Molecular Phylogenetics of the Metazoan Clade Lophotrochozoa

摘要

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 relationships between the major groups within the phylum Mollusca using sequences of the nuclear ribosomal large-subunit RNA gene (LSU rDNA). Results presented provide the first molecular evidence for a close relationship between the Scaphopoda and Cephalopoda. Chapter 3 utilizes LSU rDNA sequences to analyze relationships between phyla within the clade Lophotrochozoa. LSU rDNA sequences provided greater resolution than have previous analyses of the nuclear small-subunit ribosomal RNA gene (SSU rDNA). Analysis of LSU rDNA sequences recovered the monophyly of several phyla, such as Mollusca and Annelida, whose members are found to be paraphyletic using SSU rDNA sequences alone. Results also suggest that the clade Platyzoa may have arisen within the Lophotrochozoa. 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.