Thesis (Ph. D.)--University of Nebraska--Lincoln, 2004. / PDF text: [2] leaves abstract, [127] leaves dissertation : ill. Includes bibliographical references (leaves 110-116 of dissertation).

M.Sc. (Nematology) / An unknown dorylaim species was found at 'The Willows', Port Elizabeth. This species show affinities with the genus Paraxonchinin Krall, 1958, especially on account of the exceptionally narrow anterior end, but does not fit the general description of the genus. A historical review is given of the genus Paraxonchium, and the taxonomic position of the nominal species evaluated at the hand of the original description ...

M.Sc. (Zoology) / The morphometric diagnostic species characteristics of Labronema are presented in tabular form to be used directly in the identification of species. The inclusion of tail drawings of each species facilitates recognition of the thirty four species of Labronema. A diagnostic method, whereby morphometric data from a nematode under diagnosis is compared to tabular data in a linear fashion, is introduced. A dichotomous key is also provided as an aid to go directly to a single species using gross and finite characteristics. A short review is given of the genus Tubixaba Monteiro & Lordello, 1980, and the decription presented of Tubixaba tswanorum n. sp. from Botswana. The new species is closely related to T. parva Pretorius, Kruger and Heyns, in print, from South Africa, but can be readily distinguished from T. parva in being a larger nematode with a longer stylet, the absence of criss-cross radiations in the cuticle, a relatively thicker outer cuticle layer, and a differently shaped tail.

Nematodes are an important animal group that have shown remarkable adaptability, leading to their ubiquitous global distribution. Many are also major parasites of humans, plants and animals; therefore an understanding of nematode biology is of great importance both medically and agriculturally. The phylum is divided into three main taxa: the Chromadoria; the Dorylaimia and the Enoplia. Most studies on nematode biology tend to focus on the nematode model, Caenorhabditis elegans or other nematodes within the Chromadorea (clades III, IV and V). To date the Dorylaimia and the Enoplia (nematodes that occupy clades I and II respectively) have been poorly studied, but recent work on the Dorylaim parasite, Trichinella spiralis, is providing valuable data to help understand the evolution of the Nematoda. The recent publication of the T. spiralis genome has revealed nematode-specific features and has allowed for in depth comparative genomic analyses. These analyses have revealed that in some respects – such as highly conserved signalling pathways, T. spiralis seems to more closely resemble the arthropod outgroup than it does to other nematodes within the Chromadorea. I decided to see whether attributes seen in T. spiralis were conserved in other Dorylaimian nematodes, and extended this study to include two additional Dorylaim nematodes, the free-living Prionchulus punctatus and the parasitic Trichuris muris. T. muris was chosen as it shares a relatively recent ancestor with the lineage leading to the Trichinellidae, whereas P. punctatus, whilst still a Dorylaimian, exists outside of this group. We used transcriptome data from P. punctatus, to further our analysis and characterisation of the Wnt, Hedgehog and TGF-β signalling pathways and show that like T. spiralis, this nematode also has a much less derived set of signaling pathways compared to C. elegans and other members of the Chromadoria. Spliced Leader (SL) trans-splicing is a phenomenon that occurs throughout the nematode phylum; as such it is a trait that was most likely present in the ancestral nematode. Nematodes in the Chromadorea have been shown to use two types of SLs, first characterized in C. elegans; SL1 and SL2. Previous studies have shown that the Dorylaim T. spiralis uses a range of highly polymorphic SL sequences that have only limited similarity to C. elegans SL1 and SL2. In contrast, initial searches for SLs in P. punctatus have shown that it possesses clear SL2-like sequences. I IV investigated the nature of SL trans-splicing within the Dorylaimia. In this study I identified the SL sequences present in T. muris and showed that they are similar to the SLs found in P. punctatus, which is unexpected given that T. muris is more closely related to T. spiralis. This indicates that the complement of SLs found in T. spiralis is derived relative to other nematodes. In C. elegans, it was found that SL trans-splicing is involved in the processing of polycistronic transcription units known as operons, into monocistronic mRNAs. To date, operons have only been seen within Chromadorean nematodes, but the presence of SL trans-splicing in the Dorylaimia implies that they may be present in these nematodes also. This thesis presents, for the first time, evidence for the presence of operons in the two Dorylaimian nematodes; T. spiralis and T. muris. We show that operons are likely to be an ancient feature of the Nematoda, with evidence for a conserved operon that spans throughout different nematode species within the phylum.

D.Phil. (Nematology) / The science of taxonomy or the organisation and labelling of organisms may strike many as dull and stuffy but everyone working in this fascinating field finds that it leads to some of the most searching and interesting questions. Taxonomists are confronted by a well organised world of nature, exactly that what prompted the great taxonomist Linnaeus to develop his clear, hierarchical method of classification. But at the same time they are faced with a bewildering diversity and variation within this organised whole. Seeking to order the stable units in the midst of this diversity is the descriptive task of taxonomy. But many taxonomists go further than that, they seek a theory and ask: what causes life to be ordered? Here they land in the middle of philosophical debate and controversy. The field of taxonomy has, unfortunately, been divided by arguments about what a species is, how to demarcate a species, and even whether they are real or not. Today this "species question" is phrased in broader terms. The real question is not whether species are fixed but whether there is any stable, objective unit in nature. What do the patterns of similarity and difference mean - creation according to a common plan with the potential of variation, or descent from a common ancestor with modifications? Charles Darwin believed that change is unlimited, that species are infinitely variable. He thought that species could vary indefinitely and in any direction. Creationists on the other hand, believe that change is limited by a basic organic "unit", the "created kind" and within the boundary of that fundamental unit, variation can be profuse, but it can never lead to the creation of a new basic type. This is near the essentialism as taught by Aristotle nearly 2000 years ago. Aristotle thought that each species embodies an eternal, unchanging ideal or archetype. The problem with this view is that it assumed a single form or pattern. Most biologists until the time of Darwin held to the typological view, a view considered by many scientists today as very plausible. This theory holds that the organic world is discontinuous, that all major groups of organisms are separate and breed true to type. A species is also defined by a cluster of characteristics - each member of the species may have some but not all of the diagnostic features. Another view is cladism, founded by the entomologist, Willy Hennig. It is concerned with the patterns found in nature and involves the finding of the positive and verifiable characters of the various species and determining how all species fit into the animal kingdom.

M.Sc. / This study embraces three facets, namely a checklist of all the freeliving and plantparasitic nematodes, reported from the Kruger National Park, descriptions of the nematode species found during the present study, and a historical review of the family Aporcelaimidae with emphasis on the genus Aporcelaimellus Heyns, 1965, a species compendium and descriptions of several new species ...