Taxonomic resolution in parasite community studies: are things getting worse?

Species identification is crucial for studies of parasite diversity, yet most surveys include taxa identified only to genus or family level. Using a large dataset comprising 950 surveys of helminth communities from 650 different species of fish, bird and mammal hosts, we investigated what determines the level of taxonomic resolution achieved. Identification of all helminths down to species level was achieved in only one-third of surveys, whereas all taxa were identified at least to genus level in two-thirds of surveys. The species richness of a parasite community and past study effort on the host species did not correlate with taxonomic resolution. However, the higher the proportion of parasite taxa occurring as larvae in a community, the lower the resolution achieved. Also, taxonomic resolution was better overall for communities in birds or mammals than for those in fish, and better for trematodes and acanthocephalans than for cestodes and nematodes. Perhaps the most intriguing result was a clear significant effect of year of publication on the taxonomic resolution achieved in parasite surveys: the proportion of helminth taxa identified at least to genus level has remained high until the year 2000, but has dropped in studies published since then. The loss of expertize in parasite taxonomy happening worldwide is one possible explanation. This downward trend needs to be reversed if we are to monitor new parasite occurrences in the face of environmental changes.