Résumé
Data on parasites of Mediterranean Sea fishes, collected from previous published surveys, were used to test 5 hypotheses concerning the determinants of parasite species richness. A total of 170 parasite species belonging to 5 distinct taxonomic groups (nematodes, acanthocephalans, digeneans, monogeneans and crustaceans) were identified from 79 marine fish species (3904 individuals) collected at a regional scale. Five independent variables concerning host life traits (body size, diet, range, abundance and schooling) were investigated and controlled for host sampling effort. A comparative analysis using the independent contrasts method was conducted in order to avoid phylogenetic confounding effects. We demonstrate the importance of taking host sampling effort into account when investigating the determinants of parasite species richness. Monogeneans were the only group for which the species richness showed a significant correlation with some of the variables studied. Parasite species richness of monogeneans was positively correlated with host body size and negatively correlated with host species abundance. The positive relationship between fish body size and the number of parasite species on a regional scale may be explained by the hypothesis that larger host body size increases host vagility which in turn enhances exposure to more and more parasite species. Our findings disagree with previous studies that did not take either phylogenetic confounding effects or geographic scale into account. We demonstrate the importance of using phylogenetic information in comparative analyses by showing that fish body size was not correlated with geographical range when using phylogenetic independent contrasts. We also suggest that studying parasites of host species from the same geographical region avoids the problem of confounding various assemblages of hosts with distinct histories.