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Format:
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Author:
De la Rúa, Nicholas M.
Dept./Program:
Biology
Year:
2012
Degree:
MS
Abstract:
Systematics of disease vectors provide a framework for understanding vector capacity, biology, distribution, cataloguing, and understandings of taxa as biological units. The Triatominae, a sub-family of the Reduviidae, are a diverse assemblage of hematophagous insects capable of transmitting Trypanosoma cruzi, the etiological agent of Chagas disease. Currently, the 140 extant species are arranged in five tribes comprised of 15 genera. Only three of the 15 genera are epidemiologically important: Triatoma, Panstrongylus, and Rhodnius. Below the genus level, species have been classified into species complexes, defined as species sharing extensive morphological similarities. In order to test systematic hypotheses in a phylogenetic framework, a molecular species complex is a defined as a group of closely related species, monophyletic in their origin. This definition allows systematic topologies from diverse data to be tested using likelihood tests and assess the fit of a systematic hypothesis.
In this work, head morphometry is used to infer the evolutionary relationship of 11 species from 183 specimens of North and Central American Triatoma, creating a morphometric species complex hypothesis. The species groups inferred from morphometry and the currently proposed species complexes based on morphology are used to constrain topologies of phylogeny inferred from a 16S (mtDNA), ITS-2 (rDNA), and a combined molecular data set. The statistical support of competing hypotheses is assessed using the ShimodairaHasegawa test of topology. The analyses show the unconstrained molecular phylogenies better fit the data than any other competing phylogeny, with exception of the combined dataset. These findings provide a means to updating the systematics of the North and Central American Triatoma and clarify the relationships in a hypothesis-testing framework.
In addition to examining species relationships, intraspecific relationships within the species T. dimidiata sensu lato were inferred from mitochondrial DNA sequence data. The taxonomy and systematics of this important vector of Chagas disease in Mexico and Central America remain unclear. Molecular phylogenies based on ITS-2 have revealed the presence ofa highly divergent cryptic species, and support the sub-specific status of three populations. A 616 nt fragment of cytochrome b (mtDNA)was analyzed from 216 species of T. dimidiata sensu lato from across its geographic distribution. Prior knowledge of ITS-2 group identity was obtained from 99/116 sequences generated by this work allowing a priori hypothesis testing of congruence between molecular markers. In summary, ITS-2 and cyt b phylogeny are not congruent, and the levels of genetic variation are higher than previously reported.
Furthermore, a new, highly divergent clade at the level of a new species was identified in Cayo Creek, Belize. Cyt b sequence variation and phylogeny support the cryptic species, T. sp. aff. dimidiata, isolated in Yucatan, Mexico and Peten, Guatemala. However, cyt b does not support clear differentiation of three sub-species restricted to Southern Mexico, Central America, and Panama with Colombia, respectively, as it reveals more extensive genetic variation and divergent evolutionary lineages than does rDNA.