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Title: Evolution and biodiversity of the novel phylum cercozoa
Author: Bass, David
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2005
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Cercozoa: I) biodiversity, distribution, and ecology on a global scale, and 2) the internal phylogeny of the phylum and lower ranking taxonomic groups within it. Additionally, the relationship of Cercozoa to their closest relatives within the infrakingdom Rhizaria, Foramini fera and Radiozoa, were investigated by screening for the presence and nature of poly ubi quit in insertions (Chapter 11). Within Cercozoa and in addition to many 18S rDNA analyses, the utility of 28S rDNA sequences in cercozoan phylogenetic analyses was investigated, both as single gene analyses and when concatenated with 18S rDNA (Chapter 12). Environmental 18S rRNA gene libraries were created using phylum-specific primers from globally distributed sites and a wide range of ecological conditions. These were used to construct a new cercozoan phylogeny, and demonstrate that the number of lineages within Cercozoa is far greater than previously imagined, both within known groups and in the form of novel clades (Chapter 4). Phylum-wide patterns of geographical and ecological distribution were investigated. Some clades were only recovered from particular sampling sites, suggesting geographically and/or ecologically restricted distributions. This is a pattern seen in all environmental gene libraries analysed, but is often eroded by more intensive sampling. Further studies using molecular probes that specifically target some of these groups suggest that distribution patterns differ between lineages/clades. Statistical comparison of library compositions from New Zealand and Panama suggest that on a global scale, cercozoan communities are affected by ecological conditions, but not by geographical distance (Chapter 5). A review and meta-analysis was constructed of all publicly available environmentally-derived eukaryote sequences, showing that Rhizaria accounted for nearly 10% of all unique sequences detected and that cercozoan sequences have been recovered from all environments except pelagic and deep-sea samples (Chapter 3). New sequences were also obtained from pure cultures of diverse cercomonads (Chapter 8), heteromitids (Chapter 9), and proteomyxid and endomyxan amoebae (Chapter 10). These were combined in analyses with all available environmental sequences. The results of these studies are informative about the ecology and phylogeny of each (now known to be substantial) group, and demonstrate that many classification changes need to be made, some of which are proposed in this thesis. The very large number of cercomonad sequences generated has led to a comprehensive revision of tbe former genus Cercomonas. Many environmental 18S rDNA libraries specific to cercomonad subclades allow a comparison of distribution patterns at this fine phylogenetic scale with the broader phylum-wide surveys (Chapter 7). ITS rDNA sequences from two small cercomonad clades were used to map geographical and ecological distribution at an even higher level of phylogenetic resolution (Chapter 6)
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available