Drosophila melanogaster and many other insects harbor intracellular bacterial symbionts that are transmitted vertically from infected host mothers to their offspring. Many of these bacteria alter host reproductive developmental processes in order to increase their transmission success. For example, Spiroplasma, a spirochete that naturally infects D. melanogaster, selectively kills males during mid-embryogenesis while sparing females. Previous studies suggested that Spiroplasma interacts genetically with the male-specific dosage compensation pathway, which causes ~2-fold up-regulation of most genes located on the male’s single X chromosome so that their expression matches the levels found in females who have two Xs. To further test this idea, I used confocal microscopy to visualize dosage compensation complex (DCC) localization and activity in infected as well as uninfected embryos. In the presence of Spiroplasma, the DCC became abnormally mis-localized across the nucleus. This pattern was accompanied by abnormal acetylation of histone H4K16, a mark induced by DCC activity and needed for proper X chromatin remodeling. My results imply that Spiroplasma directly targets the DCC by misdirecting it to uncompensated regions of the genome, an effect that leads to abnormal gene mis-regulation and consequent lethality (work from other members in our group). To further investigate this interaction, we transgenically expressed low levels of MSL-2 in both Spiroplasma infected and uninfected embryos in order to cause ectopic formation of the DCC in the female sex. I found that when infected, female embryos expressing the DCC showed significantly reduced viability in comparison to uninfected transgenic females. This result supports the notion that Spiroplasma uses the DCC in a dominant gain-of-function manner to kill embryos.

Brood parasites avoid costs associated with raising young by adding eggs to another individual’s clutch and providing no parental care. When conspecific brood parasitism occurs in species with high parental investment, we expect hosts to suffer costs for raising an enlarged brood. Here I describe conspecific brood parasitism (CBP) in the prothonotary warbler using maternal exclusion analyses of 333 family groups. I found that 23.4% of clutches contained at least one offspring that was not matched to the social mother and determined that parasitism seems to be an opportunistic tactic. Hosts had lower average annual reproductive success than non-hosts, but CBP did not affect adult survival or nestling body condition and likelihood of recruitment. Clutches with CBP received less provisioning from the male, but not female, parent. Future research is needed to understand the effects of density and competition on the breeding behaviors of this and other similar species.

Assim como visto nos vertebrado, os invertebrados também possuem um sistema imune bastante complexo, apresentando respostas humorais e celulares. Esta última é a principal forma de defesa, envolvendo células amebóides móveis capazes de isolar e/ou eliminar material estranho. Em equinodermos, as células envolvidas nestas respostas são categorizadas como celomócitos, uma denominação genérica que engloba vários tipos celulares encontrados nas cavidades corporais e no tecido conjuntivo. Entretanto, além da função imune, são reportados como tendo outros papéis diversos, como excreção, digestão, transporte e estocagem de nutrientes e a síntese e deposição de fibras de colágeno e da matriz extracelular Não existe consenso sobre quais os papéis específicos desempenhados por estas células num organismo saudável e nem diante de um processo inflamatório. Assim, o presente trabalho foi realizado para caracterizar o processo inflamatório no espinho de Eucidaris tribuloides causado por sabinella troglodytes, um molusco ectoparasita no espinho. A primeira parte do trabalho traz a caracterização das células da cavidade celomática. Para investigá-las foi realizada uma abordagem integrada onde os celomócitos foram descritos por meio da utilização de células vivas, citoquímica e microscopia eletrônica de transmissão. Foram encontrados sete tipos celulares, sendo um novo e dois pouco conhecidos. Com esta abordagem inicial, foi possível obter as ferramentas necessárias para investigar o processo inflamatório. Para estudar o processo inflamatório no espinho de E. tribuloides, utilizou-se uma abordagem estrutural, combinando histologia, microscopia eletrônica de varredura e microtomografia computadorizada, assim como celular/molecular. Os dados indicam que a inflamação causada pelo molusco parece ser um evento local, que altera tanto a matriz orgânica quanto a calcária, mas parece não se propagar para a cavidade celomática do hospedeiro / The invertebrates, as well as vertebrates, also have a very complex immune system, presenting humoral and cellular responses. The latter is their main form of defense, involving mobile amoeboid cells capable of isolating and/or eliminating foreign material. In Echinodermata, the cells involved in these responses are categorized as coelomocytes. This is a generic term that encompasses various cell types found in the body cavities and connective tissue. However, in addition to immune function, they are reported as having various other roles, such as excretion, digestion, transport and nutrient storage and the synthesis and deposition of collagen fibers and extracellular matrix. There is no consensus on what the specific role played by each one of these cells in healthy individuals and the knowledge about the inflammatory process is much worse. Thus, the present study was performed to characterize the inflammatory process in the spine of Eucidaris tribuloides caused by Sabinella troglodytes, a spine ectoparasites gastropod. The first part of the study provides the characterization of the cells of the coelomic cavity. To investigate them, an integrated approach was used, where the coelomocytes were described through the use of living cells, immunocytochemistry and transmission electron microscopy. Seven cell types were found: one new and two poorly known. This initial approach enables us to obtain the necessary tools to investigate the inflammatory process. To study the inflammatory process in the spine of E. tribuloides, we used a structural approach, combining histology, scanning electron microscopy and computed microtomography, and the cellular/molecular one. The data indicate that inflammation caused by snail appears to be a local event, which alters both the organic and calcareous matrix, but does not seem to be reflected within the coelomic cavity of the host

Experimentos com diferentes objetivos têm sido conduzidos a fim de se estudar o mecanismo do parasitismo, sendo muito comuns os bioensaios para encontrar condições ótimas para a produção de parasitas e para definir estratégias para liberações inundativas no campo. Assim, por exemplo, o número de ovos parasitados depende de fatores como: espécie, tipo e densidade do hospedeiro, longevidade do adulto e densidade do parasita, tipo de alimentação, temperatura, umidade etc. Logo, o objetivo de um determinado ensaio pode ser, então, estudar o comportamento da variável resposta como função do número de parasitóides ou do número de hospedeiros ou ainda do tipo de alimentação. Pode-se verificar que, em geral, as variáveis observáveis so contagens ou somas aleatórias de variáveis aleatórias ou proporções com denominadores fixos ou aleatórios. A distribuição padrão para modelar contagens é a Poisson enquanto que para proporções é a binomial. Em geral, elas não se ajustam dados oriundos do processo de parasitismo, pois suas pressuposições não são satisfeitas, e surgiram modelos alternativos e que levam em consideração o mecanismo de evitar o superparasitismo. Alguns deles supõem que a probabilidade de fuga (evitar o superparasitismo) é função do número de ovos presentes no hospedeiro (Bakker, 1967,1972; Rogers, 1975; Griffits, 1977), outros não consideram tal processo (Daley; Maindonald, 1989; Griffths, 1977). Outros, ainda, incluem o comportamento seletivo do parasita na escolha do hospedeiro e a habilidade do hospedeiro em atrair o parasita (Hemerik et al, 2002). Alguns deles surgiram independemente, outros como generalizações, sendo, portanto, de interesse um estudo adicional para ressaltar pontos comuns entre eles. No presente trabalho, são estudados 19 modelos probabilísticos para explicar a distribuição do número de ovos postos por um parasita em um determinado hospedeiro. Foi mostrada a equivalência entre alguns deles e, além disso, foi provado que um modelo usado por Faddy (1997) na estimação do tamanho de população animal generaliza-os. As propriedades desse modelo são apresentadas e discutidas. O uso do modelo de Faddy para a distribuição do número de ovos no sistema parasita-hospedeiro é o principal resultado teórico dessa tese. / Experiments with distinct aims have been conducted in order to study the parasitism mechanism. Bioassays to find optimum conditions for parasite production and to define strategies for application in the field are very common. In this way, for example, the number of parasitized eggs depends on factors such as: species, type and host density, adult longevity and parasite density, type of food, temperature, humidity etc. Hence, the objective of a specific assay can be to study the response variable behavior as a function of the number of parasitoids, number of hosts or type of food. In general, the observable variables are counts or random sums of random variables or proportions with fixed or random denominators. Poisson is the standard distribution used to model counts, while the distribution used for proportions is the binomial. In general, they do not fit to standard distributions don’t fit to data generated by the parasitism process, because their assumptions are not satisfied and alternative models that consider the mechanism of avoidance of superparasitism have appeared in the literature. Some of them consider that the refuse probability (avoidance of superparasitism) is a function of the number of eggs in the host (Bakker, 1967, 1972; Rogers, 1975; Griffiths, 1977) others don’t consider such process (Daley and Maindonald 1989; Griffiths, 1977). Some include the selective behavior of the parasite in the choice of the host and the host ability in attract the parasite (Hemerick et al., 2002). Some of the models have appeared independently, others as generalizations. There is therefore some interest in making a study of the common points of the models. In this work 19 probability models found in the literature are presented to explain the distribution of the number of eggs laid by a parasite on a specific host. As an initial result, the equivalence between some of these models is shown. Also it is shown that a model developed by Faddy (1997) can be considered as a generalization of 18 of the models. The properties of this model are presented and discussed. The equivalence between the Janardan and Faddy models is an original and interesting result. The use of Faddy´s model as a general probability model for the distribution of the number of eggs in a parasite-host system is the main theoretical result of this thesis.

Dans tous les organismes animaux la réponse immunitaire est divisée en deux composantes : la réponse humorale, qui consiste en la production d'un grand nombre de molécules toxiques pour le pathogène, et la réponse cellulaire, qui met en jeu des cellules immunitaires produites lors de l'hématopoïèse. Chez les mammifères adultes, l'hématopoïèse se déroule dans la moelle osseuse, où un microenvironnement particulier appelé " niche hématopoïétique " contrôle l'auto-renouvèlement, la prolifération et la différenciation des Cellules Souches Hématopoïétiques (CSH) à l'origine de l'ensemble des cellules sanguines/immunitaires. Suite à une infection par un pathogène, l'homéostasie du système hématopoïétique est modifiée, afin de permettre la mise en place d'une réponse immunitaire cellulaire adaptée. Le rôle de la niche hématopoïétique dans le contrôle de l'hématopoïèse suite à une infection reste à ce jour mal connu. La drosophile est utilisée comme système modèle pour étudier in vivo l'hématopoïèse et la réponse immunitaire. L'hématopoïèse a lieu chez la drosophile au stade larvaire dans un organe spécialisé appelé Glande Lymphatique (GL). Au sein de cet organe, un petit groupe de cellules, le Centre de Signalisation Postérieur (PSC), contrôle l'équilibre entre progéniteurs hématopoïétiques et cellules immunitaires différenciées, et a donc un rôle équivalent à celui de la niche hématopoïétique des mammifères. Suite à un stress immun, tel que le parasitisme par des guêpes, une différenciation massive de cellules immunitaires spécifiques, les lamellocytes, a lieu dans la GL; puis la dispersion de la GL permet la libération des lamellocytes dans la circulation lymphatique. Lors du parasitisme, la guêpe pond un œuf dans le corps de la larve de drosophile. En absence de réponse immunitaire cellulaire, l'œuf de guêpe se développe au dépend de son hôte, entraînant sa mort. En formant une capsule autour de l'œuf de guêpe, les lamellocytes neutralisent son développement et permettent la survie de l'hôte. Au cours de ma thèse, je me suis intéressée à la réponse immunitaire cellulaire de la larve de drosophile au parasitisme par des guêpes. Je me suis plus particulièrement intéressée au rôle de la " niche hématopoïétique " dans cette réponse. Pour cela, j'ai initié une approche transcriptomique ayant pour but d'identifier les gènes spécifiquement exprimés dans le PSC en réponse au parasitisme. En parallèle, j'ai caractérisé le rôle de la voie de signalisation Toll/NF?B dans la GL lors de la réponse au parasitisme. La voie Toll/NF?B joue un rôle essentiel dans la réponse immunitaire humorale et son rôle dans la réponse immunitaire cellulaire reste à définir. Mes travaux indiquent que la voie Toll/NF?B est activée dans le PSC suite au parasitisme. Son activation est médiée par le facteur de transcription NF?B "Dorsal-related Immunity Factor" (Dif), qui est requis dans le PSC pour permettre la différenciation rapide et massive de lamellocytes et la dispersion des cellules de la GL. De plus, j'ai établi un réseau génique, impliquant les deux voies de signalisation Toll/NF?B et EGFR ainsi que les espèces réactives de l'oxygène (ROS) dans le contrôle de la réponse au parasitisme. Une augmentation du niveau de ROS dans le PSC et l'activation de la voie EGFR dans les cellules immunitaires ont été décrits comme nécessaires à l'encapsulation des œufs de guêpe après parasitisme. Mes données établissent qu'ils sont en plus requis respectivement dans les cellules du PSC et dans les progéniteurs hématopoïétiques pour permettre la dispersion de la GL après parasitisme. Basé sur la forte conservation des voies de signalisation et processus moléculaires contrôlant l'hématopoïèse entre les mammifères et la drosophile, mes résultats posent la question de la conservation du réseau génique établi chez la drosophile et du rôle de la voie NF?B dans la niche hématopoïétique des mammifères lors d'une réponse à une infection. / In all organisms, the immune response is divided into two parts: the humoral response, which consists of producing a large number of molecules to combat the pathogen, and the cellular response, which relies on immune cells produced during hematopoiesis. In adult mammals, hematopoiesis occurs in the bone marrow, where a particular microenvironment called the "hematopoietic niche" controls self-renewal, proliferation and differentiation of Hematopoietic Stem Cells (HSCs), which give rise to all blood cell types. Following a pathogenic infection, the hematopoietic system's homeostasis is modified in order to obtain an adapted cellular immune response. The role that the hematopoietic niche plays during an immune response remains unclear. Drosophila is used as a model system to study in vivo hematopoiesis and the immune response. In drosophila, hematopoiesis occurs at the larval stage in a specialized organ called the Lymph Gland (LG). Within this organ, a small group of cells termed the Posterior Signalling Center (PSC), controls the balance between hematopoietic progenitors and differentiated immune/blood cells, a role similar to the mammalian hematopoietic niche. Following an immune challenge, especially in response to wasp parasitism, a massive differentiation of specific immune cells called lamellocytes occurs in the LG. The LG subsequently disperses to release lamellocytes into the hemolymph. During parasitism, the wasp lays an egg in the drosophila larva. In the absence of a cellular immune response, the wasp egg will develop and kill its host. By forming a capsule around the wasp egg, lamellocytes impede the pathogen's development and permit the host's survival. During my PhD, I studied the drosophila larva cellular immune response to wasp parasitism. I focused my research on the role of the "hematopoietic niche". I therefore initiated a transcriptomic study, in order to identify genes expressed by the PSC in response to parasitism. In parallel, I characterized the role of the Toll/NF?B signalling pathway in the LG during parasitism. The Toll/NF?B pathway plays a key role in the humoral response both in drosophila and mammals; however its role in the cellular immune response remains unknown. My results indicate that the Toll/NF?B pathway is activated in the PSC following parasitism. Its activation is mediated by the NF?B transcription factor " Dorsal-related Immunity Factor " (Dif), which is required in the PSC for rapid lamellocyte production and LG dispersion. Furthermore, I established the existence of a genetic network comprising the Toll/NFkB and EGFR signalling pathways and Reactive Oxygen Species (ROS), in order to control the immune response to parasitism. An increase in ROS levels in the PSC and EGFR pathway activation in the immune cells, have been described as required for wasp egg encapsulation. My data suggest that the ROS and the EGFR pathway are also required for LG dispersion following wasp parasitism, in PSC cells and in hematopoietic progenitors, respectively. Based on the high conservation of signalling pathways and molecular processes controlling hematopoiesis, my results raise the question of whether such a network is conserved in the mammalian hematopoietic niche in response to pathogenic infections.

No description available.

No description available.

Intraspecific nest parasitism was studied in a group of colonial Red-breasted Mergansers (Mergus serrator) nesting on the Tern Islands of Kouchibouguac National Park in New Brunswick in 1992. Nest parasitism is very common in this colony, and may influence the high rate of nest abandonment observed. Emphasis was placed on determining rates of successful parasitism (i.e. eggs added during the laying period of the hen at that nest), which are evolutionarily significant, and can easily go undetected. Three methods were used to determine if a nest contained egg(s) from another hen: abnormally large clutch size: more than one egg laid per day: and comparisons of DNA fingerprints of the hen versus putative chicks. When eggs were added to a nest during incubation, the nest was also labelled parasitized, but such eggs were not fully incubated (non-term) and thus were not successful. A new method of blood sampling ducklings in pipped eggs was tested and found to have negative effects on survival. As many as 14.8% (13/88) of the ducklings sampled subsequently died. Researchers wishing to use this method should proceed with caution. DNA fingerprinting determined that 50.0% of nests tested (6/12) were successfully parasitized. Two of six parasitized nests would have gone undetected using the other criteria to detect parasitism, thus proving the value of DNA fingerprinting. Of hatched young genetically analyzed, 30.9% (17/55) were parasitic. Nest parasitism appears to be an alternative breeding strategy in this population. Extra-pair copulation, previously unrecorded in this species, was discovered through DNA fingerprinting in two of four nests analyzed.

The rate of intraspecific nest parasitism was determined for a colony of Red-breasted Mergansers (Mergus serrator) nesting on the Tern Islands in Kouchibouguac National Park, New Brunswick. In order to recognize instances of nest parasitism, field criteria and microsatellite analysis testing for parentage between attending hens and the eggs in their nests were used. Traditionally, molecular analysis has involved collecting blood samples from females and offspring, however, for the purpose of this study, DNA was extracted successfully from feathers, egg membranes, and unhatched embryos which were collected during the summers of 1999 and 2000. A total of 8 primer pairs which amplified microsatellite loci in closely related avian species were tested (Sfimu-2, Sfimu-3, Sfimu-4, Sfimu-5, Sfimu-6, Sfimu-7, Bcamu-6, and Alamu-1). Four of these primers produced product of the expected size (Sfimu-3, Sfimu-4, Sfimu-7, and Bcamu-6). Amplification of these loci, however was inconsistent and subsequent sequence analysis revealed that the amplicons did not contain tandem repeats and therefore were not useful in genotyping. From field criteria we were able to establish rates of parasitism of 46% and 44% for each season. Rates of parasitism tended to be higher at the beginning of the season, compared to nests initiated later. Field criteria bring support to several hypotheses on causes of nest parasitism, indicating that more than one may influence rates of parasitism in a population.

Forest tent caterpillar (Malacosoma disstria Hübner; FTC), a major defoliator of aspen trees, occupies both aspen and mixedwood forest stands in Alberta’s boreal forest. Forest stand composition could influence the spatial pattern of FTC outbreaks if mortality from natural enemies differs between stand types. I conducted field experiments to determine whether predator- or parasitoid-caused mortality of FTC differed between aspen and mixedwood forest stands and developed a spatial population model to determine the effects of variation in generalist predation on the spread of an FTC outbreak, including the effects of potential predator-caused Allee effects. Generalist predation on FTC was higher in aspen stands than in mixedwood stands, and the spatial model suggests that these observed differences may be sufficiently large to impact FTC outbreak spread rates. Forest stand composition may contribute to the spatial pattern of FTC outbreaks through variation in the impacts of predators on FTC populations. / Ecology