Le parasite Alaria alata (Goeze, 1782) est un trématode qui nécessite trois hôtes obligatoire et qui présente la particularité de pouvoir infester un grand nombre d'espèces animales (oiseaux, reptiles, mammifères) au stade mésocercaire..Depuis que la recherche de trichine par des méthodes de digestion a été rendu obligatoire chez les sangliers chassés dans l'ensemble des pays de l'union européenne, elle a permis également la détection des mésocercaires dans les muscles de ces animaux. L'étude de la répartition des déclarations de sangliers porteurs montre que les cas se situent majoritairement dans l'Est de la France. Le nombre de déclarations en augmentation entre 2007 et 2010 est probablement lié à la sensibilisation des laboratoires à la présence d'A. alata plutôt qu'une réelle émergence. A partir d'une base de données de déclaration dans le Bas-Rhin montre que la répartition spatiale des sangliers porteurs du parasite se limite à la vallée du Rhin bornée par le massif des Vosges soulignant ainsi l'importance des zones humides pour la maintien du parasite. Une relation significative existe entre le portage du parasite et les saisons printemps-été ainsi qu'une émergence réelle du parasite entre 2007 et 2010. Par une approche moléculaire le rôle de Planorbis planorbis et Anisus vortex comme premier hôte intermédiaire a été confirmée in natura lors de l'examen de mollusques. La nature des biotopes des mollusques a été abordée ainsi que leur périodes d'émission des cercaires d'A. alata ce qui explique partiellement la saisonnalité des cas observée chez les sangliers du Bas-Rhin..Des prélèvements de muscles sur 6 sangliers chassés dans des zones de forte circulation du parasite, soumis à une méthode de Baermann modifiée, ont permis de mettre en évidence des taux d'infestation de plus de 1000 mésocercaires pour 100 gr. La distribution des mésocercaires chez le sanglier est très large avec toutefois des localisations ciblées vers les tissus antérieurs au diaphragme. Nous avons également mis en évidence une sensibilité du parasite à la congélation et une longue persistance dans les viandes en décomposition.. A partir de mésocercaires isolées sur sanglier, des infestations sur souris ainsi que des tests de survie in vitro ont été effectués :. Chez les souris, chez certains amphibiens et in vitro, une encapsulation active des mésocercaires a été observée ce qui tend à montrer que le parasite dispose de moyens d'éviter la réaction de l'hôte. Si le parasite (au stade cercaires et mésocercaires) est fortement inféodé aux milieux humides, il est capable de phénomène de transfuge à une grande variété d'hôtes paraténiques qui ainsi participent très largement à son maintien et à sa dispersion. / The parasite Alaria alata (Goeze, 1782) is a flatworm which needs three obligatory hosts for its development but its particularity lies in that it can infect a wide number of hosts (birds, reptiles, mammals) at the mesocercarial stage. Since the search of trichinella by pepsinic digestion in the muscles of hunted wild boars has become mandatory in the European union, this analysis has also lead to the detection of Alaria alata in the muscles of these animals. The study of case distributions shows that most of the cases have occurred in the East of France. The number of infected wild boars has increased between 2007 and 2010 which is probably more due to the awareness of laboratories to the presence of A. alata mesocercaria than to a true emergence. Using database for the Bas-Rhin département, we were able to show a geographical cluster of positive wild boars around the Rhine Valley and bordered by the Vosges Mountains, hence showing the importance of wetland areas for the sustenance of the parasite. A significant association between A. alata positivity and the spring and summer seasons was noted as well as a true emergence of the parasite between 2007 and 2010. We then sought to identify the first intermediate snail hosts using molecular tools on snail and cercaria collected in infected areas which lead us to identify two Planorbid species: Planorbis planorbis and Anisus vortex. Search of these two species on different biotopes showed that specific environmental conditions were needed for these species, and therefore the parasite, to be present. We proceeded to test different muscular samples from 6 wild boars using a test derived from the Baermann method. Tests showed the highest parasite burdens ever observed in the literature with several samples over 1000 mesocercaria/100g. Distribution within the carcass is very wide though it appears to be oriented to the tissues anterior to the diaphragm. We also showed that the parasite was sensitive to freezing but long persisting in decaying meat. From the mesocercaria collected on the wild boars, experimental infections were performed on mice and survival tests were done in vitro. In mice, but also in amphibians and in vitro, mesocercaria actively formed an inert capsule which would tend to prove the existence of equipments to evade the host's reactions. The works presented here show two important aspects of A. alata's life cycle: the importance of wetlands for its sustenance and also the parasite's ability to persist in a wide variety of paratenic hosts which participate in its sustainance and dispersal.

Methods for Leishmania parasite detection and quantification as a tool for study of the pathogen-vector-host interactions Leishmaniasis in human is caused by total 21 species of the intracellular protozoan parasite Leishmania, which are transmitted by about 30 species of phlebotomine sand flies. Besides human, Leishmania can infect a number of vertebrate hosts. The major host cell is the macrophage, in which parasites multiply, eventually rupturing the cell and spreading to uninfected cells. Infected monocytes and macrophages circulating in the peripheral blood are thought to be carriers of the parasite to distal sites. Depending on the infected sites of the body, there are three forms of leishmaniasis: cutaneous, mucocutaneous and visceral. Leishmaniasis is a disease for which we still lack effective, affordable and easy to use drugs. In addition, surveillance and control are also neglected. This thesis summarizes the results of several projects using different approaches for parasite load measurement in the mouse model of leishmaniasis, including two methods that were developed and optimized in our laboratory. Detection and quantification of pathogens belongs to the major topics of the research of various infectious diseases. This parameter is necessary for confirmation of the diagnosis, characterization...

L’objectif de cette thèse était d’isoler de nouveaux Mimiviridae dans l’environnement marin à l’aide d’amibes, hôtes potentiels de ces derniers et surtout organismes ubiquistes phagocytaires et connus pour être parasités par des microorganismes pathogènes. Après la mise en place et la validation de protocoles d’échantillonnages et de mise en culture de prélèvements environnementaux, plusieurs échantillons ont été analysés. Un nouveau membre de la famille des Mimiviridae a été isolé à partir d’un échantillon marin côtier provenant du Chili, stocké dans un milieu enrichi en amidon (milieu riz, propice à la conservation voire à la production de virus) puis mis en coculture dans une souche d’amibe Acanthamoeba griffini. Le séquençage de son génome révèle 1260 kb, codant pour 1120 protéines putatives, ce qui en fait le plus grand génome viral connu. Nommé megavirus chiliensis, sa capside est icosaédrique et possède également des fibrilles comme Acanthamoeba polyphaga mimivirus tout en étant plus grande (diamètre apparent 520 nm vs 450 nm). Bien que les morphologies des deux virus soient similaires et que de nombreuses particularités de mimivirus soient conservées chez megavirus (stargate), 23 % des protéines de megavirus n’ont pas d’homologues chez mimivirus, et les 594 gènes orthologues partagés présentent une identité résiduelle moyenne de 50 %. De plus, megavirus présente 3 amino-acyl-ARNt-synthètases supplémentaires (IleRS, TrpRS et AsnRS) à celles de mimivirus. Ces résultats suggèrent que ces deux virus sont issus d’un génome cellulaire ancestral qui a évolué par réduction génomique. Un parasite intracellulaire obligatoire a également été isolé à partir d’échantillons de sédiments marins de la côte chilienne. Des observations au microscope électronique à transmission indiquent une forme ressemblant à une endospore, de taille très variable (de 400 nm jusqu’à 1 μm), avec une paroi multicouche épaisse (~60 nm) et un pore apical. Cependant, aucune évidence de division n’a encore été observée, laissant penser que cette entité capable de multiplication pourrait être un virus, sans ressembler aux morphologies connues à ce jour. / In order to isolate new Mimiviridae from the marine environment, we used amoeba -ubiquitous phagotrophic protozoa - as potential host for these viruses. Different sampling protocols were tested and validated before carrying out co-cultures with amoeba and environmentals samples. A new Mimiviridae giant virus was isolated from Chilean coastal seawater completed with rice media (enriched incubation). Produced in Acanthamoeba griffini, its genome sequence has 1,260 Mbp and encodes for 1120 putative proteins, making it the largest known viral genome and thus named Megavirus chiliensis. Its icosaedral capsid is covered with fibrils and its size is bigger than that of Acanthamoeba polyphaga mimivirus (520 nm vs 450 nm). Although both virions are very similar and most of the mimivirus idiosyncrasies are conserved in megavirus (stargate), 23 % of megavirus putative proteins have no mimivirus homologs. Both viruses share 594 orthologous proteins exhibiting an average identity of 50 %. Moreover, megavirus contains 3 additional amino-acyl tRNA synthetases (IleRS, TrpRS and AsnRS) compare to mimivirus. These results suggest that these viruses have evolved from an ancestral cellular genome by reductive evolution. In addition, an amoeba obligatory intracellular parasite was isolated from marine sediments from Chilean coast. Transmission electron microscopic images show a particule like endospore with variable size (from 400 nm to 1 µm), a multilayered outer wall (~60 nm) and an apical pore. No evidence of division was observed, suggesting that the multiplication of this endoparasite occurs without division, suggesting that it could be a virus without any similarity to those described today.

Les Ecdysozoaires sont des organismes caractérisés par une croissance discontinue composée de plusieurs stades morphologiques séparés par des mues. Parmi eux, certains groupes présentent un intérêt épidémiologique important en santé humaine et/ou animale, notamment les nématodes parasites gastro-intestinaux des ruminants et les phlébotomes vecteurs de leishmanies, qui font l’objet de ce travail. L’étude de la systématique de tels organismes constitue un élément de base essentiel à toute recherche appliquée à la biodiversité, l’écologie et la physiologie, ainsi qu’à leurs relations avec les autres acteurs de leur cycle biologique. Pourtant, l’identification morphologique de certaines espèces s’avère délicate voire impossible étant donnés les stades de croissance, le dimorphisme sexuel et l’existence de morphes, de complexes d’espèces, d’espèces jumelles et d’hybrides, ne concordant pas toujours avec la définition biologique de l’espèce. L’essor de la biologie moléculaire offre un panel d’outils performants au service de la systématique par l’étude de la variabilité génétique. L’objectif de la thèse est de répondre à des problématiques rencontrées en systématique (phylogénie, taxonomie, histoire évolutive d’une espèce) en étudiant la variabilité génétique de ces organismes, à l’aide d’outils moléculaires appropriés. Ce travail a permis la résolution de cas d’études concrets tels que l’inférence d’une phylogénie, l’identification d’espèces proches et l’étude de la variabilité génétique intraspécifique, pour suivre les flux de gènes et en déduire la structure génétique de populations, afin de mieux appréhender l’espèce, son histoire et son évolution dans son environnement. / Ecdysozoans are organisms characterized by discontinuous growth composed of several morphological stages separated by moults. Among them, some groups have a significant epidemiological interest in human and/or animal health, including the gastrointestinal nematodes, parasites of ruminants and phlebotomine sandflies, vectors of Leishmania, which which we focus on. The study of the systematics of such organisms is an essential basic element of any research applied to biodiversity, ecology and physiology, as well as to their relationships with other actors in their life cycle. However, the morphological identification of some species is difficult or even impossible given the stages of growth, sexual dimorphism and the existence of morphs, species complexes, sibling species and hybrids, not concordant always with the biological definition of the species. The rise of molecular biology offers a range of powerful tools for systematics by studying genetic variability. The aim of the thesis is to answer the problems encountered in systematics (phylogeny, taxonomy, evolutionary history of a species) by studying the genetic variability of these organisms, using appropriate molecular tools. This work allowed the resolution of concrete case studies such as the inference of a phylogeny, the identification of closely related species and the study of intraspecific genetic variability, to follow gene flow and deduce the structure population genetics, to better understand the species, its history and its evolution in its environment.

Biological rhythms are thought to have evolved to enable organisms to organise their activities according to the Earth’s predictable cycles, but quantifying the fitness advantages of rhythms is challenging and data revealing their costs and benefits are scarce. More difficult still is explaining why parasites that exclusively live within the bodies of other organisms have biological rhythms. Rhythms exist in the development and traits of parasites, in host immune responses, and in disease susceptibility. This raises the possibility that timing matters for how hosts and parasites interact and, consequently, for the severity and transmission of diseases. Despite their obvious importance in other fields, circadian rhythms are a neglected aspect of ecology and evolutionary biology. The ambitions of this thesis are to integrate chronobiology, parasitology and evolutionary theory with mathematical models to obtain a greater understanding about how and suggest why malaria parasites have rhythms as well as the effect of infection on host rhythms. First, I identify how malaria parasites lose their developmental rhythms in culture, when they lack any potential time cues from the host. Next, I characterise parasite rhythms inside the mammalian host in terms of synchrony and timing and demonstrate there is genotype by environment interactions for characteristics of parasite rhythms. Then, I investigate the effect that parasite infection has on host rhythms and show there is variation between parasite genotypes in their effect on host locomotor activity and body temperature rhythms during infections. Finally, I explore which host rhythms may be driving parasite synchrony and timing and demonstrate the importance of peripheral host rhythms for the timing of malaria parasite developmental rhythms. The data presented here provides novel and important information on the role of rhythms during disease and opens up a new arena for studying host-parasite coevolution.

Theileria parva is a complex protozoan parasite causing East Coast fever in Eastern and Central Africa. Vaccination using live parasites is an effective control measure and has been used in Zambia based on locally isolated and introduced T. parva stocks. Diversity among T. parva populations was investigated in parasites from two Zambian provinces with different disease epidemiologies and control histories. Isolates from the pre-vaccination era, local and exotic stocks used for vaccination, and one recent field isolate were cloned and passaged in vitro to study genomic stability over time. The results of the data from three genome-wide probes indicate a marked homogeneity and stability among the Zambian isolates in contrast to East African isolates. Results from Southern blot profiles and the polymorphic immunodominant molecule (PIM) sequence analysis suggest a common origin for the Zambian isolates from the pre-vaccination era, except for one isolate (Zam5) from Southern Province. This isolate showed characteristics suggesting a buffalo origin. Assays for genotype characterisation were developed using five allelic markers. Multilocus characterisation revealed identical profiles in a recent Zambian isolate from Southern Province and two components of an exotic cocktail vaccine, indicating the escape of one of the vaccine stocks in the field. Characterisation of T. parva field populations by RFLP-PCR assays after immunisation revealed the presence of dominant genotypes from those that had been used for vaccination. Circumstantial evidence for the involvement of one of the exotic vaccine parasites in epidemics in Southern Province is presented and a hypothesis formulated for the rapid spread of this genotype. Analysis of the characterisation data suggested the existence of two groups of T. parva parasites of different origin. The classic T. parva group, characterised by a dimorphism of the p150, p104 and p32 loci and the absence of a p67 insert and a buffalo-derived group which showed a polymorphism of p150, p104 and p32 and the presence of a p67 insert. There is evidence that recombination occurs, resulting in parasites that have characteristics of both groups. The relevance of these recombinant parasites in the epidemiology of the disease seems low. Characterisation of larger samples from areas of regular buffalo-cattle contact is necessary to clarify this. Sequence analysis of the most discriminative locus (PIM) was undertaken and gene conversion could be the main mechanism generating diversity. A more appropriate nomenclature for T. parva is proposed based on the growing evidence of molecular differences among isolates and stocks.

The success of an invasive alien species is often attributed to the ecological advantage gained from natural enemy release. Numerous factors have been suggested as contributing to the success of Harmonia axyridis as an invasive alien species, including enemy release. This thesis studied the interactions of several parasites with H. axyridis, investigating parasite transmission, growth and virulence as well as host immune responses, thereby shedding light on the potential role of enemy release in the invasion biology of this ladybird. Benefits gained by invasive alien species from enemy release diminish if parasites of native species shift hosts to exploit the novel invader. The fungal ectoparasite Hesperomyces virescens began infecting H. axyridis shortly after it invaded the UK, probably as a result of a host shift from Adalia bipunctata. This study found a rapid increase in H. virescens prevalence over three years in London H. axyridis populations. Laboratory study showed H. virescens transmission and growth to be more efficient on A. bipunctata than the novel host. In addition, reciprocal interspecific transfers of H. virescens strains isolated from A. bipunctata and H. axyridis revealed that the infection characteristics of the fungi from these two hosts differed, suggesting strains may have diverged after the initial shift from A. bipunctata to better exploit the host from which they were derived. Laboulbenialian fungi were previously thought to have negligible impacts on host fitness. A detailed examination of H. virescens infecting H. axyridis found distinct virulence, with infections resulting in a 50% reduction in host lifespan. In addition, chronic H. virescens infection in males caused acceleration in the age-associated decline in body condition while for females, infection triggered fecundity senescence and a faster age-related decline in fertility. While their role in accelerating ageing is debated, the results presented here provide evidence that infectious diseases can drive the ageing process in this insect species. In nature, multiple parasites affecting a single host are common. The effect of co-infection on the virulence caused by two fungal infections was characterised using H. axyridis and A. bipunctata hosts. The ability of two ladybird species to defend against an acute fungal parasite, while infected with the relatively avirulent H. virescens was found to be sex-specific. While for females, the presence of co-infection did not alter the virulence seen in singly infected females, a higher mortality rate existed for co-infected males compared with those infected singly. Previously, H. virescens has been considered to be avirulent, however, this study provides evidence that this chronic fungal parasite may be important when considering the mortality associated with co-infections in the field. The invasive success of H. axyridis has, in part, been attributed to a more vigorous immune ability compared with other competitor species. Previously, field studies have shown that the prevalence of the parasitoid wasp Dinocampus coccinellae in H. axyridis is considerably lower than in the UK primary host of this wasp, Coccinella septempunctata. The extent to which the prevalence asymmetry in the field is driven by differences in host encapsulation response was tested by first comparing the encapsulation ability of C. septempunctata and H. axyridis directed against an artificial implant. Following this, the encapsulation response of D. coccinellae parasitized individuals was assessed and compared between the two host species. While encapsulation ability did not differ between the host species, and D. coccinellae did not affect the immune response of H. axyridis, wasp parasitism did alter the encapsulation ability of C. septempunctata, although it was inconsistent across sexes and populations. Overall, this thesis furthers our understanding of the fungal parasite H. virescens and its association with the notorious invader H. axyridis. The research presented here also demonstrates the use of H. axyridis as a model system in areas other than invasion ecology and furthermore, contributes to understanding the role of infectious disease in the rate of ageing. Finally, sex-specific effects were found across the chapters of this thesis, demonstrating the use of H. axyridis in the study of sex-specific effects of infections.

Toxoplasma gondii est un parasite intracellulaire et obligatoire. Ce protozoa est un des parasites les plus successifs qui infectent tous les animaux à sang chaud, y compris l’humain. Ce succès est probablement à cause de la sécrétion d’une des séries de protéines effectrices, qui sont impliquées dans la modulation des voies de signalisation de la cellule hôte. Cette modulation permet aux parasites d’établir une infection chronique qui dure un long terme, et qui favorise leur transmission à un nouvel hôte. Dans cette étude, nous avons identifié un nouvel effecteur dérivé par la granule dense, appelé GRA18, qui est sécrété dans le cytoplasme de cellule hôte par les tachyzoites intracellulaires. La mutation de gra18 résulte une diminution de virulence chez les parasites de type II, qui suggère l’importance de GRA18 dans la pathogénicité de ce parasite. Afin d’étudier le mécanisme d’action de GRA18, nous avons effectué un criblage à haut-débit d’une librairie humaine chez la levure. Ce criblage nous permet d’identifier β-catenin, GSK3α/β, and PP2A-B56, ce qui sont tous les régulateurs bien connus dans la voie de signalisation canonicale de Wnt. Nous avons confirmé l’intéractome de GRA18 par l’approche biochimique. La surexpression de GRA18 induit l’accumulation de β-catenin dans le noyau de la cellule hôte, aussi que l’induition de gènes régulés par la signalisation de Wnt. Ces effets indiquent GRA18 joue un rôle de régulateur positif de β-catenin. A part de son rôle dans la prolifération, polarisation et la différentiation de cellule, β-catenin est également un facteur de transcription connu pour contrôler la réponse immunitaire et l’inflammation. L’analyse transcriptomique en comparant les macrophages dérivés par la moelle osseuse (BMDM) infectés par le sauvage (WT) et le gra18 mutant parasites confirme un rôle possible de GRA18, la modulation d’expression génique de cellule hôte, surtout ceux qui codent pour les chemokines. Cette régulation est ensuite confirmée par l’ELISA. L’hypothèse possible est que Toxoplasma sécrète GRA18 dans la cellule hôte afin de réguler positivement la production de chemokine reliée à la réponse de Th2, qui par contre atténue la réponse inflammatoire de l’hôte. Cette modulation augmente la chance de dissémination et la persistance de ce parasite par la formation de kyste. / Toxoplasma gondii, the obligate intracellular protozoan parasite, is one of the most successful pathogen that infects virtually all warm-blooded animals including humans. This success of the infection is likely due to its perfect ability to modulate numbers of host signaling pathways through the effector proteins, including those involved in immune responses. This modulation allows the parasite to establish a long-term chronic infection without causing severe symptom in the hosts, which facilitates its transmission to the new hosts. In this study, we identified GRA18, as a novel dense granule derived effector protein that is secreted into the cytoplasm of the host cell by the intracellular tachyzoite. GRA18 deficiency in type II strains attenuated the parasite virulence in mice model, suggesting the importance of GRA18 in the parasite pathogenesis. In order to investigate the mechanism of action of GRA18, we first performed a high-throughput two-hybrid screen of a human library in yeast that led to the identification of β-catenin, GSK3α/β, and PP2A-B56, all which are well known regulators of the canonical Wnt signaling pathway. We then validate the GRA18 interactome by biochemistry approach. The overexpression of GRA18 triggers the accumulation of β-catenin in the host cell nuclei as well as the induction of known canonical β-catenin target genes indicating that GRA18 is acting as a positive regulator of β-catenin. Besides its role in cell proliferation, polarization and differentiation, β-catenin is also a well-known co-transcription factor with important function in the control of inflammation and other immune responses. Transcriptomic analysis comparing mouse bone marrow–derived macrophages infected by wild type and GRA18-dificient parasite confirmed a possible role of GRA18 towards host gene expression and likely those encoding chemokines, which is further confirmed by ELISA experiments. An attractive hypothesis is that Toxoplasma delivers GRA18 to the host cell in order to regulate Th2-related chemoattractant chemokines, which in turn, dampens host inflammatory response leaving more chance for the parasites to disseminate and to cause the long-term persistence by forming the cyst.

Chez les vertébrés, la réponse immunitaire acquise représente un mécanisme sophistiqué de réponse face aux parasites dont l‟une des particularités est la possibilité qu‟il offre aux mères de transférer certains de ses effecteurs à leurs nouveau-nés. Pourtant, malgré un intérêt croissant pour les effets maternels, les déterminants écologiques et évolutifs du transfert d‟anticorps maternels n‟ont pas encore été beaucoup étudiés. L‟analyse d‟un cadre théorique spécialement développé pour inclure le transfert transgénérationnel d‟immunité montre que l‟évolution de la capacité à transférer une immunité temporaire aux jeunes dépend des caractéristiques de l‟hôte et du parasite. En particulier, l‟augmentation de l‟espérance de vie de l‟hôte favorise l‟évolution de réponses immunitaires acquises, et la protection conférée par ces réponses est aussi supposée durer plus longtemps chez les hôtes longévifs. En accord avec cette prédiction, une étude de vaccination transgénérationnelle chez une espèce d‟oiseau de mer longévive a permis de mettre en évidence une demi-vie des anticorps maternels particulièrement longue. Les conditions sociales sont aussi un élément clé, et chez une espèce de mammifère, j‟ai pu montrer qu‟elles permettent un élargissement du répertoire d‟anticorps maternels. Le transfert d‟anticorps maternels est aussi à même de modifier les dynamiques épidémiologiques et pourrait présenter un atout non négligeable si la vaccination était utilisée en conservation. Enfin, ce mécanisme pourrait être mis à profit pour estimer l‟exposition des mères, et ainsi inférer la dispersion entre différentes zones d‟habitat / In vertebrate species, acquired immune response represents a sophisticated protection mechanism against parasites that has the particularity of enabling mothers to transmit part of its effectors to their newborns. Yet, despite an increasing interest in maternal effects, ecological and evolutionary determinants of the transfer of maternal antibodies remain poorly studied. The analysis of a theoretical framework specially developed to include a transgenerational transfer of immunity show that the evolution of an ability to temporarily protect offspring depends on the characteristics of both the host and the parasite. In particular, increasing the life span of the host favors the evolution of acquired immune responses and increases the duration of the protection offered by these mechanisms. Accordingly, a transgenerational vaccination study in a long-lived seabird revealed a particularly long half-life of maternal antibodies. Social conditions also proved important in a mammal species as they can allow for the broadening of the repertoire covered by maternal antibodies. The transfer of maternal antibodies could also modify epidemiological dynamics and could bbe an interesting asset if vaccination was used as a conservation tool. Finally, this mechanism could be used to estimate the exposure of mother and thus infer the dispersal rate between different habitat patches.

<p>  </p> <p>Predators and parasites are critical, interconnected members of the community and have the potential to influence host populations. Predators, in particular, can have direct and indirect impacts on disease dynamics. By removing hosts and their parasites, predators alter both host and parasite populations and ultimately shape disease transmission. Our ability to accurately predict disease dynamics requires understanding the ecological effects of predation on prey and host densities and its role in the coevolution of host resistance and parasite virulence. While the impact of predators on disease dynamics has received considerable attention, research has focused on selective predation on infected prey. There is, however, substantial evidence that some predators avoid infected prey, preferentially attacking uninfected individuals. Such different strategies of prey selectivity by predators modulate host-parasite interactions, changing the fitness payoffs both for hosts and their parasites. I use empirical results and theoretical predictions as a framework to discuss the mechanisms by which predation for infected versus uninfected individuals can affect disease dynamics. First, by integrating hypotheses from behavioral ecology and disease ecology, I outlined novel perspectives that complement the prevailing view of selective predation of infected individuals (Chapter 1). Then, exploring short-term ecological outcomes and long-term host-parasite coevolution, I investigated patterns of <em>Daphnia dentifera</em> host population densities and host susceptibility over several generations under different types of predation pressure, including selective predation on infected and uninfected individuals (Chapter 2). Finally, building on the results of this research, I developed a high school project-based lesson plan that facilitates the instruction of the nature of science, implementing on-going ecological research in activities to improve student learning based on a constructivist approach to learning (Chapter 3). Together this research highlights the differential ecological and evolutionary outcomes of host-parasite interactions under varying community contexts.</p>