Doctoral Dissertation Improvement: The Effect of Interspecific Hybridization on MHC Diversity in Wild Baboons

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In the 'arms race' against pathogens, having less common immune genes can be advantageous. Infectious agents may have evolved to evade the defenses of the more common varieties, making organisms with rare variants more likely to survive. In primates, like all vertebrates, many proteins essential to the immune system are encoded by the Major Histocompatibility Complex (MHC), which is involved in resistance to pathogens such as HIV and tuberculosis. The advantage of having rare forms has made the MHC gene complex one of the most diverse regions in the human genome. Recently, researchers found that at least one variant of the MHC entered the human gene pool when the ancestors of some modern humans interbred with an extinct hominin. The novel form's rarity may have facilitated the introduction and spread of the MHC variant through the population. To better understand the effects of hybridization on MHC, this research by doctoral student Christina Bergey (New York University), under the guidance of Dr. Todd Disotell, focuses on a natural experiment in which two species of baboons successfully interbreed in Ethiopia. Using the latest DNA sequencing techniques, MHC loci are genetically typed and thousands of neutral markers from individuals across the hybrid zone are utilized to test whether MHC alleles are able to transfer and spread widely throughout the parental population. The Ethiopian baboon hybrid zone offers an ideal opportunity to explore the influence of selection and hybridization on MHC diversity in an appropriate primate model. The study increases our understanding of hybridization, a phenomenon that has affected our lineage numerous times. It also provides evolutionary context to primate MHC variation, which has behavioral, immunological, and biomedical importance. DNA sequences are deposited in publicly available databases and all software is made freely available online and released under open source licenses. Since increasing public understanding of evolution is an essential goal of anthropological research, new forms of outreach to publicize the results also are employed in the conduct of the project.