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Within the parasitic nematode Ancylostoma ceylanicum, a nearly 20 million-year-old Bel/Pao LTR-retrotransposon encodes an ancient viral class II envelope fusion protein. Typically, retroviruses and related degenerate retrotransposons encode a hemagglutinin-like class I envelope fusion protein. A subset of Bel/Pao LTR-retrotransposons within the phylum Nematoda have acquired a phlebovirus-like env and utilized the encoded fusion machinery to escape the genome as intact and novel exogenous retrovirus. This includes C. elegans retroelement 13 virus which was recently reclassified as a member of the genus Semotivirus. A 3.76 Å cryoEM reconstruction of the encoded membrane fusion machinery of the A. ceylanicum retroelement shows that it is a phleboviral homologue and class II fusion protein. Biophysical and biochemical characterization indicate this ancient class II fusion protein functions under specific physiological conditions targeting late-endosomal membranes much like modern viral class II fusogens. Together, this evidence points to a novel case of gene exaptation. Similarly, class II fusion homologues have been identified within the double-stranded, circular, nuclear plasmids of the slime mold Dictyostelium. While these plasmids, specifically Ddp1 and Ddp5, have been used as transfer vectors in dictyostelid studies, their relation to known viruses has gone unrecognized. Like the env captured by the BEL/Pao LTR retrotransposons of Nematoda, Ddp1 and Ddp5 encode a ‘developmental’ transcript that share features with a modern RVFV-like M-segment and likely represents another ancient class II fusion protein. Why this plasmid carries a complete set of fusion machinery and whether it forms infectious virus-like particles is yet to be determined. Regardless, the presence of Ddp1 and its potential role in sexual reproduction in Dictyostelium provide insight to the promiscuity of envs and the importance of selfish genetic elements (i.e. viruses, plasmids, and transposons) in host genomic evolution, horizontal gene transfer, and virus evolution. The work presented in this thesis highlights the role viral fusion proteins and their homologues in biological development and the evolution of sex. It demonstrates the potential of nematodes as an ideal system for the study of retrovirus evolution and retroviral degradation into LTR-retrotransposons and transposable elements. Due to the remarkable conservation of structure in the class II viral fusion protein fold, distant and likely functional homologues have been identified. In addition to the structural and biochemical analysis, the phylogenetic analysis included emphasizes the genetic exchange of envs and the potential for viral zoonoses or host shift.

In seeking new hosts, entomopathogenic nematode foraging strategies are believed to range from sit-and-wait foragers (ambushers) to widely active foragers (cruisers).  This study investigated the behaviour, dispersal and competitive ability of entomopathogenic nematodes of the genera Heterorhabditis and Steinernema in relation to soil habitat. The host finding and competitive ability of Steinernema carpocapsae, an “ambusher” and Heterorhabditis megidis, a “cruiser” in two contrasting soil habitats (sand and peat) showed “habitat-specific” differences in foraging mode between the two species.  In peat, S. carpocapsae outcompeted H. megidis in terms of host finding, whereas the opposite was true in sand.  In the appropriate habitat, both nematodes showed behaviours not predicted by their supposed foraging strategy.  Experiments examining the interspecific interactions between S. carpocapsae and H. megidis also showed significant differences in the population dynamics between the two species in relation to habitat. Nictation behaviour is frequently cited as a host finding strategy in ambush foraging nematodes. The study confirms that ambush foraging species S. carpocapsae and Steinernema scapterisci frequently nictate, but show that habitat is an important factor regulating this behaviour.  This study also demonstrates the ability of the cruise foraging nematode, H. megidis to nictate on habitats not previously examined.

The function of prolyl 4-hydroxylases (P4H) in the formation of the nematode cuticle was studied. The cuticle is one of the two major forms of extracellular matrix (ECM) in the nematode and performs vital roles in these animals including acting as an exoskeleton to maintain body morphology. Nematodes develop from an embryo through four larval moults to the adult stage. Each larval stage is characterised by the synthesis of a new cuticle and shedding of the existing structure. The nematode cuticle is a complex multi-layered structure formed principally from collagens that are synthesised by the underlying hypodermal tissue. Collagens are characterised by repeats of the amino acid sequence Gly-X-Y, where Gly is glycine and X and Y can be any residue but are most commonly proline and 4-hydroxyproline respectively. Three collagen monomers combine to form a triple helix, with the presence of 4- hydroxyproline residues stabilising the structure. The enzyme P4H modifies Y position proline residues in newly synthesised collagen molecules within the endoplasmic reticulum (ER) of the cell to produce 4-hydroxyproline. P4H role in cuticular ECM formation was examined primarily using the free-living species Caenorhabditis elegans due to its ease of handling and culture in the laboratory, the range of genetic and transgenic techniques available, and the complete genome sequence. Characterised collagen P4H from other species are most often multi-enzyme complexes formed from catalytically active beta subunits with the alpha subunit being the enzyme protein disulphide isomerase (PDI). The role of PDI in these complexes is not connected to its enzymatic activity but instead functions to keep the beta subunits in a catalytically active form within the ER of the cell. The described vertebrate P4Hs are alpha2beta2 tetramer complexes. Two different alpha subunits have been identified which form into separate enzyme complexes with a common PDI beta subunit. In this study the genes Ce-phy-1, Ce-phy-2 and Ce-pdi-2 were examined for their role in cuticular ECM formation in C. elegans. These genes were shown to be expressed throughout development in cuticle collagen synthesising hypodermal tissue in a manner reflecting the expression of their substrate, placing the encoded enzymes in the appropriate tissue for collagen modification, at times of maximal collagen synthesis. Disruption of Ce-phy-1 gene function produced nematodes with a mutant body shape known as dumpy (Dpy). This demonstrated that this gene is required for correct body morphology and led to the identification of the strain dpy-18 as a Ce-phy-1 mutant. This represented the first identification of a P4H mutant in any organism. Double disruption of Ce-phy-1 and Ce-phy-2 or Ce-pdi-2 singly resulted in an embryonic lethal phenotype due to the loss of P4H activity resulting in a cuticle unable to maintain nematode body shape. Disruption of these genes was demonstrated to have an affect on the localisation of specific cuticle collagens. The forms of P4H complex present were examined which revealed the presence of a unique mixed a subunit tetramer, in addition to the already described dimer form of the enzyme. Examination of three divergent putative Ce phy genes did not reveal any role for these in modification of the major ECMs in this nematode and showed that only Ce-PHY-1, Ce-PHY-2 and Ce-PDI-2 perform the essential modification of cuticle collagens. P4H was also studied in the human infective filarial nematode Brugia malayi which is one of the causative agents of lymphatic filariasis in humans, a disease that affects over 120 million people. A phy gene homologue, named Bm phy-1, was cloned and characterised from this organism. In contrast to the both human a subunit-encoding genes, which were shown to rescue the C. elegans dpy-18 P4H mutant, expression of Bm-phy-1 was not sufficient to repair the mutant form of these nematodes. Expression of this gene was demonstrated in all life cycle stages examined, with the gene promoter directing expression of a reporter gene to the hypodermal cells of C. elegans.

ES-62 is a filarial nematode excretory secretory glycoprotein of mass 57.8 kDa, from the rodent filarial nematode Acanthocheilonema viteae. ES-62 has been shown to possess immunomodulatory capabilities, some of which can be attributed to the phosphorylcholine moieties that are attached to certain of the carbohydrate chains of ES-62. Studies of the effects of ES-62 on B lymphocytes have shown that ES-62 downregulates B lymphocyte activation by selectively targeting protein kinases, such as ErkMAPKinase, downstream of the B cell receptor resulting in immunosuppression of the host immune system. ES-62 has been shown to have a similar effect in T lymphocytes. This thesis describes the search for structural information about ES-62. Three main techniques were employed to characterise the low resolution structure of ES-62; bioinformatics, analytical ultracentrifugation (AUC) and small angle X- ray scattering (SAXS). Bioinformatics techniques identified six proteins homologous to ES-62 on the basis of primary structure and six proteins homologous on the basis of secondary structure. Homology modelling of ES-62 in its entirety was not possible due to a lack of structural information about the six proteins homologous to ES-62 on the basis of amino acid sequence. However, residues 252-343 of ES-62 were modelled due to the homology of this region with residues 74-168 of a leucy1 aminopeptidase from Aeromonas proteolytica for which the structure is known. AUC and SAXS techniques demonstrated that ES-62 exists mainly in a tetrameric state and is slightly elongated in structure. A low resolution structure of ES-62 was also obtained using DAMMIN (Svergun,1999), a computer program which allows the ab initio determination of a three-dimensional structure from the small angle scattering curve of a protein. In addition, this thesis describes the establishment of two recombinant ES-62 expression systems, one of which was unsuccessful due to the aggregation of the expressed protein and the other, while producing rES-62, was contaminated by the presence of a compound absorbing at 260 nm resulting in the rES-62 produced being unsuitable for biochemical or biophysical studies. The search for the receptor through which ES-62 interacts with cells and the fate of ES-62 following this interaction are also discussed. These studies demonstrate that ES-62 binds to specific proteins on the surface of different immune system cells but unfortunately attempts to identify these proteins have not so far yielded a definitive answer. ES-62 has also been shown to locate to both the nucleus and cytoplasm following interaction with cells and appears to be present in different forms in these two locations. This demonstrates that ES-62 is internalised following receptor binding and may induce some of its immunomodulatory effects through interactions with intracellular proteins. Its presence in the nucleus of cells could explain the modulation of transcription factors shown to occur in B lymphocytes following exposure to ES-62.

This thesis describes a series of three experiments designed to estimate the nutritional cost of the immune response to the gastrointestinal nematodes Trichostrongylus colubriformis and Teladorsagia circumcincta in sheep. For each experiment, animals were allocated hierarchically by liveweight into one of four groups that were either infected (group IF), similarly infected and concurrently immuno-suppressed with weekly intramuscular injections of 1.3mg kg liveweight (LW)⁻¹ of methylprednisolone acetate (group ISIF), immunosuppressed only (group IS) or remained as controls (group C). Body composition of all animals was estimated using x-ray computer tomography prior to infection and at the conclusion of each study with bodyweight and faecal nematode egg counts (FEC; eggs gram⁻¹ of fresh faeces (epg)) measured along with blood samples taken for the determination of levels of serum proteins, phosphate and antibodies. In the first trial (Chapter 3), the nutritional cost of both the acquisition and maintenance of immunity to gastro-intestinal nematodes was investigated using immunologically naive 5-month-old lambs and immunologically competent 17-month-old ewes during infection with 2,000 and 4,000 L3 infective T. colubriformis larvae d⁻¹, respectively (80 L3 T. colubriformis larvae kgLW⁻¹ d⁻¹). Profiles of FEC and comparative worm burdens at slaughter indicated an effective immune response was maintained in IF ewes and developed in IF lambs while successfully suppressed in both ISIF lambs and ISIF ewes and was confirmed by serum antibody titres. The typical reduction in voluntary feed intake as a consequence of infection was observed in IF lambs (0.30, p0.05). Infection proportionately reduced the gross efficiency of ME utilization in immunologically normal animals by 0.23 in HIF (p=0.09) and by 0.51 in LIF (p=0.01), but not in immuno-suppressed animals. Immuno-suppression did not suppress serum L3 IgA levels in seven of the eight HISIF and four of the eight LISIF animals. Furthermore, only four out of the eight immunologically normal animals from both the HIF and LIF groups displayed an L3 IgA response. Consequently, regardless of immunosuppression treatment, animals were termed as IgA responders (HR or LR) or non-responders (HN or LN). Feed intake was proportionately reduced from day 22 by 0.15 in HR (p=0.03) and by 0.32 in LR (p=0.01), but was not significantly reduced in HN or LN. Gross efficiency of ME utilization was significantly reduced for LN animals only, being proportionately 0.59 (p

Abstract: Masters thesis. Life cycle, levels of infection and patterns of transmission of the parasite Protostrongylus boughtoni were studied in populations of snails and snowshoe hares near Slave Lake, Alberta and in laboratory experiments.

Abstract: Doctoral thesis. Study of several aspects of the ecology of free-living soil nematodes on the Truelove Lowland high arctic terrestrial ecosystem on Devon Island.

Abstract: Doctoral thesis. Study area was within a 9 km radius of Jasper townsite.

RESUMEN. Estudiamos las alteraciones más generales en la composición de cierta fauna de suelo (ácaros, colémbolos y nematodos) de un hayedo natural, un hayedo talado recientemente y un hayedo replantado con alerce en Navarra (Norte de España). Los 476 taxones identificados muestran diferencias de distribución entre los tres biotopos que parecen indicar un efecto disruptivo de la introducción del alerce superior al de la propia tala y al factor estacional. La diversidad faunística es superior en el hayedo natural, a pesar de ser un biotopo fenológicamente más homogéneo.