Male, but not female, preference for an ornament expressed in both sexes of the polygynous mosquito Sabethes cyaneus

The evolution of female ornaments in species with a female-biased operational sex ratio (OSR) and intense female competition is well understood. In contrast, the adaptive value of female ornaments in species with a male-biased OSR and male competition remains largely unresolved. Mutual mate choice is one proposed explanation for the evolution of ornaments expressed in both males and females, a hypothesis supported by the increasing empirical evidence of mutual mate choice in species with a male-biased OSR. None the less, the evolution of female ornaments remains constrained, as investment in ornaments may detract from any direct benefits being signalled to males and females may fail to reap benefits sufficient to outweigh the costs of signalling. We used phenotypic engineering (i.e. manipulation of ornament size) to ask whether both sexes show a preference for sexually homologous ornaments in the polygynous mosquito, Sabethes cyaneus. We found a directional male preference for ornamented females, but no female preference for ornamented males. There was no evidence of assortative mating based on ornament size. We discuss these results within the framework of current sexual selection theory, addressing implications for both the evolution of male mate choice and the evolution of female ornaments.