Abstract:
DNA sequencing and phylogenetic analyses were conducted to investigate evolutionary
relationships between taxa within the metazoan clade Lophotrochozoa. Chapter 1
presents an introduction to phylogenetics of the Metazoa and the clade Lophotrochozoa.
Chapter 2 analyzes higher level relationships between the major groups within the
phylum Mollusca using sequences of the nuclear ribosomal large-subunit RNA gene
(LSD rDNA). Results presented provide the first molecular evidence for a close
relationship between the Scaphopoda and Cephalopoda. Phylogenetic trees with this
topology were found to have likelihood scores significantly better than those for
phylogenies constrained to fit the Diasoma hypothesis grouping Scaphopoda and Bivalvia
as sister taxa. Chapter 3 utilizes LSU rDNA sequences to analyze relationships between
diverse phyla within the clade Lophotrochozoa. LSU rDNA sequences were found to
provide greater resolution than has been provided by previous analyses of the nuclear
small-subunit ribosomal RNA gene (SSU rDNA). Analysis ofLSU rDNA sequences
recovered the monophyly of several phyla, such as Mollusca and Anelida, whose
members are found to be paraphyletic using SSU rDNA sequences alone. Results also
suggest that the clade Platyzoa, including rotifers and platyhelminthes, may have arisen
within the Lophotrochozoa, rather than as a sister group to lophotrochozoans. Chapter 4
investigates the Hox gene complement of the bryozoan Bugula turrita. Six Hox genes
were recovered, including an ortholog of the posterior class gene Post2, which is a
synapomorphy for the Lophotrochozoa. The identification of a Post2 ortholog provides
evidence of a close relationship between the Bryozoa and other lophotrochozoan phyla.
