SEXUAL DICHROMATISM IN NORTH-AMERICAN FRESH-WATER FISH - DO PARASITES PLAY A ROLE

North American freshwater fish were scored for parasites and sexual dichromatism to test the interspecific prediction of the Hamilton-Zuk hypothesis that more sexually dichromatic fish species should harbour more parasites. We used two measures of parasite load, the mean number of helminth species per individual host and the total number of parasite genera reported per host species. Study effort was shown to be significantly positively correlated with both dichromatism and the total number of parasites per host. No significant correlation was found between the mean number of helminth parasites per host and dichromatism. Age at maturity, size, host range area and diet did not significantly alter the lack of a relationship between parasitism and dichromatism. In conclusion, we found no support for the Hamilton-Zuk hypothesis in this data set of freshwater fish. Because of the potentially large effect of study effort on host-parasite lists, we urge caution at using such lists for testing evolutionary hypotheses.