Drosophila simulans;

genotype 9 environment interaction; honest signalling; sexual selection; signal quality. Genotype-by-environment interactions (G 9 Es) describe genetic variation for phenotypic plasticity. Recent interest in the role of these interactions in sexual selection has identified G 9 Es across a diverse range of species and sexual traits. Additionally, theoretical work predicts that G 9 Es in sexual traits could help to maintain genetic variation, but could also disrupt the reliability of these traits as signals of mate quality. However, empirical tests of these theoretical predictions are scarce. We reared iso-female lines of Drosophila simulans across two axes of environmental variation (diet and temperature) in a fully factorial design and tested for G 9 Es in the expres-sion of cuticular hydrocarbons (CHCs), a multivariate sexual trait in this species. We find sex-specific environmental, genetic and G 9 E effects on CHC expression, with G 9 Es for diet in both male and female CHC profile and a G 9 E for temperature in females. We also find some evidence for ecological crossover in these G 9 Es, and by quantifying variance compo-nents, genetic correlations and heritabilities, we show the potential for these G 9 Es to help maintain genetic variation and cause sexual signal unreli-ability in D. simulans CHC profiles