Meeting Abstract
In teleost fishes, the most posterior branchial arches form a highly modified feeding apparatus known as the pharyngeal jaws. The 3rd and 4th pharyngobranchials form the upper pharyngeal jaw while the 5th ceratobranchial forms the lower pharyngeal jaw. Cypriniformes in particular have undergone further modifications to their feeding morphology, including extreme hypertrophy of the lower pharyngeal jaw and loss of the upper pharyngeal jaws. While in more basal telosts the ceratobranchials decrease in size anterior to posterior, the cypriniform fifth ceratobranchial is often significantly larger than the preceding ceratobranchials. How this hypertrophied fifth ceratobranchial develops throughout ontogeny in comparison to ceratobranchials 1-4 has not been carefully studied. To investigate the possible developmental mechanisms behind this modified morphology, we compared the ontogeny of a cypriniform pharyngeal jaw (Danio rerio) with the ontogeny of the pharyngeal jaws of more basal related species (Anchoa mitchilli and Brevoortia tyrannus). Here we present comparative data from morphometric analyses of the ceratobranchial arches in larval to adult specimens of D. rerio, A. mitchilli, and B. tyrannus. We find that multiple heterochronic events, including sequence and rate of chondrogenesis, sequence and rate of ossification, and overall growth of the ceratobranchials, may contribute to the greatly hypertrophied fifth ceratobranchial. These data provide a glimpse at a few potential ontogenetic pathways to morphological innovations.
