this parasite, T. thorsborneae sp. nov., that was deeply divergent from T. gallinae and T. vaginalis. Further investigation into the trichomonads of Australasian pigeons and doves, including the sampling of almost half of the world's columbid genera, led me to discover a total of six new lineages of Trichomonas, including a basally branching clade of species found in Ptilinopus fruit-doves. Such genetic diversity strongly supports a columbid host for the ancestral Trichomonas. Despite evidence for host-parasite cospeciation it is clear that a variety of events including host switching need to be invoked to explain the evolutionary history of the genus Trichomonas. Such a prolonged association with Trichomonas has likely led to a degree of coevolution between columbids and their parasite. My finding of very high abundance of T. thorsborneae sp. nov. in individual Pied Imperial-Pigeons for instance was not associated with alterations in key fitness parameters such as metabolic stores. This suggests the evolution of tolerance or trade-offs for the maintenance of Trichomonas in columbid hosts. An unusual possibility is that a fitness benefit is incurred to populations of these hosts through release from predator pressure when birds of prey feeding on columbids experience morbidity and mortality due to trichomonosis, a well-recognised phenomenon. The ancestral association of the genus Trichomonas with columbids infers an extraordinary example of host-switching, that of T. vaginalis in humans. Both the genomic architecture of human-isolated T. vaginalis and the genotypic diversity of columbid-isolated strains of this organism support my hypothesis of a columbid origin for one of humanity's most prevalent sexually transmitted infections.
|Qualification||Doctor of Philosophy|
|Award date||01 Sep 2012|
|Place of Publication||Australia|
|Publication status||Published - 2013|