The evolution of costly traits like deer antlers and peacock trains, which drove the formation of Darwinian sexual selection theory, has been hypothesised to both reflect and affect patterns of genetic variance across the genome, but direct tests are missing. Here, we used an evolve and re-sequence approach to reveal patterns of genome-wide diversity associated with the expression of a sexually-selected weapon that is dimorphic among males of the bulb mite, Rhizoglyphus robini. Populations selected for the weapon showed reduced genome-wide diversity compared to populations selected against the weapon, particularly in terms of the number of segregating non-synonymous positions, indicating enhanced purifying selection. This increased purifying selection reduced inbreeding depression, but outbred female fitness did not improve, possibly because any benefits were offset by increased sexual antagonism. The majority of single nucleotide polymorphisms (SNPs) that consistently diverged in response to selection were initially rare and overrepresented in exons, and enriched in regions under balancing or relaxed selection, suggesting they are likely moderately deleterious variants. These diverged SNPs were scattered across the genome, further demonstrating that selection for or against the weapon and the associated changes to the mating system can both capture and influence genome-wide variation. 

Experiemntal evolution carried out in large replicated populations of R. robini. Artifically selecting for either fighter males or scrambler males. Phenotypic assays were perfromed at various generations throughtout the experiement - tracking morph proportion, fecundity assays, longevity assays and survival assays.