Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references. Also available in electronic version.

Diss.--Theologische Fakultät--Würzburg--Julius-Maximilians-Universität, 1980.

Plastic debris is an emerging environmental issue, with >10 million tons of plastics debris per annum entering the sea. Exposure to marine conditions facilitates the exponential fragmentation of plastic to micro-sized particles (microplastics). Marine and coastal sediments are a sink for microplastic pollution. Consequently, the ingestion of microplastics by a range of benthic marine invertebrates, including polychaete worms, has been reported in situ. Microplastics are vectors for priority pollutants capable of eliciting adverse health effects. However, the particle and chemical toxicity which microplastics could incur to ecologically-important marine invertebrates is unknown. This thesis aims to determine the potential for microplastics to cause harm in the marine environment, with a focus on benthic polychaete worms. Specifically, it assesses the potential particle toxicity which could arise from chemical-free microplastics; and the potential chemical toxicity which could arise from leached endogenous chemical additives or sorbed chemical pollutants. To address these, an integrative approach was employed, primarily using laboratory-based whole-sediment in vivo exposures, established cellular and whole-tissue toxicity assays, and analytical chemistry. For the first time, this thesis reports that chemical-free microplastics cause particle toxicity in the lugworm Arenicola marina. Feeding activity was reduced during exposure to 5% microscopic unplasticised polyvinylchloride (UPVC) by sediment weight, whilst exposure to ≥1% UPVC by sediment weight significantly reduced energy reserves relative to control animals. Evidence for the transfer and toxicity of endogenous additives from PVC to lugworms is provided. Lugworms exposed to 1% PVC by sediment weight exhibited a 70% increase in additive concentration, coinciding with inhibited mucus production and enhanced lipid reserves and oxygen consumption, compared to control lugworms. Ragworms (Hediste diversicolor) exposed to leached toxicants from bioplastic cigarette debris were found to exhibit significantly longer burrowing times, >30% weight loss, and >2-fold increase in DNA damage compared to control ragworms. Bio-concentration factors for nicotine – the biomarker of exposure - were 500 fold higher from leachates in seawater than from microfibres in sediment. Overall, this thesis provides evidence to suggest that the incorporation of microplastics into marine sediments can significantly impact the health of marine polychaete worms due to both particle and chemical effects. This emphasises the need to reconsider the classification of plastic as non-hazardous and questions whether we as humans are also at risk.

Chez les animaux, l’hermaphrodisme et le gonochorisme sont tous deux apparus plusieurs fois de manière indépendante. Cependant, les voies évolutives impliquées dans la transition entre les systèmes sexuels sont en grande partie inconnues. L’objectif de cette thèse était donc d’étudier la transition évolutive de l’hermaphroditisme vers des sexes séparés chez les vers du genre Ophryotrocha, en s'intéressant en particulier à la manière dont la coopération et la compétition entre individus peuvent déterminer l’allocation de ressources reproductives chez les hermaphrodites, soit en favorisant l'évolution de sexes séparés ou en stabilisant l'hermaphrodisme. Nos résultats ont révélé que les vers hermaphrodites échangent réciproquement des œufs, une forme de coopération qui favorise une allocation des ressources sexuelles biaisée en faveur de la fonction femelle et qui stabilise ainsi l'hermaphrodisme. Toutefois, lorsque les hermaphrodites sont exposés à une forte compétition pour l'accouplement, ils transfèrent les ressources de la fonction femelle vers la fonction mâle, ce qui diminue la production d’œufs et les soins parentaux, mais augmente la motilité et l'agressivité. À des niveaux élevés de compétition pour l'accouplement, motilité et agression peuvent améliorer la recherche et la monopolisation du partenaire, favorisant ainsi la propagation des hermaphrodites biaisés en faveur de la fonction mâle, promouvant ainsi l'évolution de mâles purs et, ensuite, de femelles pures. Enfin, nous avons montré que les hermaphrodites prêts à s'accoupler en tant que mâles uniquement (sans œufs matures) préfèrent des partenaires hermaphrodites prêts à s'accoupler en tant que femelles, qui, en revanche, n'expriment aucune préférence. Globalement, ce travail montre que la coopération et la compétition sont tous deux des facteurs importants dans la répartition des sexes chez les hermaphrodites et suggère que des changements dans l’environnement social ont pu jouer un rôle central dans l’évolution des systèmes sexuels chez les vers du genre Ophryotrocha. / In animals, both simultaneous hermaphroditism and gonochorism originated independently several times. Yet the evolutionary pathways involved in the transition between sexual systems are largely unknown. The aim of this thesis is therefore to investigate the evolutionary transition from hermaphroditism to separate sexes in Ophryotrocha worms, focusing on how cooperation and competition between individuals shape hermaphrodite sex allocation, either promoting the evolution of separate sexes or stabilizing hermaphroditism. Our results revealed that hermaphroditic worms reciprocally exchange egg-clutches, a form of cooperation that favor a female-biased sex allocation and stabilizes hermaphroditism. However, when hermaphrodites are exposed to high level of mate competition, they reallocate resources from the female to the male function, decreasing egg production and parental care and increasing motility and aggression. Under high mate competition level, motility and aggression may improve mate searching and partner monopolization and may favor the spread of male-biased hermaphrodites, promoting the evolution of pure males and, later, pure females. Finally, we showed that hermaphrodites ready to mate as males only (without ripe eggs) prefer hermaphrodites ready to mate as females as partners, which, in contrast, do not express any preference. Overall, this work shows that both cooperation and competition are important factors in hermaphrodite sex allocation, and suggests that changes in the social environment may have played a central role in the evolution of sexual systems in Ophryotrocha worms.

Thesis (Ph. D. (Botany)) -- University of Limpopo, 2020 / Colophospermum mopane (Benth.) J. Léonard, commonly known as mopane, is a dominant tree or shrub in the mopane woodland. It is distributed in the low-lying areas of southern Africa’s savannas. Mopane maintains its foliage well into the dry season, and thus provides nutritional forage for browsers such as Tragelaphus strepsiceros, commonly known as the greater kudu. Despite its wide distribution and value as a source of forage for browsers, especially during the dry season, knowledge of the effect of browsers on mopane leaf quality is limited. There is also inadequate knowledge of the diet composition of the greater kudu during different seasons in the mopane woodland. Such information is important for proper management of browsers in the mopane woodland. As a result, a field experiment was conducted at Musina Nature Reserve, Limpopo Province, South Africa to determine the effect of pruning on mopane leaf phenology, production, macronutrients, trace elements and secondary metabolites. Pruning was conducted to simulate the effect of browsing by large herbivores such as the greater kudu on mopane leaf quality. In addition, rumen content analysis of greater kudu was conducted in order to quantify the amount of mopane and other plants browsed during the dry and wet seasons. Collected datasets were analysed using descriptive and inferential statistics. A two-tailed Mann-Whitney U-test was used to test the effect of pruning on mopane leaf phenology and production. The effect of pruning on the monthly concentration of macronutrients, trace elements and secondary metabolites was tested using a two-tailed t-Test: Two-Sample Assuming Equal Variance. The seasonal and annual effect of pruning on the concentration of macronutrients, trace elements and secondary metabolites was tested using One-Way Anova. Rumen datasets were analysed using the Pearson Correlation Coefficient. This study found that the rate of leaf phenology and production, including the concentration of certain macronutrients (Ca, K, N, P, S, Cl, Na, protein and fibre), trace elements (Fe, Mn, Mo, Cu, Zn and Se) and secondary metabolites (TP, CT and PPT) increased during leaf flush in October and then declined as the leaves ii matured and aged. However, the concentration of selected macronutrients (Mg and NO3) and trace elements (B, Co and F) increased when the leaves reached maturity in June, particularly during the leaf senescence stage, and declined thereafter. The concentration of macronutrients, trace elements and secondary metabolites between the control and pruned trees was statistically insignificant at P>0.05 for most samples. This study further showed that C. mopane contributed most (47%) to the diet of the greater kudu during the dry season. Other important dry season browse plants were Dichrostachys cinerea (30%), Commiphora edulis (12%), Grewia bicolor (6%) and Combretum apiculatum (5%). However, when gender was considered, the diet of the female greater kudu during the dry season consisted mainly of C. mopane (71%) and D. cinerea (22%). The diet of the male greater kudu contained less C. mopane (33%), but similar proportions of D. cinerea (31%) and other browse species. However, during the wet season, the diet of the greater kudu was mainly composed of C. apiculatum (43%). Other wet season browse plant species were Sclerocarya birrea (24%), C. mopane (12%) and Senegalia nigrescens (8%), with the contribution of the remaining species to the diet being insignificant. The diet of the female greater kudu in the wet season consisted mainly of C. apiculatum (44%) and C. mopane (20%), while the diet of the male mostly contained S. birrea (38%) and C. apiculatum (34%). It is concluded that the concentration of macronutrients, trace elements and secondary metabolites in mopane leaves is not dependent on <10% pruning, but seems to be associated with leaf growth stages. It is further concluded that the concentration of nutrients and chemical compound in mopane leaves has implications on the diet composition of browsers such as the greater kudu in the mopane woodland. The dependency of the greater kudu on species such as C. mopane and C. apiculatum as main sources of browse indicates the importance of these species to the diet of the greater kudu in the mopane woodland. / Deutscher Akademischer Austausch Dienst (DAAD) , National Research Foundation (NRF) and University of Limpopo (Biodiversity Research Chair)

This study was prompted by the scarcity of information on helminths in Sceloporus lizards of Utah. It reports these worms and includes references to parasites of reptiles in the appendix. A microscopic examination of the coelom, mesenteries, liver, lungs, esophagus, stomach, and intestines of 55 lizards was made, but helminths were recovered only from stomachs and intestines. Examination of S. graciosus yielded Opchoristica scelopori, a cestode found in the duodenum, and Cyrtosomum penneri, C. readi, and C. heynemani, three nematodes of the cecum. The latter two are new nematodes for this host species. Examination of S. undulatus yielded three new nematodes for this host. Skrjabinoptera phrynosoma from the stomach, Physaloptera retusa and Pharyngodon giganticus from the cecum. Examination of S. occidentalis yielded O. scelopori from the duodenum, P. retusa from the stomach, and P. giganticus in the cecum. Examination of S. magister yielded S. phrynosoma and Thubunaea iguanae from the stomach, and from the cecum P. giganticus, C. penneri, and C. readi. New nematodes of S. magister reported in this study are S. phrynosoma, P. retusa, and C. readi.

A study was made of the postulated fission-inhibiting substance located in the cephalic region of Dugesia dorotocephala. Rearing decapitated planaria in four different concentrations (25, 50, 75 or 100 ug/ml) of head or whole body extract resulted in a positive correlation between the inhibition of fission rate and the concentration of extract. The difference in inhibitory activity between the two types of extracts was three percent at maximum. The inhibitory substance was partially inactivated at 60° C. There was a direct correlation between the length of time that the extract was heated and the inactivation of inhibitor. The active substance was precipitable with ammonium sulfate. Fractionation of whole body extracts with a Sephadex G-200 column showed the presence of three peaks. The material from all three peaks exhibited inhibitory activity, possibly indicating the presence of more than one inhibitory substance. Fractionation procedures with DEAE anion exchange columns inactivated the inhibitory substance(s). The mechanism of action of the inhibitory substance(s) is not known. The animals must be exposed to the extract within 24 hours after decapitation in order for maximum inhibition to be obtained.

A survey of helminth parasites of sheep and cattle was conducted to determine the incidence and distribution of these parasites that could be detected by post-mortem examination. Animals were obtained from local abattoirs within the valley, and the viscera were examined for the presence of helminth parasites. Parasites identifies from sheep in order of highest incidence were: Haemonchus contorus, Ostertagia cicumcinta, Chabertia ovina, Nematodirus spathiger, Trichostongylus colubriformis, Thysanosoma actinioides, Trichuris ovis, N. filicollis, Echinococcus granulosus, Strongyloides papillosus, O. ostertagi, Cooperia oncophora, Cysticercus tenuicollis, Fasciola hepatica, Oesophagostomum venulosum, Moniezia expansa, and M. benedieni. Those recovered from cattle in order of highest incidence were: Cooperia oncophora, Ostertagia ostertagi, Fasciola hepatica, C. mcmasteri, O. circumcinta, Moniezia benedeni, Seteria cervi, M. expansa, Chabertia ovina, Haemonchus placei, and Nematodirus spathiger. Many of the parasites encountered require a moist environment for development and survival of the free-living stages. Utah Valley is situated in a semi-arid environment and the additional moisture needed to produce optimal condidtions for larval development, survival, and subsequent transmission is added through irrigation.

Network worms that scan random computers have caused billions of dollars in damage to enterprises across the Internet. Earlier research has concentrated on using epidemiological models to predict the number of computers a worm will infect and how long it takes to do so. In this research, one possible approach is outlined for predicting the spatial flow of a worm within the local area network (LAN). The approach in this research is based on the application of mathematical models and variables inherent in plant epidemiology. In particular, spatial autocorrelation has been identified as a candidate variable that helps predict the spread of a worm over a LAN. This research describes the application of spatial autocorrelation to the geography and topology of the LAN and describes the methods used to determine spatial autocorrelation. Also discussed is the data collection process and methods used to extract pertinent information. Data collection and analyses are applied to the spread of three historical network worms on the Virginia Tech campus and the results are described. Spatial autocorrelation exists in the spread of network worms across the Virginia Tech campus when the geographic aspect is considered. If a new network worm were to start spreading across Virginia Tech's campus, spatial autocorrelation would facilitate tracking the geographical locations of the spread. In addition if an infection with a known value of spatial autocorrelation is detected, the characteristics of the worm can be identified without a complete analysis. / Master of Science

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