Publication Date:
2022-05-25
Description:
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
Description:
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.
Description:
This work was supported by a grant from the National Science Foundation, DEB-0075618
"Genomic approaches to metazoan evolution; lophotrochozoans and Hox genes" to Kenneth
Halanych. Bryozoan Hox research was supported by a Doctoral dissertation Improvement Grant
from the National Science Foundation, DEB-OI04984 "Phylogenetic inference from bryozoan
Hox genes" to Kenneth Halanych and Yale Passamaneck. Additional support was provided by
the Woods Hole Oceanographic Institution Education Office.
Keywords:
Mollusks
;
Phylogeny
;
Evolution
;
Genome mapping
;
Homeobox genes
;
Recombinant DNA
;
Cladistic analysis
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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