Parasites and Sexual Selection in Birds of Paradise

Abstract

We studied blood parasite infections in relation to aspects of sexual selection and mate choice in 10 species of birds of paradise. Across species there was a significant, positive correlation between relative parasite intensity and showiness in males. Parasite infections also correlated across species with the degree of sexual dimorphism and varied with mating systems. Promiscuous species were showier and had significantly higher parasite prevalences than monogamous species. Within one species, Lawes' Parotia ( Parotia lawesii ), parasite intensity was negatively correlated with all phenotypic traits examined, a pattern significantly different than random. The mating success of males with low parasite intensities varied, but males with high intensities did not mate. Sampling of individual males on repeated occasions revealed large temporal differences in parasite counts which spanned the range believed to affect behavior and mating success. Whereas the interspecific correlations support one prediction of the Hamilton and Zuk hypothesis on parasites and sexual selection, the intraspecific data are equivocal with respect to a second prediction of this hypothesis. Parasites appear to influence the behavior of Lawes' Parotia, but alternative explanations to that of Hamilton and Zuk for this effect are equally plausible and there is no evidence of a link between female choice and the traits in males indicative of parasite loads. We suggest that female Lawes' Parotia may be avoiding highly infected males rather than actively choosing parasite-resistant males.