Deleteriuous Mutations, Variable Epistatic Interactions, and the Evolution of Recombination

In this paper, we examine the conditions that allow increased recombination to evolve in the presence of recurrent deleterious mutation. We focus on a three-locus model first studied by Feldman et al. (1980), which follows the dynamics of a modifier locus that alters the recombination rate between two loci subject to deleterious mutation. Although Feldman et al. (1980) indicated that increased recombination might be favored if there is diminishing-returns epistasis between the loci under selection. Even with synergistic epistasis, evolution at the modifier locus will lead to decreased recombination if the modifier locus is loosely linked and epistasis is strong. Using multi-locus analysis of Barton (1995), we show that variability among loci in the sign and strength of epistasis also tends to select for decreased recombination. We conclude that the conditions that favor increased recombination in the presence of deleterious mutations are fairly restrictive, especially if, as seems likely, epistatic interactions are highly variable among loci.