Comparative evidence for a positive correlation between haematozoan prevalence and mortality in waterfowl

Abstract

Hamilton and Zuk (1982) suggested a new hypothesis to explain the evolution of secondary sexual characters, namely that male ornaments may represent honest signals of male capacity to resist parasites. Since then several authors have addressed the question of the role played by parasites in the evolution of host secondary sexual characters. Comparative analyses of Hamilton and Zuk's hypothesis have, however, failed to show the predicted positive association between parasitism levels and sexually‐selected traits. One possible explanation for this discrepancy involves a low pathogenicity of the parasites used to test the hypothesis. Here we show that haemosporidians are positively correlated with mortality rates in a sample of waterfowl, and that the correlation between the two variables is of similar magnitude in both males and females. Contrary to the expectations based on the Hamilton and Zuk's hypothesis, we did not find any correlation between plumage brightness and haemosporidian prevalence. These results indicate that haemosporidians may have a pathogenic effect on their avian hosts and that plumage brightness is likely to have evolved in response to ecological factors other than parasitism infections.