What does sex have to do with it: tracking the fate of deleterious mutations in sexual populations.

Abstract

Deleterious mutations sometimes revert into beneficial mutations via epistatic interactions with subsequent mutations. This type of interaction among mutations is called “sign-epistasis.” Recent works have explored the role of signepistasis in the evolution of asexual populations. Some have indicated that the fixation of sign-epistasic deleterious mutations may be critical for adaptive evolution. However, sign-epistasis is considered to be important only for asexual populations, because recombination in sexual populations tends to disrupts linkage between epistatically interacting mutations. Here, we tested the hypothesis that recombination prevents adaptation via sign-epistatic fitness reversions, by examining deleterious mutations in sexually-reproducing digital organisms. We examined every deleterious mutation that arose on the genealogy between the original ancestor and the final dominant genotype (the “graph of descent”). We show that sign-epistatic pairs of mutations emerged in several replicate populations, and that they contributed positively to the long-term adaptation of the population.