Pathogens and parasites are increasingly recognized as important components within host populations, communities, and ecosystems. Parasite contributions to ecosystem function most likely manifest as density-mediated impacts of parasites on their hosts, the direct contributions of parasite biomass to a system, and via parasite-induced changes in host behavior and physiology (trait-mediated impacts). Here, a framework was constructed that can be used to conceptualize parasite contributions to ecosystem function (Chapter 1). Then the influence of parasite attack on host movement was explored to further evince the mechanistic underpinnings of trait-mediated parasite impacts (Chapter 2). Additionally, mesocosms were created across a gradient of parasitism to examine how these mechanisms are likely to unfold at larger biological scales (Chapter 3). Lastly, a series of differential equations was created to model host-parasite-ecosystem interactions and generate theoretical predictions about how and when parasites are likely to influence ecosystem processes (Chapter 4). Parasites have many characteristics of ecosystem engineers, but their role has historically been ignored. These studies begin to explore the role that parasitism may have as one of the drivers of ecosystem processes.

Giardia intestinalis is a unicellular protozoan parasite responsible for 280 million gastrointestinal infections every year. When colonizing its host, Giardia interacts closely with the small intestine epithelium by attaching to enterocytes and releasing multiple proteins to the extracellular environment. Some of the released proteins have been shown to aid the parasite’s survival in the intestine by disrupting various host defense mechanisms. Here, we attempt to characterize the specific localization of five proteins after their secretion by Giardia. In parallel we aim to produce and identify parasite’s molecules potentially working as triggers of the immune response built during infection. To study the localization of specific secreted proteins during in vitro interactions with differentiated Caco-2 cells, we started by creating transgenic parasites expressing the ADI, EF1α and G3PD proteins with a downstream detectable tag. To identify candidate proteins from Giardia, thought by our lab to be involved in immune system activation, we established a mammalian expression system for the production of recombinant versions of the selected candidate giardial PAMPs. We achieved the expression of the VSP1267 protein, natively present on the parasite’s surface. However, we found that this protein was not secreted after expression, thus complicating its purification and later use in TLR-activation experiments. In the future, we aim to localize the tagged proteins, expressed by the produced transgenic trophozoites, and optimize the mammalian expression system in order to identify candidate immune triggers during giardiasis.

Le parasitisme est omniprésent dans l’environnement et une attention croissante est récemment apportée sur son impact sur les communautés écologiques. En effet, les parasites peuvent affecter la valeur adaptative des animaux sauvages, en altérant leur physiologie et/ou leur comportement. Ainsi, le rôle des parasites dans le maintien ou l’érosion des différences persistantes comportementales et cognitives entre individus est le sujet de nombreux débats et recherches. La relation entre l’infection parasitaire et le comportement de l’hôte est souvent complexe. Le comportement des individus agit sur leur susceptibilité au parasitisme, mais l’infection parasitaire peut aussi modifier le comportement de l’hôte, favorisant parfois la transmission du parasite. En outre, l’inclusion d’un proxy de santé, tel que la condition corporelle est importante à considérer dans des populations naturellement infectées où la santé des individus peut varier. Dans cette étude, nous avons examiné la relation entre un gradient de densité parasitaire, la personnalité (exploration et témérité), la cognition (apprentissage par stimuli aversifs) et la condition corporelle (Indice K de Fulton) chez les crapets-soleil (Lepomis gibbosus) sauvages, naturellement infectés par des endoparasites, comme le trématode responsable de la maladie du point noir (Trematoda : Apophallus sp. et Uvulifer sp.) et le ver solitaire de l’achigan (Cestoda : Proteocephallus ambloplites). Nous avons trouvé que l’exploration, mais pas la témérité, était répétable ce qui suggère que ce trait reflète la personnalité. De plus, l’exploration a diminué avec l’augmentation de la densité de parasites et la diminution de la condition corporelle de l’hôte. Ainsi, étant donné que la relation entre le comportement explorateur et la densité de parasites variait avec la condition corporelle, il est possible que les parasites aient un effet indirect sur le comportement de l’hôte en impactant sa physiologie. L’exploration variait également selon la densité de points noirs et la densité de cestodes, suggérant un potentiel conflit entre ces deux parasites, leurs hôtes finaux étant différents. Les individus avec plus de cestodes ont moins bien exécuté la tâche d’apprentissage, ce qui laisse à penser que ces parasites imposeraient un coût énergétique qui réduit les performances cognitives de l’hôte. Nos résultats contribuent à démontrer que les parasites et la condition corporelle de l’hôte doivent être pris en considération dans les études écologiques, comportementales ou physiologiques afin de mieux comprendre le maintien des variations inter-individuelles au sein des populations sauvages. / Parasites are ubiquitous in nature and increasing attention is given to their impact on ecological communities. Indeed, parasites can affect host fitness through changes in physiology and/or behaviour. Thus, their role in maintaining or eroding persistent inter-individual differences in behaviour (i.e. personality) and cognitive abilities in hosts is the subject of increasing study and debate. The relationship between parasite infection and host behaviour can sometimes be complex. For instance, personality traits may affect an individuals’ susceptibility to parasites. Conversely, parasite infection can itself modify host behaviour, sometimes favouring the parasite’s own transmission. In addition, including a general fitness proxy, such as body condition, is important when studying naturally infected populations, where individual health can vary greatly among individuals. Here, we examine the relationships among host body condition (Fulton’s K index), personality (i.e. exploration, boldness), cognition (aversive learning) and parasite density in wild pumpkinseed sunfish (Lepomis gibbosus), naturally infected with endoparasites, including trematodes causing blackspot disease (Trematoda: Apophallus sp. and Uvulifer sp.) and bass tapeworms (Cestoda: Proteocephallus ambloplites). We found that exploration but not boldness was repeatable, which suggests that this trait reflects personality. Host exploration decreased with both increasing parasite density and decreasing host body condition. Because the relationship between exploration and parasite density varied with body condition, this suggests a possible indirect effect of parasites on host behaviour through effects on host physiology. Exploration varied depending on blackspot and bass tapeworm density suggesting a possible conflict between these two parasites, as their final hosts are different. Inhibitory avoidance learning decreased with increasing cestode density, suggesting that these parasites could impose an energetic cost which decreases host cognitive performances. Our results provide more evidence that including host body condition and parasite density in ecological, behavioural or physiological studies can help better understand the persistence of inter-individual differences in wild populations.

<p>The crossing of host barriers (intestinal, blood-brain, and placental) is a critical step for systemic infections caused by entero-invasive pathogens. In the intestine, the epithelial cells are the first line of defense against enteric pathogens. <i>Listeria monocytogenes</i> is a facultative-intracellular foodborne pathogen that first crosses the intestinal barrier to cause a systemic infection. However, the underlying mechanism is not well understood.</p><p><br></p> <p>We demonstrate that <i>Listeria</i> adhesion protein (LAP) promotes the translocation of <i>L. monocytogenes </i>across the intestinal barrier in mouse models (A/J and C57BL/6). Relative to the wild-type (WT; serotype 4b) or the isogenic bacterial invasion protein Internalin A mutant (Δ<i>inlA</i>) strain, the <i>lap^─</i> strain showed significant defect in translocation across the intestinal barrier and colonization of the mesenteric-lymph nodes, liver and spleen in the early phase of infection (24 h and 48 h). LAP induces intestinal epithelial barrier dysfunction for increased translocation as evidenced by increased permeability to 4-kDa FITC-dextran (FD4), a marker of paracellular permeability, in the serum and urine of WT and Δ<i>inlA</i>- infected mice and across Caco-2 cell barrier, but not the <i>lap^─</i> mutant strain. Microscopic examination confirmed localization of the WT and Δ<i>inlA</i> strains in the tight junction, a crucial barrier of intestinal paracellular permeability, in the mouse ileal tissue but the <i>lap^─</i> strain remained confined in the lumen. LAP also upregulates TNF-α and IL-6 in intestinal epithelia of mice and in Caco-2 cells for increased permeability. </p><p><br></p> <p>Investigation of the underlying molecular mechanisms of LAP-mediated increase in intestinal permeability by using <i>lap^─</i> mutant strain, purified LAP and shRNA-mediated Hsp60 suppression, we demonstrate that LAP interacts with its host receptor, Hsp60, and activates the canonical NF-κB signaling, which in turn facilitates myosin light-chain kinase (MLCK)-mediated opening of the epithelial barrier via the cellular redistribution of major epithelial junctional proteins claudin-1, occludin, and E-cadherin. Pharmacological inhibition of NF-κB or MLCK in cells or genetic ablation of MLCK in mice (C57BL/6) prevents mislocalization of epithelial junctional proteins, intestinal permeability and <i>L. monocytogenes</i> translocation across the intestinal barrier.</p> <p><br></p><p>Furthermore, LAP also promotes <i>L. monocytogenes </i>translocation across the intestinal barrier and systemic dissemination in a Mongolian gerbil that are permissive to the bacterial invasion proteins; InlA-and InlB-mediated pathways; similar to that in humans. We show a direct LAP-dependent and InlA-independent pathway<i> </i>for <i>L. monocytogenes</i> paracellular translocation across the intestinal epithelial cells that do not express luminally accessible E-cadherin. Additionally, we show a functional InlA/E-cadherin interaction pathway that aids <i>L. monocytogenes</i> translocation by targeting cells with luminally accessible E-cadherin such as cells at the site of epithelial cell extrusion, epithelial folds and mucus-expelling goblet cells. Thus, <i>L. monocytogenes</i> uses LAP to exploit epithelial innate defense in the early phase of infection to cross the intestinal epithelial barrier, independent of other invasion proteins.</p><p><br></p> <p>This work fills a critical gap in our understanding of <i>L. monocytogenes </i>pathogenesis and sheds light to the complex interplay between host-pathogen interactions for bacterial crossing of the crucial intestinal barrier.</p> <br>

Dans un contexte de changements globaux, comprendre les interactions entre les parasites et l’environnement est essentiel afin de prévoir les futurs dynamiques d’infection ainsi que les changements dans le fonctionnement des écosystèmes. Cela dit, les patrons de distribution des parasites ainsi que les moteurs d’infection varient dans le temps et l’espace rendant la compréhension des mécanismes sous-jacents très complexes. Dès lors, les études comparatives se basant sur des données empiriques doivent prendre en considération les facteurs de variations entrant en jeu dans l’estimation des paramètres d’infection chez les populations naturelles. Dans une approche multiéchelles, nous avons exploré les sources de variation dans l’estimation de la prévalence d’infection en nous concentrant sur la maladie du point noir chez les communautés littorales de poissons dulcicoles. Nos résultats ont montré que la prévalence de l'infection est spatialement hétérogène dans le paysage, témoignant de l'existence de points chauds et de points froids de l'infection. Les biais d’échantillonnage lié aux méthodes ont mené à d’importantes variations dans l’estimation de la prévalence et dans les patrons spatiaux d’occurrence de la maladie. Nos résultats ont indiqué également qu’un faible échantillonnage a tendance à sures4mer la prévalence d’infection dans le paysage et que l’effort d’échantillonnage nécessaire pour estimer une prévalence fiable dépend de la méthode d’échantillonnage employée. Les caractéristiques physico-chimiques de l’eau et la structure locale des communautés de poissons se sont révélées les meilleurs prédicteurs d’infection à petite échelle. Nos résultats suggèrent notamment des effets de dilution par barrières d’obstruction et de compatibilité limitant la survie des cercaires. Plusieurs relations entre la prévalence d’infection et les prédicteurs environnementaux ont révélé de la nonlinéarité suggérant des interactions complexes. Notre étude contribue au développement de la compréhension des interactions entre les parasites et leur environnement, ainsi qu’aux biais potentiels dans l’étude des dynamiques d’infection. / In a context of global change, understanding the interactions between parasites and their environment is essential to predict future infection dynamics and changes in ecosystem functioning. That said, parasite distribution patterns and drivers of infection vary in time and space, making understanding the underlying mechanisms highly complex. Comparative studies based on empirical data must therefore take into account the factors of variation involved in estimating infection parameters in natural populations. Using a multi-scale approach, we explored the sources of variation in the estimation of infection prevalence, focusing on black spot disease in littoral freshwater fish communities. Our results showed that infection prevalence is spatially heterogeneous across the landscape with evidence of infection hotspots and coldspots. Method-related sampling biases led to significant variations in prevalence estimates and spatial patterns of disease occurrence. Our results also indicated that low sampling effort tend to overestimate the prevalence of infection in the landscape, and that the sampling effort required to estimate infection prevalence depends on the sampling method employed. Water physico-chemical characteristics and local fish community structure were found to be the best predictors of small-scale infection. Furthermore, our results suggest dilution effects due to obstruction and compatibility barriers limiting cercarial survival. Several relationships between infection prevalence and environmental predictors revealed non-linearity, suggesting complex interactions. Our study contributes to the development of our understanding of the interactions between parasites and their environment, as well as potential biases in the study of infection dynamics.

Die Einschleppung gebietsfremder Parasiten durch den Menschen ist einer der Hauptgründe für das Auftreten neuer Krankheiten in the letzten Jahrzehnten. Neue Wirte sind oftmals anfälliger für diese invasiven Parasiten als die ursprünglichen Wirte. In schwerwiegenden Fällen können invasive Parasiten zu Massensterben und zum Aussterben ihrer neuen Wirte führen. Der ursprüngliche Wirt des Aalparasiten Anguillicola crassus ist der Japanische Aal. In den frühen 1980er Jahren wurde der Parasit in die Population des Europäischen Aals eingeschleppt. Er ist einer der Faktoren, die für den Populationsrückgang des Europäischen Aals verantwortlich sind. Die molekularen Prozesse, die zur stärkeren Anfälligkeit des Europäischen Aals im Vergleich zum Japanischen Aal führen, sind noch nicht zureichend bekannt. Die Analyse transkriptomweiter differenzieller Genexpression von Immungewebe ergab, dass im Europäischen Aal sowohl Immun- als auch Nichtimmungene differenziell exprimiert waren. Dies war im Japanischen Aal nicht der Fall und deutet darauf hin, dass der Europäische Aal eine ineffiziente und kostspielige Immunantwort auslöst. Die Resultate ensprechen jenen die schon in anderen Wirbeltierwirt-invasiven Parasiten-Systemen beobachtet wurden. Ausserdem stützen diese Resultate die Hypothese, dass neuen Wirten eine wirksame Immunantwort fehlt und sie deuten darauf hin, dass Nichtimmunprozesse wesentlich zur höheren Anfälligkeit von neuen Wirten beitragen. Als Reaktion of die negativen Fitnesseffekte können neue Wirte Abwehrmechanismen entwickeln. Im Europäischen Aal entspricht das der Einkapselung von A. crassus. Einkapselung führte zu eine niedrigere Abundanz adulter A. crassus. Dies deutet darauf hin, dass das Einkapseln sich positiv auf die Gesundheit infizierter Aale auswirkt. Jedoch war die Abundanz zweier nativer Parasiten höher in Aalen, die A. crassus einkapselten. Eine verbesserte Abwehr des eingeschleppten Parasiten könnte daher die Abwehr nativer Parasiten beeinträchtigen. / The human-mediated translocation of non-native parasites into foreign regions is one of the primary factors for the emergence of new diseases in recent decades. Novel hosts are often more susceptible to these invasive parasites than the native host. In severe cases, invasive parasites can lead to population declines and extinctions of their novel hosts. The eel parasite Anguillicola crassus is native to the Japanese eel. In the early 1980s it was introduced into the European eel population and is now considered to be one factor contributing to the population decline of its novel host. The underlying molecular processes determining higher susceptibility in the European eel compared to the Japanese eel are not well understood. Using whole-transcriptome differential gene expression analysis of immune organs, I found that genes involved in both immune and non-immune processes were differentially expressed in the European eel but not the Japanese eel, suggestive of an ineffective and costly immune response in the former. These results are in line with those observed between susceptible and resistant hosts in other vertebrate host-invasive parasite systems. Furthermore, the results support the hypothesis that novel hosts lack an effective immune response. The results also suggest that alteration of non-immune processes contributes substantially higher susceptibilities of novel hosts. In response to the negative fitness effects of invasive parasites, novel hosts can evolve coping mechanisms. The European eel has the capacity to encapsulate and kill A. crassus. Using natural infections, I found a lower abundance of adult A. crassus, the most costly parasitic stage in those eels encapsulating the parasite, suggesting that encapsulation can potentially improve health of infected eels. At the same time, the abundance of two native parasites was higher in those eels encapsulating A. crassus. Thus, coping with A. crassus may come at the expense of coping with native parasites.

No description available.

<p>Eastern black walnut (<i>Juglans nigra</i> L.) ranks among the most highly valued timber species in the central hardwood forest and across the world. This valuable tree fills a critical role in native ecosystems as a mast bearing pioneer on mesic sites. Along with other <i>Juglans</i> spp. (Juglandaceae), <i>J. nigra</i> is threatened by thousand cankers disease (TCD), an insect-vectored disease first described in 2009. TCD is caused by the bark beetle <i>Pityophthorus juglandis</i> Blackman (Corthylini) and the phytopathogenic fungus <i>Geosmithia morbida</i> Kol. Free. Ut. & Tiss. (Bionectriaceae). Together, the <i>P. juglandis</i>-<i>G. morbida</i> complex has expanded from its historical range in southwest North America throughout the western United States (U.S.) and Europe. This range expansion has led to widespread mortality among naïve hosts <i>J. nigra</i> and <i>J. regia</i> planted outside their native distributions.</p> <p> The severity of TCD was previously observed to be highest in urban and plantation environments and outside of the host native range. Therefore, the objective of this work was to provide information on biotic and abiotic environmental factors that influence the severity and impact of TCD across the native and non-native range of <i>J. nigra</i> and across different climatic and management regimes. This knowledge would enable a better assessment of the risk posed by TCD and a basis for developing management activities that impart resilience to natural systems. Through a series of greenhouse-, laboratory- and field-based experiments, environmental factors that affect the pathogenicity and/or survival of <i>G. morbida</i> in <i>J. nigra</i> were identified, with a focus on the microbiome, climate, and opportunistic pathogens. A number of potentially important interactions among host, vector, pathogen and the rest of the holobiont of TCD were characterized. The <i>holobiont</i> is defined as the whole multitrophic community of organisms—including <i>J. nigra</i>, microinvertebrates, fungi and bacteria—that interact with one another and with the host.</p> <p>Our findings indicate that interactions among host, vector, pathogen, secondary pathogens, novel microbial communities, and novel abiotic environments modulate the severity of TCD in native, non-native, and managed and unmanaged contexts. Prevailing climatic conditions favor reproduction and spread of <i>G. morbida</i> in the western United States due to the effect of wood moisture content on fungal competition. The microbiome of soils, roots, and stems of trees and seedlings grown outside the host native range harbor distinct, lower-diversity communities of bacteria and fungi compared to the native range, including different communities of beneficial or pathogenic functional groups of fungi. The pathogen <i>G. morbida</i> was also associated with a distinct community of microbes in stems compared to <i>G. morbida</i>-negative trees. The soil microbiome from intensively-managed plantations facilitated positive feedback between <i>G. morbida</i> and a disease-promomting endophytic <i>Fusarium solani</i> species complex sp. in roots of <i>J. nigra</i> seedlings. Finally, the nematode species <i>Bursaphelenchus juglandis</i> associated with <i>P. juglandis</i> synergizes with <i>G. morbida</i> to cause foliar symptoms in seedlings in a shadehouse; conversely, experiments and observations indicated that the nematode species <i>Panagrolaimus</i> sp. and cf. <i>Ektaphelenchus</i> sp. could suppress WTB populations and/or TCD outbreaks.</p> <p>In conclusion, the composition, function, and interactions within the <i>P. juglandis</i> and <i>J. nigra</i> holobiont play important roles in the TCD pathosystem. Managers and conservationists should be aware that novel associations outside the host native range, or in monocultures, intensive nursery production, and urban and low-humidity environments may favor progression of the disease through the effects of associated phytobiomes, nematodes, and climatic conditions on disease etiology. Trees in higher diversity, less intensively managed growing environments within their native range may be more resilient to disease. Moreover, expatriated, susceptible host species (<i>i.e.</i>, <i>J. nigra</i>) growing in environments that are favorable to novel pests or pest complexes (<i>i.e.</i>, the western U.S.) may provide connectivity between emergent forest health threats (<i>i.e.</i>, TCD) and native host populations (<i>i.e.</i>, <i>J. nigra</i> in its native range).</p>