What would it take to describe the global diversity of parasites?

Abstract

How many parasites are there on Earth? Here, we use helminth parasites to highlight how little is known about parasite diversity, and how insufficient our current approach will be to describe the full scope of life on Earth. Using the largest database of host-parasite associations and one of the world's largest parasite collections, we estimate a global total of roughly 100,000 to 350,000 species of helminth endoparasites of vertebrates, of which 85% to 95% are unknown to science. The parasites of amphibians and reptiles remain the most undescribed, but the majority of missing species are likely parasites of birds and bony fish. Missing species are disproportionately likely to be smaller parasites of smaller hosts in undersampled countriesspecies that have mostly been understudied over the last century. At current rates, it would take centuries to comprehensively sample, collect, and name vertebrate helminths. While some have suggested that macroecological inference can work around existing data limitations, we argue that patterns described from a small and biased sample of diversity aren't necessarily reliable, especially as host-parasite networks are increasingly altered by global change. In the spirit of moonshots like the Human Genome Project and the Global Virome Project, we call for a global effort to transform parasitology and describe as much of global parasite diversity as possible.

Checklist and state of knowledge of helminths in wild birds from Chile: an update

“…Helminths are defined as metazoan parasites including phyla Platyhelminthes (class Cestoda and Trematoda), Nematoda and Acanthocephala, all of them having been reported parasitising wild birds around the world (Wobeser 2008, Roberts et al 2013. Around 24,000 helminth species have been estimated as infecting birds, although this figure could underestimate the real number of parasitic species for this host group (Carlson et al 2019). Thus, these organisms should also be considered as an important component of the biodiversity from any territory (Poulin and Morand 2004).…”

What determines parasite species richness across host species?

“…The genus Peromyscus not only highlights the potential issue of geographic scale, but also the influence of sampling and detection biases of host-parasite associations (Carlson et al, 2020;Dallas, Huang, et al, 2017). Dominant species in a community should be more easily sampled, increasing the probability of detecting a host-parasite association.…”

“…However, using predictive models to examine parasite sharing with humans or closely related species could be a way to estimate zoonotic potential (Farrell, Berrang-Ford, & Davies, 2013), or by network-based approaches which explicitly consider host and pathogen species associations Evans, Dallas, Han, Murdock, & Drake, 2017). Further, standardized global sampling will promote our understanding of the spatial distribution of parasite species, and how this may be affected by climate change (Carlson et al, 2020). While standardizing global sampling may be logistically infeasible, leveraging existing data from museum records, published data and governmental surveys may provide some insight into large-scale patterns of parasite diversity and host-parasite associations.…”

Taxonomic resolution affects host−parasite association model performance

“…While the LNHM's helminth data represent one of the most extensive host−parasite databases to date, especially considering the taxonomic scope of the parasites considered (Gibson et al ., 2005; Dallas et al ., 2018), it is important to acknowledge that the recorded interactions between host and helminth parasite are not exhaustive. Host species that are more abundant, more conspicuous, or easier to sample may be over-represented in the host−helminth association data (Carlson et al ., 2020). If this differential sampling is associated with host taxonomy, this bias could inflate the importance of host taxonomy in estimating host−helminth associations.…”