The Hamilton and Zuk hypothesis revisited: A meta-analytical approach

The Hamilton & Zuk (1982) hypothesis of parasite-mediated sexual selection has been the subject of both inter- and intraspecific tests. Past reviews have used vote counting to determine whether this hypothesis is supported by empirical evidence. This study reanalysed 199 separate quantitative assessments of a central prediction of the Hamilton & Zuk hypothesis using meta-analytical techniques. Overall, our meta-analysis showed that there was a significant negative effect of parasites on male showiness as predicted. However the magnitude of this effect varied between host taxa and between endo and ectoparasitic taxa. As a whole intraspecific correlations between parasite load and male showiness provided very little support for the hypothesis with only the effect of parasites on fish morphology matching the Hamilton & Zuk prediction. There was more support for the hypothesis from interspecific studies especially those based upon the original Hamilton & Zuk (1982) data set, although other bird studies provided weaker support. The generality of the Hamilton & Zuk hypothesis in respect to parasite mediated sexual selection across taxa is thrown into doubt by these results. However, in some specific host-parasite systems the role of parasites appears important and future intraspecific tests of parasite-mediated sexual selection should perhaps focus on such systems.