27 Oral - Platform Session #3 Speciation, Hybridization, and Introgression
Thursday June 09, 9:00 AM - 9:15 AM

Authors:
Arielle Fogel ¹; Tauras Vilgalys ^1,2; Elizabeth Archie ³; Susan Alberts ¹; Jenny Tung ¹

Affiliations:
1) Duke University, Durham, NC; 2) University of Chicago, Chicago, IL; 3) University of Notre Dame, Notre Dame, IN

Keywords:
Speciation & hybridization

Admixture is a common feature across the tree of life. Nonetheless, many species that hybridize remain phenotypically and genetically distinct, even when natural hybrids are both viable and fertile. To understand what maintains taxonomic integrity in the face of gene flow, we combined genome-wide local ancestry analysis with five decades of field data from naturally hybridizing wild baboons to investigate barriers to gene flow at the genetic and behavioral levels. Study subjects (n=442) are members of a hybrid baboon (Papio cynocephalus x P. anubis) population in which signatures of selection against introgression resemble those observed for hominins. Thus, they also serve as “living models” for understanding admixture dynamics in human history, including the role of behavior, which does not leave a trace in the fossil record.

To identify barriers to admixture at the genetic level, we found pairs of physically unlinked, ancestry-informative markers in which two-locus genotypes of the same ancestry were enriched in our sample (1,185 locus pairs corresponding to 1,276 unique loci; the most extreme 99.99% tested). Such cases produce a positive correlation in ancestry states across loci, consistent with the removal of mismatched ancestry states (i.e., genotype combinations from different species) due to assortative mating by ancestry or intrinsic or extrinsic hybrid incompatibilities.

Within this set of unlinked, ancestry-correlated sites, we found 92 locus pairs (131 unique loci) at which baboons with matched homozygous ancestry were more likely to mate than those with mismatched ancestry, controlling for sociodemographic factors known to influence baboon mating behavior (10% FDR; 11,597 potential mating pairs; 140 males, 103 females). Baboons mated more assortatively based on overall ancestry at these 131 loci than they did based on ancestry-associated morphological traits (∆AIC=14.5) or ancestry genome-wide (∆AIC=13.3). Introgressed ancestry is depleted near assortative mating-related loci compared to the genomic background, consistent with a role in restricting gene flow (mean=0.296 vs. 0.353 ± 0.008 s.d. for random markers). Assortative mating-related loci also fall near genes that are weakly enriched for nervous system traits (FDR=0.13) and expression (FDR=0.12), suggesting a role in behavioral modulation. Together, our results point to novel candidate loci involved in complex mating behavior in the wild. They emphasize a key role for behavior in shaping ancestry patterns along primate genomes, suggesting that behavioral barriers may also have played a role in hominin admixture.