Male courtship pheromones as indicators of genetic quality in an arctiid moth (Utetheisa ornatrix)

One of the fundamental issues regarding sexual selection is whether females select males based on signals that represent direct phenotypic or indirect genetic benefits. In Utetheisa ornatrix (Lepidoptera: Arctiidae), females choose males based on a courtship pheromone, hydroxydanaidal (HD), derived from defensive pyrrolizidine alkaloids (PAs). At mating, virgin males transfer a spermatophore whose contents are proportional to the HD titer and body size; as a result, females receive both phenotypic benefits (more nutrients and PAs) and genotypic benefits (genes for larger body size inherited by the offspring). Previous data from field-collected individuals, however, indicated that the HD signal of nonvirgin males may not correlate with the spermatophore contents. Using chemical analyses, we determined that the HD signal does not change based on mating history, thereby supporting the importance of HD in advertising a male’s genetic quality. Thus, male HD represents original body size and PA levels, and females, by choosing males based on this pheromone, are providing their offspring with genes to sequester chemicals that confer survival and reproductive advantages. We discuss the implications regarding the relative importance of direct and indirect selection in maintaining female preferences.