The evolutionary fate of divergent genomes in hybrid zones between selfing and outcrossing species

Hybridization is a natural process whereby two diverging evolutionary lineages reproduce and create offspring of mixed ancestry. Differences in mating systems (e.g., self-fertilization and outcrossing) are expected to affect the direction and extent of hybridization and introgression in hybrid zones. Among other factors, selfers and outcrossers are expected to differ in their mutation loads. This has been studied both theoretically and empirically; however, conflicting predictions have been made on the effects mutation loads of parental species with different mating systems can have on the genomic composition of hybrids. Here we develop a multi-locus, selective model to study the effects of selective interference and homozygosity on (i) the mutation load of selfers and outcrossers, and (ii) the long-term genetic composition of resulting hybrid populations. Notably, our results tend to discard mutational meltdown in self-fertilizing populations. Selfers’ genomes tend to be of higher quality and dominate the hybrids genome composition in the long-term regardless of the hybrid’s own mating system (e.g., selfer or outcrosser). Taken together, these results provide a “null” hypothesis for the genetic composition of hybrids in hybrid zones containing species with different mating systems.