The morphology and distribution of cuticular setae on the uropods and walking legs of the Norway lobster Nephrops norvegicus (L.) has been studied using both light microscopy and Scanning Electron Microscopy. Three types of setae are present on the uropods, plumose setae, simple setae and guard hairs. Hair peg and hair fan organs were also seen.The propodus and dactyl of the 2nd and 3rd legs of Nephrops are similar in both their structure and in the form and distribution of their cuticular setae. Three main areas of setal distribution are found: squamous setae are distributed 1) in bunches on the flat surfaces of the propodus and dactyl and 2) along the lateral edges of the propodus and dactyl and 3) hedgehog hairs line the inner edges of the propodus and dactyl.Most of the setae on the 4th and 5th legs are found around the propodus-dactyl (P-D) joint. Three rows of simple setae are found on the dactyl, and both serrate setae with simple scales and squamous setae are found overlapping the P-D joint. Also found near the joint are CAP organs and hedgehog hairs.All of the setae on the uropods show responses to tactile and vibratory stimulation as do the hedgehog hairs, the serrate setae, the simple setae and the squamous setae on the legs.The responses of afferents from the uropods and walking legs and of the abdominal interneurones have been tested in response to water borne vibrations of different frequences produced both as surface waves and in an acoustic tube. The uropod afferents show range fractionation and have therefore been divided into three nested categories based on the upper limit of their frequency response. Low frequency units respond from 2-20Hz, intermediate units from 2-50Hz and high frequency units from 2-100Hz. The leg afferents also show range fractionation and have also been divided into three nested categories: low frequency units respond from 20-60Hz, intermediate units from 20-200Hz and high frequency units from 20-450Hz. Preliminary studies have indicated that the leg afferents show directional sensitivity. The abdominal interneurones have been categorised as either intermediate or high frequency; intermediate interneurones respond from 2-100Hz and high frequency interneurones from 2-200Hz. The receptive fields of mechanosensory interneurones have also been determined.The postural responses of Nephrops to water borne vibrations have been studied using video analysis. An abdominal extension response is reliably elicited which varies with the frequency of stimulation in a distinct way. From 20-80Hz the animals respond immediately, and abdominal extension is accompanied by rapid leg movements, swimmeret beating and very occasionally tail flipping. From 100-180Hz the response occurs with a delay, the duration of which seems unrelated to frequency within this range. No responses were seen above 180Hz.The nervous control of the abdominal extension response has been studied by recording from abdominal motor roots (superficial root three and root two) which supply the two muscles involved (the superficial flexor and extensordmuscles). It has been shown that abdominal extension is produced by both central and peripheral inhibition of flexor muscle activity in combination with excitation of the extensor muscle. The neuronal basis of the delay seen in the behavioural experiments has been investigated, and a number different patterns of nervous activity have been found which might produce this delay.Behavioural studies have been conducted in the field to investigate the responses of freely moving animals to sound in their natural environment. Investigations have been conducted of changes in the emergence rhythm and changes in the transient behaviour of the animals. Tests to investigate changes in the burrow emergence rhythm with the underwater loudspeakers at 10m from the animal failed to produce any response. However small changes occur in the transient behaviour of Nephrops when they are very close to the loundspeaker even though the sound pressure levels are similar to those used at 10m. These tests have been repeated in laboratory tanks where clear locomotory responses, predominantly backwards walking, are seen in response to stimuli from 20-80Hz in both blind and sighted animals.Tests have been conducted in a free acoustic field to determine the behavioural response threshold of Nephrops to sound using the postural response as a monitor. The animals showed no responses with the loudspeaker at 1m but showed clear responses with the speaker at 0.09m even when the sound pressure levels were similar, yielding a threshold in terms of particle displacement of the water of 0.874m which is independent of frequency. This indicates that the Nephrops is sensitive to the particle motion component of sound rather than the pressure component.

Ecologists would like to understand how complexity persists in nature. In this thesis I have taken two fundamentally different routes to study ecosystem stability of model ecosystems: classical community ecology and classical population ecology. In community ecology models, we can study the mathematical mechanisms of stability in general, large model ecosystems. In population ecology models, fewer species are studied but greater detail of species interactions can be incorporated. Within these alternative contexts, this thesis contributes to two consuming issues concerning the stability of ecological systems: the ecosystem stability-complexity debate; and the causes of cyclic population dynamics. One of the major unresolved issues in community ecology is the relationship between ecosystem stability and complexity. In 1958 Charles Elton made the conjecture that the stability of an ecological system was coupled to its complexity and this could be a “wise principle of co-existence between man and nature” with which ecologists could argue the case for the conservation of nature for all species, including man. The earliest and simplest model systems were randomly constructed and exhibited a negative association between stability and complexity. This finding sparked the stability-complexity debate and initiated the search for organising principles that enhanced stability in real ecosystems. One of the universal laws of ecology is that ecosystems contain many rare and few common species. In this thesis, I present analytical arguments and numerical results to show that the stability of an ecosystem can increase with complexity when the abundance distribution is characterized by a skew towards many rare species. This work adds to the growing number of conditions under which the negative stability - complexity relationship can been inverted in theoretical studies. While there is growing evidence that the stability-complexity debate is progressing towards a resolution, community ecology has become increasingly subject to major criticism. A long-standing criticism is the reliance on local stability analysis. There is growing recognition that a global property called permanence is a more satisfactory definition of ecosystem stability because it tests only whether species can coexist. Here I identify and explain a positive correlation between the probability of local stability and permanence, which suggests local stability is a better measure of species coexistence than previously thought. While this offers some relief, remaining issues cause the stability-complexity debate to evade clear resolution and leave community ecology in a poor position to argue for the conservation of natural diversity for the benefit of all species. In classical population ecology, a major unresolved issue is the cause of non-equilibrium population dynamics. In this thesis, I use models to study the drivers of cyclic dynamics in Scottish populations of mountain hares (Lepus timidus), for the first time in this system. Field studies currently favour the hypothesis that parasitism by a nematode Trichostrongylus retortaeformis drives the hare cycles, and theory predicts that the interaction should induce cycling. Initially I used a simple, strategic host-parasite model parameterised using available empirical data to test the superficial concordance between theory and observation. I find that parasitism could not account for hare cycles. This verdict leaves three options: either the parameterisation was inadequate, there were missing important biological details or simply that parasites do not drive host cycles. Regarding the first option, reliable information for some hare-parasite model parameters was lacking. Using a rejection-sampling approach motivated by Bayesian methods, I identify the most likely parameter set to predict observed dynamics. The results imply that the current formulation of the hare-parasite model can only generate realistic dynamics when parasite effects are significantly larger than current empirical estimates, and I conclude it is likely that the model contains an inadequate level of detail. The simple strategic model was mathematically elegant and allowed mathematical concepts to be employed in analysis, but the model was biologically naïve. The second model is the antipode of the first, an individual based model (IBM) steeped in biological reality that can only be studied by simulation. Whilst most highly detailed tactical models are developed as a predictive tool, I instead structurally perturb the IBM to study the ecological processes that may drive population cycles in mountain hares. The model allows delayed responses to life history by linking maternal body size and parasite infection to the future survival and fecundity of offspring. By systematically removing model structure I show that these delayed life history effects are weakly destabilising and allow parameters to lie closer to empirical estimates to generate observed hare population cycles. In a third model I structurally modify the simple strategic host-parasite model to make it spatially explicit by including diffusion of mountain hares and corresponding advection of parasites (transportation with host). From initial simulations I show that the spatially extended host-parasite equations are able to generate periodic travelling waves (PTWs) of hare and parasite abundance. This is a newly documented behaviour in these widely used host-parasite equations. While PTWs are a new potential scenario under which cyclic hare dynamics could be explained, further mathematical development is required to determine whether adding space can generate realistic dynamics with parameters that lie closer to empirical estimates. In the general thesis discussion I deliberate on whether a hare-parasite model has been identified which can be considered the right balance between abstraction and relevant detail for this system.

Population numbers change in space and time. The construction of models to investigate the spatial and temporal dynamics of populations may offer a means to identify the processes driving this change. In this thesis, we make use of models to examine the population ecology of three species of upland birds: red grouse, meadow pipit and capercaillie. Populations of red grouse in the British Isles exhibit cyclic fluctuations in abundance. Time series data from 287 grouse moors across the United Kingdom were analysed to investigate co-variation in these fluctuations. Results indicate high levels of synchrony between populations on neighbouring moors, with synchrony declining with increasing intermoor distance. At distances greater than 100km, populations exhibit only weak synchrony. Synchrony is shown to be a product of strong coupling events, which occur on average every one in six years. In the absence of such events, synchrony is shown to dissipate within three years. Further, we present evidence which suggests this coupling is driven (at least in part) by dispersal between populations. The density dependent structures are also found to be sufficiently homogeneous to allow correlations in climate to synchronise dynamics, but examination of three climate variables failed to detect a relationship. We also studied the population dynamics of meadow pipits in upland grassland ecosystems. Data, collected as part of an ongoing grazing field experiment, were analysed to construct a Bayesian model of population growth, and predict the effect of grazing intensity on meadow pipit populations. Results suggest grazing has a significant impact on population growth. Grazing may act to improve meadow pipit foraging efficiency and thus productivity. Finally, a spatially explicit population viability model was constructed to predict changes in the future abundance and distribution of capercaillie. Published estimates of key demographic variables were drawn from the literature to parameterise the model. The spatial structure of the population was inferred from spatial data, documenting the extent and configuration of remnant pine woodlands in Scotland. The model predicts a low probability of extinction for capercaillie in the future, and offers insights into key processes affecting the distribution and abundance of this species. The development of these models has advanced our understanding of the environmental processes driving changes in the spatial and temporal dynamics of these species. The results of these studies may be useful in anticipating the future consequences of various drivers of change on the ecology of upland species.

No description available.

Injection of 4-hydroxytamoxifen (4-OHT) activates the oncogene c-myc in transgenic pIns-c-MycERTAM mice, triggering β-cell proliferation in the short term as well as apoptosis and reduced insulin secretion, leading to hyperglycaemia. This hyperglycaemia is preceded by a short period of hypoglycaemia, which may be caused by: (i) increased insulin secretion or release from dying cells; (ii) rapid β-cell proliferation; and (iii) increased insulin sensitivity. This thesis characterizes the initial stages of the expression of c-MYC in the plns-c-MycERTAM mouse model and attempts to identify the causes of the transient hypoglycaemia using mathematical models. Furthermore, microarray data were analysed to investigate the early hypoglycaemia from the point of view of transcriptomics. The size and mass of β-cells were quantified during the transient period of hypoglycaemia by means of immunohistochemistry. These data were incorporated in a detailed mathematical model of β-cell dynamics.

Loss of large segments of bone creates critical size defects (CSDs). These fail to heal spontaneously and present major clinical challenges to orthopaedic surgeons. The research described in this thesis is based upon the hypothesis that the healing of CSDs is responsive to the ambient mechanical environment, and can be accelerated by mechanical modulation. This hypothesis was tested in rat, femoral CSDs treated with recombinant, human, bone morphogenetic protein-2. For this study I designed novel external fixators allowing experimental control over the local mechanical environment. These were characterised by extensive mechanical testing prior to evaluation in the rat model. Low stiffness fixators induced callus formation 9 days after surgery, whereas rigid fixation delayed it until 2 weeks. All defects were radiologically bridged after 3 weeks. Rats were euthanised after 8 weeks and the defects evaluated by a battery of imaging, mechanical and histological tests. All confirmed the superiority of the lowest stiffness fixators. Based upon these data, I hypothesised that healing would be improved by imposing low stiffness for the first two weeks of healing, followed by high stiffness for the remaining six weeks. The experimental data confirm that this regimen dramatically accelerated callus formation and maturation, and induced faster remodelling of endosteal and periosteal callus. This was associated with higher failure strength, fewer trabeculae, decreased callus size and thicker and more uniform distribution of new cortical bone. Histologically it was not possible to detect cartilage within the defects prior to the appearance of bone, suggesting that healing either does not occur through endochondral ossification, or that this process is very rapid. These data confirm that the healing of CSDs is highly responsive to the ambient mechanical environment, allowing the rate and quality of healing to be manipulated. This information will help develop more efficient ways to heal CSD clinically.

The study of pluripotent cells in mouse has revealed a core transcription factor network. Pluripotent cells have not been identified in many non-mammalian organisms, but cells with pluripotent properties are found in axolotl (Ambystoma mexicanum) a urodele amphibian. Similarities, between the morphological processes in amniotes and those in urodeles led to the suggestion that amniotes may have arisen from a urodele-like ancestor. Thus, studying the pluripotency network in axolotl may be key to understanding the evolution of mechanisms governing pluripotency in amniotes. This study describes the investigation of two of the core pluripotency trancription factors, Axnanog and Axoct4. Coexpression of axnanog and axoct4 was detected in the undifferentiated tissues of blastula and gastrula stage embryos, suggesting a conserved role in pluripotency/multipotency. Antisense morpholino oligonucleotides were employed to investigate the function of these two molecules. Gastrulation was disrupted in Axnanog morphant embryos. Additionally, they maintained expression of genes associated with pluripotency and early lineage specification, but only expressed low levels of terminal differentiation markers. There are two explanations for this phenotype, a cell migration defect or a developmental block. Axoct4 morphant embryos had a similar phenotype suggesting that Axoct4 may function in a common pathway. Primordial germ cells (PGCs) are the only cells that retain the ability throughout development to derive all of the tissues of the embryo, upon fertilisation, and these cells express many pluripotency-associated factors. Little is known about PGC development in axolotl. In this study, the roles of Axoct4, Axnanog and Axblimp1 were investigated. Neither Axnanog nor Axoct4 were found to have a role in PGC development. Axblimp1 is unlikely to have a role in PGC specification, as in mouse, but a role in PGC maintenance was not ruled out.

The role of parasites as agents of selection on their hosts has been well established, but less is known about how parasites facilitate divergence among host populations. In this thesis, I used the three-spined stickleback, Gasterosteus aculeatus, as a model organism to explore spatial variation in host-parasite interactions and the consequences for divergence of host traits. First, I established the extent of spatial variation in natural infection in the study system, North Uist, Outer Hebrides, Scotland, by conducting a survey of macroparasite communities in twelve freshwater lochs over two years. I found substantial geographic variation in parasite communities that was remarkably stable in time. Assuming that differences in parasite community composition correspond to differences in parasite-mediated selection, it suggests that North Uist stickleback populations experience divergent parasite-mediated selection that is consistent in time. Next, I carried out a series of artificial infection experiments with lab-reared sticklebacks from five populations using three widespread macroparasite species (Gyrodactylus gasterostei, Diplostomum spathaceum and Schistocephalus solidus), to assess geographic variation in parasite resistance and a component of the innate immune system, the respiratory burst response. There was significant variation among populations in resistance to G. gasterostei and D. spathaceum, and the innate immune response. To some extent the variation was related to natural infection levels, suggesting that divergent parasite-mediated selection may drive investment in these traits. Lastly, I conducted a growth experiment with the five stickleback populations and showed that there was significant population-level variation in juvenile growth rate, an important life history trait. In spite of considerable variation in all traits, I found no evidence for genetic trade-offs across populations between juvenile growth rate, and macroparasite resistance or the innate immune response. This thesis adds to a growing body of work that emphasises the importance of space in shaping host-parasite interactions.

This thesis describes a series of experiments investigating the neural underpinnings of the ‘efficacy’ or ‘value’ of food reinforcers in the control of operant behaviour. A number of methods have been devised for measuring reinforcer value. The experiments described in this thesis employed the progressive-ratio schedule, in which the number of responses required to obtain a reinforcer is progressively increased with each successive reinforcer. The performance of rats on this schedule was analysed using a quantitative model of schedule-controlled behaviour, Killeen’s (1994) ‘Mathematical Principles of Reinforcement’ (MPR) model. An advantage of this approach is that MPR provides a theoretical basis for discriminating between the effects of interventions on ‘motivational’ and ‘motor’ aspects of operant behaviour. According to MPR, schedule-controlled behaviour may be characterized by an ‘activation’ parameter, a, which measures the reinforcer efficacy or value, a ‘response time’ parameter, δ, which measures the minimum inter-response time, and a ‘coupling’ parameter’ β which expresses the weight in short-term memory assigned to the most recent response. Chapter 1 reviews the background literature related to the main themes of the project: the neurobiology and behavioural functions of the orexinergic and the dopaminergic systems of the brain, and the use of the progressive-ratio schedule in behavioural neuroscience. Special emphasis is given to MPR and its application to behavioural neuroscience. Experiment 1 (Chapter 2) examined the effect of destruction of orexinergic neurones of the lateral hypothalamic area (LHA), which have been proposed to control reward processes and food intake. Orexinergic neurones were destroyed by intracerebral injection of a selective neurotoxin, the orexin-B-saporin conjugate (OxSap). OxSap-induced lesions had no effect on the parameter a and did not alter food intake. However, they did increase the response time parameter δ, suggesting that the lesion had a motor debilitating effect. Experiment 2 (Chapter 3) investigated the effect of disconnecting the LHA from the ventral tegmental area (VTA), a major area of projection of the orexinergic neurones. Functional disconnection was achieved by unilateral injection of OxSap into the LHA on one side and into the VTA on the contralateral side of the brain. The lesion had no effect on a or any other of the motivational measures used, or on food intake. However δ was increased, suggesting that the lesion mainly affected motor functioning. Since OxSap has a preferential destructive effect on neurones that express the orexin-2 (OX2) receptor, the possibility was considered that the putative role of orexins in regulating reinforcer value may be mediated by orexin-1 (OX1) receptors, rather than OX2 receptors. In order to explore this possibility, Experiment 3 (Chapter 4) examined the effect of acute functional disconnection of the LHA from the nucleus accumbens shell (AcbS), an area rich in OX1 receptors. Disconnection was achieved by unilateral OxSap-induced lesions of the LHA and infusion of the OX1 receptor antagonist, SB-334867-A (1-(2-methylbenzoxazol-6-yl)-3-[1,5]naphthyridin-4-yl-urea hydrochloride) into the contralateral AcbS via indwelling intracerebral cannulae. The results showed a reduction of the activation parameter a, with no effect on any of the other parameters. These findings are consistent with the notion that OX1 receptors are involved in the control of the reinforcer value, whereas the OX2 receptors are more involved in the control of motor-related processes. Experiment 4 (Chapter 5) examined the effect of cyproheptadine, a drug with 5-hydroxytryptamine (5HT2A) and histamine (H1) receptor blocking action. Cyproheptadine’s effect on progressive-ratio schedule performance was compared with the effects of the ‘atypical’ antipsychotic drug clozapine, which shares many of cyproheptadine’s pharmacological actions, and the ‘conventional’ antipsychotic haloperidol, whose principal action is antagonism of D2-like dopamine receptors. In addition, the effects of two drugs with known effects on food intake, Δ9-tetrahydrocannabinol (THC) and chlordiazepoxide, were also examined. Cyproheptadine and clozapine increased both a and δ. Haloperidol reduced a and increased δ and chlordiazepoxide increased a. Unexpectedly, THC had no effect on the parameters of MPR; this negative result was explored further in Experiment 6 (see below). Experiment 5 (Chapter 6) examined the differential involvement of D1-like and D2-like dopamine receptors in the control of progressive-ratio schedule performance reinforced with a sucrose solution or corn oil. Performance maintained by both reinforcers conformed to the equation derived from MPR. Blockade of D2-like receptors by haloperidol equally affected performance maintained by corn oil and sucrose, reducing a and increasing δ. However blockade of D1-like receptors by SKF-83566 (bromo-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7-ol hydrobromide) reduced both a and δ in rats trained with the sucrose reinforcer but had no effect on the rats reinforced with corn oil. This is consistent with the notion that D1-like and D2-like dopamine receptors exert differential influences on the values of different kinds of food reinforcer. Experiment 6 (Chapter 7) examined the effect of THC on progressive-ratio schedule performance of rats reinforced with corn oil and sucrose. The rats were tested under food deprived and free feeding conditions. In addition, the effect of THC on food intake was assessed. The results confirmed that THC did not affect any of the parameters of MPR. When the animals were transferred from the food deprived to the free feeding condition they showed a reduction of a but no change of δ. This is in agreement with the assumption of MPR that a and δ are independent parameters. Finally, there was a trend for THC to increase sucrose consumption and to reduce corn oil intake, suggesting that cannabinoid receptors may mediate different effects on the reinforcing values of these two foods. Chapter 8 summarises the results of the experiments from the project, and discusses some of their implications. The implications of the findings of Experiments 1-3 for the role of orexinergic mechanisms in the regulation of reinforcer value and motor processes are discussed. The results of Experiments 4 and 5 are considered in the context of the putative involvement of dopamine receptors in reinforcement processes and the effects of conventional and atypical antipsychotics on motivated behaviour. The failure of THC to affect progressive-ratio schedule performance (Experiments 4 and 6) is discussed in the context of the relationship between reinforcer ‘value’ and food consumption. The general implications of these findings for behavioural pharmacology and MPR are considered. Finally, some futures lines of investigation are proposed.

Climate-driven changes in the overall abundance or phenology of food resources may be critical factors affecting migratory populations, which depend on suitable conditions at widely-spaced locations across the planet. Numerous studies have described associations between climatic change and breeding success, survival and the timing of migration among migrant birds, but we used an experimental approach to investigate the causal mechanisms underlying these widely-reported correlations. Specifically, we used food-supplementations to simulate experimentally the impact of changes in food availability across the annual cycle of a model species of long-distance migrant bird, the northern wheatear (Oenanthe oenanthe). Food supplementation modified migratory schedules of wheatears by affecting migratory fuelling, but the strength of this impact varied between stages of the annual cycle and between two subspecies with contrasting migration strategies. Food supplementation advanced hatching date of wheatears in the UK, and led to some supplemented individuals increasing their reproductive output through multiple breeding attempts. Food-supplemented wheatears exhibited higher rates of annual survival than control wheatears, and the strength of this effect was most pronounced on survival of young immediately following fledging. These experiments highlight aspects of wheatear performance that are currently limited by food availability and are thus most sensitive to climate-driven changes in food supply (primarily migratory fuelling, number of breeding attempts and survival). We used experimental manipulations of temperature and soil moisture of upland grassland turfs to simulate the impact of climate change on the abundance and emergence phenology of the wheatear’s arthropod prey. Warming by 2 ºC and low soil moisture levels led to a reduction in arthropod abundance later in the season, indicating how such climate-driven changes would affect food availability to wheatears across the breeding season. These studies together provide experimental evidence for the mechanisms by which climate change is expected to influence population changes in migratory taxa.