Parasites and Sexual Selection

Parasites may impose heavy energetic costs on their hosts, and it may often benefit animals to choose mates that are relatively free of parasites. According to the Hamilton-Zuk hypothesis, choosing mates on the basis of parasite resistance may be particularly beneficial if such resistance is heritable, and sexual signals may have evolved in part to convey information about parasite resistance. As evidence for this, females in species ranging from jungle fowl to crickets seem to prefer males that have fewer parasites and/or a stronger immune response. Testosterone may provide a mechanistic link between parasite resistance and sexual signaling in vertebrates, as it both enhances the signal and depresses the immune system. Further work in the field should address such questions as the degree to which the evolution and development of sexual signals depends on parasites and how this may influence differences between the sexes.