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 genotype combinations maintained by selection. We here synthesize recent experimental evolution studies on the adaptive consequences of sex and recombination in constant environments, emphasizing insights gained from population genomic data. We discuss evidence showing how meiotic segregation (sex) and crossovers (recombination) disrupt negative disequilibrium between alleles within and between loci and enhance selection efficacy. While sexual reproduction can facilitate adaptation when compared to asexual reproduction, the benefits of higher and variable rates of sex and recombination under facultative sexual reproduction or facultative outcrossing are less clear, especially when overdominance and epistatic interactions 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 co-adapted genotype combinations.