Sexual selection and conflict can act on genes with important metabolic functions, potentially shaping standing genetic variance in such genes, and thus evolutionary potential of populations. Here, using experimental evolution, we show how reproductive competition intensity and thermal environment affect selection on phosphogluconate dehydrogenase (6Pgdh) – a metabolic gene involved in sexual selection and conflict in the bulb mite. The S allele of 6Pgdh increases male success in reproductive competition, but is detrimental to S-bearing males’ partners. We found that the rate of the S allele spread increased with the proportion of males in the experimental populations, illustrating that harm to females is more easily compensated for males under more intense sexual competition. Furthermore, we found that under equal sex ratio, the S allele spreads faster at higher temperature. While the direction of selection on 6Pgdh was not reversed in any of the conditions we tested, which would be required for environmental heterogeneity to maintain polymorphism at this locus, our study highlights that ecological and sexual selection can jointly affect selection on important metabolic enzymes.

Munbers of S and F alleles assessed based on genotyping a random sample of 30 individuals per population after generations 1, 5 and 10 of experimental evolution at diferent temperatures and sex rations.