In this paper, we investigate two mechanisms that may help to explain these observations: (1) a high genomic mutation rate to recessive lethal alleles, and (2) selective interference among loci with deleterious recessive mutations under partial selfing.
Selective interference among loci with deleterious recessive mutations occurs under partial selfing because inbreeding depression reduces the fitness of viable selfed genotypes at individual loci, decreasing the opportunity for selection produced by self-fertilization.
Because of selective interference among loci, and because partial selfing creates identity disequilibrium (positive associations between homozygous genotypes at different loci, even in the absence of linkage; Haldane 1949; Weir and Cockerham 1973), it is difficult to analyze an exact model of the maintenance of high inbreeding depression by recessive lethal mutations.
It also has some advantages over the Kondrashov model for analyzing selective interference among loci, completely recessive lethals, and parameter variation among loci.
Selective interference among lethal producing loci is incorporated in the secondary selfing rate that appears in (2) instead of the primary selfing rate, which would be appropriate for a classical single-locus model.
Figure 1 reveals that with high genomic mutation rates to recessive or slightly dominant lethals, selective interference among loci can greatly increase the mean number of lethals per plant maintained in a partially selfing population.
Thus, when 2n[square root of [Mu]] [greater than] 10 selective interference among loci creates a threshold selfing rate necessary for purging recessive lethal mutations.
In this sense, a very high inbreeding depression creates selective interference among loci with recessive deleterious mutations, which reduces the opportunity for selection on individual loci under partial self-fertilization.