Phylogenetic diversity, host specificity and geographic distribution of avian malaria in Africa.

Abstract

Abstract available in PDF.

Three genera of haemosporidians malaria parasites (Plasmodium, Haemoproteus, and Leucocytozoon) are known to infect birds across the globe. Molecular-based research on avian malaria parasites have rapidly increased over recent years. As a consequence, databases such as MalAvi have been constructed as a research platform to promote data accessibility. Centralization of data now allows for metanalyses of data to identify broad scale continental patterns. In this thesis I aim to review all published work on molecular-based avian malaria research in Africa. In Chapter 2 this thesis explores the geographic extent of studies in Africa and highlights important research gaps. Using sequence data available for Africa, in Chapter 3 I tested if the cytochrome b gene, used to detect the presence of parasite DNA within avian host blood, could also be used to delimit different species of parasite. Using the established phylogenetic species, in Chapter 4 I aimed to identify the distribution of these parasite lineages across Africa and examine the extent of their host ranges. Focusing on avian malaria prevalence among hosts distributed in fragmented forests of South-Eastern South Africa, in Chapter 5 I tested for presence of the three genera of parasites in four sympatric bird species (Camaroptera brachyura, Cossypha dichroa, Phylloscopus ruficapilla and Pogonocichla stellata). A total of 460 birds were tested for the three malaria genera using PCR methods. Phylogenetic methods were then used to identify host specificity and the geographic distribution of parasites. This provides important information for how habitat fragmentation affects host-parasite relationships. By reviewing all avian malaria studies in Africa, I found that research effort was not uniform across the continent. Most avian malaria research was conducted on Plasmodium, with most research conducted in the Canary Islands, the Gulf of Guinea, Madagascar and South Africa. Using cytochrome b sequence data available for Africa from MalAvi, I tested for the difference between inter- and intraspecific genetic distances within each of the three genera of avian malaria. A distinct “gap” was recorded in Plasmodium and Haemoproteus, allowing me to divide sequences into OTUs analogous to species. For Leucocytozoon, the gap used came from a suggested distance threshold by previous studies. Using the OTUs and additional information on geography and avian hosts, I tested the hypothesis that species belonging to Haemoproteus are more host specific than Plasmodium which is more generalist infecting a large taxonomic diversity of birds. This was found to be true as well as OTUs which had greater host ranges also had larger geographic ranges. Focusing on a smaller spatial scale I investigated the prevalence of avian malaria in the four sympatric forest bird species occurring in the naturally fragmented forests of South-Eastern South Africa. My research revealed that three of the four avian hosts had low levels of parasite prevalence (10.4-12.1%). The fourth avian host, C. dichroa, had a remarkably higher parasite prevalence (55.6%). The phylogenetic structure of the parasites revealed that there was a higher diversity of host-specific parasite species and lineages that were geographically isolated. In contrast, the most abundant Haemoproteus species was found in all forest types and all four host species. My research has shown that there are still large gaps in our knowledge on these parasites in particular, a wider range of hosts should be examined in geographical regions that are understudied. This study provides a valuable large-scale review of all current knowledge on avian malaria in Africa and contributes significantly towards the field of host-parasite research.