Trypanosoma cruzi is the parasite that causes Chagas disease, which infects 8-9 million people in rural Latin America, and the Southern U.S. Despite its importance, little is known in terms of how and where this parasite evolved. There are competing hypotheses pointing either to marsupials or bats as original hosts of T. cruzi and its closest relatives before jumping to other mammals, including humans. However, no definitive data have been gathered to favor one hypothesis over the other. This project will dissect the evolutionary relationships among mammalian trypanosomes to clarify the host and geographic origins of these parasites through the generation of DNA sequence data from both museum specimens and contemporary samples followed by molecular phylogenetic and biogeographic analyses.
This research will promote awareness of the importance of museum collections to research efforts. Also, a new website "PhyloTryp" will be implemented, which will provide standardized tools and data to facilitate evolutionary research on trypanosomes. Finally, the training of an undergraduate student will be accomplished through the AMNH REU program. By the end of the program, the student will have gained basic laboratory and analytical skills, and a peer-review publication will be prepared with the mentee.
The parasite Trypanosoma cruzi causes Chagas disease, an important zoonosis of humans and other mammals in the Americas. As a human pathogen this parasite has been studied extensively; however, research on the populations of T. cruzi infecting exclusively wild mammals and other species of closely related trypanosomes (the T. cruzi clade) have been neglected despite their importance for understanding the origins of Chagas disease and the interplay between trypanosomes and their mammalian hosts. With the main objective of having a better understanding of the diversity and biogeography of the Trypanosoma cruzi clade, we accomplished the following objectives: 1) to provide a phylogenetic hypothesis of T. cruzi sensu lato and the T. cruzi clade, 2) to test species limits within T. cruzi sensu lato and the T. cruzi clade, and 3) to infer the biogeographic, and host-parasite history of the T. cruzi clade 1) We generated two phylogenies, a multilocus phylogeny of T. cruzi sensu lato, and a phylogeny of the T. cruzi clade. The phylogeny of T. cruzi sensu lato contained all non-hybrid lineages, including all lineages that infect bats. To obtain the phylogeny of the T. cruzi clade, we increased the taxon sampling of the members of the clade, by screening > 1,000 samples of mammalian trypanosomes in museum’s tissue collections. Samples originally came from wild mammals collected from multiple locations in Africa, the New World, Australasia, and Southeast Asia. 2) With the wealth of new data acquired, and the phylogenies generated, it was possible to test whether each of the T. cruzi sensu lato lineages (with a special emphasis on the bat-exclusive lineages), actually warrant specific status, as well as determining the number of species that are part of the T. cruzi clade. To accomplish this, we performed three different species delimitation approaches. These delimitations resulted in the recognition of at least three species within T. cruzi sensu lato, and the number of members of the T. cruzi clade exceeds 30 species. These results indicate that our previous knowledge on the diversity of trypanosome species of the T. cruzi clade has been largely underestimated. Previously, we knew that this clade was comprised by 18 species. 3) The members of the T. cruzi clade are distributed on all continents except Antartica, and inferring their biogeographic history has been elusive. Here, with increased taxon sampling it was possible to reconstruct the biogeographic history of the group by conducting analyses using a model-based approach that is able to account for uncertainty in the phylogeny. Additionally, we reconstructed the ancestral hosts (i.e., bat, bat and non-volant host, and only non-volant host) for the T. cruzi clade. Our reconstructions indicate that the origins of the T. cruzi clade likely occurred in Africa or South America, and that the ancestral hosts of the clade were bats. Moreover, only a handful of host switches are required to explain the current host-trypanosome associations. As part of this project, an undergraduate student from Carnegie Mellon University (Michelle Yu) received training in molecular techniques (i.e., DNA extraction, PCR, and DNA sequencing, and basic analyses with DNA sequences) during the summer months of 2013.
