The Hamilton-Zuk theory and initial test: an examination of some parasitological criticisms

It has been supposed repeatedly that the Hamilton & Zuk paper of 1982 was parasitologically misconceived. These criticisms are shown to be inconsistent or mistaken. Various assumptions deemed unjustifiable by critics were either not made in the original paper, or have been made commonly, reasonably and pragmatically, by parasitologists themselves. The requirement by the theory for pathogenicity is examined, as is the need for the individuals to encounter the relevant parasites. The possible roles of parasite aggregation, parasites other than those directly involved, and costs of resistance, in making sosigonic selection less feasible are put into perspective. The rationale, interpretation and value of the preliminary comparative test with haematozoa are discussed. The advisability of incorporating host age, the location and timing of any sampling for parasites, and the actual ability of successful mates to resist disease is acknowledged. Attention is directed towards several specific observations. (1) It is a little recognised fact that Hamilton and Zuk assessed prevalence-showiness associations within surveys in restricted localities. (2) Many parasitological studies have not properly addressed the need to control for sampling effort when using prevalence data. (3) Contrary to some claims, the notion that haematozoa are sufficiently pathogenic is not unrealistic. (4) That non-resistant as well as resistant individuals might be free of patent or even latent infection at the time of mate choice was one of the possibilities mentioned originally. (5) In 1984, Eshel & Hamilton emphasised that environmental variation (whatever its source) has the potential to make mate selection for heritable characters based on perceptible variation less likely to evolve. (6) Hamilton & Zuk concluded that their findings "hint" that parasitism could be one agitator required for "good genes" sexual selection, a stance which is not immoderate. Lastly, the potential importance in evolutionary biology of parasite-mediated sexual selection as a form of co-evolution is considered briefly.