M.S. (Master of Science)
Department of Biological Sciences
Acanthocephala--Phylogeny; Worms--Phylogeny; Ribosomes; Nucleotide sequence
Phylogenetic relationships within the Phylum Acanthocephala have remained unresolved. Past efforts have focused on creating classifications with little phylogenetic consideration. The Phylum Acanthocephala is currently divided into three classes, Archiacanthocephala, Palaeacanthocephala, and Eoacanthocephala. The taxonomic division into three classes is based on morphological similarities and ecological considerations of the intermediate and definitive hosts. In this study, eleven acanthocephalan species representing the three recognized classes were collected from vertebrate definitive or invertebrate intermediate hosts. Nucleic adds were isolated and PCR was used to amplify a 1,766 base-pair region of the 18S rDNA. Spin-filtered PCR product was ligated into p-GemT vector plasmid and recombinant plasmids were used as templates in a two- step cyde sequencing procedure (A Taq kit, United States Biochemical). Preliminary alignment of nudeotide sequences was performed using the CLUSTAL V computer program. Maximum parsimony, maximum likelihood, neighbor-joining, and Fitch-Margoliash methods were used to estimate phylogenetic relationships. The robustness of inferred trees (except maximum likelihood) was assessed by using bootstrap resampling with 1000 replications. All methods of analysis support the monophyly of the classes Archiacanthocephala, Palaeacanthocephala, and Eoacanthocephala. The Polymorphida (Palaeacanthocephala) and Polymorphidae were also monophyletic. Monophyly of acanthocephalan taxonomic groupings indicates that the current higher-order taxonomic scheme reflects phylogenetic relationships. The phylogeny is able to provide information regarding the evolutionary significance of various morphological and ecological characteristics of the Acanthocephala. Levels of 18S rDNA sequence divergence among acanthocephalans, when compared to other metazoans, indicates that the group may predate its arthropod and vertebrate hosts. Based on levels of sequence divergence, a Cambrian origin of the Acanthocephala is hypothesized.
Near, Thomas J., "Phylogenetic relationships of the acanthocephala inferred from 18S ribosomal DNA sequences" (1995). Graduate Research Theses & Dissertations. 4381.
Northern Illinois University
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