The current study evaluated whether NO synthase (NOS) contributes to cutaneous vasodilation and sweating during prolonged exercise in the heat. In addition, we determined if prolonged exercise-induced increases in reactive oxygen species (ROS) and activation of angiotensin II type 1 receptors (AT1R) impair heat loss responses. On two separate days, eleven young men completed 90-min of continuous cycling at ~600W of metabolic heat production followed by 40-min of recovery in the heat (40ºC). To evaluate the role of excess fluid loss via sweating, participants completed a second session of the same protocol while receiving fluid replacement (FR) determined during the first session (No-FR). Cutaneous vascular conductance (CVC) and local sweat rate (LSR) were measured at four intradermal microdialysis forearm sites perfused with either: (1) lactated Ringer (Control); (2) 10 mM NG-nitro-L-arginine methyl ester (L-NAME, NOS inhibition); (3) 10 mM ascorbate (non-selective anti-oxidant); or (4) 4.34 nM Losartan (AT1R inhibition). Ascorbate treatment increased CVC at 60- and 90-min of exercise versus Control during the FR (P < 0.02), but not the No-FR condition (P > 0.31). CVC was reduced at the L-NAME treated site (P < 0.02), but was not different relative to Control at the Losartan treated site (P > 0.19) irrespective of condition. LSR did not differ between sites or as a function of condition (all P > 0.10). We conclude that NO regulates cutaneous vasodilation but not sweating, irrespective of fluid replacement, and ascorbate sensitive ROS impair cutaneous vasodilation during prolonged exercise in the heat with FR.

Climate change is an important contributor to the modification of many bumblebee species’ range boundaries. It was linked to widespread decline at the southern edge of their distribution and to their inability to colonize new areas at the northern edge. Additionally, bumblebee decline is aggravated by other anthropogenic threats like land use change, agricultural practices and pathogen spillover. Predicted consequences are numerous, and could lead to severe economic and ecological impacts on human populations. A species-specific assessment of potential climate change impacts on North American bumblebees, based on the most recent global change scenarios as used in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), was done for the first time. Using a massive dataset of georeferenced bumblebee observations and general circulation models, a series of species distribution models explore the impact of different climate change scenarios on climatically suitable areas of 30 bumblebee species. Northward range shifts occur in most bumblebee species’ projected climatic niches, revealing potential hotspots – places projected to be climatically suitable to multiple species – under future climate scenarios. Areas where species are likely to be lost in the absence of intervention are substantial, particularly in eastern parts of the continent. Models showed significant contractions of current ranges even under the very optimistic scenario in which all species disperse at 10 km/year. Results indicate that managed relocation as well as habitat management should be considered as a conservation strategy for some species. This research serves as a foundation for broader discussion and research in a nascent research area. It may assist in establishing localities where first conservation efforts could be directed for vulnerable bumblebee species.

The Stefan-Maxwell equations are a system of nonlinear partial differential equations that describe the diffusion of multiple chemical species in a container. These equations are of particular interest for their applications to biology and chemical engineering. The nonlinearity and coupled nature of the equations involving many variables make finding solutions difficult, so numerical methods are often used. In the engineering literature the system is inverted to write fluxes as functions of the species gradient before any numerical method is applied. In this thesis it is shown that employing a mixed finite element method makes the inversion unnecessary, allowing the numerical solution of Stefan-Maxwell equations in their primitive form. The plan of the thesis is as follows, first a mixed variational formulation will be derived for the Stefan-Maxwell equations. The nonlinearity will be dealt with through a linearization. Conditions for well-posedness of the linearized formulation are then determined. Next, the linearized variational formulation is approximated using mixed finite element methods. The finite element methods will then be shown to converge to an approximate solution. A priori error estimates are obtained between the solution to the approximate problem and the exact solution. The convergence order is then verified through an analytic test case and compared to standard methods. Finally, the solution is computed for another test case involving the diffusion of three species and compared to other methods.

This thesis attempts to uncover the reasons why Canada, unlike the United States and Australia, does not have stand alone federal endangered species legislation. In particular, I will focus upon the history of Bill C-65, the proposed federal endangered species statute which died on the Order Table in 1997. Using the "policy regime" framework developed by George Hoberg, I examine the ideas, actors, and institutions that have combined within a given set of background conditions to produce this distinctive lack of a policy outcome, assessing the relative causal importance of each variable in terms Bill C-65's failure. Using Peter Haas' epistemic community approach, the causal knowledge of conservation scientists' regarding habitat loss is found not to have influenced the policy substance of Bill C-65. However, it is argued that scientists did play an important role in the legislative failure insofar as they joined forces with environmentalists to discredit the weak scope and substance of the bill. These pro-environment actors, however, were matched throughout the interest group competition by the parallel forces of industry and private landowner groups, who criticized Bill C-65 as a litigious, punitive and "American" style of legislation. The provinces, for their part, sided with the landowners and industry groups, arguing that the federal government had overstepped its wildlife management jurisdiction. Given a context of low public concern for environmental issues, and the institutional trend towards regulatory decentralization, the federal government had very few incentives to introduce a strong bill. However, the provinces, landowners, and industry groups, all felt it was too strong, while environmentalists and scientists felt just the opposite. Bill C-65's failure, therefore, was the result of the federal government's inability to satisfy anyone on this issue. Determining who "won" this first endangered species battle, however, is quite difficult without knowing whether Cabinet felt the bill was too strong or too weak, and without knowing what the next legislative proposal will entail. In conclusion, it is found that all three regime components of ideas, actors, and institutions were equally important factors in bringing about the failure of Bill C-65, and the current policy delay that continues to this day. / Arts, Faculty of / Political Science, Department of / Graduate

With the increase in the number of fast-moving vehicles and the simultaneous development of road building technology, roadside bird mortality has become an increasingly important environmental issue that has the potential to do serious damage to already vulnerable bird populations. This project was therefore initiated after an alarming number of owls were found dead along the N17 and R550 roads in the rural areas between Springs and Devon in the East Rand highveld of Gauteng Province. Five hundred and fifty four owls of four species, namely Marsh Owls, the Red Data listed Grass Owl, Barn Owl and the Spotted Eagle Owl were collected on the stretches of the R550 and N17 during the period between October 2001 and September 2003. They accounted for 53.6%, 27.4%, 17.5% and 1.3% of the mortalities respectively. Unidentified species of owls accounted for the remaining 0.2%. It was found that the monthly mortality rates of the birds varied throughout the year, with the greatest losses being suffered during July, as opposed to relatively lower mortalities occurring during the warmer months. All carcasses were collected, their GPS locations plotted on a map, and ‘hotspot areas’ identified as places of highest incidences of mortalities of the owls. Vehicle-induced mortalities are then discussed in relation to these hotspots, in terms of vegetation and habitat descriptions, daily vehicle counts along the route, as well as fixtures found along the route. It was found that traffic density was indirectly proportional to owl mortalities, with higher traffic speeds definitely having an increasingly detrimental effect on the owl mortalities. Weather conditions also play a role in mortality counts, with the mortalities being significantly negatively correlated to rainfall. Moon phases were also related to the times of highest mortalities, however, this factor did not play a significant role in influencing road mortalities. Another factor that was studied was the influence of differing tarmac road surface temperatures as opposed to gravel road verge surface temperatures, and how these temperatures differed from the ambient temperature. It was found that there was not a big enough difference in the temperatures that would warrant (the previously thought notion) that the owls were attracted to the roads at night to gain heat. Gravel roads had very low incidences of owl mortalities with the highest mortalities recorded along tarmac roads that are bordered by open grasslands or cattle grazing paddocks. It was shown that tarmac roads, bordered by croplands, had a lesser effect on the owl mortalities. Another factor influencing the road mortalities of the owls is grain that is spilled on the road during transport. This initially seemed to be the major factor in attracting granivorous rodents to the roads, and in turn, attracting the owls to prey on them. Rodents identified from recovered pellets and the stomach contents of dead owls confirmed the fact that the majority of rodent prey items were indeed granivorous species, namely Mastomys natalensis and Rhabdomys pumilio. This is in disagreement with previous studies that indicated that a large proportion of the prey species of the Grass Owl was Otomys irroratus, a grass-eating species, even though a rodent trapping study to determine prey abundance within the area indicated a healthy population of O. irroratus. Further studies into prey items of the owls that were dissected indicated that the majority of the prey items recovered were not caught directly on the road as it was already partially digested, suggesting that the prey was caught prior to the owl being killed. From the pellet analyses, other prey items were also found to form part of the owls’ diets. It was found that insects formed largely the diet of the Marsh Owl during the spring, summer and autumn months, with them resorting to smaller rodents during the winter months. Spotted Eagle Owls also preyed almost exclusively on insects. Grass Owls, on the other hand, preyed on small mammals exclusively, with the very rare exception of some insects also being taken. Of all of the dead owls recovered on the roads, post mortems were carried out on only 78 of the carcasses. All of the dead owls examined were in good health prior to death. Various morphometrics of the examined owls were noted. Comparisons of body mass showed that females were larger than males for most species. This was also found for most other measurements as well. It was also found that, according to body mass comparisons, Barn Owls and Marsh Owls were significantly similar. Conducting ANOVA analysis on other morphometrics to determine gender differences, it was found that Grass Owl males were significantly different to females in terms of body mass and length. Marsh Owl males were significantly different to females in terms of body mass and tail length; with Barn Owl males being significantly different in terms of tarsus length to females. Except for Spotted Eagle Owl tarsus lengths all other measurements were in favour of females being significantly larger. These findings were also confirmed when applying the Dimorphism Index to all morphometrics measurements, especially body mass. The degree of parasite infestation was also studied during post mortem examinations. Very few cestodes and nematodes were found, with too few to have an effect on the overall health of the birds prior to death. The vegetation type was studied at transects that coincided with hotspot and non-hotspot sites. Using the PRIMER statistical software package, hotspot sites were found to have highest plant cover and diversity, whereas nonhotspot sites showed lowest plant cover and diversity, generally dominated by Hyparrhenia hirta. During these studies, the degree of available nesting habitat was determined and nesting sites were identified, using the ropedragging technique to flush out roosting and nesting owls that would otherwise have been impossible to find in the thick cover. It was found that Grass Owls preferred a habitat rich in thick grass cover that was relatively high (0.75 m–1 m). It was found that the grass species preferred by these owls were Eragrostis curvula, Paspalum sp., Setaria sp., Sporobolis sp., with few other small herbaceous plants. Marsh Owls, on the other hand, seemed not to be too partial regarding roosting and nesting sites, with them roosting and breeding in more mixed vegetation grasslands that had sparser cover, not reaching the height of the grass cover typical of the habitat preferred by the Grass Owls. Opposed to this were the non-hotspot vegetation sites. These sites were found to have vegetation cover unsuited to both the Marsh and Grass owls, with mixed H. hirta grassland not forming the dense cover, or the height, needed by those two species of owls. Foraging owls were also observed, with the vegetation type in the immediate vicinity noted. Vegetation types similar to breeding areas were noted in these foraging areas. Habitat preferences as well as breeding performance were noted for both grassland species of owls, and found to be directly related to land usage in terms of varying agricultural practices and regimes. Fallow, undisturbed lands were found to be highly productive for the owls. Lands planted with Eragrostis sp. were also found to be very productive, but only if left undisturbed for a period of time sufficient to allow the grassland owls to colonise it. Maize-planted fields were found to be utilised only as foraging fields and no breeding of owls was found to take place close to these fields. After extensive nest searching, it was found that both Marsh and Grass owls were breeding from late March to early June, with the Barn Owls breeding in October and again in March. Grass Owls occur in the study area because of the presence of a natural corridor of suitable habitat that runs parallel with the Blesbokspruit. This favourable habitat of the study area is thus conducive to high population density of grassland owls utilising these uncultivated patches of dense and tall vegetation. The high incidence of mortalities on the road in the study area is due to the concomitant high population densities. This healthy population seems to be sustaining the losses occurring on roads. Owls also seem to be gathering in larger numbers in hotspot zones because of the easy available prey, which are attracted to these high productive areas. Agricultural practices in the area lead to the spillage of grain on the road during transportation. Potential prey species foraging on the roads expose themselves to the nocturnal hunters offering an easy dinner. This process leaves these owls vulnerable to vehicle collisions. The overall population size may be larger than previously thought, not with standing the high mortalities already recorded. The small patches of viable habitat in the study area remains suitable for the breeding of the two grassland owl species allowing for such high densities to occur in the area. The Grass Owl, nonetheless, remains severely threatened as it already occurs as a high priority species for conservation concern in the Gauteng Province. This study provides the first assessment of this owl species of this scale in South Africa and this will ultimately promote the long-term survival of these owls. / Dr. V. Wepener

One of the main goals of computational methods is to identify reasonable geometries for target materials. Organometallic complexes have been investigated in this dissertation research, entailing a significant challenge based on transition metal diversity and the associated complexity of the ligands. A large variety of theoretical methods have been employed to determine ground state geometries of organometallic species. An impressive number of transition metals entailing diverse isomers (e.g., geometric, spin, structural and coordination), different coordination numbers, oxidation states and various numbers of electrons in d orbitals have been studied. Moreover, ligands that are single, double or triple bonded to the transition metal, exhibiting diverse electronic and steric effects, have been investigated. In this research, a novel de novo scheme for structural prediction of transition metal complexes was developed, tested and shown to be successful.

Much research has been published on Mycosphaerella spp. causing Mycosphaerella Leaf Disease (MLD) on Eucalyptus spp. The first chapter of this thesis presents a review of the literature on this topic and focuses on the taxonomy, phylogeny and population biology of Mycosphaerella spp. occurring on Eucalyptus. From the published literature, it is clear that the majority of research conducted on MLD has focussed on the epidemiology and taxonomy of Mycosphaerella spp and the susceptibility of Eucalyptus hosts to species of Mycosphaerella. Advances in DNA-based technologies have, however, lead to extensive DNA sequence datasets of Mycosphaerella spp occurring on Eucalyptus. These datasets have provided substantial insight into species concepts for Mycosphaerella and have led to the realisation that many morphological species are complexes of several cryptic phylogenetic taxa. Furthermore, a recent application to the study of Mycosphaerella spp. occurring on Eucalyptus is that concerning their population dynamics. Such studies will aid in our understanding of the genetic structure of Mycosphaerella populations and their movement between countries. These population-based studies will aid forestry companies in establishing Eucalyptus breeding programmes to produce tolerant Eucalyptus genotypes that may be deployed in commercial forestry operations. Mycosphaerella spp. are difficult to identify, due to their conserved teleomorph morphology and the lack of natural occurrences of anamorph structures. DNA sequence data have, therefore, become the definitive technique used to identify Mycosphaerella spp. The Internal Transcribed Spacer (ITS) region of the ribosomal RNA operon has traditionally been targeted for DNA sequence comparisons. However, this gene region does not offer sufficient resolution to discriminate cryptic taxa or resolve deeper nodes within Mycosphaerella. Results presented in chapter two of this thesis present a multi-gene phylogeny for the identification of Mycosphaerella spp. occurring on Eucalyptus. This is based on DNA sequence data from four nuclear gene regions. The generation of these sequence datasets has allowed for competent elucidation of cryptic taxa, species complexes and the greater resolution of deeper nodes within Mycosphaerella. Furthermore, these results have also led to recognising that Mycosphaerella ambipyhlla and M. vespa is a synonym of Mycosphaerella molleriana and Pseudocercospora epispermogonia is recognised as the asexual state of Mycosphaerella marksii. A serious foliar disease of Eucalyptus camaldulensis and hybrids of this species has been known from Thailand and Vietnam for many years. This disease has been known to be caused by a species of Pseudocercospora and was attributed to the cosmopolitan Pseudocercospora eucalyptorum. Results of a study presented in chapter three of this thesis have, however, clearly shown that P. eucalyptorum is not the causal agent of the disease observed on E. camaldulensis in Thailand. By employing classical morphological techniques and DNA sequence data from four nuclear gene regions, I have shown that an undescribed species of Pseudocercospora is responsible for epidemics of this leaf disease. This species is formally described as Pseudocercospora flavomarginata. P. flavomarginata is only known from Thailand and Vietnam. However, considering that E. camaldulensis is planted in other south-east Asian countries and that E. camaldulensis is the most commonly found Eucalyptus sp. in Australia, further surveys in these areas will most likely lead to the discovery of the pathogen from these countries. Techniques that have been used to identify Mycosphaerella spp. include classical morphological comparisons and analyses of DNA sequence data. These techniques have, however, allowed only for the study of the evolutionary history within Mycosphaerella and for species identification. Recent advances in the field of population biology have led to the study of many fungal pathogens at a population level. One of the main tools used to study population biology involves applying DNA-based microsatellite markers. Chapter four of this thesis focuses on the development of DNA-based microsatellite markers for the Eucalyptus leaf pathogen Mycosphaerella nubilosa. By employing specific enrichment protocols, I was able to develop ten polymorphic microsatellite markers for M. nubilosa. These microsatellite markers exhibit high specificity for M. nubilosa and did not cross amplify with other Mycosphaerella spp. that are closely related to M. nubilosa. Mycosphaerella nubilosa has been extensively studied with respect to its taxonomy and epidemiology. However, nothing is known regarding the population biology of this important Eucalyptus leaf pathogen. Therefore, DNA-based microsatellite markers developed in chapter four of this thesis were used to study the population biology of M. nubilosa from several different geographic locations. Results presented in chapter five of this thesis show that populations of M. nubilosa from eastern Australia are genetically more diverse than those populations from western Australia, Africa and Europe. This indicates that eastern Australia is the likely centre of origin for M. nubilosa. Furthermore, based on shared haplotypes between M. nubilosa populations used in this study, I have proposed a pathway of gene flow of M. nubilosa. This suggests that the pathogen moved from eastern Australia to both western Australia and South Africa and then from South Africa into other countries in Africa and finally into Europe. An interesting result emerging from the population biology study presented in chapter five, is the finding that M. nubilosa appears to employ a homothallic mating strategy. Thus, opportunities exist, in countries with limited genetic diversity of M. nubilosa, to breed for Eucalyptus resistance. From the high number of M. nubilosa haplotypes observed in Australia and South Africa, it is also important that this pathogen be added to quarantine action lists to prevent the movement of contaminated Eucalyptus germplasm. This is necessary to prevent novel M. nubilosa haplotypes from moving into new environments where susceptible Eucalyptus spp. are propagated. Mycosphaerella nubilosa is one of the most pathogenic Mycosphaerella spp. causing MLD on Eucalyptus. Surveys of diseased Eucalyptus plantations from several countries where this pathogen occurs, have resulted in an extensive collection of M. nubilosa isolates. Recently, DNA-based studies have led to the hypothesis that M. nubilosa may represent two distinct taxa. Results of studies presented in chapter six of this thesis indicate that two distinct ITS phylogenetic lineages are represented by M. nubilosa sensu lato. These are characterized by defined geographic distributions and Eucalyptus host associations. M. nubilosa ITS lineage 1 is found exclusively in New Zealand, Tasmania and Victoria, eastern Australia occurring on E. globulus. M. nubilosa ITS lineage 2 has a broader geographic distribution and can be found in Spain, Portugal, Tanzania, Kenya, Ethiopia, South Africa, western Australia, Victoria and New South Wales, eastern Australia, where it occurs on E. globulus and several other Eucalyptus spp. that are used in commercial forestry including E. nitens. It is envisaged that results presented in chapter six will lead to more extensive studies into M. nubilosa sensu lato that may result in the description of a new Mycosphaerella sp. represented by M. nubilosa ITS lineage 1. / Thesis (PhD)--University of Pretoria, 2011. / Microbiology and Plant Pathology / Unrestricted

Pinus patula is the single most important commercial plantation forest tree species in South Africa. It accounts for 52% approximately (700,000 ha) of total commercial plantation area in the country and is utilised for saw logs and pulp and paper production. P. patula is a tropical pine species indigenous to Mexico. Excellent ex situ conservation and range-wide provenance trials have been established for P. patula in South Africa and South America. These highly organised trials provide the opportunity to perform association genetic studies with the long term aim to identify trait linked markers for future molecular improvement of P. patula. In this study, the first gene-based assessment of allelic diversity in P. patula was performed. This pilot study focused on two cellulose biosynthetic genes as representatives of wood formation genes and assayed molecular evolution parameters such as nucleotide diversity, allelic diversity and linkage disequilibrium (LD) in a species-wide reference population of P. patula. Two novel cellulose synthase (CesA) genes were isolated and characterised in P. patula. One of these genes, PpCesA1, is putatively involved in the biosynthesis of secondary cell walls of tissues such as xylem (wood), while the other, PpCesA2 is proposed to be associated with primary cell wall formation in rapidly growing tissue types. The genomic DNA copies of PpCesA1 and PpCesA2 were 6025 bp and 6365 bp in length, respectively. The corresponding cDNA sequences encoded 1083 and 1058 amino acids, respectively, and differed considerably from each other (73% amino acid identity). Both amino acid sequences contained the key domains and motifs characteristic of functional CESA proteins isolated in other higher plants. Phylogenetic analysis revealed that PpCesA1 was most similar (99%) to its putative ortholog in Pinus taeda, PtCesA3, and PpCesA2 was highly similar to a putative ortholog in Pinus radiata, PrCesA2 (99% identity). This phylogenetic analysis supported previous findings that the divergence between the primary and secondary cell wall associated CESA proteins occurred before the divergence of angiosperms and gymnosperms approximately 300 million years ago. A fragment of a putative paralogous gene copy of PpCesA1, named PpCesA1-B was also isolated. The PpCesA1-B gene fragment was found to differ from PpCesA1 by 22 nucleotide polymorphisms and its non-allelic (paralogous) status was confirmed by segregation analysis in P. patula. In order to gain an understanding of molecular genetic variation that might affect wood formation in P. patula, we sequenced multiple allelic variants of PpCesA1, PpCesA1-B and PpCesA2, which we sampled from a species-wide reference population of P. patula. The average levels of nucleotide diversity were found to be low for all three genes (π ≈ 0.0015), which may be a property of functional members of the CesA gene family. As a result of the low nucleotide diversity, only small numbers of pair-wise informative sites were available for LD analysis and the decay in LD could only be studied in PpCesA2 where it was found to decay very rapidly (within 200 bp). Tests of neutrality suggested that the exon sequences of PpCesA1 and PpCesA2 were under significant positive (adaptive) selection. Comparison of levels of nucleotide diversity and selection in different parts of the two genes indicated that the highest levels of adaptive selection occurred in areas where amino acid substitutions could alter protein structure or function. This study provides valuable insights for designing future allele discovery efforts in P. patula with the ultimate goal of developing gene-based markers for the molecular improvement of wood formation in this tree species. / Dissertation (MSc (Genetics))--University of Pretoria, 2009. / Genetics / unrestricted

Abduction of young girls by older men has been thought and also defined as culture, by those who believe in abduction. However, some people have come to realize that it is not culture but violence and abuse of women by male species. For too long, women have been treated as second class citizens and or objects. One day the researcher witnessed six men abducting a fifteen year old girl, while she was on her way to school. The girl said “no” but no one cared. She cried bitterly but they continued to drag her away. The girl shouted for help but the adults who were there turned a blind eye. One of the women who were there said: “we were also abducted too and this is the way how things are done. The researcher is ministering among the Bhaca people who are no strangers to this cruel practice. Some parents do not care about their children’s education, in a way that they orchestrate their children’s abduction. Their concern is the number of cattle they will get for their daughters. Perpetrators too do not care that they a ruining the girls future and their program of education is disturbed. The girls’ childhood is cut short, and they become mothers too soon and this leads them to traumatic experiences. Ministering among broken souls made the researcher’s pastoral work difficult hence, ninety percent of the congregants bear scars and hatred caused by abduction experiences. The whole community needed to be educated about abduction; men, women, young and old. Young women needed to be educated about their rights, restoration of their dignity, and the importance of their education. Some of the girls manage to escape from their forced marriages, when they arrive at their homes, their parents or relatives force them to return to their husbands. The church decided to build a care centre to accommodate those who are not welcomed at their homes. The government has passed a law, which stipulates that whoever abducts a girl, should be imprisoned together with the parents or relatives who orchestrated the plan. The girls are learning about their rights. The care centre is sheltering 34 girls under the age of 20years, who ran away form their forced marriages. These stress survivors decided to pursue their dreams. Some are taking part in athletic sport and some are helping newly admitted victims to deal with their pain, and focus on hope and a brighter future. Those who decide to stay in their marriages, are taught forgiveness, so that they can move away from their pain and learn to depend on what they can achieve, rather that their husband’s money. / Dissertation (MA(Theol))--University of Pretoria, 2011. / Practical Theology / unrestricted

Philosophiae Doctor - PhD / There has been extensive growth in nanoscale technology in the last few decades to such a degree that nanomaterials (NMs) have become a constituent in a wide range of manufactured commercial and domestic products. This surge has resulted in uncertainties regarding their environmental impact, due to the significant increases in the amount of NMs released into the environment (Dowling et al., 2004) through intentional and unintentional releases. Like many other toxins, the aquatic environment is particularly vulnerable as it acts as a sink for nanoparticles (NPs) (Scown et al., 2010). The escalating growth of NMs has not advanced without efforts to understand its properties. Despite the dramatic advances in both the production and application of NMs, very little is known regarding their interaction with and effects on environmental and human health. Given the lack in scientific knowledge, particularly under various environmental conditions, it is often difficult to accurately assess the potential exposure pathways to ecological receptors of all NMs, silver nanoparticles (AgNPs) are the most widely used NPs, present in several consumer products mainly because of their anti-bacterial properties. It is estimated that the annual production exceeds 1000 tons/year (Piccinno et al., 2012). The increase uses of AgNPs in consumer products (e.g. textiles, cosmetics and personal hygiene), household appliances (e.g. washing machines and vacuum cleaners) and medical equipment have led to their increase release into the environment, thereby posing an environmental risk and human health concern. Silver NPs are known to induce the production of Reactive Oxygen Species (ROS) (Ahamed et al., 2010; Levard et al., 2012; Piao et al., 2011). Also since AgNPs are oxidized to ionic Ag (Ag+), it is still unclear whether the effects of ROS can be attributed to Ag+ release or to the AgNP itself (Fabrega et al., 2009; Miao et al., 2009). The behaviour of AgNPs is collectively influenced by inherent (nanoparticle size, shape, surface area, surface charge, crystal structure, coating, solubility/dissolution) and environmental factors (temperature, pH, ionic strength, salinity, organic matter). Climate change predictions indicate that the frequency, intensity and duration of extreme natural events (such as temperature elevations) will increase in the future (IPCC, 2001; IPCC, 2007). Global warming and climate change could increase atmospheric temperatures by 2.4 – 6.4 °C (IPCC, 2001; IPCC, 2007). The main feature associated with global climate change is the anticipation of wetter winters (i.e. increased flood events) and drier, warmer summers (i.e.extreme temperatures). These changes are likely to affect the inputs of contaminants into the environment as well as affect their behaviour, fate and transport, and toxicity in aquatic environments. It is known that the current temperature predictions in climate change scenarios could directly affect aquatic ecosystem communities (Carpenter et al., 1992), since temperature is also regarded as an important abiotic factor influencing growth and production of primary producers (i.e. algae, macrophytes etc.), and may also affect species distribution. For example, Liu et al. (2010) reported higher dissolution rates of AgNPs with increased temperature. Similarly, sudden hydrographic activity like high flood conditions may cause resuspension and redistribution of sediments. Few studies have linked the foreseeable climate change with contaminant release and ecosystem impacts. Similarly, few studies have analyzed the behaviour of NMs in the environment considering these predicted changes in mean temperatures. This thesis focuses on the effects of AgNPs on oxidative stress responses in the Cape River crab Potamonautes perlatus. The present work was undertaken to interpret the biological effects of AgNPs (< 100 nm) on P. perlatus, as well as to assess its effects under different environmental conditions. To understand the uptake, accumulation and biological effects of AgNPs, freshwater microcosms were produced to mimic a typical aquatic environment and temperature manipulated microcosms to which a commercially-available AgNP powder was added. Nanoparticles were characterized in the dry state and in suspension under different environmental conditions. Dissolution of total Ag was measured by inductively coupled plasma mass spectrometry (ICP-OES). Nanoparticle toxicity was assessed by measuring mortality and biomarkers of oxidative stress (CYP450, SOD, CAT, GST) evaluated in crab tissues. The overall results demonstrated that: (1) AgNPs may be transformed in both size and state under variable environmental conditions. The formation of smaller aggregates at higher temperatures suggests higher toxicity, (2) the release of free metal ions from NPs and NPs aggregates contribute to a higher toxicity towards aquatic organisms, (3) oxidative stress is a significant mechanism of AgNP toxicity and consequently enzymatic activation/inhibition with increasing AgNP concentration and temperatures, (4) oxidative stress responses to AgNPs particles were significantly modulated by temperature stress in P. perlatus, (5) mortality was observed from day 2 with maximum mortality achieved at day 7, (6) enzymes involved in detoxification, i.e. CYP450, has functional significance in the haemocytes, (7) P. perlatus has proved to be a significant target for AgNP exposure and, furthermore, has proved to be a suitable species to assess the ecotoxicity of AgNP in the aquatic environment, (8) antioxidant enzymes activities (are valuable tools to assess the oxidative status of crab tissues co-exposed to AgNPs and temperature. Furthermore, the results obtained in this study contributed to the understanding of the behaviour, bioavailability, uptake and toxicity of AgNPs under variable temperatures. / National Research Foundation (NRF) Thuthuka Fund and CSIR