngeal jaws SOU, E*; HERNANDEZ, LP; George Washington University; George Washington University emilys525@gmail.com

Significant hypertrophy of the pharyngeal jaws characterizes most cypriniforms. Here we use both a phylogenetic approach, as well as an ontogenetic analysis of growth to examine the origin and evolution of the hypertrophied ceratobranchials. A phylogenetic survey of basal teleosts and Ostariophysans to determine the relative size of ceratobranchials early in teleostean evolution has never been undertaken. Our findings suggest that it is only at the base of Cypriniformes that we see a greatly hypertrophied ceratobranchial 5. Indeed in several more basal clades, including Gonorhynchiforms (sister to Cypriniformes) and Clupeomorpha, the fifth ceratobranchial is markedly smaller than more anterior ceratobranchials. Interestingly other otophysan groups are also characterized by a smaller ceratobranchial 5. We also measured ceratobranchials of other teleostean groups to assess the number of times such hypertrophied pharyngeal jaws have evolved from a basal condition characterized by smaller 5th ceratobranchials. To better understand the developmental mechanisms via which such changes in ultimate size may have occurred we used zebrafish to examine increase in length and surface area of ceratobranchials from their first origin as cartilaginous elements at early larval stages until adulthood when all elements had undergone ossification. Growth rate of all ceratobranchials changed significantly during larval development, with a marked increase in growth rate corresponding to the onset of mineralization. Timing of initial differentiation as cartilaginous elements, earlier mineralization, and increased growth rate (especially of surface area) all appear to be involved in the generation of zebrafish hypertrophied jaws.