The Genetic Architecture of Speciation in a Primate Hybrid Zone

Abstract

Speciation is the fundamental evolutionary process that generates biodiversity. A major goal is to identify regions of the genome that underlie this process, including regions conferring selective advantages to diverging lineages and regions associated with the maintenance of reproductive isolation between them. Advancements in sequencing technology and methods along with falling costs of genome-wide sequencing has led to great insights in speciation research, however, investigation has been biased to model systems often studied under unnatural laboratory conditions (e.g., Drosophila, Mus). To help address this gap, I use differential introgression in a natural howler monkey hybrid zone system to identify candidate genomic regions that may underlie adaptation and reproductive isolation. In hybrid zones, regions that are advantageous on the genomic or ecological background of the opposite species may be selected for and reach high frequency when they enter the population (i.e., adaptive introgression may occur). However, regions with interspecific alleles that are deleterious on the genomic or ecological background of the other species will exhibit reduced introgression due to selection against unfit hybrids that carry combinations of such incompatible alleles. Using these regions identified here, I investigate (1) the functional role of genes associated with directional and reduced introgression, (2) the role of the X chromosome in reproductive isolation, and (3) the role of selection in shaping genomic regions with reduced introgression. My results are consistent with a weak signature of functional organization shaping patterns of gene introgression, an important role of the X chromosome in reproductive isolation that may be consistent across primate systems, and the influence of multiple forms of selection on the evolution of reproductive isolation in this system.