Targets of sexual selection on the Drosophila wing

Identification of traits causally linked to fitness allows for direct tests of the adaptive value of traits. In the case of Drosophila and other insects, wing interference patterns – striking structural color variation generated by optical thin-film interference – have been implicated in mate choice and sexual selection. Yet, we expect wing interference patterns may covary with many aspects of wing morphology, such as size and shape. Here, we used a competitive mating assay in Drosophila melanogaster to assess the degree to which sexual selection acts on wing color independently of wing size and shape. We found that 16% of multivariate wing color, and 17% of corresponding estimated wing thickness, can be explained by wing size and shape. Selection analysis revealed that sexual selection on the multivariate combination of color traits most strongly correlated with fitness, as identified by a projection pursuit regression using only color traits, was only apparent; selection on this color axis was eliminated when including multivariate shape. However, significant selection on other combinations of color traits remains even after accounting for wing morphology. Our results suggest that sexual selection may act on a complex combination of wing color and morphology in flies.