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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Parasite dynamics and community richness in a naturally fragmented water vole (Arvicola amphibious) metapopulation

Davies, Claire Louise January 2014 (has links)
Fragmentation can drive local populations to become smaller and more isolated, and consequently more susceptible to extinction. Movement between patches, however, can interconnect such populations so that they effectively behave as larger and more stable metapopulations. Over the past two decades metapopulations have been used to shed light on the complex interactions that occur between hosts and parasites. Effectively every host can be considered as a discrete habitat patch from the perspective of a parasite. As such, host-parasite interactions naturally lend themselves to being examined within the metapopulation paradigm. In this thesis I examine empirically how various aspects of metapopulation structure, such as local host population size and landscape isolation/connectivity, combine to determine the extinction and recolonization dynamics of parasites in the landscape. Using a naturally fragmented water vole (Arvicola amphibious) metapopulation, I describe the spatial and temporal variation in parasite infection prevalence or burden in a Scottish landscape. I specifically address the spatial and temporal dynamics of both ectoparasites, and vectortransmitted microparasites, since these are two groups of parasites commonly found in natural systems yet often overlooked in the host-parasite metapopulation literature. In addition, I attempt to understand how specific parasite characteristics, such as transmission mode and infectious period, can influence how parasites respond to host population structure. In the final chapter, I bring together a number of parasite groups to examine the impact of metapopulation dynamics on parasite communities as a whole by investigating its impact of parasite community richness. Overall the findings of my study indicate that host spatial structure and the level of connectivity between patches are important factors that affect parasite dynamics and community richness. However, the exact level of connectivity required to sustain a parasite population locally depended on specific parasite characteristics. In contrast, local effects host/vector population size and patch infection history) had no discernible impact on most parasite groups.
2

Spatial and temporal characteristics of bacterial parasite communities in outbreaking fossorial water vole (Arvicola terrestris) populations : static uniformity or dynamic heterogeneity? / Caractéristiques spatiales et temporelles des communautés de parasites bactériens dans les populations de campagnols terrestres (Arvicola terrestris) : uniformité statique ou hétérogénéité dynamique ?

Villette, Petra 28 June 2018 (has links)
Le campagnol terrestre, Arvicola terrestris, occasionne en France, lors de ses pullulations cycliques interannuelles, d’importants dégâts aux prairies de montagne. Un groupe de travail constitué des équipes de recherche de l’Université de Franche-Comté (UFC), de l’INRA (Centre de Biologie et de Gestion des Populations) et d’organismes agricoles (Fédération Régionale de Défense contre les Organismes Nuisibles de Franche-Comté, FREDON), ont privilégié une approche « systémique » dans laquelle les interactions entre les campagnols, leur habitat (paysage, prédateurs) et les pratiques agricoles sont analysées de façon hiérarchisées (spatialement et temporellement). Un des objectifs est de mettre en évidence le plus grand nombre possible de facteurs de contrôle sur lesquels il est possible d’agir, et l'échelle à laquelle ces actions sont pertinentes. Ces études ont permis d’initier une stratégie, expérimentée avec succès, notamment en Franche-Comté et en Auvergne, et qui privilégie la lutte raisonnée. Il subsiste néanmoins des zones d’ombre relatives à la compréhension du cycle, notamment concernant les déterminants de la phase de déclin. Le rôle du cortège de pathogènes (parmi lesquels certains peuvent être transmis à l’homme) reste pour l’instant sujet de débat dans la littérature scientifique. La compréhension des facteurs clés déterminant cette phase devrait permettre aux éleveurs de mieux anticiper les impacts économiques et adopter les stratégies de contrôles des population les plus adéquates. Objectifs de la thèse (1) Tester les hypothèses des pathogènes et de la sénescence pour expliquer le déclin démographique. (2) Rechercher des indicateurs biologiques (diversité des pathogènes et/ou indicateurs immunitaires) qui permettent de prédire les phases de déclin et d’anticiper des mesures agricoles appropriées pour restaurer les prairies. (3) Evaluer le rôle de la transition entre la phase de forte densité et de déclin démographique pour l’émergence de pathogènes circulants par les populations de campagnols et responsables de maladies humaines. Méthodologie générale Des suivis de populations avec des prélèvements réguliers (mensuels) seront réalisés sur plusieurs populations (répliquats) dans la période qui encadre le déclin démographique. Des méthodes fondées sur le séquençage à haut débit (NGS : Next Generation Sequencing) pour l’épidémiologie permettent d’établir des catalogues complets des pathogènes (virus, bactéries, parasites) hébergées par les populations, et d’en mesurer les prévalences. / Context In France, during cyclic population surges, water voles, Arvicola terrestri, cause extensive damage to mountain grassland. A working group consisting of researchers from the University of Franche-Comté (UFC), INRA (Centre de Biologie et de Gestion des Populations) agricultural organizations (Fédération Régionale de Défense contre les Organismes Nuisibles de Franche-Comté, FREDON) are working on systems approach in which interactions between voles, their habitat (landscape, predators) and agricultural practices are analysed hierarchically (in space and time). One of the objectives is to highlight the largest possible number of control factors on which it is possible to act, and the scale at which these actions are relevant. These studies have helped initiate a strategy, successfully tested in Franche-Comté and in Auvergne, which promotes the integrated control of water vole populations. Nevertheless, there are still grey areas in the understanding of the cycle, particularly on the determinants of the decline phase. The role of pathogen communities (some species may even be transmitted to humans) so far remains the subject of debate in the scientific literature. The understanding of the key factors determining this phase should allow farmers to better anticipate economic impacts and to adopt optimal strategies for vole population control Objectives: (1) To test the pathogens and senescence hypotheses in order to explain the population decline. (2) To look for biological indicators (diversity of pathogens and / or immune indicators) that may predict the decline phase in order to anticipate appropriate measures to restore grasslands. (3) To assess the role of the transition between high population density phase and the decline phase for the emergence of pathogens in vole populations that may cause human diseases.General Methodology Population monitoring with regular (monthly) sampling will be made on several populations (replicates) in the period that brackets the vole population declines. Methods based on Next Generation Sequencing (NGS) makes it possible to establish extensive catalogues of pathogens (viruses, bacteria, other parasites) hosted by vole populations and to measure the prevalence.

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