Experimental tests on the evolution of sex and recombination and their adaptive significance.

Sex and recombination generate genetic variation and facilitate adaptation by reducing selective interference, but they can also disrupt allelic combinations maintained by selection. We here review experimental evolution studies on the adaptive significance of sex and recombination in constant environments, emphasizing insights gained from population genomic data. We discuss evidence showing how meiotic segregation (sex) and crossing-over (recombination) disrupt negative disequilibrium between alleles within and between loci and as a consequence increase the fitness variance of populations and enhance selection efficacy. While sexual reproduction can facilitate adaptation when compared with asexual reproduction, the advantages of high rates of sex and recombination under facultative sexual reproduction or facultative outcrossing and self-fertilization are less clear, especially when overdominance and epistasis cause segregation and recombination loads. We further discuss the challenges of measuring interference between selected alleles, particularly under polygenic adaptation and segregation of multiple modifiers of recombination, and propose directions for future research. Our discussion underscores the nuanced role of sex and recombination in adaptation, shaped by a balance between increased genetic variation and the disruption of beneficial allele combinations.