Abstracts Anthropology

Genomic and Phenotypic Consequences of Hybridization in Wild Baboons

by Arielle Sarine Fogel

Hybridization, the process of interbreeding between distinct taxa, was once thought to be rare in animals. However, in the past two decades, new data have challenged this paradigm. Ancient and/or ongoing hybridization has now been documented in a wide variety of animals, including in our own lineage. A key puzzle that emerges from these observations is that despite the pervasiveness of hybridization, many species nevertheless remain distinct. My dissertation addresses this puzzle by integrating long-term field data on morphology, behavior, demography, and ecology with newly generated genomic data from a natural hybrid zone between yellow baboons (Papio cynocephalus) and anubis baboons (P. anubis) in Kenya. My work addresses three main themes: (i) the effects of ancestry on fitness-related traits in hybrid zones; (ii) the role of behavior in mediating gene flow between species; and (iii) the genomic signature of natural selection post-hybridization. I show that genetic ancestry predicts male-female social bonds, a predictor of lifespan in this population. Animals with more introgressed ancestry (i.e., genetic regions transferred via hybridization) are more likely to affiliate with the opposite sex, and pairs of animals with similar ancestry show an increased propensity for affiliation. These findings suggest that affiliative behavior may simultaneously promote and constrain baboon hybridization, through additive and assortative effects of ancestry, respectively. My research also rules out the possibility that fetal loss—a major cost to female fertility—acts as a strong isolating barrier. Fetal loss is independent of maternal genetic ancestry; instead, age and ecological stressors are the main determinants of pregnancy outcomes in baboons. Notably, although these analyses fail to identify clear costs to hybrid ancestry, population genomic evidence points to selection against introgression in baboons, suggesting subtle but important phenotypic effects of ancestry that have yet to be revealed. Finally, I identify specific regions of the baboon genome that may serve as barriers to gene flow. A subset of these genomic regions may explain ancestry-based assortative mating behavior in the hybrid zone. Together, my work demonstrates how hybridization has shaped the genomes and phenotypes of interbreeding baboons. It also provides a much-needed comparative perspective against humans, illuminating the shared and distinctive features of admixture as an evolutionary process in human evolution, and more broadly reveals how primates fit into our changing concept of animal evolution more broadly.