Parasite specialization in a unique habitat: hummingbirds as reservoirs of generalist bloodparasites of Andean birds

Abstract

1.Understanding how parasites fill their ecological niches requir es information on the pro-cesses involved in the colonization and exploitation of unique host species. Switching to hostswith atypical attributes may favour generalists broadening their niches or may promotespecialization and parasite diversification as the consequence. 2.We analysed which blood parasites have successfully colonize d hummingbirds, and howthey have evolved to exploit such a uniq ue habitat. We specifically asked (i) whether theassemblage of Haemoprot eus parasites of hummingbirds is the result of single or multiple col-onization events, (ii) to what extent these parasites are specialized in hummingbirds or sharedwith other birds and (iii) how hummingbirds contribute to sustain the populations of theseparasites, in terms of both prevalence and infection intens ity. 3.We sampled 169 hummingbirds of 19 species along an elevation gradient in SouthernEcuador to analyse the host specificity, diversity and infection intensity of Haemoproteus bymolecular and microscopy techniques. In addition, 736 birds of 112 species were analysed toexplore whether hummingbird parasites are shared with other birds. 4.Hummingbirds hosted a phylogenetically diverse assemblage of generalist Haemoproteuslineages shared with other host orders. Among these parasites, Haemoproteus witti stood outas the most generalized. Interestingly, we found that infection intensities of this parasite wereextremely low in passerines (with no detectable gametocytes), but very high in hummingbirds,with many gametocytes seen. Moreover, infec tion intensities of H. witti were positively corre-lated with the prevalence across host species. 5.Our resul ts show that hummingbirds have been colonized by generalist Haemoproteus lin-eages on multiple occasions. However, one of these generalist parasites (H. witti) seems to behighly dependent on hummingbirds, which arise as the most relevant reservoirs in terms ofboth prevalence and gametocytaemia. From this perspective, this generalist parasite may beviewed as a hummingbird specialist. This challenges the current paradigm of how to measurehost specialization in these parasites, which has important implications to understand diseaseecology.