Abstract
Parasites are ubiquitous organisms that represent one of the most successful life-history strategies globally. They can have profound indirect and direct effects in the ecosystem by modulating their hosts’ fitness and survival. Due to their intimate relationship with their hosts, host characteristics can shape parasite ecological and evolutionary dynamics. For instance, migratory habits have the potential to modulate parasite transmission by transporting parasites to new habitats, with distinct environmental and biotic conditions.
In this thesis, I evaluated the role of avian migration in shaping the transmission of malaria and malaria-like parasites (avian haemosporidians), focusing on the South American continent. Avian malaria and malaria-like parasites are a highly prevalent, diverse, and cosmopolitan parasite group in nature. These parasites occur on all continents but Antarctica, with more than four thousand parasite lineages already described. Moreover, since avian migration is a widespread and well-documented behavior, avian haemosporidians represent an ideal model to investigate the influence of animal migration on parasite life-history.
I conducted multiple big data modelling techniques to elucidate the role of migration in avian haemosporidian transmission at distinct spatial and ecological scales. Additionally, I also tested for different patterns of parasite and host cophylogenetic congruence between resident and migratory birds. By doing so, I demonstrate the potential of migration to shape parasite ecology and evolution.
I have evidenced how host migration has the potential to couple parasite species by enhancing their distribution and modulating parasite transmission and diversity at regional and global level. Concomitantly, at species level, I have demonstrated that full migratory species harbor greater richness and prevalence of parasites, possibly as a consequence of exposure to a wider range of parasite species. Migratory species also occupy more central positions in host-parasite association networks. Nonetheless, most haemosporidian diversity is harbored by resident species. Meanwhile, at evolutionary scale, they present as strong cophylogenetic congruence with their hosts and resident species. Finally, I found that avian functional traits emerged as the main driver of haemosporidian diversity; strong territoriality and resident status were positively associated with haemosporidian diversity whereas migratory behavior, host geographical range and body mass were negatively associated with it.
Overall, migratory behavior increases infection among migrants, structures parasite transmission and diversity dynamics, and has the potential to introduce parasites into new territories. Hence, migrants enhance the ability of parasites to colonize new environments or distinct regions of the globe. Nonetheless, how migration shapes parasite and host communities depend on the spatial scale considered and in many cases also on the parasite taxa.