Abstracts (first author)
Evolution under monogamy feminizes gene expression
Many genes have evolved sexually dimorphic expression as a consequence of divergent selection in males and females. However, the degree to which evolution can shape gene expression independently in each sex is controversial. It is possible to directly test whether genetic constraints have prevented sex-specific optima from being obtained by enforcing a monogamous mating system, which eliminates both female choice and male-male competition. This relaxed selection on males should result in evolution towards female-specific optima for any genes previously under antagonistic selection in males. Here we demonstrate broad constraints on the evolution of sexually dimorphic gene expression by maintaining populations of Drosophila melanogaster for 65 generations under strict monogamy. Compared to polygamous controls, monogamous populations evolved lower expression of male-biased transcripts and higher expression of female-biased transcripts. This pattern of feminization was present in both sexes, evident throughout the genome and across tissue types, and strongest for genes located on the X chromosome, a known hotspot for sexually antagonistic genetic variation. The breadth of the evolutionary response to monogamy indicates that sexually antagonistic selection is ubiquitous in the genome and likely to play a major role in maintaining genetic variation, driving the evolution of sex chromosomes, and reducing population-level fitness.