The evolution of plastic recombination

Abstract

Empirical data suggest that recombination rates may change in response to stress. To study the evolution of plastic recombination, we develop a modifier model using the same theoretical framework used to study conventional (nonplastic) modifiers, thus allowing direct comparison. We examine the evolution of plastic recombination in both haploid and diploid systems. In haploids, a plastic modifier spreads by forming associations with selectively favored alleles. Relative to nonplastic effects, selection on the plastic effects of a modifier is both much stronger and less sensitive to the specifics of the selection regime (e.g., epistasis). In contrast, the evolution of plastic recombination in diploids is much more restricted. Selection on plasticity requires the ability to detect DNA damage or cis-trans effects as may occur through maternal effects on fitness.

Figure 1.

Recombination rate of a plastic modifier. The recombination rates of individuals with different haploid genotypes are illustrated. Individuals carrying the m allele always have the baseline level of recombination regardless of the alleles they carry at the fitness loci. Individuals carrying the plastic modifier allele M have a recombination rate that depends on their fitness. We assume that w_ab < w_aB < w_Ab < w_AB. In cases M₁ and M₂ (Δr > 0), individuals with low fitness have more recombination than individuals with high fitness (FAR). The FAR modifier causes an incidental increase in recombination on average when w_ref = w_AB (case M₁) but decreases recombination on average when w_ref = w_ab (case M₂). In cases M₃ and M₄ (Δr < 0), individuals with low fitness have less recombination than individuals with high fitness (anti-FAR). The anti-FAR modifier decreases recombination on average when w_ref = w_AB (M₃) but increases recombination on average when w_ref = w_ab (M₄).