INDIVIDUAL VARIATION IN INBREEDING DEPRESSION - THE ROLES OF INBREEDING HISTORY AND MUTATION

We use mutation-selection recursion models to evaluate the relative co ntributions of mutation and inbreeding history to variation among indi viduals in inbreeding depression and the ability of experiments to det ect associations between individual inbreeding depression and mating s ystem genotypes within populations. Poisson mutation to deleterious ad ditive or recessive alleles generally produces far more variation amon g individuals in inbreeding depression than variation in history of in breeding, regardless of selfing rate. Moreover, variation in inbreedin g depression can be higher in a completely outcrossing or selfing popu lation than in a mixed-mating population. In an initially random matin g population, the spread of a dominant selfing modifier with no pleiot ropic effects on male outcross success causes a measurable increase in inbreeding depression variation if its selfing rate is large and inbr eeding depression is caused by recessive lethals. This increase is obs ervable during a short period as the modifier spreads rapidly to fixat ion. If the modifier alters selfing rate only slightly, it fails to sp read or causes no measurable increase in inbreeding depression varianc e. These results suggest that genetic associations between mating loci and inbreeding depression loci could be difficult to demonstrate with in populations and observable only transiently during rapid evolution to a substantially new selfing rate.