UVM Theses and Dissertations
Format:
Print
Author:
Martinsen, Ellen S.
Dept./Program:
Biology
Year:
2009
Degree:
PhD
Abstract:
The avian malaria parasites (genera Plasmodium, Haemoproteus, and Parahaemoproteus) are diverse, infect a broad range ofbirds on all warm continents, and are implicated as important agents of infectious disease in bird populations. Traditional taxonomy by use of morphological characters has guided understanding of the evolutionary history, relationships, and distribution of these parasites across bird hosts. With advances in molecular phylogenetics and the availability of gene loci from all three genomes of the malaria parasites (nuclear, mitochondrial, and plastid), we are now in better position to examine the systematics ofthese important parasites of birds and to study host-parasite associations including the incidence of host switching.
As demonstrated in my first chapter, traditional methods to survey and identify malaria parasites within a bird community may be informative in describing new host-parasite associations as well as the relative prevalence of different parasite genera. When put to test by genetic and phylogenetic analysis of the mitochondrial cytochrome b gene, the majority of traditionally described parasite species investigated conformed to evolutionary lineages. However, by analysis of a single gene, many of the parasite relationships were unresolved and cryptic lineages of parasites were not distinguishable on the basis of morphological criteria alone. To test the evolutionary significance of morphological characters at broader taxonomic scales, I then subjected the avian Plasmodium subgenera to molecular phylogenetic analysis of two mitochrondrial genes. Morphological characters, in addition to being of limited availability in the vast majority of infections, also varied in their phylogenetic significance, with two of the five Plasmodium subgenera found to not be monophyletic.
By increasing the number of gene loci used for inference of evolutionary relationships, I reconstructed the first well resolved phylogeny for the malaria parasites and closely related genera. The results again demonstrate a cryptic diversity, with the genus Haemoproteus comprised of two divergent clades of parasites, likely representative of distinct genera. This study also illustrated the incidence of host shifts by Plasmodium parasites repeatedly between lizard and bird hosts as well as the importance of vector shifts in parasite diversification. Finally, the study defined the malaria parasites as the clade, that contains the three genera Plasmodium, Haemoproteus, and Parahaemoproteus.
Using four genes, I then addressed traditional species hypotheses and presented for the first time a well resolved phylogeny for the nominate genus Parahaemoproteus. A substantial cryptic diversity was revealed with an actual species diversity twice that currently recognized for the genus. Underlying cryptic diversity is a convergence in morphology based upon host association, with divergent parasite lineages displaying identical morphology when found to infect closely related host species. Last, by surveying the parasites of native and non-native North American birds, phylogenetic analysis of the cytochrome b gene revealed the switching of parasites with both narrow and wide host ranges into novel bird hosts. These results indicate that a diversity of malaria parasites are readily able to host switch in recent time and indicate the threat they pose as agents of disease to naIve bird populations and species.
As demonstrated in my first chapter, traditional methods to survey and identify malaria parasites within a bird community may be informative in describing new host-parasite associations as well as the relative prevalence of different parasite genera. When put to test by genetic and phylogenetic analysis of the mitochondrial cytochrome b gene, the majority of traditionally described parasite species investigated conformed to evolutionary lineages. However, by analysis of a single gene, many of the parasite relationships were unresolved and cryptic lineages of parasites were not distinguishable on the basis of morphological criteria alone. To test the evolutionary significance of morphological characters at broader taxonomic scales, I then subjected the avian Plasmodium subgenera to molecular phylogenetic analysis of two mitochrondrial genes. Morphological characters, in addition to being of limited availability in the vast majority of infections, also varied in their phylogenetic significance, with two of the five Plasmodium subgenera found to not be monophyletic.
By increasing the number of gene loci used for inference of evolutionary relationships, I reconstructed the first well resolved phylogeny for the malaria parasites and closely related genera. The results again demonstrate a cryptic diversity, with the genus Haemoproteus comprised of two divergent clades of parasites, likely representative of distinct genera. This study also illustrated the incidence of host shifts by Plasmodium parasites repeatedly between lizard and bird hosts as well as the importance of vector shifts in parasite diversification. Finally, the study defined the malaria parasites as the clade, that contains the three genera Plasmodium, Haemoproteus, and Parahaemoproteus.
Using four genes, I then addressed traditional species hypotheses and presented for the first time a well resolved phylogeny for the nominate genus Parahaemoproteus. A substantial cryptic diversity was revealed with an actual species diversity twice that currently recognized for the genus. Underlying cryptic diversity is a convergence in morphology based upon host association, with divergent parasite lineages displaying identical morphology when found to infect closely related host species. Last, by surveying the parasites of native and non-native North American birds, phylogenetic analysis of the cytochrome b gene revealed the switching of parasites with both narrow and wide host ranges into novel bird hosts. These results indicate that a diversity of malaria parasites are readily able to host switch in recent time and indicate the threat they pose as agents of disease to naIve bird populations and species.