Fitness-dependent recombination can be evolutionarily advantageous in diploids under mutation-selection balance

Recombination9s omnipresence in nature is a most intriguing problem in evolutionary biology. The question of why recombination exhibits certain general features is no less interesting than that of why it exists at all. One such feature is its dependence on genotype fitness. The evolution of fitness-dependent recombination in diploids remains theoretically unexplained, despite empirical evidence for this phenomenon, mostly from diploids. Here, using numerical analysis of modifier models with infinite population size, we show that fitness-dependent recombination can be evolutionarily advantageous in diploids under selection against deleterious mutations. With unlinked modifier locus, this advantage originates entirely from benefits of recombination-rate plasticity within the selected system (indirect effect). With a linked modifier locus, it is accompanied by benefits of variation in modifier linkage to the selected system induced by fitness dependence of recombination rates between the selected loci (direct effect). Together with our earlier results on cyclical selection and Red Queen dynamics, these findings suggest that the evolutionary advantage of fitness-dependent recombination based on an indirect effect can be universal in diploids. Remarkably, fitness-dependent recombination is often favored in situations where constant non-zero recombination is rejected, thereby relaxing the constraints on the evolution of non-zero recombination in classical models with non-plastic recombination.