Ecology, phylogeny, and host traits shape avian malaria infections and interaction networks in high Andean Polylepis forests

Parasites play important roles in ecological and evolutionary processes, yet host–parasite dynamics in high-elevation Neotropical ecosystems remain poorly understood. Specifically, we asked whether haemosporidian assemblages at extreme elevations are dominated by Leucocytozoon, whether infection patterns are phylogenetically and ecologically structured across avian hosts, and whether infections produce detectable physiological costs at the community level. We sampled 214 individuals representing 37 bird species across three Polylepis forest sites (~3700–4000 m a.s.l.) in northern Ecuador, and screened blood samples for Plasmodium, Haemoproteus, and Leucocytozoon. Overall infection prevalence was 39.7%, with Leucocytozoon accounting for 88.2% of infections. We identified 63 parasite lineages, including 40 previously undescribed lineages. Infection probability varied among host species, increased with body mass, and showed phylogenetic structure, with closely related host species tending to show similar infection probability. Host-specific analyses revealed non-random phylogenetic structure of parasite assemblages in several bird species. Quantitative host–parasite interaction networks showed low connectance, moderate specialization, and significant departures from null expectations, suggesting that only a limited subset of potential host–parasite associations is realized. Despite high prevalence and frequent coinfections, infection status was not associated with body condition, hemoglobin concentration, or hematocrit. Together, these results indicate that haemosporidian communities in high Andean Polylepis forests are highly diverse and exhibit pronounced non-random and phylogenetic structure in their host–parasite associations. The presence of numerous novel lineages further suggests that parasite diversity in tropical high-elevation ecosystems remains substantially underestimated.