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

Hybridization is a common occurrence in natural populations, and introgression is a major source of genetic variation. Despite the evolutionary importance of adaptive introgression, classical population genetics theory does not take into account hybrid fitness effects (HFEs). Specifically, heterosis (i.e., hybrid vigor) and Dobzhansky-Muller incompatibilities (DMIs) influence the fates of introgressed alleles. Here, we explicitly account for polygenic, unlinked HFEs when tracking an introgressed marker allele. These HFEs quickly decay over time due to repeated backcrossing, enabling a separation-of-timescales approach. Using branching process and diffusion theory in combination with computer simulations, we formalize the intuition behind how HFEs affect introgressed alleles. We find that HFEs can either hinder or boost the fixation probability of introgressed alleles, depending on the relative strength of heterosis and DMIs effects. We show that the inclusion of a correction factor (α, representing the compounded effects of HFEs over time) into classic population genetics theory yields accurate fixation probabilities. Despite this, HFEs only subtly change the distribution of fitness effects of introgressed alleles that reach fixation. Although strong DMI effects may expedite the loss of introgressed alleles, fixation times are largely unchanged by HFEs.

Hybrid fitness effects modify fixation probabilities of introgressed alleles