The current state of parasite discovery and taxonomy
The latest Paper of the Month from Parasitology is ‘The geography of parasite discovery across space and over time’ by Robert Poulin and Fátima Jorge.
In this blog post, Robert Poulin and Fátima Jorge reflect on the current state of parasite discovery and taxonomy, and on the best way forward.
About a decade ago, our research group was regularly finding new parasite species as part of our expanding investigations on marine and freshwater animals of New Zealand. Over a period of 3-4 years, we averaged one new parasite species found per month, none of which had previously been reported from New Zealand waters, almost all of them being new to science. As we lacked the necessary taxonomic expertise, initially most of these parasites remained undescribed. Later, through collaborations or by recruiting new group members with taxonomic skills, we formally described and named several of these species. Still, this story illustrates that the discovery of new parasite species is often accidental, and that whether they get described, given a Latin name and added to the global inventory of known species is far from guaranteed.
Our paper looks at large-scale patterns of parasite species discovery, to see whether they match what we would expect if the search for parasite biodiversity is generally more organised than in the above example. Firstly, we would expect some congruence in the spatial distribution of diversity across different taxa of helminth parasites. For example, all else being equal, you would expect that if more trematode species are discovered in the freshwater fish fauna from one geographical area of the world than in the fish fauna from a different part of the world, then the same should be true of nematodes or cestodes. Well, that’s not what we found: new species discoveries show no spatial congruence across helminth taxa from any group of vertebrate hosts. This suggests a lack of coordination among taxonomists specialising in different types of parasites. We suspect that when many new parasites are recovered from a survey of wild animals, those for which the researchers have taxonomic expertise get described, whereas the others get shelved indefinitely.
Secondly, we also found that parasite species discovery shows no temporal continuity at a local scale. Imagine that a taxonomist makes a huge contribution to the knowledge of, say, the nematode parasites from mammals in one geographical region, describing many species over the course of a 25-year career. What happens when she retires? The simple answer is that the rate of new nematode species being found and described drops dramatically for that region.
Our paper is not a critique of parasite taxonomy. We simply provide empirical evidence for patterns that were long suspected by those in the field. We also propose a solution that would remove some of the idiosyncrasy and discontinuity plaguing our quest for a global parasite inventory. In a nutshell, taxonomic expertise must be disconnected from where taxonomists live and work, to spread the taxonomic effort more evenly across the world. As a first step, a global database of undescribed specimens would allow qualified taxonomists to access material from anywhere in the world. It is often said that parasites account for over half of the species on Earth; however, without a coordinated effort, we’ll never know for sure.
Robert Poulin and Fátima Jorge are researchers in the Department of Zoology at the University of Otago, New Zealand. This research was funded by a University of Otago Research Grant.
Read the full article ‘The geography of parasite discovery across taxa and over time‘ for free until August 31st.