Host-specialization and species diversity in fish parasites: phylogenetic conservatism?

The pattern of parasite species diversification and specialization, appreci ated by host rang, is investigated in fish parasites. We test whether host range is linked with phylogeny at a high taxonomic level, and if there is a relationship between host range and host species diversification. For this purpose we used two sets of data, one on macro-parasites of marine fishes of the Mediterranean Sea and the other on macroparasites of marine and fres hwater fishes of Canada. Similar patterns of host range among parasitic gro ups were found. Our findings suggest that habitat (marine freshwater) and g eographic localization (Canada vs Mediterranean region) play ii role in det ermining the observed patterns of host range. We highlight the potential in fluence of phylogeny (high-taxonomic level) on the level host range in para sites. We find that parasites with free-swimming larval stages and with dir ect life cycles have a narrower range of host species than do parasites wit h indirect life-cycle: even if we cannot control for phylogenetic effects b ecause of the lack of variation of life cycles within each parasitic group. Finally, a positive relationship was found between the number of known hos ts and parasite species diversity in the case of Mediterranean parasite spe cies. The relationship between host range and species diversification shoul d be related to the mechanism of cospeciation.