View Program - 2022 Population, Evolutionary, and Quantitative Genetics Conference

The genomic era has made clear that introgression, or the movement of genetic material between species, is a common feature of evolution. Examples of introgression that is both adaptive and selected against exist in a variety of systems. What is unclear is how the fitness of an introgressing haplotype changes as species diverge, or as the size of the introgressing haplotype changes. In a simple model, we show that early in the process of divergence, introgression of large haplotypes can be favored more than introgression of individual alleles. This is because introgressing haplotypes bring in not only potential incompatibilities in the form of deleterious epistasis with the receiving genome, but also positive epistasis in the form of co-adapted alleles on the same haplotype. The build up of incompatibilities between diverging species begins to favor the introgression of small haplotypes in the long run, while in highly diverged species even single alleles with positive direct effects can be selected against. This model generates several novel predictions - while it is consistent with observations of a positive relationship between recombination rate and introgression frequency across the genome, the model suggests this relationship may not exist or be entirely inversed in recently diverged species pairs. The model also generates predictions about asymmetry in the direction of introgression.

The fitness of an introgressing haplotype