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Molecular phylogenetic studies on filarial parasites
Abstract
This thesis is the first large-scale molecular phylogenetic study on filarial parasites (family Onchocercidae) which includes 16 species of 6 genera: Brugia malayi, B. pahangi, B. timori, B. patei, B. beaveri, B. buckleyi, Wuchereria bancrofti, W. kalimantani, Mansonella perstans, Loa loa, Onchocerca volvulus, O. ochengi, O. gutturosa, Dirofilaria immitis, Acanthocheilonema viteae and Litomosoides sigmodontis. Two sets of sequence data (5S rDNA spacer and HHa I repeat) were collected by PCR, cloning and dideoxy sequencing. The 5S rDNA gene spacer region sequences were aligned and analyzed by maximum parsimony algorithms, distance methods (neighbor-joining, UPGMA and Fitch-Margoliash methods) and maximum likelihood methods to construct phylogenetic trees. Bootstrap analysis was used to test the robustness of the different phylogenetic reconstructions. The data indicated that both 5S spacer region sequences and Hha I repeat sequences are highly conserved within species yet differ significantly between species. Spliced leader sequences were observed in all of the 5S rDNA spacers sequenced with no sequence variation, although flanking region length heterogeneity was observed even within species. The 5S rDNA spacer sequence data set was used to resolve the branching order of the six genera studied. The various tree-building methods gave very similar results. This study identified four clades which are strongly supported by bootstrap analysis: the Brugia clade; the Wuchereria clade; the Brugia-Wuchereria clade and the Onchocerca clade. Ascaris lumbricoides was used as an outgroup to root the trees generated using 5S sequence data. The analyses indicated that L. sigmodontis and A. viteae may be the most primitive among the 16 species studied. The results of this study do not support the classification which places Loa loa and D. immitis into the Dirofilariinae subfamily. Hha I repeat sequences are 322 nucleotides long, highly repeated and tandemly arranged sequences unique to the nuclear genomes of the genus Brugia. Phylogenetic analyses on the Hha I repeat sequence data set identified at least two clades: the B. pahangi-B. beaveri clade and the B. malayi-B.timori-B. buckleyi clade. Results from the analyses of both data sets were combined and a hypothesis for the phylogeny of the sixteen species of filarial parasites was proposed.
Subject Area
Molecular biology|Genetics
Recommended Citation
Xie, Hong, "Molecular phylogenetic studies on filarial parasites" (1993). Doctoral Dissertations Available from Proquest. AAI9408364.
https://scholarworks.umass.edu/dissertations/AAI9408364