ALBERTSON, R. Craig*; STREELMAN, J. Todd; KOCHER, Thomas D.; YELICK, Pamela C.; Forsyth Institute; Georgia Institute of Technology; Univ. of New Hampshire; Forsyth Institute: Integration and Evolution of the Teleost Mandible: The Molecular Basis of Alternate Feeding Strategies

The cichlid jaw is an icon of Darwinian evolution by natural selection. Highly specialized modes of feeding have evolved rapidly and repeatedly in various lineages resulting in impressive trophic diversity. The opening and closing lever mechanisms of the lower jaw have traditionally been used to describe the mechanics of feeding behavior in bony fishes. Here we explore the molecular basis of this biomechanical system. Quantitative genetic analyses demonstrate that the opening and closing mechanism of the cichlid jaw are genetically modular and therefore free to evolve independently. Bmp4 is one of two loci that segregate with the mechanical advantage of closing, and account for over 30% of the phenotypic variance of this trait. Species-specific differences in jaw shape are obvious early in cichlid larval development and are correlated with alternate patterns of bmp4 expression in the mandibular primordium. When bmp4 is over expressed in the obligate suction feeder, Danio rerio, mechanical advantage increases, and mandibular morphology adopts a surprisingly specific biting design. This work demonstrates the potential of integrating studies in natural populations and model organisms to address questions relating to evolution and development. We conclude that patterns of morphological integration of the cichlid jaw reflect a balance struck among conflicting functional demands. Further, we demonstrate that bmp4 has the potential to alter mandibular morphology in a way that mimics adaptive variation among fish species.