Co- and mixed-infections of avian haemosporidian parasites in great tits and blue tits of the French Pyrenees

Abstract

Avian haemosporidia have played a significant role in advancing our understanding of vectored disease epidemiology, and continue to do so. These diverse blood parasites (inclusive of those responsible for avian malaria) are globally distributed, adopt both host-generalist and host-specialist infection strategies, and can be highly pathogenic. Due the diversity of haemosporidia, many avian populations play host to species rich communities of blood parasites. Interactions between parasites coinfecting a single host can lead to increased pathological costs, between-parasite competition may additionally influence spatial and/or temporal parasite distributions. However, many questions remain regarding the implications of these parasite-parasite interactions and their relevance in nature. In this thesis, I study three genera of avian haemosporidia (Haemoproteus, Leucocytozoon, and Plasmodium) which form a community infecting two geographically overlapping host species, blue tits (Cyanistes caeruleus) and great tits (Parus major). In chapter one, I apply a novel-PCR detection method, which improves the sensitivity of such techniques, to survey the complete local haemosporidian community infecting these birds. Leucocytozoon is the most prevalent genus, infecting >90% of individuals. I identify a significant negative association between Leucocytozoon and Haemoproteus spp., which exists despite similar spatial distributions. An interaction is also identified between two clades of Leucocytozoon, Clade A and Clade D, as mixed-infections are lower than predicted. In chapter two, I further explore this Leucocytozoon clade interaction. Clade A is more prevalent in great tits, while Clade D more prevalent in blue tits, neither impact reproductive measures in their typical host. Clade A has lower prevalence in blue tits, but does carry reproductive costs. Blue tits which have Clade D infections are less likely to be infected by Clade A, which implies a conferred resistance against this great tit-typical parasite. Collectively, these studies reveal complex interactions occurring within a multi-host, multi-parasite community which have important implications for haemosporidia epidemiology and parasite-host co-evolution.