Molecular phylogenetics of the Metazoan clade Lophotrochozoa

DNA sequencing and phylogenetic analyses were conducted to investigate evolutionaryrelationships between taxa within the metazoan clade Lophotrochozoa. Chapter 1presents an introduction to phylogenetics of the Metazoa and the clade Lophotrochozoa.Chapter 2 analyzes higher level relationships between the major groups within thephylum Mollusca using sequences of the nuclear ribosomal large-subunit RNA gene(LSD rDNA). Results presented provide the first molecular evidence for a closerelationship between the Scaphopoda and Cephalopoda. Phylogenetic trees with thistopology were found to have likelihood scores significantly better than those forphylogenies constrained to fit the Diasoma hypothesis grouping Scaphopoda and Bivalviaas sister taxa. Chapter 3 utilizes LSU rDNA sequences to analyze relationships betweendiverse phyla within the clade Lophotrochozoa. LSU rDNA sequences were found toprovide greater resolution than has been provided by previous analyses of the nuclearsmall-subunit ribosomal RNA gene (SSU rDNA). Analysis ofLSU rDNA sequencesrecovered the monophyly of several phyla, such as Mollusca and Anelida, whosemembers are found to be paraphyletic using SSU rDNA sequences alone. Results alsosuggest that the clade Platyzoa, including rotifers and platyhelminthes, may have arisenwithin the Lophotrochozoa, rather than as a sister group to lophotrochozoans. Chapter 4investigates the Hox gene complement of the bryozoan Bugula turrita. Six Hox geneswere recovered, including an ortholog of the posterior class gene Post2, which is asynapomorphy for the Lophotrochozoa. The identification of a Post2 ortholog providesevidence of a close relationship between the Bryozoa and other lophotrochozoan phyla.

This work was supported by a grant from the National Science Foundation, DEB-0075618"Genomic approaches to metazoan evolution; lophotrochozoans and Hox genes" to KennethHalanych. Bryozoan Hox research was supported by a Doctoral dissertation Improvement Grantfrom the National Science Foundation, DEB-OI04984 "Phylogenetic inference from bryozoanHox genes" to Kenneth Halanych and Yale Passamaneck. Additional support was provided bythe Woods Hole Oceanographic Institution Education Office.

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2003