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1
Keeling, Matthew James. "The ecology and evolution of spatial host-parasite systems". Thesis, University of Warwick, 1995. http://wrap.warwick.ac.uk/30/.
Testo completoAbstract (sommario):
All ecological and epidemiological systems are embedded in space and composed of individuals; these facts often have a profound effect on the dynamics and means many tools and definitions require reformulation. Modelling has always been about taking highly complex dynamical systems, such as the natural environment, and attempting to simplify them to a leve that can be conceptualised, in the process losing all the features that are not understood or not anticipated. The individual based spatial models which form the basis of this work start from the simple rules for individuals and build up to a complex system, allowing new, unexpected phenomenon to arise naturally. The local interactions in spatial models lead to short scale correlations and self-induced spatial heterogeneity as the small fluctuations of environmental noise are amplified into macro-scale patterns. These spatial patterns can lead to ephemeral refuges for hosts from where they can disperse stabilising the dynamics. After discussing the importance and variety of host-parasite interactions several techniques to be used in this work are developed and explained on simple examples. Chapters III and IV introduce a caricature host-pathogen model and how how this deviates from the standard mean field theory approximations. Attention is then turned to host-parasitoid systems and the spatially extended Nicholson-Bailey equations; probems with this coupled map lattice are highlighted and an alternative artificial ecology is formulated. Remaining with the Nicholson-Bailey equations these are forced to be integer based by utilising stochastic events, this greatly stabilises the dynamics hence the method was applied to the persistence of measles epidemics in small populations (=500000). Chapter VII demonstrates how the inclusion of space enhances the effects of parasitism in increasing the evolutionary advantage of sexual hosts over asexual ones. Finally general techniques are developed to implicitly model the effects of spatial correlations and stochastic individual based interactions.
2
Crosswaite, Matthew John. "Parasite distribution and specificity in anuran host complexes". Thesis, Queen Mary, University of London, 1994. http://qmro.qmul.ac.uk/xmlui/handle/123456789/26224.
Testo completoAbstract (sommario):
This study was based on the parasite fauna of three anuran systems. In two of the systems; the spadefoot toads, Scaphiopus bombifrons and S. multiplicatus and the fire and yellow-bellied toads, Bombina bombina and B.variegata, inter-species hybridisation occurs. In the third system an autopolyploid species complex involves the Gray treefrogs, Hyla chrysoscelis and H.versicolor. The status of the Scaphiopus hybrid zone in Arizona was re-assessed by cellulose-acetate gel electrophoresis. Genotypic frequencies were comparable to those previously documented, indicating that a region of 'balanced introgression' may exist. Specimens were collected in areas of host sympatry and the distribution of helminths within hosts of different genetic constitution investigated. From extensive surveys of all three systems, parasite frequency distributions were typically aggregated with no evidence of any change in host genetic predisposition to infection. In addition, the surveys have documented a number of new host and/or parasite locality records for each system. Of particular interest was the discovery of the digenean Clinostomum complanatum in a desert environment, an introduction related to human management of the ecosystem. Particular reference was made to the specificity of the polystomatid monogeneans, Polystoma nearcticum infecting members of the H.chrysoscelis- H.versicolor complex and Neodiplorchis scaphiopodis infecting S.bombifrons and S.multiplicatus. For Polystoma, worms from H.chlysoscelis and H.versicolor could not be separated by morphology, which was supported by preliminary crossinfections. This suggests that P.nearcticum infects both members of this complex. For Neodiplorchis, morphological similarity was confirmed by cross-infections which revealed that N.scaphiopodis can reach sexual maturity and produce fully developed larvae in heterospecific hosts. The neotenic development of P. nearcticum and the initial post-oncomiracidial stages of N.scaphiopodis were documented. Furthermore, certain aspects of transmission dynamics were examined by the experimental infection of H. versicolor tadpoles with P. nearcticum.
3
Gubbins, S. "Dynamics and control of host-parasite systems in heterogeneous and disturbed environments". Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599772.
Testo completoAbstract (sommario):
Using a combination of mathematical analysis, model fitting and parameter estimation, this thesis examines the dynamics and control of host-parasite systems in heterogeneous and disturbed environments. The first chapter introduces and tests models for the population dynamics of Sclerotinia minor, an economically important fungal plant parasite, and the fungal hyperparasite Sporidesmium sclerotivorum in a closed system from which any host of S. minor is excluded. Model structures are identified that reflect experimental data rather than models that are simply mathematical abstractions. Various elaborations of this simple model are discussed in the next chapter and, specifically, the effect of a latent period of infection and the influence of differentiating between primary and secondary infections are considered. In the following chapter, models are developed in which the dynamics of a host crop (lettuce) of S. minor are included. Various mechanisms that contribute to the observed persistence of the parasite are examined and, in particular, the roles played by discontinuities due to planting and harvesting of the lettuce crop, spatial heterogeneity and changes in environmental conditions are considered. Although the models discussed in the first three chapters are developed with close reference to the S. minor-S. sclerotivorum system, they are of broad applicability. In the remaining largely theoretical chapters, the population dynamics of the models are analysed, paying particular attention to thresholds for invasion and persistence. The persistence of host-parasite interactions in disturbed environments (where the host is not continuously present or does not continuously reproduce) is considered first. In the penultimate chapter, thresholds for invasion in plant-parasite systems are derived. These systems are characterised by dual sources of inoculum (primary and secondary infection) and a host response to infection load. Finally, the simple model fitted to the S. minor-S. sclerotivorum data is used to examine the effects of heterogeneous mixing on invasion and persistence.
4
Miller, Martin Roy. "Theoretical models for the evolution and ecological dynamics of host-parasite systems". Thesis, University of Sheffield, 2006. http://etheses.whiterose.ac.uk/14903/.
Testo completoAbstract (sommario):
Natural organisms are infected by many different parasites, and as a consequence, hosts have evolved a wide range of defences to cope with them. Resistance may be conferred through mechanisms that reduce susceptibility to infection ('avoidance') or increase the rate of clearance ('recovery'). Other forms of resistance reduce the deleterious effects of infection ('tolerance'), or inhibit the parasite's growth ('control'). In addition to these innate forms, hosts may also benefit from immunological memory ('acquired immunity'). The evolution of resistance is expected to be costly in terms of other life history traits. In the presence of such 'trade-offs', the host population may evolve towards an evolutionarily stable strategy (ESS) that balances the costs and benefits of resistance. Another possibility is that a process of evolutionary branching occurs, leading to polymorphism of distinct strategies. Parasites also show adaptation to their hosts and have generally not evolved to be avirulent. Again, this is the result of trade-offs between virulence and other aspects of life history. Often, a higher transmission rate is attained at the cost of increased virulence. This thesis uses a mathematical modelling approach to examine hostparasite interactions. The first part considers the evolutionary dynamics of quantitative host resistance and parasite traits, employing fitness expressions constructed using the techniques of adaptive dynamics. The second part examines the population dynamics of host-parasite interactions; in particular, how different assumptions about the nature of the transmission process may affect the dynamics.
5
Keppel, Michelle [Verfasser], e Bernd [Akademischer Betreuer] Sures. "Mutual adaptation in differently evolved host-parasite systems / Michelle Keppel ; Betreuer: Bernd Sures". Duisburg, 2016. http://d-nb.info/1116941791/34.
Testo completo
6
Rasmussen, Justin Lee. "Investigations of evolutionary arms races and host diversity in avian brood parasite systems". Thesis, University of Canterbury. Biological Sciences, 2013. http://hdl.handle.net/10092/8959.
Testo completoAbstract (sommario):
Obligate brood parasites rely solely on other species, the hosts, to incubate their eggs and raise their offspring, which often reduces the host’s reproductive output. This reproductive cost has led to the evolution of anti-parasite adaptations among hosts, which in turn, has led to better trickery by parasites, a process termed an evolutionary arms race. The objective of this thesis was to investigate host-parasite coevolutionary arms races to address questions of host-use diversity. Host diversity varies dramatically among brood-parasitic species, but reasons for variations in host-use among brood parasites are not well understood. In Chapter 2, I address questions on host diversity specifically, whereas I address questions about coevolutionary interaction between hosts and parasites in Chapters 3, 4 and 5 using two host-parasite systems, one in New Zealand and one in North America.
Chapter 2 investigates if host diversity is constrained by aggressive nest defence behaviour. I compared the nest defence behaviour of the exclusive host of the shining cuckoo Chrysococcyx lucidus lucidus on the main islands of New Zealand, the grey warbler Gerygone igata, to two other potentially suitable hosts that are not currently parasitised, the fantail Rhipidura fuliginosa and the silvereye Zosterops lateralis. The results suggest that grey warblers are as aggressive as fantails and silvereyes towards shining cuckoos at the nest and thus, host specialisation in shining cuckoos in New Zealand, at least, does not appear to be the result of nest-defence constraints imposed by potential but unused host species.
Chapter 3 investigates if red-winged blackbirds Agelaius phoeniceus, a species that typically accepts the eggs of parasites, recognises, as indicated by changes in incubation behaviour, when they have been parasitised by brown-headed cowbirds Molothrus ater. Recognition without rejection suggests that rejection may be context-dependent but the results suggest that red-winged blackbirds do not recognise when their nests have been parasitised by brown-headed cowbirds, at least at the egg stage. This study was the first to investigate if hosts that almost invariably accept the eggs of parasites recognise when they have been parasitised.
Chapter 4 investigated the possibility of coevolutionary arms races occurring through olfactory channels in contrast to earlier work that focussed only on visual and auditory cues. Recent research has revealed that olfactory abilities in birds are more common than previously thought. Uropygial gland secretions are posited to be a key source of avian body odour and its composition has been found to vary among species and individuals as well as between the sexes. I compared gas-chromatography (GC-FID) traces of shining cuckoo preen wax to the GC-FID traces of the grey warbler, the only host of the shining cuckoo in mainland New Zealand, as well as the preen wax of seven other species for evidence of mimicry. Preliminary results suggest there is evidence for mimicry and the potential for odour-based nestling discrimination in grey warblers. Further tests recording the response of grey warblers to odour-manipulated nestlings are necessary.
Finally, in Chapter 5, I investigated the response of the song thrush Turdus philomelos, a species that rejects the eggs of the common cuckoo Cuculus canorus and conspecifics at intermediate and low frequencies, respectively, to nest-odour manipulations using the preen wax of conspecifics and heterospecifics. The results suggest song thrush do not use odour to assess the risk of parasitism at least as indicated in terms of changes in incubation behaviour. Investigations of the role of olfaction in avian brood parasite systems can provide a better understanding of brood-parasite coevolution. Only by considering all channels of communication can we be sure to completely understand the coevolutionary dynamics between brood parasites and their hosts.
7
Bradley, Aoibhinn Maire. "Analysis of nonlinear spatio-temporal partial differential equations : applications to host-parasite systems and bubble growth". Thesis, University of Strathclyde, 2014. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=24405.
Testo completoAbstract (sommario):
The mountain hare population currently appears to be under threat in Scotland. The natural population cycles exhibited by this species are thought to be, at least in part, due to its infestation by a parasitic worm. We seek to gain an understanding of these population dynamics through a mathematical model of this system and so determine whether low population levels observed in the field are a natural trough associated with this cycling, or whether they point to a more serious decline in overall population densities. A generic result, that can be used to predict the presence of periodic travelling waves (PTWs) in a spatially heterogeneous system, is reported. This result is applicable to any two population host-parasite system with a supercritical Hopf bifurcation in the reaction kinetics. Application of this result to two examples of well studied host-parasite systems, namely the mountain hare and the red grouse systems, predicts and illustrates, for the first time, the existence of PTWs as solutions for these reaction advection diffusion schemes. One method for designing bone scaffolds involves the acoustic irradiation of a reacting polymer foam resulting in a final sample with graded porosity. The work in this thesis represents the first attempt to derive a mathematical model, for this empirical method, in order to inform the experimental design and tailor the porosity profile of samples. We isolate and study the direct effect of the acoustic pressure amplitude as well as its indirect effect on the reaction rate. We demonstrate that the direct effect of the acoustic pressure amplitude is negligible due to a high degree of attenuation by the sample. The indirect effect, on reaction rate, is significant and the standing wave is shown to produce a heterogeneous bubble size distribution. Several suggestions for further work are made.
8
Wezena, Cletus Adiyaga [Verfasser], e Marcel [Akademischer Betreuer] Deponte. "The cytosolic glyoxalase systems of the host-parasite unit are dispensable during asexual blood-stage development of the malaria parasite Plasmodium falciparum / Cletus Adiyaga Wezena ; Betreuer: Marcel Deponte". Heidelberg : Universitätsbibliothek Heidelberg, 2018. http://d-nb.info/1177252058/34.
Testo completo
9
Okolo, C. J. "Studies on lectin binding sites of Glossina in relation to host parasite interactions with particular reference to Glossina trypanosome systems". Thesis, University of Salford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293804.
Testo completo
10
Meizis, Roland [Verfasser], e Anita [Akademischer Betreuer] Winter. "Metric two-level measure spaces : a state space for modeling evolving genealogies in host-parasite systems / Roland Meizis ; Betreuer: Anita Winter". Duisburg, 2019. http://d-nb.info/1191693414/34.
Testo completo
11
Deshpande, Jhelam Nitin. "Eco-evolutionary feedbacks and networks : from genes to landscapes". Electronic Thesis or Diss., Université de Montpellier (2022-....), 2024. http://www.theses.fr/2024UMONG011.
Testo completoAbstract (sommario):
Il est reconnu depuis longtemps que l'écologie et l'évolution se rétroagissent l'une sur l'autre. En partant d'une compréhension mécaniste des liens entre l'écologie et l'évolution au niveau des processus, des mécanismes et des patrons, je présente les principaux défis à relever pour comprendre les rétroactions éco-évolutives : échelles de temps, interactions au sein des échelles d'organisation et entre elles, et structure spatiale (chapitre 1). Ensuite, en utilisant une perspective de réseaux hiérarchiques, je pose la question suivante : comment la prise en compte explicite des interactions au niveau des gènes et de la structure spatiale par la modélisation des réseaux de régulation génétique (chapitre 2) et des réseaux spatiaux (chapitres 3--6) respectivement, a-t-elle un impact sur les rétroactions éco-évolutives ? C'est pourquoi, dans cette thèse, j'ai développé des modèles basés sur l'individu qui fournissent une preuve de concept de la manière dont l'assouplissement des hypothèses standard d'additivité dans l'architecture génétique et les structures spatiales simplifiées ont un impact sur les rétroactions éco-évolutives. Je montre que la prise en compte explicite des réseaux géno-régulateurs et spatiaux modifie effectivement les schémas écologiques et évolutifs par rapport aux modèles simplifiés. Plus précisément, je constate que l'expansion de l'aire de répartition dans des gradients environnementaux externes crée des conditions dans lesquelles les réseaux de régulation génétique qui sont plus sensibles à la mutation, et qui s'adaptent donc plus rapidement à de nouvelles conditions, se retrouvent au front de l'aire de répartition (de l'écologie à l'évolution ; eco-to-evo). L'évolution d'une plus grande sensibilité à la mutation entraîne à son tour une accélération de la dynamique d'expansion de l'aire de répartition (evo-to-eco). Ce résultat ne peut être obtenu dans des architectures additives simples. A l'autre extrême, dans le cas des réseaux spatiaux où l'écologie est plus rapide que l'évolution (Chapitres 3--5), je montre que les réseaux spatiaux terrestres et aquatiques fluviaux distribuent les densités d'hôtes et de parasites d'une manière caractéristique. Cela conduit à une structuration à la fois démographique et génétique (kin) des partenaires en interaction. La structure génétique, telle qu'elle est capturée par la parenté des parasites, conduit à des modèles caractéristiques d'évolution de la virulence (eco-to-evo) dans les paysages terrestres et fluviaux (chapitre 3) et la structure démographique (chapitre~4) conduit à sa coévolution avec la dispersion des hôtes (chapitre 5). Les différences dans la virulence évoluée des parasites ont également un impact sur la distribution des hôtes et des parasites dans l'espace (chapitre 3 ; evo-to-eco). Enfin, en ce qui concerne la coévolution de la dispersion de l'hôte et de la virulence du parasite, limitée par la variation génétique permanente, au cours de l'expansion des aires de répartition dans les réseaux spatiaux (chapitre 6), je montre, pour l'ensemble des paramètres étudiés, que l'expansion des aires de répartition crée des conditions dans lesquelles les effets évolutifs de la structure des réseaux spatiaux sont fortement réduits (eco-to-evo). Cela conduit à ce que la vitesse des expansions de l'aire de répartition soit déterminée par la seule structure du réseau spatial (evo-to-eco). Par conséquent, mes résultats appellent à une étude systématique de l'impact de la complexité des systèmes biologiques sur les rétroactions éco-évolutives à tous les niveaux : gènes, individus, populations et communautés, en tenant compte explicitement de l'espace et des échelles de temps éco-évolutives (Discussion générale ; chapitre 7)It has long been recognised that ecology and evolution feed back onto each other. Starting from a mechanistic understanding of links between ecology and evolution at the level of processes, mechanisms, and patterns, I outline key challenges to understanding eco-evolutionary feedbacks: timescales, interactions within and between scales of organisation, and spatial structure (Chapter 1). Then, using a hierarchical networks perspective, I ask the question: how does explicitly accounting for interactions at the level of genes and spatial structure by modelling gene-regulatory (Chapter 2) and spatial networks (Chapters 3--6) respectively, impact eco-evolutionary feedbacks? Therefore, in this thesis, I developed individual-based models that provide proof-of-concept for how relaxing standard assumptions of additivity in genetic architecture and simplified spatial structures impact eco-evolutionary feedbacks. Specifically, I develop models of range expansion into an external environmental gradient and represent the genetic architecture of local adaptation and dispersal as gene-regulatory networks (Chapter 2). I also develop an eco-evolutionary model of a host-parasite system in which parasite virulence and host dispersal may evolve (Chapters 3--6) representing realistic spatial network structure: terrestrial and riverine aquatic landscapes are modelled by random-geometric graphs and optimal channel networks, respectively. By analysing these models, I show that explicitly accounting for gene-regulatory and spatial networks does indeed change ecological and evolutionary patterns relative to simplified models. Specifically, I find that range expansions into external environmental gradients create conditions in which gene-regulatory networks that are more sensitive to mutation, hence adapting faster to novel conditions, end up at the range front (ecology to evolution; eco-to-evo). The evolution of greater sensitivity to mutation in turn leads to accelerating range expansion dynamics (evo-to-eco). This result cannot be obtained in simple additive architectures, indicating that when ecology and evolution are on similar timescales and evolution is mutation limited, the structure of the genotype-to-phenotype map must be taken into account. At the other extreme, in the case of spatial networks when ecology is faster than evolution (Chapters 3--5), I show that terrestrial and riverine aquatic spatial networks distribute densities of hosts and parasites in a characteristic way. This leads to both demographic and genetic (kin) structuring of the interacting partners. Genetic structure as captured by parasite relatedness leads to characteristic patterns of virulence evolution (eco-to-evo) in terrestrial and riverine aquatic landscapes (Chapter~3) and demographic structure (Chapter 4) drives its co-evolution with host dispersal (Chapter~5). Differences in evolved parasite virulence also further impact the distributions of hosts and parasites in space (Chapter~3; evo-to-eco). These results demonstrate that understanding classical eco-evolutionary mechanisms (e.g. kin selection) in terms of the structure of spatial networks is a way forward to a more general theory of eco-evolutionary feedbacks in complex landscapes. Finally, for standing genetic variation limited co-evolution of host dispersal and parasite virulence during co-range expansions into spatial networks (Chapter 6), I show for the range of parameters explored that range expansions create conditions in which the evolutionary effects of spatial network structure are greatly reduced (eco-to-evo). This leads to the speed of co-range expansions being determined by spatial network structure alone (evo-to-eco). Therefore, my results call for a systematic study of the impact of biological system complexity on eco-evolutionary feedbacks at all levels: genes, individuals, populations, and communities explicitly accounting for space and eco-evolutionary timescales (General Discussion; Chapter 7)
12
Figueiredo, Ana Sofia Cabrita. "Mathematical models of IL-10 regulation in macrophages stimulated with immunomodulatory molecules of parasitic nematodes". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16541.
Testo completoAbstract (sommario):
Der parasitische Nematode Acanthocheilonema viteae kann die Immunantwort seines Wirtes abschwächen, indem er in diesem die Produktion immun-regulatorischer Cytokine Interleukin-10 (IL10) induziert. In dieser Arbeit entwickelte ich spezifische mathematische Modelle um die Mechanismen der IL10 Regulation zu erforschen. Die Annahmen des Modells waren: 1) Av17, ein immun-modulatorisches Protein von A. viteae, zur Phosphorylierung der MAP-Kinasen ERK und p38 führt; 2) Av17 induzierte IL10 ist ERK und p38 abhängig. Beide Annahmen waren in Übereinstimmung mit experimentellen Ergebnissen zur Aktivierung von ERK and p38. Weiter habe ich mehrere Signalregulationsmodelle getestet und eine Methode entwickelt, die theoretische und experimentelle Ansätze kombiniert. Von hier aus konnte ich ein Modell auswählen, dass unabhängige experimentelle Daten korrekt vorhersagt. Modelle selection identifizierten die Duale-Spezifizität Kinasen (DUSP) als integrale Rückkopplungsregulatoren dieses Systems. Eine Sensitivitätsanalyse zeigte, dass p38 durch DUSP, ERK beeinflusst, das Gegenteil aber nicht. Dieser Befund legt eine autokrine Rückkopplung der Signalkomponenten nahe, die auch experimentell bestätigt werden konnte. Allgemein müssen die immunoregulatorischen Mechanismen im Wirt robust gegen Störungen, z.B. durch Parasiten wie A. viteae, sein. Dies veranlasste mich mit Hilfe eines Monte-Carlo Ansatzes die Robustheit der ausgewählten Modelle gegenüber Variationen zu testen. Ich verglich das zuvor ausgewählte Modell und ein Modell mit transienter Rückkopplung. Das Resultat ließ darauf schließen, dass in diesem Fall die integrale Rückkopplung robuster gegenüber Variationen ist als eine transiente Rückkopplung. Insgesamt verbindet der systembiologische Ansatz meiner Arbeit erfolgreich theoretisches Wissen mit experimenteller Expertise um einen Mechanismus vorzuschlagen, der beschreibt, wie der Parasit A. viteae mit Makrophagen seines Wirtes interagiert, um IL10 Exprimierung zu induzieren.The parasitic nematode Acanthocheilonema viteae can downregulate the immune response of its host by inducing immunoregulatory cytokines such as interleukin-10 (IL10). In this thesis, I developed specific mathematical models to investigate IL10 regulation mechanisms. These models assumed that Av17, an immunomodulatory protein secreted by A.viteae, leads to the Mitogen Activated Protein Kinases (MAPK) ERK and p38 phosphorylation and that IL10 transient expression was dependent on the activation of both MAP kinases. These assumptions were validated with experimental data on ERK and p38 activation. Further, I tested alternative ways of signalling regulation and developed a method of model selection that combines the theoretical predictions with experimental evidences. Model selection identified dual specificity phosphatase (DUSP) as integral feedback regulators in this system. Dedicated experiments showed that DUSP1 was responsible for regulation of ERK and p38 phosphorylation and controlled IL10 expression in this system. Furthermore, a sensitivity analysis suggested that p38 affects ERK via DUSP, but ERK does not affect p38, revealing a negative feedback between the components. This model prediction was validated experimentally. Generally, host immune regulation mechanisms should be robust against variations, e.g., by parasites like A. viteae. This prompted me to test the robustness of the selected model against noise, by comparing it with a transient feedback model. The results suggest that the integral feedback model is more robust against noise than the transient feedback model, in the case under study. In summary, based on a systems biology approach that successfully combines theoretical and experimental expertise, this thesis proposes a mechanism that describes how the parasite A. viteae interacts with its host macrophages to induce IL10 expression.
13
Cuco, Ana Patrícia Domingues. "Host-parasite interactions in environmental stress scenarios". Doctoral thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/22246.
Testo completoAbstract (sommario):
Doutoramento em BiologiaThe overarching objective of this thesis was to explore ecologically relevant scenarios of contamination by agrochemical fungicides, in particular their interaction with disease (a ubiquitous and relevant natural stressor), using a host (Daphnia spp.) × parasite (Metschnikowia bicuspidata) system as an experimental model. Because parasites act as modulators of population dynamics and genetic diversity, interaction scenarios between disease and anthropogenic factors (namely pollution) are important to clarify. For this work, copper sulphate and tebuconazole were selected as chemical stressors, given their widespread use as fungicides and frequent detection in aquatic systems. This thesis presents a sequential series of research steps that were undertaken to assess the hazards posed by these chemicals under multi-stressor (i.e., realistic) scenarios. First, we assessed the toxicity of copper sulphate and tebuconazole in two host (Daphnia) clones, considering their joint effects with increasing temperatures. This allowed simulating two important agents of environmental change. Temperature was the most influencing factor on Daphnia fitness, although both copper and tebuconazole reduced the fecundity and survival of Daphnia. A temperature-dependent pattern was found for both fungicides, although this was highly context-dependent. Second, we investigated the reciprocal effects of these pollutants and parasite challenge, using the Daphnia-M. bicuspidata experimental system. The toxicants decreased Daphnia fitness, whilst the parasite strongly reduced host survival. Whilst copper sulphate and parasite effects were mostly independent, tebuconazole suppressed the M. bicuspidata infection at an environmentally relevant range of concentrations (> 6.25 μg l-1). Third, these contrasting outcomes were assessed at two distinct temperatures, because temperature is an important modulator of both toxicity and hostparasite relationships. Indeed, we observed that temperature increased parasite virulence and acted as a modulator of existent interactions between pollution and disease (in the case of tebuconazole). Based on these evidences, we directed our focus to the observed anti-parasitic effect of tebuconazole, which we hypothesize that is more widespread than reported. In a fourth step, we evaluated the influence of different exposure scenarios to tebuconazole (timing × concentration) on the Daphnia-M. bicuspidata experimental system. Infection data revealed an “all-or-nothing” effect, with tebuconazole suppressing infection within a narrow range of tebuconazole concentrations (3.65–13.5 μg l-1). We were able to confirm that tebuconazole inhibited sporulation of M. bicuspidata, and possibly also the vegetative growth of the yeast cells. Finally, we determined if M. bicuspidata could adapt to this anthropogenic selective pressure, by experimentally promoting the rapid evolution of M. bicuspidata lineages to tebuconazole. Infectivity, spore load and survival time of the infected hosts revealed that evolved parasite lineages performed worse than naive lineages, although this could be easily reversed after removal of the stressor. This demonstrates that there were transient costs of prolonged exposure to tebuconazole and that the microparasitic yeast M. bicuspidata did not reveal potential for rapid evolution to the fungicide. Altogether, our findings support the idea that long term exposure to tebuconazole is hazardous to non-target fungi at environmentally realistic concentrations, putatively affecting numerous microparasites and decomposers, as well as the processes were they intervene (disease and decomposition). Copper sulphate, on the other hand, revealed a less contextdependent toxicity pattern, without interacting with parasitism in this case. Our findings with tebuconazole demonstrate negative ecological effects of antifungal agents (which include agrochemicals and pharmaceuticals, many sharing mode of action), which may have so far been overlooked.
O objetivo fundamental desta tese centrou-se na exploração de cenários ecologicamente relevantes de contaminação por fungicidas, e em particular a sua interação com a doença (um factor de stress natural e omnipresente), usando para isso um modelo experimental composto por um hospedeiro (Daphnia spp.) e um parasita (Metschnikowia bicuspidata). Tendo em conta o papel importante dos parasitas como moduladores da diversidade genética e dinâmica das populações, torna-se importante clarificar cenários de interação entre doença e factores antropogénicos (nomeadamente a poluição). Neste trabalho, selecionou-se o sulfato de cobre e o tebuconazole como fatores de stress químico, devido ao seu amplo uso como fungicidas e frequente deteção em sistemas aquáticos. Esta tese apresenta-se como uma sequência de etapas de investigação, realizadas com o intuito de avaliar os perigos apresentados por estes agentes químicos em cenários de stress múltiplo (i.e. mais próximos da realidade). Primeiro, a toxicidade de sulfato de cobre e tebuconazole foi determinada em dois hospedeiros (dois genótipos de Daphnia), considerando os seus efeitos interativos com o aumento de temperatura. Estes cenários permitiram-nos simular dois agentes importantes de mudanças ambientais. Apesar de ambos os fungicidas (cobre e tebuconazole) reduzirem a fecundidade e sobrevivência de Daphnia, a temperatura foi o factor mais preponderante no desempenho de Daphnia. Neste sentido, observou-se um padrão de toxicidade dependente da temperatura para ambos os fungicidas, apesar de altamente dependente do contexto. Em segundo lugar, os efeitos recíprocos destes poluentes e do parasitismo foram avaliados, usando o modelo experimental Daphnia- Metschnikowia. Enquanto os poluentes diminuiram o desempenho reprodutivo de Daphnia, o parasita afetou principalmente a sobrevivência do hospedeiro. Além disso, enquanto os efeitos do sulfato de cobre e do parasita foram maioritariamente independentes, o tebuconazole suprimiu a infeção de M. bicuspidata a concentrações ambientalmente relevantes (> 6,25 μg l-1). Em terceiro lugar, e tendo em conta o potencial da temperatura como moduladora de toxicidade dos contaminantes e das relações hospedeiro-parasita, avaliámos o desfecho da interação parasita × contaminante quando o modelo experimental foi exposto a duas temperaturas distintas. De facto, a temperatura revelou ser capaz de aumentar a virulência do parasita e de modular interações existentes entre a poluição e a doença (no caso do tebuconazole). Tendo em conta as evidências recolhidas até este ponto, o foco do nosso trabalho foi dirigido para o efeito anti-parasitário do tebuconazole, que hipotetizamos ser mais disseminado do que o reportado até agora. Assim, numa quarta etapa investigativa, a influência de diferentes cenários de exposição ao tebuconazole (tempo de exposição × concentração) foi determinada, usando o modelo experimental Daphnia-Metschnikowia. Os dados de infetividade revelaram um efeito “tudo-ou-nada” causado pelo tebuconazole, confirmado pela supressão da infeção dentro de uma gama estreita de concentrações (3,65–13,5 μg l-1). Com estes resultados, foi possível confirmar que o tebuconazole inibiu a esporulação de Metschnikowia, e possivelmente o crescimento vegetativo das células desta levedura. Finalmente, com o intuito de determinar se M. bicuspidata conseguiria adaptarse a esta pressão seletiva, promovemos experimentalmente a rápida evolução de linhagens de Metschnikowia ao tebuconazole. A infectividade, o número (carga) de esporos e o tempo de sobrevivência dos hospedeiros infetados revelaram que as linhagens expostas ao tebuconazole tiveram um pior desempenho quando comparados com as linhagens não expostas ao tebuconazole. Ainda assim, este efeito negativo foi facilmente revertido após a remoção desta pressão selectiva. Estas evidências demonstram custos transientes associados a uma exposição prolongada ao tebuconazole, sendo que o microparasita M. bicuspidata não revelou potencial para uma evolução rápida ao tebuconazole. Em conjunto, os nossos resultados confirmam que a exposição prolongada a concentrações ambientalmente relevantes de tebuconazole é nociva para comunidades de fungos não-alvo, podendo assim afetar numerosos microparasitas e decompositores, assim como os processos onde eles intervêm (doença e decomposição). O sulfato de cobre, por outro lado, revelou um padrão de toxicidade menos dependente do contexto, e sem qualquer interação com o parasitismo. As nossas descobertas demonstraram potenciais efeitos ecológicos negativos de agentes anti-fúngicos (que incluem agroquímicos e fármacos, muitos dos quais partilham o mesmo modo de ação), que poderão ter sido negligenciados até agora.
14
Rahn, Anna-Katrin [Verfasser]. "Ecological and host behavioural aspects of parasite dispersal in a simple and a complex host–parasite system / Anna-Katrin Rahn". Bonn : Universitäts- und Landesbibliothek Bonn, 2018. http://d-nb.info/1200019776/34.
Testo completo
15
Méléard, Sylvie, e Sylvie Roelly. "A host-parasite multilevel interacting process and continuous approximations". Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5169/.
Testo completoAbstract (sommario):
We are interested in modeling some two-level population dynamics, resulting from the interplay of ecological interactions and phenotypic variation of individuals (or hosts) and the evolution of cells (or parasites) of two types living in these individuals. The ecological parameters of the individual dynamics depend on the number of cells of each type contained by the individual and the cell dynamics depends on the trait of the invaded individual. Our models are rooted in the microscopic description of a random (discrete) population of individuals characterized by one or several adaptive traits and cells characterized by their type. The population is modeled as a stochastic point process whose generator captures the probabilistic dynamics over continuous time of birth, mutation and death for individuals and birth and death for cells. The interaction between individuals (resp. between cells) is described by a competition between individual traits (resp. between cell types). We look for tractable large population approximations. By combining various scalings on population size, birth and death rates and mutation step, the single microscopic model is shown to lead to contrasting nonlinear macroscopic limits of different nature: deterministic approximations, in the form of ordinary, integro- or partial differential equations, or probabilistic ones, like stochastic partial differential equations or superprocesses. The study of the long time behavior of these processes seems very hard and we only develop some simple cases enlightening the difficulties involved.
16
Schaik, Antoon Jacobus van [Verfasser]. "The influence of host social system on host-parasite evolutionary dynamics / Antoon Jacobus van Schaik". Konstanz : Bibliothek der Universität Konstanz, 2016. http://d-nb.info/1118373596/34.
Testo completo
17
Titus, Lauren. "Parasite Induced Host Compensatory Feeding in the Drosophila-Macrocheles Mite System". University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511860712984619.
Testo completo
18
Jewell, Kelly Jean. "Landscape analysis of distribution and demographic consequences in a brood parasite-host system". Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31399.
Testo completoAbstract (sommario):
Source-sink dynamics may occur where variation in predation or parasitism is
sufficient to cause spatial variation in population performance. Brood parasitic brownheaded
cowbirds Molothrus ater locally reduce host reproductive success, but little is
known about their regional effects on demography. I aimed to predict, using detailed
empirical data, the effect of cowbirds on the spatial dynamics of a preferred host, the
song sparrow Melospiza melodia. My objectives were to: (1) predict the distributions of
parasite and host based on landscape features; (2) predict parasitism rates from cowbird
occurrence and relate this to sparrow fecundity; and (3) map expected population growth
rates (λ) for song sparrows given parasitism, testing if spatial refuges from parasitism
exist.
I used logistic regression to predict cowbird occurrence by analyzing >500 avian
point counts in the Southern Gulf Islands (SGI), BC. I also evaluated alternate
hypotheses for landscape features thought to influence cowbird distribution elsewhere.
Cowbird occurrence in the SGI was best predicted by proximity to potential feeding areas
and landcover. The best logistic model included landcover, cattle, and distance to urban
and agriculture. Autologistic regression improved model performance, and models using
widely available data performed only slightly worse than those including all data. All
models of cowbird occurrence compared favorably with parasitism rates observed in 12
populations studied from 1 -8 years.
To estimate the regional effect of cowbirds, I employed data from 10 islands
studied from 2-8 years to estimate λ in song sparrow populations subject to parasitism.
Predicted growth rates were strongly influenced by cowbird distribution and land use, and were consistent with independent estimates of local population trend and findings relating
parasitism rates to landscape features elsewhere in their range.
My results suggest that the ratio of source to sink populations within a study
region will depend on land use patterns, their effect on cowbird distribution, and the
influence of parasitism on host reproduction. I use my results to suggest improvements
for future habitat modelling studies, management to limit cowbird distribution and
identify host refuges, and an approach to estimate the regional effect of enemies on the
spatial population demography of species of conservation concern.Forestry, Faculty of
Graduate
19
Webster, Lucy M. I. "The effects of gene flow on local adaptation in a natural host-parasite system". Thesis, University of Glasgow, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433575.
Testo completo
20
González, Tortuero Enrique [Verfasser], e Justyna [Akademischer Betreuer] Wolinska. "Host-parasite dynamics in a natural system : revealing the evolutionary change in parasite populations infecting Daphnia / Enrique Gonzalez Tortuero ; Betreuer: Justyna Wolinska". München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2016. http://d-nb.info/1119073332/34.
Testo completo
21
Gordon, David M. "Population dynamics of a host-parasitoid system with particular reference to age-structure effects". Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75358.
Testo completoAbstract (sommario):
An experimental study of laboratory populations of the stored-products moth, Cadra cautella (Lepidoptera: Phycitidae) and its larval parasitoid, Venturia canescens (Hymenoptera: Ichneumonidae) identified and quantified density- and age-dependent demographic characteristics of the host-parasitoid system. Host imago longevity and fecundity depended on larval weight at pupation. Observed effects of C. cautella larval competition for food on larval mortality, stage duration, and weight at pupation were successfully captured in a mathematical model. Host larval age significantly influenced inter-stage cannibalism and susceptibility to mortality resulting from parasitoid oviposition wounds. Both larval parasitoid developmental rates and adult parasitoid attack rates depended on host larval age. Long-term population experiments of host and host-parasitoid populations revealed that host populations fluctuated with a period slightly in excess of host generation time and that parasitoid populations were in synchrony with host populations.
22
Schulting, Maureen Joan. "The genetics of disease interaction in the lodgepole pine : western gall rust host : parasite system". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28335.
Testo completoAbstract (sommario):
One hundred and eighty, three year old lodgepole pine (Pinus contorta var. latifolia Dougl.) seedlings, representing eighteen half sibling families were each inoculated with five different spore sources of western gall rust (Endocronartium harknessii (J.P. Moore) Hiratsuka) in June 1985 to investigate the genetics of disease interaction in this host:parasite system. Possible early symptoms of infection were recorded fourteen days after inoculation. Tabulations of the number of galls per shoot and shoot length were made in September 1985 and June 1986. Fifty-two percent (567 out of 1088) of the inoculated shoots became infected. The mean number of galls per infected shoot was 3.33. Statistical analyses indicated that only horizontal (quantitative) resistance was present in the lodgepole pine -western gall rust pathosystem. The lodgepole pine half sibling families and seedlings varied greatly in their horizontal resistance. The variation in levels of resistance found in lodgepole pine will allow for a successful western gall rust resistance breeding program. The number of galls per tree for the female parent trees did not significantly correlate with the percentage of shoots infected on the half-sibling progeny. Hence, tree breeders will have to test the resistance of progeny. Red staining was found more frequently on shoots that became infected suggesting that red staining is a possible early symptom of infection by western gall rust.Forestry, Faculty of
Graduate
23
Macnab, Vicki. "Studies investigating the outcome of a host-parasite interaction using the stickleback-schistocephalus model system". Thesis, University of Leicester, 2012. http://hdl.handle.net/2381/10178.
Testo completoAbstract (sommario):
This thesis firstly investigates the effect of the cestode parasite Schistocephalus solidus on the reproduction of its intermediate host, the three spined stickleback. The results indicated that the parasite reduced host reproduction and the physiological basis behind this was established. In males, parasite infection reduced the fish’s ability to produce 11-ketotestosterone which resulted in reduced reproductive behaviour and sexual development. In infected females, vitellogenin production was reduced which prevented egg maturation. The adaptive nature of these changes seemed to be variable among different populations. This variation may result from genetic differences in the host or parasite population, co-evolutionary processes or reflect differences in the environmental conditions experienced by populations. The second part of this thesis investigates the effect of two types of anthropogenic stressors – endocrine disrupting chemicals and temperature change as an outcome of global climate change – on disease progression in the stickleback-Schistocephalus system. The results indicated that the natural steroid 17β estradiol (E2) had a significant impact on disease progression in a sex and dose dependent manner, with males exposed to the high 100ngLˉ¹ E2 treatment harbouring significantly larger parasites compared to females in this treatment and fish from the lower E2 and solvent control treatment. Elevated temperatures were also found to significantly increase parasite growth and reduce host growth. In addition, a behavioural study showed that fish harbouring infective parasites seek out high temperatures which could be adaptive on the part of the parasite as it would allow them to grow faster and potentially increase their reproductive output. The clear outcome of this thesis is that anthropogenic stressors increase disease progression in the stickleback-Schistocephalus system and this is likely to lead to reduced host reproduction and increased parasite transmission and reproduction, potentially leading to the evolution of higher virulence in this host-parasite interaction.
24
Koskella, Britt L. "An examination of host-parasite coevolution and negative frequency-dependent selection in a snail-trematode system". [Bloomington, Ind.] : Indiana University, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3331252.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Indiana University, Dept. of Biology, 2008.Title from PDF t.p. (viewed on Jul 27, 2009). Source: Dissertation Abstracts International, Volume: 69-11, Section: B, page: 6617. Adviser: Curt M. Lively.
25
Stange, Jörg. "Studies on host-pathogen interactions at mucosal barrier surfaces using the murine intestinal parasite Eimeria falciformis". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16716.
Testo completoAbstract (sommario):
Wir nutzten in dieser Studie den apikomplexen Parasiten Eimeria falciformis als Modell. Unsere Ergebnisse zeigen, dass das in infizierten Wildtypmäusen dominierende Zytokin IFN-γ für Immunschutz und für die Entwicklung der Darmpathologie entbehrlich war. E. falciformis-infizierte IFN-γR-/- and IFN-γ-/- Mäuse zeigten extremen Körpergewichtsverlust und starke Pathologie im Darm. Die Entwicklung des Parasiten in diesen Mäusen war überraschenderweise reduziert. Diese Beobachtungen gingen mit einer drastisch erhöhten Produktion von parasiten-spezifischem IL-17A und IL-22 durch CD4+ T Zellen einher. Gleichzeitige Neutralisierung von IL-17A und IL-22 in E. falciformis-infizierten IFN-γR-/- Mäusen verringerte den Körpergewichtsverlust und die Darmpathologie, und führte zu einer erhöhten Ausscheidung von Parasiten. Die Behandlung einer E. falciformis-infizierten intestinalen Epithelzelllinie mit IL-17A oder IL-22 führte zu einer signifikant reduzierten Entwicklung von E. falciformis in vitro. Diese Daten demonstrieren erstmalig einen anti-parasitären Effekt von IL-22 im Darm und deuten auf redundante Rollen von IL-17A und IL-22 im Hinblick auf die Förderung von Darmpathologie in Abwesenheit von IFN-γ hin. Um E. falciformis als Modellsystem weiter zu entwickeln, haben wir die Transfektion von E. falciformis Sporozoiten mit verschiedenen Plasmiden die den Reporter YFP und den Resistenzmarker DHTS enthalten etabliert. Rektal in Mäuse injizierte Sporozoiten entwickelten sich erfolgreich zu Oocysten, wenn auch mit geringerer Effizienz im Vergleich zur oralen Infektion mit Oozysten. Wiederholte in vivo Selektion YFP-exprimierender Oozysten führte zu Populationen mit maximal 34 % YFP-exprimierenden Parasiten. Wir demonstrieren in dieser Arbeit zum ersten Mal die Transfektion von E. falciformis und zeigen Perspektiven im Hinblick auf die Etablierung einer stabil transgenen Parasitenlinie auf.The roles of Th1 and Th17 responses as mediators of host protection and pathology in the intestine are the subjects of intense research. Here we investigated a model of intestinal inflammation driven by the intracellular apicomplexan parasite Eimeria falciformis. Although IFN-γ was the predominant cytokine during E. falciformis infection in wild type mice, it was found to be dispensable for host defence and the development of infection-driven intestinal inflammation. E. falciformis-infected IFN-γR-/- and IFN-γ-/- mice developed dramatically exacerbated body weight loss and intestinal pathology, but surprisingly harboured fewer parasites. This was associated with a striking increase in parasite-specific IL-17A and IL-22 production in the mesenteric lymph nodes and at the site of infection. Concurrent neutralisation of IL-17A and IL-22 in E. falciformis infected IFN-γR-/- mice resulted in a reduction in infection induced body weight loss and inflammation and significantly increased parasite shedding. Taken together these data demonstrate for the first time an anti-parasitic effect of IL-22 during an intestinal infection and suggest that IL-17A and IL-22 have redundant roles in driving intestinal pathology in the absence of IFN-γ signalling. To further develop E. falciformis as a model system, we established transfection of E. falciformis sporozoites using various plasmids that contain the fluorescent reporter YFP and the resistance marker DHTS. Sporozoites applied rectally to mice were shown to complete their life cycle, albeit with a lower efficiency in comparison to oral infection with oocysts. Repeated in vivo selection using pyrimethamine and/or FACS and manual sorting led to a maximum percentage of 34 % YFP-expressing oocysts. Taken together, we demonstrate for the first time transfection of E. falciformis and provide perspectives for further work on the establishment of a stable transgenic parasite line.
26
Suetsugu, Kenji. "Diverse interactions of heterotrophic plants with their hosts, pollinators and seed dispersers". Kyoto University, 2014. http://hdl.handle.net/2433/192205.
Testo completoAbstract (sommario):
Kyoto University (京都大学)0048
新制・課程博士
博士(人間・環境学)
甲第18605号
人博第701号
新制||人||167(附属図書館)
26||人博||701(吉田南総合図書館)
31505
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 加藤 眞, 教授 市岡 孝朗, 教授 瀬戸口 浩彰, 教授 宮本 嘉久, 教授 新宮 一成
学位規則第4条第1項該当
27
Erin, Noémie I. [Verfasser]. "Multiple ecological scales of host-parasite interactions using the three-spined stickleback and Schistocephalus solidus model system / Noémie I. Erin". Kiel : Universitätsbibliothek Kiel, 2017. http://d-nb.info/1142154769/34.
Testo completo
28
Pinheiro, Rafael Barros Pereira. "Trade-offs and resource breadth processes as drivers of performance and specificity in a host-parasite system: a new integrative hypothesis". Universidade Federal de Minas Gerais, 2015. http://hdl.handle.net/1843/BUBD-9VZG9F.
Testo completoAbstract (sommario):
One of the unresolved issues in the ecology of parasites is the relationship between host specificity and performance. Previous studies tested this relationship in different systems and resulted in all possible outcomes. Therefore, two main hypotheses have been proposed to explain those conflicting results: the trade-off and resource breadth hypotheses, which are treated as alternative explanations in the literature and were corroborated by different studies. Here, we performed an extensive study, using specificity indices and network analysis, in order to test for a relationship between host specificity and prevalence in a rich avian malaria system. There was no correlation between specificity and prevalence, which contradicts both the trade off and resource breadth hypotheses. In addition, we detected a modular structure in our host-parasite network and found that its modules were not composed of geographically close, but of phylogenetically close host species. Despite trade-off and resource breadth hypotheses leading to opposite predictions, after performing our study we reached the conclusion that they are not mutually exclusive. As a conceptual solution we propose The Integrative Hypothesis of Parasite Specialization, a novel hypothesis that explains the contradictory results found so far and shows that the trade-off and resource breadth hypotheses are two sides of the same coin.Uma questão ainda não resolvida na ecologia de parasitos é a relação entre a especificidade de hospedeiros e desempenho de parasitos. Estudos anteriores testaram essa relação em diferentes sistemas e encontraram todos os possíveis resultados. Consequentemente, duas hipóteses principais foram propostas para explicar esses resultados conflitantes: a hipótese do trade-off e a hipótese da amplitude de nicho, as quais são tratadas na literatura como explicações alternativas e são corroboradas por diferentes estudos. Nesse trabalho realizamos um estudo aprofundado, utilizando índices de especificidade e análises de rede, com o objetivo de testar a relação entre especificidade de hospedeiros e prevalência em um sistema rico de malária aviária. Não houve correlação entre especificidade e prevalência, o que contradiz tanto a hipótese de trade-off quanto a de amplitude de nicho. Além disso, nós detectamos uma estrutura modular em nossa rede parasito-hospedeiro e descobrimos que esses módulos não são compostos por espécies hospedeiras geograficamente relacionadas, mas por espécies hospedeiras filogeneticamente próximas. Apesar das hipóteses de trade-off e amplitude de nicho possuírem predições opostas, depois de realizarmos nosso estudo concluímos que elas não são mutuamente exclusivas. Como uma solução conceitual nós propomos a Hipótese Integrativa da Especialização de Parasitos, uma nova hipótese que explica os resultados contraditórios encontrados até o momento na literatura científica e mostra que as hipóteses de trade-off e amplitude de nicho são dois lados da mesma moeda.
29
Ferreira, do Vale Pedro Filipe. "Infection outcomes under genetic and environmental variation in a host-parasite system : implications for maintenance of polymorphism and the evolution of virulence". Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/3189.
Testo completoAbstract (sommario):
Virulence (the harm to the host during infection) is the outcome of continuous coevolution between hosts and parasites. This thesis adds to a growing body of work on host-parasite interactions, and describes experiments that study the effects of variation in the genetic and the environmental contexts of infection. All of them focus on interaction between the planktonic freshwater crustacean Daphnia magna and a naturally occurring parasite, the spore-forming bacterium Pasteuria ramosa. I show that elevated minimum temperatures that facilitate parasite growth drive natural epidemics of this parasite. I also demonstrate that the expression of infection traits in P. ramosa is temperature-dependent in a genotype-specific manner [genotype-by-environment (GxE) interactions]. These GxE interactions could maintain polymorphism through environment-dependent selection. Next, I test if GxG interactions for infectivity can be altered by environmental variation (GxGxE interactions), and find that this trait is quite robust to thermal variation. Infectivity is also more important in determining parasite fitness relative to the production of transmission stages, highlighting the importance of considering natural infection routes, an aspect sometimes overlooked in studies of host-parasite systems. Another experiment under different food and temperature regimes showed evidence for environment-dependent virulence-transmission relationships, a fundamental component of virulence evolution models. Lastly, I show that variation in temperature does not increase the cost to the host of resisting infection.
30
Lindström, Karin M. "Bird-parasite interactions : Using Sindbis virus as a model system". Doctoral thesis, Uppsala University, Department of Evolutionary Biology, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-486.
Testo completoAbstract (sommario):
This thesis focuses on the evolutionary interactions between birds and a parasite, the mosquito-borne Sindbis virus (Togaviridae, Alphavirus). In conclusion, the results show that the Sindbis virus is widespread among birds, and that the fitness of infected hosts may be reduced by the virus. Furthermore, viruclearance ability was revealed by male plumage traits, and viraemia was related to hormonal- and social status.
The distribution of Sindbis virus infections among passerine birds was examined in five areas in Sweden. Almost all species tested were infected, and three species of thrushes weridentified as the main hosts. In a series of experimental infections, greenfinches (Carduelis chloris) kept in aviaries were used ahosts. First, the behavioural consequences of an infection were investigated. During the infection, birds tended to reduce thespontaneous locomotion activity, and when escaping from a simulated predator attack, infected birds had reduced take-off spee Furthermore, when comparing virus clearance rate between male greenfinches, I found that males with large yellow tail ornaments hafaster virus clearance rates as compared to those with smaller ornaments. Thus, male virus clearance ability was honestly revealed by the size of an ornament. Moreover, males with experimentally elevated testosterone levels experienced a delayed, but not increased viraemia as compared to controls. When the relationship between male social ranand viraemia was examined, I found no evidence that high-ranked males suffered reduced rank during the infection. Nevertheless, viraemipatterns of males were related to their social rank, so that low-ranked birds had a delayed viraemia as compared to high-ranked birds.
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Solazzo, Gaetano [Verfasser], R. F. A. [Akademischer Betreuer] Moritz, P. [Akademischer Betreuer] Nowicki e J. [Akademischer Betreuer] Thomas. "Host-parasite interactions in the Phengaris (Maculinea) nausithous-Myrmica rubra system : [kumulative Dissertation] / Gaetano Solazzo. Betreuer: R. F. A. Moritz ; P. Nowicki ; J. Thomas". Halle, Saale : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2015. http://d-nb.info/1070497819/34.
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Urbini, Laura. "Models and algorithms to study the common evolutionary history of hosts and symbionts". Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1214/document.
Testo completoAbstract (sommario):
Lors de cette thèse, je me suis intéressée aux modèles et aux algorithmes pour étudier l'histoire évolutive commune des hôtes et des symbiotes. Le premier objectif était d'analyser la robustesse des méthodes de réconciliation des arbres phylogénétiques, qui sont très utilisées dans ce type d'étude. Celles-ci associent (ou lient) un arbre, d'habitude celui des symbiotes, à l'autre, en utilisant un modèle dit basé sur des évènements. Les évènements les plus utilisés sont la cospéciation, la duplication, le saut et la perte. Les phylogénies des hôtes et des symbiotes sont généralement considérés comme donnés, et sans aucune erreur. L'objectif était de comprendre les forces et les faiblesses du modèle parcimonieux utilisé et comprendre comment les résultats finaux peuvent être influencés en présence de petites perturbations ou d'erreurs dans les données en entrée. Ici deux cas sont considérés, le premier est le choix erroné d'une association entre les feuilles des hôtes et des symbiotes dans le cas où plusieurs existent, le deuxième est lié au mauvais choix de l'enracinement de l'arbre des symbiotes. Nos résultats montrent que le choix des associations entre feuilles et le choix de l'enracinement peuvent avoir un fort impact sur la variabilité de la réconciliation obtenue. Nous avons également remarqué que l'evènement appelé “saut” joue un rôle important dans l'étude de la robustesse, surtout pour le problème de l'enracinement. Le deuxième objectif de cette thèse était d'introduire certains evènements peu ou pas formellement considérés dans la littérature. L'un d'entre eux est la “propagation”, qui correspond à l'invasion de différents hôtes par un même symbiote. Dans ce cas, lorsque les propagations ne sont pas considérés, les réconciliations optimales sont obtenues en tenant compte seulement des coûts des évènements classiques (cospeciation, duplication, saut, perte). La nécessité de développer des méthodes statistiques pour assigner les coûts les plus appropriés est toujours d'actualité. Deux types de propagations sont introduites : verticaux et horizontaux. Le premier type correspond à ce qu'on pourrait appeler aussi un gel, à savoir que l'évolution du symbiote s'arrête et “gèle” alors que le symbiote continue d'être associé à un hôte et aux nouvelles espèces qui descendent de cet hôte. Le second comprend à la fois une invasion, du symbiote qui reste associé à l'hôte initial, mais qui en même temps s'associe (“envahit”) un autre hôte incomparable avec le premier, et un gel par rapport à l'évolution des deux l'hôtes, celui auquel il était associé au début et celui qu'il a envahi. Nos résultats montrent que l'introduction de ces evènements rend le modèle plus réaliste, mais aussi que désormais il est possible d'utiliser directement des jeux de données avec un symbiote qui est associé plusieurs hôtes au même temps, ce qui n'était pas faisable auparavantIn this Ph.D. work, we proposed models and algorithms to study the common evolutionary history of hosts and symbionts. The first goal was to analyse the robustness of the methods of phylogenetic tree reconciliations, which are a common way of performing such study. This involves mapping one tree, most often the symbiont’s, to the other using a so-called event-based model. The events considered in general are cospeciation, duplication, host switch, and loss. The host and the symbiont phylogenies are usually considered as given and without any errors. The objective here was to understand the strengths and weaknesses of the parsimonious model used in such mappings of one tree to another, and how the final results may be influenced when small errors are present, or are introduced in the input datasets. This may correspond either to a wrong choice of present-day symbiont-host associations in the case where multiple ones exist, or to small errors related to a wrong rooting of the symbiont tree. Our results show that the choice of leaf associations and of root placement may have a strong impact on the variability of the reconciliation output. We also noticed that the host switch event has an important role in particular for the rooting problem. The second goal of this Ph.D. was to introduce some events that are little or not formally considered in the literature. One of them is the spread, which corresponds to the invasion of different hosts by a same symbiont. In this case, as when spreads are not considered, the optimal reconciliations obtained will depend on the choice made for the costs of the events. The need to develop statistical methods to assign the most appropriate ones therefore remains of actuality. Two types of spread are introduced: vertical and horizontal. The first case corresponds to what could be called also a freeze in the sense that the evolution of the symbiont “freezes” while the symbiont continues to be associated with a host and with the new species that descend from this host. The second includes both an invasion, of the symbiont which remains with the initial host but at the same time gets associated with (“invades”) another one incomparable with the first, and a freeze, actually a double freeze as the evolution of the symbiont “freezes” in relation to the evolution of the host to which it was initially associated and in relation to the evolution of the second one it “invaded”. Our results show that the introduction of these events makes the model more realistic, but also that it is now possible to directly use datasets with a symbiont that is associated with more than one host at the same time, which was not feasible before
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Lourenço, Sofia Isabel Castro Gil 1975. "Ecology of a host-parasite system : a study in temperate cave-dwelling bats". Doctoral thesis, 2008. http://hdl.handle.net/10451/1581.
Testo completoAbstract (sommario):
Tese de doutoramento em Biologia (Ecologia), apresentada à Universidade de Lisboa através da Faculdade de Ciências, 2009Os parasitas englobam, segundo algumas estimativas, cerca de metade das espécies conhecidas do planeta. Pela sua vasta distribuição e diversidade, associada ao elevado grau de adaptação ao meio onde vivem (i.e. os seus hospedeiros), o parasitismo pode ser considerado uma das formas de vida mais bem sucedidas. A transição de um estilo de vida livre para o parasitismo trouxe inúmeras vantagens a estes organismos, nomeadamente o uso de um ambiente mais estável, uma maior mobilidade, e a redução dos custos relacionados com várias funções vitais como a digestão e a procura de alimento, que passaram a ser maioritariamente desempenhados pelos seus hospedeiros. No entanto, no decorrer da evolução para esta forma de vida, os parasitas enfrentaram diversos desafios adaptativos, relacionados com as características intrínsecas dos seus hospedeiros. Neste contexto, a imprevisibilidade espacial e temporal de algumas espécies hospedeiras constitui um dos maiores obstáculos à conclusão do ciclo de vida de um parasita, dado dificultar significativamente a sua dispersão. Paralelamente, estes organismos tiveram de se adaptar à presença frequente de outras espécies de parasitas num mesmo hospedeiro, e explorando os mesmos recursos. Adicionalmente, devido à sua dependência em relação ao hospedeiro para uma reprodução e dispersão bem sucedidas, a maioria dos parasitas necessitou de evoluir de maneira a maximizar a exploração dos recursos do hospedeiro e ao mesmo tempo evitar a sua morte. A presente tese teve como principal objectivo contribuir para o conhecimento sobre os mecanismos desenvolvidos por alguns ectoparasitas para contornarem estes desafios e se adaptarem com sucesso à vida nos seus hospedeiros. Para tal, usaram-se duas espécies de morcegos de regiões temperadas, o morcego-de-peluche Miniopterus schreibersii e o morcego rato-grande Myotis myotis, e os seus ectoparasitas como sistemas modelo. Apesar dos morcegos se encontrarem geralmente fortemente parasitados, pouco se sabe sobre a dinâmica e o funcionamento destes sistemas parasita-hospedeiro. Para alcançar o objectivo delineado, foram estabelecidos quatro objectivos específicos, cada qual abordado num capítulo distinto da presente tese.
Parasitism is one of the most successful modes of life displayed by living organisms. Thetransition to a parasitic lifestyle brought many advantages to parasites, namely a stable environment, mobility and a lesser investment in nutricional functions. However, it also entailed a set of adaptative challenges that had to be met by parasites. These had to find a way of dispersing between hosts often discontinuously distributed in space and time. Moreover, they had to adapt to the frequent presence of other potential competing parasites within the host's body. Lastly, due to their dependence on hosts for successfully reproducing and dispersing, parasites had to balance the exploitation of resources of a host with the need to keep it alive. The main aim of this thesis was to determine how bat ectoparasites have overcome some of these challenges and successfully adapted to their hosts, using two temperate-zone cave dwelling bats (Miniopterus schreibersii and Myotis myotis) and its ectoparasites as model systems. Results showed that a group of specific bat ectoparasites, the nycteribiids, was able to overcome the spatial unpredictability of its hosts within caves by evolving efficient sensorial mechanisms to locate them from a distance. In addition, some parasitic mites, ticks and nycteribiids were found to deal with the temporal unpredictability of their bat hosts, by maximising their reproduction during the reproductive period of bats, when more hosts were more available and particularly vulnerable. Results also showed that competition is likely to occur among bat parasite species, even if for shortterm periods, influencing the structure of their communities. Finally, a suggestion was found of potential costs induced by a parasitic mite on the body condition of its bat host. It is discussed how these potential costs may play a role in the social structure of the bat. Overall, this study provided evidences that bat parasites have tightly coevolved with their hosts. Some of conclusions discussed here are likely to apply to other host-parasite systems involving bats in temperate-zones.
Fundação para a Ciência e Tecnologia (FCT), (SFRH/ BD/ 10717/2002)
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"An examination of host-parasite coevolution and negative frequency-dependent selection in a snail-trematode system". INDIANA UNIVERSITY, 2009. http://pqdtopen.proquest.com/#viewpdf?dispub=3331252.
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Roy, Pamela L. "Quantifying aggregation of the parasites of the Lyme disease system in Menominee County, Michigan". Diss., 2008.
Cerca il testo completoAbstract (sommario):
Thesis (M.S.)--Michigan State University. Dept. of Fisheries and Wildlife, 2008.Title from PDF t.p. (viewed on July 30, 2009) Includes bibliographical references (p. 176-183). Also issued in print.
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Prakash, C. S. "Aspects of genetics of host pathogen interaction in Populus-Melampsoaa medusae system". Phd thesis, 1985. http://hdl.handle.net/1885/142891.
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Morais, Catia Alexandra Pimentel. "Relatórios de Estágio e Monografia intitulada "A aplicação das vesículas extracelulares de parasitas no desenvolvimento de vacinas"". Master's thesis, 2019. http://hdl.handle.net/10316/88327.
Testo completoAbstract (sommario):
Relatório de Estágio do Mestrado Integrado em Ciências Farmacêuticas apresentado à Faculdade de FarmáciaNa última década estudos sobre as funções das vesículas extracelulares (VEs) nas doenças parasitárias expandiram consideravelmente revelando a sua importância na patogénese e suscetibilidade da doença, bem como na comunicação célula-célula e na resposta imune. As VEs estão envolvidas numa grande variedade de processos biológicos, sendo a sua biogénese um fenómeno altamente conservado em organismos vivos. Morfologicamente consistem em pequenas esferas envolvidas numa bicamada lipídica, sendo libertadas a partir de diferentes tipos de células (procarióticas e eucarióticas) e contêm grandes quantidades de substâncias importantes como proteínas, lipídios, ácidos nucleicos e pequenos metabolitos essenciais para a comunicação celular.As VEs são geralmente categorizadas em exossomas, microvesículas (MV) e corpos apoptóticos, com base no tamanho, biogénese e composição. Os exossomas são as vesículas de menor tamanho, podendo apesentar um diâmetro compreendido entre 40 a 100 nm. As microvesículas são as mais heterogéneas e apresentam um tamanho entre 100nm a 1 µm e as vesículas com mais de 1 µm são designadas por corpos apoptóticos. As VEs desempenham um papel muito importante na transmissão de informações e substâncias entre células, resultando numa série de alterações bioquímicas que ocorrem no hospedeiro, incluindo a modulação do sistema imunológico. Em algumas doenças infecciosas, como as doenças parasitárias, as VEs foram ganhando impacto como mediadores na interação parasita-hospedeiro. Estas vesículas permitem a transferência dos fatores de virulência e moléculas efetoras dos parasitas para o hospedeiro, regulando, assim, a expressão de genes no hospedeiro e respostas imunes, mediando, consequentemente, o processo patogénico. Assim, tendo em conta o papel das VEs na interação parasita-hospedeiro e a sua capacidade imunológica, estas poderão fornecer perspetivas futuras para novos biomarcadores, vacinas inovadoras e contribuir também para o desenvolvimento de terapias podendo assim abrir novos caminhos para combater doenças infecciosas.
In the last decade research and studies on the functions of extracellular vesicles (EVs) in parasitic diseases have expanded considerably revealing their importance in disease pathogenesis and susceptibility, as well as cell-cell communication and immune response.Extracellular vesicles are involved in a wide range of biological processes, and their biogenesis is a highly conserved phenomenon in living organisms. Morphologically they consist of small spheres enveloped in a lipid bilayer, being released from different cell types (prokaryotic and eukaryotic) and contain large amounts of important substances such as proteins, lipids, nucleic acids and small metabolites essential for cellular communication. EVs are generally categorized into exosomes, microvesicles (MVs) and apoptotic bodies, based on size, biogenesis and composition. Exosomes are the smallest vesicles and may have a diameter between 40 and 100 nm. The microvesicles exhibit a size between 100nm - 1 µm and they are also more heterogeneous, and the vesicles with more than 1 μm size are called apoptotic bodies.EVs play a very important role in the transmission of information and substances between cells, resulting in a series of biochemical changes occurring in the host, including modulation of the immune system. In some infectious diseases, such as parasitic diseases, EVs have gained impact on communication mediation during parasite-host interactions. EVs allow the transfer of virulence factors and parasite effector molecules to host, regulating host gene expression and immune responses and mediating the pathogenic process. Thus, taking into account the role of EVs in parasite-host interaction and their immunological capacity, they may provide future perspectives for new biomarkers, innovative vaccines and also contribute to the development of therapies and thus open new avenues for combating infectious diseases.
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Wielgoss, Sébastien [Verfasser]. "Population genetic aspects of a newly established parasite-host system between the nematode invader Anguillicola crassus, and the NorthAtlantic freshwater eels, Anguilla sp. / vorgelegt von Sébastien Wielgoss". 2009. http://d-nb.info/1012499391/34.
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Pinto, Rafaela David Lourenço Victorino da Rocha. "Relatório de Estágio e Monografia intitulada “Vesículas Extracelulares de Protozoários Flagelados: Potencial Aplicação em Vacinas"". Master's thesis, 2020. http://hdl.handle.net/10316/93087.
Testo completoAbstract (sommario):
Relatório de Estágio do Mestrado Integrado em Ciências Farmacêuticas apresentado à Faculdade de FarmáciaExtracellular vesicles (EVs) are small vesicles bounded by a double lipid layer, which are attached to the plasma membrane and are released by unicellular and multicellular organisms. These structures according to their size, biogenesis and content can be classified into exosomes (30-150 nm), microvesicles (MVs) (100-1000 nm) and apoptotic bodies (100-5000 nm).Flagellated protozoan parasites such as Giardia lamblia, Leishmania spp., Trichomonas vaginalis and Trypanosoma spp. release EVs loaded with various virulence factors that are essential in the parasite-host interaction, namely in modulating the host's immune system, which can assist in the establishment of infection and consequently its exacerbation.There are several applications of EVs, namely as diagnostic markers, therapeutic agents and also in the scope of vaccines. However, studies on the application of these EVs in vaccines targeting parasitic diseases are still scarce, so it is essential to have a better understanding of these structures and the way they work in order to eventually evolve towards the development of vaccines for this type of infections.Extracellular vesicles (EVs) are small vesicles bounded by a double lipid layer, which are attached to the plasma membrane and are released by unicellular and multicellular organisms. These structures according to their size, biogenesis and content can be classified into exosomes (30-150 nm), microvesicles (MVs) (100-1000 nm) and apoptotic bodies (100-5000 nm).Flagellated protozoan parasites such as Giardia lamblia, Leishmania spp., Trichomonas vaginalis and Trypanosoma spp. release EVs loaded with various virulence factors that are essential in the parasite-host interaction, namely in modulating the host's immune system, which can assist in the establishment of infection and consequently its exacerbation.There are several applications of EVs, namely as diagnostic markers, therapeutic agents and also in the scope of vaccines. However, studies on the application of these EVs in vaccines targeting parasitic diseases are still scarce, so it is essential to have a better understanding of these structures and the way they work in order to eventually evolve towards the development of vaccines for this type of infections.
As vesículas extracelulares (VEs) são pequenas vesículas delimitadas por uma dupla camada lipídica, que se encontram ligadas à membrana plasmática e são libertadas tanto por organismos unicelulares como multicelulares. Estas estruturas de acordo com o seu tamanho, biogénese e conteúdo podem ser classificadas em exossomas (30-150 nm), microvesículas (MVs) (100-1000 nm) e corpos apoptóticos (100-5000 nm).Parasitas protozoários flagelados como Giardia lamblia, Leishmania spp., Trichomonas vaginalis e Trypanosoma spp. libertam VEs carregadas com diversos fatores de virulência que são essenciais na interação parasita-hospedeiro, nomeadamente na modulação do sistema imunológico do hospedeiro, podendo auxiliar no estabelecimento da infeção e consequentemente na exacerbação da mesma.Várias são as aplicações das VEs, nomeadamente como marcadores de diagnóstico, agentes terapêuticos e também no âmbito das vacinas. No entanto, ainda são escassos os estudos sobre a aplicação das VEs em vacinas direcionadas para as doenças parasitárias, pelo que é essencial um melhor conhecimento destas estruturas e da maneira como estas atuam para eventualmente se poder evoluir no sentido do desenvolvimento de vacinas para este tipo de infeções.As vesículas extracelulares (VEs) são pequenas vesículas delimitadas por uma dupla camada lipídica, que se encontram ligadas à membrana plasmática e são libertadas tanto por organismos unicelulares como multicelulares. Estas estruturas de acordo com o seu tamanho, biogénese e conteúdo podem ser classificadas em exossomas (30-150 nm), microvesículas (MVs) (100-1000 nm) e corpos apoptóticos (100-5000 nm).Parasitas protozoários flagelados como Giardia lamblia, Leishmania spp., Trichomonas vaginalis e Trypanosoma spp. libertam VEs carregadas com diversos fatores de virulência que são essenciais na interação parasita-hospedeiro, nomeadamente na modulação do sistema imunológico do hospedeiro, podendo auxiliar no estabelecimento da infeção e consequentemente na exacerbação da mesma.Várias são as aplicações das VEs, nomeadamente como marcadores de diagnóstico, agentes terapêuticos e também no âmbito das vacinas. No entanto, ainda são escassos os estudos sobre a aplicação das VEs em vacinas direcionadas para as doenças parasitárias, pelo que é essencial um melhor conhecimento destas estruturas e da maneira como estas atuam para eventualmente se poder evoluir no sentido do desenvolvimento de vacinas para este tipo de infeções.