An inbreeding model of associative overdominance during a population bottleneck

Associative overdominance, the fitness difference between heterozygotes and homozygotes at a neutral locus, is classically described using two categor ies of models: linkage disequilibrium in small populations ol identity dise quilibrium in infinite, partially selfing populations. In both cases, only equilibrium situations have been considered. In the present study, associat ive overdominance is related to the distribution of individual inbreeding l evels (i.e., genomic autozygosity). Our model integrates the effects: of ph ysical linkage and variation in inbreeding history among individual pedigre es. Hence, linkage and identity disequilibrium, traditionally presented as: alternatives, are summarized within a single framework. This allows studyi ng nonequilibrium situations in which both occur simultaneously. The model is applied to the case of all infinite population undergoing a sustained po pulation bottleneck. The effects of bottleneck size, mating system, market gene diversity, deleterious genomic mutation parameters, and physical linka ge are evaluated. Bottlenecks transiently generate much larger associative overdominance than observed in equilibrium finite: populations and represen t a plausible explanation of empirical results obtained, for instance, in m arine species. Moreover, the main origin of associative overdominance is ra ndom variation in individual inbreeding whereas physical linkage has little effect.