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This thesis characterises species richness and community structure over a habitat-patch size gradient of a typical bog-pool complex, investigating the effect of pool size on aquatic invertebrate communities. In this study, twenty-two pools were surveyed ranging in area from 8.6 m2 to 280.9 m2 within a single complex at Forsinard in the north of Scotland. Three different sampling methods were used: baited and unbaited activity traps and a sediment sampler. Univariate and multivariate methods were used to investigate the effects of pool size and pool location within the complex on species richness and community structure. The research expands our knowledge of peatland pool invertebrates by providing a comprehensive survey of the aquatic invertebrate fauna representative of the Flow Country of northern Scotland. Two IUCN British Red Data Book species were recorded: the Northern Damselfly, Coenagrion hastulatum (Charpentier), and the cased caddisfly, Nemotaulius punctatolineatus (Retzius). Three species of aquatic Coleoptera were collected that have Nationally Notable status according to Ball (1986): Dytiscus lapponicus Gyllenhal, Ilybius aenescens Thomson and Gyrinus minutus Fabricius. All these species are typical of, and often restricted to, this habitat type. The three different sampling methods differed in their sampling efficiency and each gave a different species spectrum. A distinct seasonal change in the samples was also observed. The number of taxa caught per standardised sampling unit (taxon density) was investigated over the pool size gradient. Relationships between taxon density and area were weak or non-existent in both unbaited activity traps and sediment samples. However, the number of beetle species caught in baited activity traps increased significantly with pool size, indicating that the total number of beetle species per pool may also increase over the size gradient. Ratios of the number of predator taxa to prey (non-predator) taxa for each pool ranged from 0.34 to 0.78 with a mean of 0.49 and were not affected by pool area or total taxonomic richness. Taxa displayed a positive abundance-occupancy relationship and the possible underlying mechanisms involved in creating this pattern are discussed. Multivariate techniques showed that pool area, depth, and distance from the centre of the pool complex (periferality) all had a small but significant affect on community composition and that between certain taxa there were distinctly different optima along the pool size gradient. These results are discussed in the context of species area theory.

1. Zooplankton are key organisms in the transfer of energy between trophic levels in standing waters. They have been used as model organisms in studies of competition, dispersal, predator-prey interactions and in the development of general ecological theory. However, studies of zooplankton in natural lakes have been far more numerous than those in artificial water bodies. 2. Available literature suggests that several areas of zooplankton community ecology have been relatively neglected in artificial lakes. These include i) direct comparisons between zooplankton assemblages in artificial and natural lakes, despite their differences in age ii) hydrological and morphological factors that could potentially cause variations within and between lakes iii) the effects of lake management on seasonal zooplankton dynamics and zooplankton distribution iv) over-wintering populations v) zooplankton functional traits, and trait character in relation to possible environmental selection. Zooplankton case studies in lowland, artificial, urban lakes are surprisingly rare given that such lakes are now often developed for amenity, recreation, conservation and flood storage, in addition to their role in water supply. 3. In this thesis, a series of hypotheses were developed in order to address the above gaps in knowledge and tested in Cardiff Bay, a recently formed and highly managed urban freshwater lake in South Wales (UK). Specific questions addressed were: 1) Globally, do artificial water bodies support different zooplankton assemblages from those in natural lakes 2) Does the zooplankton community of Cardiff Bay vary in ways predicted by ecological theory, and particularly as predicted by the Plankton Ecology Group (PEG) qualitative model of plankton succession 3) In Cardiff Bay, is there a persisting community of interacting zooplankton species even over less productive periods of the year 4) Do spatial and temporal dynamics in the zooplankton community of Cardiff Bay reflect local water quality 5) Do management practices in Cardiff Bay influence the temporal and spatial dynamics of zooplankton 6) Do the traits of zooplankton species in Cardiff Bay vary spatio-temporally in ways that might reflect environmental variation?

This thesis examined the adverse effects of engineered nanomaterials (NMs) and their potential mechanisms of toxicity. The research focussed on the toxicity of NMs and their dissolved ions, as well as bulk particles (larger size), if applicable, in the nematode, Caenorhabditis elegans. The physicochemical properties of chosen NMs were characterised using various techniques. The toxicity of NMs regarding their ability to kill nematodes was concentration-dependent. The dissolved ions of each type of NM were be the most toxic form. On the other hand, the mortality of nematodes was not observed when they were exposed to CuO NMs and bulk particles, which led to the decision to discontinue their study. The toxicity of AgNMs regarding the inhibition of reproduction was also in a concentration-dependent manner. Moreover, the concentrations inducing a decrease in the number of progeny were lower than those used in the mortality test, which suggested reproduction to be a more sensitive endpoint. The induction of oxidative stress, which was investigated by determination of reactive oxygen species (ROS) and related enzymes, was studied when nematodes were exposed to all silver substances. Nevertheless, there were differences observed across the different strains of nematodes. The initiation of apoptosis was examined by visualisation and determination of apoptotic proteins. However, induction of apoptosis was not observed in the testing conditions used in this thesis. The studies of transcriptome and proteome of nematodes treated with spherical AgNM, JRCNM03002a (previously NM300K) revealed that genes and proteins involved in ribosome and protein synthesis were mostly affected by the exposure to JRCNM03002a. However, time of exposure had an impact on the pathways of toxicity. The expression of genes and proteins in the pathways of oxidative stress were altered significantly within 30 minutes of exposure, while these pathways were not involved in 24 hours of exposure. In conclusion, engineered NMs, especially AgNMs, can trigger adverse effects in C. elegans. Although it was proven that the pathway of oxidative stress was related to the observed toxicity, the initiation of apoptosis was not established in the conditions used in this study.

Meloidogyne incognita induces a unique feeding structure, termed giant cells, by reprogramming plant cells in the feeding site within host plant roots. The nematode modifies the function of cells including giant cell wall composition. Characterisation of pectin, hemicellulose and glycoproteins of giant cell walls formed in different hosts was analysed. In addition the role of cell-wall genes in nematode feeding site development was also analysed. In situ analysis was performed to determine the presence and distribution of giant cell wall components; cell wall elements were quantified using enzyme linked immunosorbent assay in nematode feeding sites on different host plants Arabidopsis thaliana (Brassicaceae), Vigna angularis (Fabaceae) and Zea mays (Poaceae). The cell wall compositions in the M. incognita feeding site were observed by comparison with uninfected root tissues. There were distinct responses in terms of detection of cell wall polysaccharides in the nematode feeding site of the different hosts. Modifications of cell wall polysaccharides in giant cells formed in Arabidopsis were minor compared to uninfected sections. By contrast, analysis of the giant cell wall formed in Vigna angularis revealed decreased amounts of mannan, xylan, galactan, processed arabinan, arabinogalactan protein and extensin. In Zea mays, xyloglucan, methyl esterified pectic homogalacturonan, galactan, arabinogalactan proteins increased in abundance in giant cell walls. Arabidopsis plants that carried mutations in cell-wall related genes were analysed. Mutants for genes important in the formation of hemicellulose (GLZ1, MSR1 and MUR3) together with those of the pectin related genes BGAL5 and RGXT1 all resulted in smaller gall development together with a concomitant reduction in nematode size in addition to a reduction in the number of nematodes recovered. Converselymutation of the pectin-related genes ARAD1 and ARAD2 or the glycoprotein-related genes led to increased susceptibility to the nematodes.

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The strategy by which infective A. suum larvae gain entry into their hosts' intestinal tissue has been investigated. The infective larvae develop in the egg between the temperatures 16 °+ 1°C and 34° + 1°C. Within this temperature range, increase in temperature increased the rate of development. The maximum rate of development of the eggs was attained at 31° + 1°C. Eggs embryonated at 280 + 1°C and above gave rise to infective larvae which had a lesser ability to hatch in vitro, shorter longevity when aged in phosphate buffered saline (pH 7.2) at 37°C, and a limited ability to penetrate tissue membranes in vitro, compared with those embryonated at lower temperatures. Maximum larval viability was achieved when eggs were embryonated at 220 +1 °C. These results suggest that the optional temperature for rate of development and larval viability or survivability are not the same. In mice, given large oral infections, eggs hatched mainly in the small intestine. In vitro studies showed that the infective larvae (13 /um in diameter) actively emerged through a hole in the egg shell wall 9.7/um in diameter. This hatching mechanism is considered to contract with the situation in some hookworm eggs where the infective larva is liberated from the egg following splitting of the egg shell under high internal pressure. The egg shell retained its shape during and after hatching. There was no major configurational change in the structure of the egg shell. The inner lipid layer of the shell was broken down during hatching. The location of the hole on the egg shell through which the infective larva emerged varied and was not restricated to any one position. How the hole is made was not obvious. The presence of an opercular structure in the egg shell has been suggested but clear evidence for this was not found. Ultrastructural study indicated that the infective larva possessed no specialised cuticular structures that might either assist its emergence from the egg shell or entry into the host tissue. Soon after hatching, the infective larvae invaded the host intestinal tissue mainly in the regions of the posterior third of the small intestine, the caecum and the colon. Penetration of the larvae into the host tissue was principally via the crypts of liberakun. Direct penetration via the villi appeared to be non-existent. Entry into and subsequent passage of the infective larvae through the tissues was related to the production of larval secretions which caused changes in the acellular materials of the host tissue. These made it easier for the larvae to separate the cells and fibres as they migrated. Passage of the infective larvae did not involve any extensive digestion of the host tissue. Enzymatic studies of the larvae revealed a correlation between the larval secretions and the ability to cause these changes. Incubation with azocoll revealed that the larvae produced secretions which are capable of releasing dye from azocoll. These secretions were neither gelatinolytic nor histolytic. The time course of penetration and subsequent migration to the liver and lungs of mice was followed and a possible mechanism for migration postulated. The results are discussed in relation to the epidermiology of ascariasis and the known biology of the parasite.