Avian host composition, local speciation, and dispersal drive the regional assembly of avian malaria parasites in South American birds

Identifying the ecological factors that shape parasitedistributions remains a central goal in disease ecology. These factors include dispersal capability, environmental filters and geographic distance. Using 520 haemosporidian parasitegenetic lineages recovered from 7,534 birds sampled across tropical and temperate South America, we tested (a) the latitudinal diversity gradient hypothesis and (b) the distance–decayrelationship (decreasing proportion of shared species between communities with increasing geographic distance) for this host– parasitesystem. We then inferred the biogeographic processes influencing the diversity and distributions of this cosmopolitan group of parasitesacross South America. We found support for a latitudinal gradient in diversity for avian haemosporidian parasites, potentially mediated through higher avian host diversity towards the equator. Parasitesimilarity was correlated with climate similarity, geographic distanceand host composition. Local diversification in Amazonianlineages followed by dispersal was the most frequent biogeographic events reconstructedfor haemosporidian parasites. Combining macroecologicalpatterns and biogeographic processes, our study reveals that haemosporidian parasitesare capable of circumventing geographic barriers and dispersing across biomes, although constrained by environmental filtering. The contemporary diversity and distributions of haemosporidian parasitesare mainly driven by historical (speciation) and ecological (dispersal) processes, whereas the parasitecommunity assembly is largely governed by host composition and to a lesser extent by environmental conditions.