The evolutionary advantage of fitness-dependent recombination in diploids: a deterministic mutation–selection–balance model

Recombination’s omnipresence in nature is one of the most intriguing
problems 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 recombination’s fitness dependence
(FD). The so far developed population-genetics models have focused on the
evolution of FD recombination mainly in haploids, although the empirical
evidence for this phenomenon comes mostly from diploids. Using numerical
analysis of modifier models for infinite panmictic populations, we show
here that FD recombination can be evolutionarily advantageous in diploids
subjected to purifying selection. We ascribe this advantage to the
differential rate of disruption of lower- vs higher-fitness genotypes,
which can be manifested in selected systems with at least three loci. We
also show that if the modifier is linked to such selected system, it can
additionally benefit from modifying this linkage in a fitness-dependent
manner. The revealed evolutionary advantage of FD recombination appeared
robust to crossover interference within the selected system, either
positive or negative. Remarkably, FD recombination was often favored in
situations where any constant non-zero recombination was evolutionarily
disfavored, implying a relaxation of the rather strict constraints on
major parameters (e.g., selection intensity and epistasis) required for
the evolutionary advantage of non-zero recombination formulated by
classical models.