NSF Award
0522112
Almost all of our physical and behavioral traits have changed since the human lineage separated from that of the chimpanzees. Among the most important changes and those best reflected in the fossil record involved the shape of the head, related to language, diet, defense, threat, olfaction, intelligence, vision, and posture. These include shortening the face and tucking it under the braincase, smaller teeth (especially canines), increased brain size, and reorientation of the cranial base. Our knowledge of the evolution of these traits will remain limited until we understand their underlying biological, and in particular, genetic bases. <br/>The purpose of this pilot project is to identify genetic factors underlying the nature and timing of changes in skull shape during the evolution of humans, apes, and Old World monkeys. A combined strategy will: (1) identify the dimensions of natural craniofacial development, variation and evolution from living and fossil primate skulls, (2) identify genes that in baboons and mice are associated with variation in those dimensions, and (3) experimentally confirm that these genes are appropriately expressed during craniofacial developmental networks that may be responsible for evolution of craniofacial shape within and between species. <br/>3D reconstructions of a set of computed X-ray tomography (CT) scans acquired from a set of fossil African papionin skulls will be analyzed quantitatively to identify single and multivariate axes of craniofacial variation. These results will be coupled with observations from the literature to identify features of craniofacial variation that were important in the evolution of these animals. Similar CT scans will be obtained from approximately 250 baboon skulls in a large, known genealogy at the Southwest Foundation for Biomedical Research (SFBR), that have been genotyped for about 350 microsatellite markers across the genome. Linkage mapping will be done to identify chromosomal regions in the baboons that affect these axes of variation. Mice and primates share the basic processes of skeletal development, so the mouse is a phenotypic and genetic model for identifying these processes, and two gene mapping approaches will be taken to do that. Chromosomal regions identified by mapping in the mouse and baboon will be tested experimentally by examining gene expression and DNA sequence changes in coding or regulatory regions that affect the axes of craniofacial change that were identified from the CT scans. <br/> This is an integrated developmental evolutionary approach to understand the genetic elements of craniofacial variation. Current phylogenetic approaches use craniofacial features in the absence of knowledge of their genetic basis. One consequence is that we cannot discriminate between change due to common genetic determination and adaptive convergence and this has led to inconsistencies between molecular and morphologically based phylogenies. The identification of developmental genetic pathways will provide tests of the homology of such traits. <br/> Intellectual Merit -- The general problems and approaches to the developmental genetics of complex metric traits are of widespread interest to biologists of all types because similar problems and processes are widespread in nature.<br/> Broader Impact -- The researchers will create a major archive of 3D CT images of baboon skulls, genetic materials, and quantitative methods, and make them available to other investigators. This project involves several institutions here and abroad, and will include undergraduate, graduate, and post-doctoral students. Post docs working in the various laboratories will travel to the Southwest Foundation to train in methods of analysis. Women and minority students are regularly trained in these labs and minority students will be actively recruited.
