We use modifier theory to compare the evolution of recombination
under mutation–selection and
migration–selection balance models. Recombination between loosely
linked loci subject to weak
multilocus selection is controlled by the genotype at a selectively
neutral modifier locus. We show
that the success of a new modifier depends on the sign and amount
of epistasis as well as on the
linkage of the modifier locus to the loci under selection. With
both migration and mutation, for
recombination to increase requires negative (synergistic)
epistasis. When epistasis is sufficiently
weak, increased recombination is always favoured under mutation–selection
balance and never
under migration–selection balance. With stronger negative epistasis,
there exists a critical
recombination value. In this case, a recombination-increasing
allele invades the population under
mutation–selection balance if its recombination rate with the
major loci is less than the critical
recombination value, whereas with weak migration it must be above this
value. These results are
the same for haploid and diploid populations.