Empirical and theoretical investigations of aspects of the ideal free distribution (IFD) are presented, with particular emphasis on interactions between individuals within foraging groups. An overview of the theory is presented, and the implications of the work included in this thesis to ideal free distribution theory are discussed. The effect of group size on the relative competitive ability of individual fish within a foraging group is shown to be dependent upon the difference in body size between two focus individuals in a group, but this difference itself has no direct effect on relative competitive ability. A subsequent empirical test of a novel mathematical tool reveals that there is no simple general rule for describing how relative competitive ability will change with group size, and that very specific knowledge of the system under study is needed in order to produce robust predictions. The relative abilities of individual chiclids to obtain food under scramble competition are shown to be highly repeatable between trials. However, when given a choice between two patches differing only in their temporal variability in input about an identical mean, an individual's rank based on intake in one patch was uncorrelated with either its uptake in the other patch or its intake in either of two different trial types. The basis for, and consequence of, this dependence of relative competitive ability on the context of the foraging situation are discussed. The general case (previously unexposed in the literature) where the effect of interference can vary between patches is examined. Simulations from an individual-based model reveal a decrease in the number of stable equilibrium distributions as the competitive advantage of the dominant phenotype declines in one patch, leading eventually to a single stable equilibrium, in which both phenotypes are found on both patches.

The work reported in this thesis is divided into 3 main sections as follows. Section 1. The external morphology of byssus threads produced by Mytilus edulis and Modiolus modiolus was studied by scanning electron microscopy. Section 2. Several laboratory experiments were performed to determine how sediment with stones at different layers and of different particle size ranges affects byssus thread production. These experiments were: (i) An initial experiment to determine the rate of byssus thread production. (ii) The response of single animals and groups of animals to different particle size ranges of sediment. (iii) The response of single animals and groups of animals to experimental sediments (particle size range < 2.0cm) with stones present or not present at different depths. Section 3. Experiments were performed to determine the effects of single animals and groups of animals on sediment stability. All experiments were performed under controlled conditions in an experimental sea water flume. These experiments were: (i) the effects of single animals on sediment stability in different particle size ranges of sediment. (ii) the effects of groups of animals on sediment stability in different particle size ranges of sediment. (iii) the effects of groups of animals on sediment stability in sediment of particle size < 2.00mm, with stones present or not present at different depths.

No aInitially, the thesis investigated the ecological energetics of N. norvegicus in order to construct an energy budget which could be used to estimate scope for growth. The diet of the Norway lobster Nephrops norvegicus in the Firth of Clyde was found to consist of crustaceans, molluscs, and to a lesser extent polychaetes and echinoderms. The proportion of bivalves was higher in the diet of N. norvegicus from south of Little Cumbrae than in the diet of N. norvegicus from south of Ailsa Craig which contained larger proportions of crustaceans and echinoderms. This appears to reflect the faunal composition of the areas. Despite a number of measures taken to preserve stomach contents, a large proportion of the diet was found to be macerated beyond recognition, particularly in the stomachs of animals from the south of Ailsa Craig stocklet. There were marked interspecific differences in the energy contents and organic contents of prey organisms. The calorific values of the prey items were found to vary according to the proportion of organic matter in the tissue. Organisms with low organic contents such as brittle stars had lower calorific values than organisms with a large organic proportion such as soft-bodied polychaetes. Amounts of food consumption were calculated in 4h intervals over a 24h period. Results suggested that foraging is highest during the night at 2200-0200. A smaller increase in food consumption was also noticed during the morning at 0600-1000 and 1000-1400. The lowest amount of food was consumed between 1400-1800. Two different models were used to estimate the daily amounts of food consumption. The values obtained ranged from 476.5mg day-1 (wet weight) at Ailsa Craig in November to 1206.2 mg day-1 (wet weight) at Little Cumbrae in May.

The work in this thesis shows that it is possible to design a diffusion cell which will allow access to the flux and lag time of a permeant without the need for invasive sampling and that this novel cell is both sensitive and reproducible. It was also shown that the cell could be used in conjunction with both simple model membranes and more complex biological membranes, namely the epidermis. From the data achieved from the cell it was possible to derive a series of equations which allowed access to thermodynamic parameters such as ?H, ?G and ?S. An extension of this calculational approach revealed that manipulation of the van’t Hoff isochore, under the condition where enthalpy is constant over the temperature range, it should be possible to calculate the partition coefficient. Ultimately these parameters can be used in the description of structure activity relationships. The systems described in this thesis are of a complex biological nature consequently the returned data reflect this complexity. In order to utilise the data to their full potential some method for dealing with this complexity was sought. One approach widely discussed in the literature is that of chemometric analysis or soft modelling. Initial studies into the use of chemometric analysis proved positive for the data presented in this thesis, and suggested that formulation contributions from components with close absorbance maxima could be separated.

No description available.

The present work, employing biochemical, biophysical and electrophysiological techniques, attempted to identify specific receptor sites in the vertebrate olfactory system for heterocyclic odorants. An in vitro rat preparation was developed and characterised for use in vapour-phase chemical modification experiments; the EOG responses obtained from this preparation were stable for up to 5 hours after the death of the animal. The signals to various compounds were differentially reduced when brominated odorants were employed as vapour-phase labelling reagents; the responses obtained to these derivatives and to their non-reactive analogues were preferentially diminished. The effect of concanavalin A on ECGs obtained from an in vivo frog preparation was examined. This lectin was found to preferentially inhibit the signals elicited by small, sweaty-smelling carboxylic acids; the responses to most of the non-carboxylic acid odorants tested were not significantly inhibited. The failure to identify specific receptor sites by electrophysiological techniques prompted the performance of odorant binding studies. Examinations of the interaction of [3H] 2-isobutyl-3- methoxypyrazine with 13,000 x g supernatant fractions of sheep olfactory epithelium showed that a component of the homogenate fraction exhibited high affinity saturable binding of this odorant (KD-10-8M). However, the presence of large amounts of non-specific binding, substantially decreased the sensitivity and accuracy of the assay. Non-specific binding was observed with tissue fractions of sheep respiratory epithelium, brain and liver. An investigation of binding specificity showed that other bell pepper odorants competed for the 2-iscbutyl-3-methoxypyrazine binding site. The steno requirements for the protein binding of various substituted heterocyclic odorants were examined using nuclear magnetic relaxation techniques. Model studies performed with bovine serum albumin showed that particular side chains of the odorants tested were primarily involved in the binding interaction. The methoxy group of 2-isopropyl-3-methoxypyrazine was found to be responsible for primary recognition by 13,000 x g supernatant fractions of sheep olfactory epithelium.

This thesis examines the development ofnatural history in the Spanish Empire (1750-1850). I explore why the Spanish Crown promoted scientific institutions and expeditions in the second halfofthe eighteenth century, and I situate Spanish engagement with natural history within an imperial context. One Spanish commentator, scrutinising the contents ofthe Real Gabinete de Historia Natural in 1788, gloried that 'we have seen form this immense collection of singularities ofnature, brought at considerable expense, not only from all regions ofEurope, but also from Asia, Africa and America; so that all parts ofthe world may contribute to forming the most complete treasure ofNatural History that exists in the Universe'. I suggest that Spain's capacity to procure and exhibit exotic natural treasures reflected the potency ofher imperial structures. I also address the social, religious and economic benefits associated with the classification, collection and cultivation of natural objects. I am especially interested in the part that Spanish Americans played in this process, and the ways in which the development ofthe natural sciences on the imperial periphery intersected with the evolution of creole patriotism in the late colonial period. I consider how the creation, legitimisation and dissemination of scientific knowledge reflected broader questions of imperial power and national identity. I examine the ambiguous position ofcreole naturalists, who were simultaneously anxious to secure European recognition for their work, to celebrate the natural wealth oftheir homelands and, in some cases, to vindicate local forms of knowledge against purportedly universal European systems such as Linnaean botany, and I extend this analysis beyond independence, asking whether political freedom fomented or compromised the pursuit of natural history in the former colonies.

D-serine is a co-agonist at NMDA receptors in the brain but the study of this amino acid is restricted by current techniques. I have designed highly sensitive D-serine biosensors that permit accurate real-time recordings of D-serine in the brain in a selective manner. I demonstrate that these tools are ideal for investigating factors involved in the regulation of this amino acid and the role that D-serine plays in excitotoxic cell death mediated via NMDA receptors. I have established that the extracellular basal concentrations of D-serine in the rat brain are heterogeneous and vary even within brain structures. This suggests that Dserine is an important regulatory constraint for NMDA receptor activation, as receptor response can only be potentiated in regions with low D-serine content. Additionally, I show that these microelectrode biosensors have the potential to be used in vivo to detected extracellular D-serine levels. In addition I have observed real-time activity dependent regulation (both loss and release) of D-serine by ionotropic glutamate receptor agonists AMPA, NMDA and kainate, PAR1-agonist TFFLLRNH2 and high frequency stimulation in vitro in a number of brain areas. A decrease in D-serine concentration is potentially neuroprotective as it suggests a reduction in NMDA receptor activation. However, D-serine release can be observed in regions where the co-agonist site of the NMDA receptor is likely to be already saturated implying an alternative function of D-serine in the brain. These findings indicate multifaceted regulation of this amino acid that is brain-region specific. Finally, I have investigated the role of D-serine release during models of stroke (hypoxia and ischemia) and found that D-serine levels are reduced in brain regions deprived of oxygen. This is ultimately neuroprotective as it will reduce over - excitation at the NMDA receptor during these insults. In the more profound model of stroke, oxygen-glucose deprivation, D-serine is eventually released. This release precedes anoxic depolarisation and could therefore contribute to its initiation via enhanced activation of the NMDA receptor.

Theoretical modelling of the microtubule-Dam1-ring force generation mechanism and the pulling of tubes from surface-supported lipid bilayers are presented and discussed. Atomic force microscopy (AFM) force data of tube pulling experiments is analysed and compared with theoretical predictions. Featurescommonto recent computational models are simplified and examined independently where possible. In particular, the steric confinement of the Dam1 ring on a microtubule (MT) by protofilaments (PFs), the powerstroke produced by curling PFs, the depolymerisation of the MT, and the binding attraction between Dam1 and the MT are modelled. Model parameters are fitted to data. Functional force generation is equally demonstrated when attachment is maintained by steric confinement alone (protofilament model) or by a binding attraction alone (binding model). Moreover, parameters amenable to experimental modification are shown to induce differences between the protofilament model and the binding model. Changing the depolymerisation rate of MTs, the diffusion coefficient of the Dam1 ring, or applying an oscillating load force will allow discrimination of these two different mechanisms of force generation and kinetochore attachment. A previously described theoretical model of pulling lipid bilayer tubes from vesicles is modified for the case of pulling tubes from surface-supported lipid bilayers. A shape equation for axisymmetric membranes is derived variationally and solved numerically for zero pressure. Free energy profiles and force curves are calculated for various AFM probe sizes and compared to experimental data where a ground flat AFM probe is used to pull tubes from surface-supported lipid bilayers. The predicted force curves partially fit the experimental data, although not at short distances, and estimates of the bilayer surface tension are given. Pressure and volume profiles are calculated for the extension of the model to the nonzero pressure case.

In the absence of telomerase, Saccharomyces cerevisiae telomeres erode leading to senescence. Rare cells can survive after this stage as they can elongate their telomeres utilizing homologous recombination. Two different types of survivors can be easily distinguished by Southern blot. Type I survivor cells, elongate the telomere by amplifying Y elements and require RAD51, RAD54, RAD55 and RAD57 for establishment. Type II survivors elongate their telomere by amplifying TG1-3 repeats, however, they require the following genes to be established: RAD50, MRE11 and XRS2, RAD59, SGS1 and KU80 in some cases. Both types require the gene RAD52. In this study several candidate genes were deleted individually in diploid type II survivor strains. The main aim of this work was to see if these genes were required for type II telomere maintenance. Most of these genes are not required for type II telomere maintenance at least until ~150 generations after deleting these genes. The exceptions were KU80 and RPB9. Ku80Δ strains switched to a new survivor type that is similar to type I and continued for the long term. RPB9 was required for two independent type II survivor strains to survive, whereas the third type II strain did not require this gene at ~150 generations after deleting the gene. After many generations (~ 350), this strain switched to type I. At long term propagation (~500 generations) after deletion of the candidate genes, all type II strains displayed telomere shortening until the propagation was stopped. However, Rad50Δ strains switched to type I after long term. Finally, the absence of the candidate genes did not affect the sensitivity of type II survivor strains to temperature. On the other hand, type II survivor strains with some genes deleted displayed sensitivity to UV.