Graduation Year

2008

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Biology

Major Professor

James R. Garey, Ph.D.

Keywords

Evolution, G3PDH, SERCA, Animalia, Molecular cladistics

Abstract

Genetic sequence data have been widely used to analyze metazoan phylogenies for two decades, and numerous datasets have been generated for testing relationships at many different taxonomic levels. The rapid divergence of major metazoan body plans during the Cambrian explosion confounds the determination of phylogenetic relationships among metazoan phyla. Few molecular analyses at this level have used both multiple genes and broad taxonomic representation. Furthermore, most studies have relied exclusively on the small ribosomal subunit rRNA gene (SSU). Many of the other genes that have been examined have possessed substitution rates that are inappropriate for resolving the relationships among metazoan phyla. High substitution rates produce homoplasy, while low rates limit informative changes. Glycerol 3-phosphate dehydrogenase (G3PDH) and sarco/endoplasmic reticulum Ca²? channel ATPase (SERCA) were chosen for phylogenetic analysis.

These genes have low copy numbers, ubiquitous expression, and similar substitution rates among taxa, which complement the substitution rate of SSU. These genes were sequenced from 17 metazoan phyla for comparison to SSU phylogenies. Various combinations of the new datasets and a dataset of SSU sequences from comparable taxa were examined using Bayesian, Maximum Likelihood and Neighbor Joining phylogenetic methods. The new genes produced metazoan trees similar in topology to SSU phylogenies. Resolution and nodal support values increased with dataset size. Deuterostomia, Arthropoda and Lophotrochozoa were further examined to determine if dataset combinations could provide better resolution than SSU data alone. The analysis of combined datasets provided high support for the monophyly of all examined bilaterian phyla except Annelida and Platyhelminthes.

Sipuncula consistently grouped within Annelida, while Acoela branched at the base of Bilateria away from the monophyletic Euplatyhelminthes. Support was also found for the monophyly of Euchordata, Ambulacraria and Echinozoa within Deuterostomia; Insecta, Pancrustacea, Euchelicerata and Chelicerata within Arthropoda; and Eulophotrochozoa, Lophophorata and a clade comprising (Nemertea (Annelida (Mollusca + Lophophorata)) within Lophotrochozoa. However, the positions of Ophiuroidea, Collembola, Myriapoda, Rotifera and Euplatyhelminthes varied among analyses. Many of these results have been predicted by other genetic and morphological analyses. However, this is the first time that molecular analyses have produced resolution within Eulophotrochozoa.

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