STRUCTURED COALESCENT PROCESSES ON DIFFERENT TIME SCALES

It is demonstrated that the structured coalescent model can readily be extended to include phenomena such as partial selfing and background selection through the use of an approximation based on separation of t ime scales. A model that includes these phenomena, as well as geograph ic subdivision and linkage to a polymorphism maintained either by loca l adaptation or by balancing selection, is derived, and the expected c oalescence time for a pair of genes is calculated. It is found that ba ckground selection reduces coalescence times within subpopulations and allelic classes, leading to a high degree of apparent differentiation . Extremely high levels of subpopulation differentiation are also expe cted for regions of the genome surrounding loci important in local ada ptation. These regions will be wider the stronger the local selection, and the higher the selfing rate.