1Department of Orthopaedic Surgery, University of California, San Francisco, 2Department of Anthropology, The George Washington University, 3Department of Anthropology, University College London
Friday 4:30-4:45, Galleria South
Modularity and integration are key mechanisms bridging development and evolution and are fundamental to understanding evolvability. Using the mouse model system, we investigate modularity and integration of the craniofacial skeleton with the aim of understanding its morphological evolution. We are particularly interested in mechanisms regulating jaw length and robusticity, especially as they relate to robust vs. gracile hominin phenotypes. Here we use our investigations of Satb2- and Fgf8-regulated craniofacial development as examples of how modules may be established and integrated during craniofacial development to propose a model for modular evolution. We use a comparative evolutionary developmental approach to show that Satb2 regulates a distal module of the jaw through its coordinated expression in the symmetric, complementary domains of the mesenchyme of the developing upper and lower jaws. We show that the mandibular Satb2+ domain varies in relation to epithelial Fgf8 expression, suggesting that modulation of Fgf8 could provide a mechanism for evolutionary change in this domain. Additionally, we have found that Fgf8 dosage affects mandibular length and robusticity. Based on these and other data from similar studies in Vertebrates, we identify patterns of character co-variation that might lead to robust hominin phenotypes and test these hypotheses using data collected from murine and primate crania. Our results suggest that Fgf8 acts as an integrator of mandibular morphology, interacting with other signaling factors to establish nested, hierarchical modules of the developing jaw. Evolutionary alterations in Fgf8 signaling may therefore have contributed to morphological diversification in the hominin craniofacial skeleton.