Data from: The effect of operational sex ratio and density on the strength of sexual selection against mutant males in Drosophila melanogaster

Higher male:female operational sex ratio (OSR) is often assumed to lead to
stronger sexual selection on males. Yet, this premise has been directly
tested by very few studies, with mixed outcomes. We investigated how OSR
affects the strength of sexual selection against two deleterious alleles,
a natural ebony mutant and a transgenic GFP insertion, in Drosophila
melanogaster. To this end, we estimated the relative paternity share of
homozygous mutant males competing against wildtype males under different
OSRs (1:2, 1:1, 2:1). We also manipulated the mating pool density (18, 36
or 54 individuals), and assessed paternity over three consecutive days,
during which the nature of sexual interaction changed. The strength of
sexual selection against the ebony mutant increased with OSR, became
weaker after the first day and was little affected by density. In
contrast, sexual selection against the GFP transgene was markedly affected
by density: at the highest density it increased with OSR, but at lower
densities it was strongest at 1:1 OSR, remaining strong throughout the
experiment. Thus, while OSR can strongly affect the strength of sexual
selection against “bad genes”, it does not necessarily increase
monotonically with male:female OSR. Furthermore, the pattern of
relationship between OSR and the strength of sexual selection can be
locus-specific, likely reflecting the specific phenotypic effects of the
mutation.