DETERMINANTS OF PARASITE SPECIES RICHNESS IN MEDITERRANEAN MARINE FISHES

Data on parasites of Mediterranean Sea fishes, collected from previous published surveys, were used to test 5 hypotheses concerning the dete rminants 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 mari ne fish species (3904 individuals) collected at a regional scale. Five independent variables concerning host life traits (body size, diet, r ange, abundance and schooling) were investigated and controlled for ho st sampling effort. A comparative analysis using the independent contr asts method was conducted in order to avoid phylogenetic confounding e ffects. We demonstrate the importance of taking host sampling effort i nto account when investigating the determinants of parasite species ri chness. 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 wit h host body size and negatively correlated with host species abundance . The positive relationship between fish body size and the number of p arasite species on a regional scale may be explained by the hypothesis that larger host body size increases host vagility which in turn enha nces exposure to more and more parasite species. Our findings disagree with previous studies that did not take either phylogenetic confoundi ng effects or geographic scale into account. We demonstrate the import ance of using phylogenetic information in comparative analyses by show ing that fish body size was not correlated with geographical range whe n using phylogenetic independent contrasts. We also suggest that study ing parasites of host species from the same geographical region avoids the problem of confounding various assemblages of hosts with distinct histories.