Effects of selfing on speciation through the accumulation of Dobzhansky-Muller incompatibilities

Phylogenetic analyses suggest that self-compatible lineages have higher speciation rates than self-incompatible lineages. However, the effects of selfing on speciation remain unclear. Although a selfing population can resist gene flow from other populations, selfing may increase gene flow from a focal population to other populations. This study investigates the effects of selfing rates of two populations on the waiting time to speciation through the accumulation of Dobzhansky-Muller incompatibilities (DMI). Generally, a higher mean selfing rate of two populations facilitates speciation when incompatibility-controlling alleles are recessive and are weakly selected, and when gene flow is mainly through pollen dispersal instead of seed dispersal. However, the selfing rate difference between two populations can retard speciation, especially when the selfing rate of immigrants remains unchanged after migration. When the selfing rates of two populations differ, speciation may be fastest when the mean selfing rate is intermediate. Given that selfing rates often vary among conspecific populations in plant species, the results indicate that lineages with higher mean selfing rates may not necessarily have higher rates of speciation through the accumulation of DMI, and also call for an estimation of the dependency of speciation rates on selfing rates.