Poor geographical match between the distributions of host diversity and parasite discovery effort

Mapping global parasite diversity is crucial to identify geographical hotspots of emerging disease, and guide public health and conservation efforts. In principle, assuming a bottom-up coupling between the diversity of resources and consumers, the geographical distribution of parasite diversity should match that of host diversity. We test the expected spatial congruence between host and parasite diversity for helminth parasites of vertebrate hosts, across grid cells of a global map. Using high-resolution databases on host species distributions and newly compiled data on the geographical distribution of parasite species discovery, we found positive covariation between host species richness and the number of parasite species discovered, for all vertebrate groups, regardless of the analytical method used, spatial autocorrelation, and spatial resolution. However, all associations were very weak, indicating a poor match between host species richness and parasite species discovery. The research deficit in parasite discovery peaks in areas corresponding to hotspots of host diversity, where disproportionately fewer new parasites are discovered than expected based on local host richness. This spatially biased research effort prevents a full inventory of parasite biodiversity, and impedes predictions of where new diseases may emerge. The host taxon-specific maps we produced, however, can guide future efforts to uncover parasite biodiversity.