Dose reconstruction in the context of tomotherapy

In vivo dosimetry is a way to verify the radiation dose delivered to the patient in measuring the dose generally during the first fraction of the treatment. It is the only dose delivery control based on a measurement performed during the treatment. In today's radiotherapy practice, the dose delivered to the patient is planned using 3D dose calculation algorithms and volumetric images representing the patient. Due to the high accuracy and precision necessary in radiation treatments, national and international organisations like ICRU and AAPM recommend the use of in vivo dosimetry. It is also mandatory in some countries like France. Various in vivo dosimetry methods have been developed during the past years. These methods are point-, line-, plane- or 3D dose controls. A 3D in vivo dosimetry provides the most information about the dose delivered to the patient, with respect to ID and 2D methods. However, to our knowledge, it is generally not routinely applied to patient treatments yet. The aim of this PhD thesis was to determine whether it is possible to reconstruct the 3D delivered dose using transmitted beam measurements in the context of narrow beams. An iterative dose reconstruction method has been described and implemented. The iterative algorithm includes a simple 3D dose calculation algorithm based on the convolution/superposition principle. The methodology was applied to narrow beams produced by a conventional 6 MV linac. The transmitted dose was measured using an array of ion chambers, as to simulate the linear nature of a tomotherapy detector. We showed that the iterative algorithm converges quickly and reconstructs the dose within a good agreement (at least 3% / 3 mm locally), which is inside the 5% recommended by the ICRU. Moreover it was demonstrated on phantom measurements that the proposed method allows us detecting some set-up errors and interfraction geometry modifications. We also have discussed the limitations of the 3D dose reconstruction for dose delivery error detection. Afterwards, stability tests of the tomotherapy MVCT built-in onboard detector was performed in order to evaluate if such a detector is suitable for 3D in-vivo dosimetry. The detector showed stability on short and long terms comparable to other imaging devices as the EPIDs, also used for in vivo dosimetry. Subsequently, a methodology for the dose reconstruction using the tomotherapy MVCT detector is proposed in the context of static irradiations. This manuscript is composed of two articles and a script providing further information related to this work. In the latter, the first chapter introduces the state-of-the-art of in vivo dosimetry and adaptive radiotherapy, and explains why we are interested in performing 3D dose reconstructions. In chapter 2 a dose calculation algorithm implemented for this work is reviewed with a detailed description of the physical parameters needed for calculating 3D absorbed dose distributions. The tomotherapy MVCT detector used for transit measurements and its characteristics are described in chapter 3. Chapter 4 contains a first article entitled '3D dose reconstruction for narrow beams using ion chamber array measurements', which describes the dose reconstruction method and presents tests of the methodology on phantoms irradiated with 6 MV narrow photon beams. Chapter 5 contains a second article 'Stability of the Helical TomoTherapy HiArt II detector for treatment beam irradiations. A dose reconstruction process specific to the use of the tomotherapy MVCT detector is presented in chapter 6. A discussion and perspectives of the PhD thesis are presented in chapter 7, followed by a conclusion in chapter 8. The tomotherapy treatment device is described in appendix 1 and an overview of 3D conformai- and intensity modulated radiotherapy is presented in appendix 2. - La dosimétrie in vivo est une technique utilisée pour vérifier la dose délivrée au patient en faisant une mesure, généralement pendant la première séance du traitement. Il s'agit de la seule technique de contrôle de la dose délivrée basée sur une mesure réalisée durant l'irradiation du patient. La dose au patient est calculée au moyen d'algorithmes 3D utilisant des images volumétriques du patient. En raison de la haute précision nécessaire lors des traitements de radiothérapie, des organismes nationaux et internationaux tels que l'ICRU et l'AAPM recommandent l'utilisation de la dosimétrie in vivo, qui est devenue obligatoire dans certains pays dont la France. Diverses méthodes de dosimétrie in vivo existent. Elles peuvent être classées en dosimétrie ponctuelle, planaire ou tridimensionnelle. La dosimétrie 3D est celle qui fournit le plus d'information sur la dose délivrée. Cependant, à notre connaissance, elle n'est généralement pas appliquée dans la routine clinique. Le but de cette recherche était de déterminer s'il est possible de reconstruire la dose 3D délivrée en se basant sur des mesures de la dose transmise, dans le contexte des faisceaux étroits. Une méthode itérative de reconstruction de la dose a été décrite et implémentée. L'algorithme itératif contient un algorithme simple basé sur le principe de convolution/superposition pour le calcul de la dose. La dose transmise a été mesurée à l'aide d'une série de chambres à ionisations alignées afin de simuler la nature linéaire du détecteur de la tomothérapie. Nous avons montré que l'algorithme itératif converge rapidement et qu'il permet de reconstruire la dose délivrée avec une bonne précision (au moins 3 % localement / 3 mm). De plus, nous avons démontré que cette méthode permet de détecter certaines erreurs de positionnement du patient, ainsi que des modifications géométriques qui peuvent subvenir entre les séances de traitement. Nous avons discuté les limites de cette méthode pour la détection de certaines erreurs d'irradiation. Par la suite, des tests de stabilité du détecteur MVCT intégré à la tomothérapie ont été effectués, dans le but de déterminer si ce dernier peut être utilisé pour la dosimétrie in vivo. Ce détecteur a démontré une stabilité à court et à long terme comparable à d'autres détecteurs tels que les EPIDs également utilisés pour l'imagerie et la dosimétrie in vivo. Pour finir, une adaptation de la méthode de reconstruction de la dose a été proposée afin de pouvoir l'implémenter sur une installation de tomothérapie. Ce manuscrit est composé de deux articles et d'un script contenant des informations supplémentaires sur ce travail. Dans ce dernier, le premier chapitre introduit l'état de l'art de la dosimétrie in vivo et de la radiothérapie adaptative, et explique pourquoi nous nous intéressons à la reconstruction 3D de la dose délivrée. Dans le chapitre 2, l'algorithme 3D de calcul de dose implémenté pour ce travail est décrit, ainsi que les paramètres physiques principaux nécessaires pour le calcul de dose. Les caractéristiques du détecteur MVCT de la tomothérapie utilisé pour les mesures de transit sont décrites dans le chapitre 3. Le chapitre 4 contient un premier article intitulé '3D dose reconstruction for narrow beams using ion chamber array measurements', qui décrit la méthode de reconstruction et présente des tests de la méthodologie sur des fantômes irradiés avec des faisceaux étroits. Le chapitre 5 contient un second article intitulé 'Stability of the Helical TomoTherapy HiArt II detector for treatment beam irradiations'. Un procédé de reconstruction de la dose spécifique pour l'utilisation du détecteur MVCT de la tomothérapie est présenté au chapitre 6. Une discussion et les perspectives de la thèse de doctorat sont présentées au chapitre 7, suivies par une conclusion au chapitre 8. Le concept de la tomothérapie est exposé dans l'annexe 1. Pour finir, la radiothérapie «informationnelle 3D et la radiothérapie par modulation d'intensité sont présentées dans l'annexe 2.

FIB-SEM tomography in biology.

Three-dimensional information is much easier to understand than a set of two-dimensional images. Therefore a layman is thrilled by the pseudo-3D image taken in a scanning electron microscope (SEM) while, when seeing a transmission electron micrograph, his imagination is challenged. First approaches to gain insight in the third dimension were to make serial microtome sections of a region of interest (ROI) and then building a model of the object. Serial microtome sectioning is a tedious and skill-demanding work and therefore seldom done. In the last two decades with the increase of computer power, sophisticated display options, and the development of new instruments, an SEM with a built-in microtome as well as a focused ion beam scanning electron microscope (FIB-SEM), serial sectioning, and 3D analysis has become far easier and faster.Due to the relief like topology of the microtome trimmed block face of resin-embedded tissue, the ROI can be searched in the secondary electron mode, and at the selected spot, the ROI is prepared with the ion beam for 3D analysis. For FIB-SEM tomography, a thin slice is removed with the ion beam and the newly exposed face is imaged with the electron beam, usually by recording the backscattered electrons. The process, also called "slice and view," is repeated until the desired volume is imaged.As FIB-SEM allows 3D imaging of biological fine structure at high resolution of only small volumes, it is crucial to perform slice and view at carefully selected spots. Finding the region of interest is therefore a prerequisite for meaningful imaging. Thin layer plastification of biofilms offers direct access to the original sample surface and allows the selection of an ROI for site-specific FIB-SEM tomography just by its pronounced topographic features.

Toxicokinetics of captan and folpet biomarkers in orally exposed volunteers

The time courses of key biomarkers of exposure to captan and folpet was assessed in accessible biological matrices of orally exposed volunteers. Ten volunteers ingested 1 mg kg(-1) body weight of captan or folpet. Blood samples were withdrawn at fixed time periods over the 72 h following ingestion and complete urine voids were collected over 96 h post-dosing. The tetrahydrophthalimide (THPI) metabolite of captan along with the phthalimide (PI) and phthalic acid metabolites of folpet were then quantified in these samples. Plasma levels of THPI and PI increased progressively after ingestion, reaching peak values ~10 and 6 h post-dosing, respectively; subsequent elimination phase appeared monophasic with a mean elimination half-life (t(½) ) of 15.7 and 31.5 h, respectively. In urine, elimination rate time courses of PI and phthalic acid evolved in parallel, with respective t(½) of 27.3 and 27.6 h; relatively faster elimination was found for THPI, with mean t(½) of 11.7 h. However, phthalic acid was present in urine in 1000-fold higher amounts than PI. In the 96 h period post-treatment, on average 25% of folpet dose was excreted in urine as phthalic acid as compared with only 0.02% as PI. The corresponding value for THPI was 3.5%. Overall, THPI and PI appear as interesting biomarkers of recent exposure, with relatively short half-lives; their sensitivity to assess exposure in field studies should be further verified. Although not a metabolite specific to folpet, the concomitant use of phthalic acid as a major biomarker of exposure to folpet should also be considered. Copyright © 2011 John Wiley & Sons, Ltd.

An architecture for adaptive replication-based multimedia streaming in P2P networks

This PhD thesis addresses the issue of scalable media streaming in large-scale networking environments. Multimedia streaming is one of the largest sink of network resources and this trend is still growing as testified by the success of services like Skype, Netflix, Spotify and Popcorn Time (BitTorrent-based). In traditional client-server solutions, when the number of consumers increases, the server becomes the bottleneck. To overcome this problem, the Content-Delivery Network (CDN) model was invented. In CDN model, the server copies the media content to some CDN servers, which are located in different strategic locations on the network. However, they require heavy infrastructure investment around the world, which is too expensive. Peer-to-peer (P2P) solutions are another way to achieve the same result. These solutions are naturally scalable, since each peer can act as both a receiver and a forwarder. Most of the proposed streaming solutions in P2P networks focus on routing scenarios to achieve scalability. However, these solutions cannot work properly in video-on-demand (VoD) streaming, when resources of the media server are not sufficient. Replication is a solution that can be used in these situations. This thesis specifically provides a family of replication-based media streaming protocols, which are scalable, efficient and reliable in P2P networks. First, it provides SCALESTREAM, a replication-based streaming protocol that adaptively replicates media content in different peers to increase the number of consumers that can be served in parallel. The adaptiveness aspect of this solution relies on the fact that it takes into account different constraints like bandwidth capacity of peers to decide when to add or remove replicas. SCALESTREAM routes media blocks to consumers over a tree topology, assuming a reliable network composed of homogenous peers in terms of bandwidth. Second, this thesis proposes RESTREAM, an extended version of SCALESTREAM that addresses the issues raised by unreliable networks composed of heterogeneous peers. Third, this thesis proposes EAGLEMACAW, a multiple-tree replication streaming protocol in which two distinct trees, named EAGLETREE and MACAWTREE, are built in a decentralized manner on top of an underlying mesh network. These two trees collaborate to serve consumers in an efficient and reliable manner. The EAGLETREE is in charge of improving efficiency, while the MACAWTREE guarantees reliability. Finally, this thesis provides TURBOSTREAM, a hybrid replication-based streaming protocol in which a tree overlay is built on top of a mesh overlay network. Both these overlays cover all peers of the system and collaborate to improve efficiency and low-latency in streaming media to consumers. This protocol is implemented and tested in a real networking environment using PlanetLab Europe testbed composed of peers distributed in different places in Europe.

Outcome and Prognostic Factors in Adenosquamous Carcinoma of the Head and Neck: A Multicenter Rare Cancer Network Study

Purpose/Objective(s): Adenosquamous carcinoma (AC) of the head and neck is a distinct entity first described in 1968. Its natural history is more aggressive than squamous cell carcinoma but this is based on very small series reported in the literature. The goal of this study was to assess the clinical profile, outcome, patterns of failure and prognostic factors in patients with AC of the head and neck treated by radiation therapy (RT) with or without chemotherapy (CT).Materials/Methods: Data from 18 patients with Stage I (n = 3), II (n = 1), III (n = 4), or IVa (n = 10) AC, treated between 1989 and 2009, were collected in a retrospective multicenter Rare Cancer Network study. Median age was 60 years (range, 48 - 73 years). Fourteen patients were male and 4 female. Risk factors, including perineural invasion, lymphangitis, vascular invasion, positive margins, were present in 83% of the patients. Tumor sites included oral cavity in 4, oropharynx in 4, hypopharynx in2, larynx in 2, salivary glands in 2, nasal vestibule in 2, nasopharynx in 1, and maxillary sinus in 1 patient. Surgery (S) was performed in all but 5 patients. S alone was performed in only 1 patient, and definitive RT alone in 3 patients. Fourteen patients received combined modality treatment (S+RT in 10, RT+CT in 2, and all of the three modalities in 2 patients). Median RT dose to the primary and to the nodes was 66 Gy (range, 50 - 72 Gy) and 53 Gy (range, 44 - 66 Gy), respectively (1.8 - 2.0 Gy/fr., 5 fr./ week). In 4 patients, the planning treatment volume included the primary tumor site only. Seven patients were treated with 2D RT, 7 with 3D conformal RT, and 2 with intensity-modulated RT.Results: After a median follow-up period of 38 months (range, 9 - 62 months), 8 patients developed distant metastases (lung, bone, mediastinum, and liver), 6 presented nodal recurrences, and only 4 had a local relapse at the primary site (all in-field recurrences). At last follow-up, 6 patients were alive without disease, 1 alive with disease, 9 died from progressive disease, and 2 died from intercurrent disease. The 3-year and median overall survival, disease-free survival (DFS) and locoregional control rates were 52% (95% confidence interval [CI]: 28 - 76%) and 39 months, 36% (95% CI: 13 - 49%) and 12 months, and 54% (95% CI: 26 - 82%) and 40 months, respectively. In multivariate analysis (Cox model), DFS was negatively influenced by the presence of extracapsular extension (p = 0.02) and advanced stage (IV versus I-III, p = 0.003).Conclusions: Overall prognosis of locoregionally advanced AC remains poor, and distant metastases and nodal relapse occur in almost half of the cases. However, local control is relatively good, and early stage AC patients had prolonged DFS when treated with combined modality treatment.

Male reproductive success: paternity contribution to queens and workers in Formica ants

The relative number of workers and female sexuals fathered by two males mated with a queen were directly assessed using microsatellite and allozyme markers in field colonies of the ants Formica exsecta and F. truncorum. In both species one of the two males consistently fathered more offspring than the other. There was, however, no evidence that one male might be particularly successful in fathering a disproportionally high proportion of female sexuals relative to the proportion of workers. Moreover, in F. exsecta, the proportions of worker pupae and worker adults fathered by each male did not differ significantly between cohorts. The most likely explanation for this pattern is that females store different amounts of sperm from the two males they mated with.

Early Iron Age Pottery: A Quantitative Approach, Proceedings of the International Round Table organized by the Swiss School of Archaeology in Greece (Athens, November 28-30, 2008)

Quantitative approaches in ceramology are gaining ground in excavation reports, archaeological publications and thematic studies. Hence, a wide variety of methods are being used depending on the researchers' theoretical premise, the type of material which is examined, the context of discovery and the questions that are addressed. The round table that took place in Athens on November 2008 was intended to offer the participants the opportunity to present a selection of case studies on the basis of which methodological approaches were discussed. The aim was to define a set of guidelines for quantification that would prove to be of use to all researchers. Contents: 1) Introduction (Samuel Verdan); 2) Isthmia and beyond. How can quantification help the analysis of EIA sanctuary deposits? (Catherine Morgan); 3) Approaching aspects of cult practice and ethnicity in Early Iron Age Ephesos using quantitative analysis of a Protogeometric deposit from the Artemision (Michael Kerschner); 4) Development of a ceramic cultic assemblage: Analyzing pottery from Late Helladic IIIC through Late Geometric Kalapodi (Ivonne Kaiser, Laura-Concetta Rizzotto, Sara Strack); 5) 'Erfahrungsbericht' of application of different quantitative methods at Kalapodi (Sara Strack); 6) The Early Iron Age sanctuary at Olympia: counting sherds from the Pelopion excavations (1987-1996) (Birgitta Eder); 7) L'aire du pilier des Rhodiens à Delphes: Essai de quantification du mobilier (Jean-Marc Luce); 8) A new approach in ceramic statistical analyses: Pit 13 on Xeropolis at Lefkandi (David A. Mitchell, Irene S. Lemos); 9) Households and workshops at Early Iron Age Oropos: A quantitative approach of the fine, wheel-made pottery (Vicky Vlachou); 10) Counting sherds at Sindos: Pottery consumption and construction of identities in the Iron Age (Stefanos Gimatzidis); 11) Analyse quantitative du mobilier céramique des fouilles de Xombourgo à Ténos et le cas des supports de caisson (Jean-Sébastien Gros); 12) Defining a typology of pottery from Gortyn: The material from a pottery workshop pit, (Emanuela Santaniello); 13) Quantification of ceramics from Early Iron Age tombs (Antonis Kotsonas); 14) Quantitative analysis of the pottery from the Early Iron Age necropolis of Tsikalario on Naxos (Xenia Charalambidou); 15) Finding the Early Iron Age in field survey: Two case studies from Boeotia and Magnesia (Vladimir Stissi); 16) Pottery quantification: Some guidelines (Samuel Verdan)

A detailed urinary excretion time course study of captan and folpet biomarkers in workers for the estimation of dose, main route-of-entry and most appropriate sampling and analysis strategies

Captan and folpet are two fungicides largely used in agriculture, but biomonitoring data are mostly limited to measurements of captan metabolite concentrations in spot urine samples of workers, which complicate interpretation of results in terms of internal dose estimation, daily variations according to tasks performed, and most plausible routes of exposure. This study aimed at performing repeated biological measurements of exposure to captan and folpet in field workers (i) to better assess internal dose along with main routes-of-entry according to tasks and (ii) to establish most appropriate sampling and analysis strategies. The detailed urinary excretion time courses of specific and non-specific biomarkers of exposure to captan and folpet were established in tree farmers (n = 2) and grape growers (n = 3) over a typical workweek (seven consecutive days), including spraying and harvest activities. The impact of the expression of urinary measurements [excretion rate values adjusted or not for creatinine or cumulative amounts over given time periods (8, 12, and 24 h)] was evaluated. Absorbed doses and main routes-of-entry were then estimated from the 24-h cumulative urinary amounts through the use of a kinetic model. The time courses showed that exposure levels were higher during spraying than harvest activities. Model simulations also suggest a limited absorption in the studied workers and an exposure mostly through the dermal route. It further pointed out the advantage of expressing biomarker values in terms of body weight-adjusted amounts in repeated 24-h urine collections as compared to concentrations or excretion rates in spot samples, without the necessity for creatinine corrections.

Multiple mating and offspring quality in Lasius ants

Genetic diversity benefits for social insect colonies headed by polyandrous queens have received intense attention, whereas sexual selection remains little explored. Yet mates of the same queen may engage in sperm competition over the siring of offspring, and this could confer benefits on queens if the most successful sire in each colony (the majority sire) produces gynes (daughter queens) of higher quality. These benefits could be increased if high-quality sires make queens increase the percentage of eggs that they fertilize (unfertilized eggs develop into sons in social hymenopterans), or if daughters of better genetic quality are over-represented in the gyne versus worker class. Such effects would lead to female-biased sex ratios in colonies with high-quality majority gynes. I tested these ideas in field colonies of Lasius niger black garden ants, using body mass of gynes as a fitness trait as it is known to correlate with future fecundity. Also, I established the paternity of gynes through microsatellite DNA offspring analyses. Majority sires did not always produce heavier gynes in L. niger, but whenever they did do so colonies produced more females, numerically and in terms of the energetic investment in female versus male production. Better quality sires may be able to induce queens to fertilize more eggs or so-called caste shunting may occur wherever the daughters of better males are preferentially shunted to into the gyne caste. My study supports that integrating sexual selection and social evolutionary studies may bring a deeper understanding of mating system evolution in social insects.

Defining molecular components of symbiotic phosphate uptake in rice

Phosphate (Pi) acquisition of crops via arbuscular mycorrhizal (AM) symbiosis acquires increasing importance due to the limited rock Pi reserves and the demand for environmentally sustainable agriculture. However, the symbiotic Pi uptake machinery has not been characterized in any monocotyledonous plant species. Among these, rice is the primary staple food for more than half of the human population and thus central for future food security. However, the relevance of the AM symbiosis for rice Pi nutrition is presently unclear. Here, we show that 70% of the overall Pi acquired by rice is delivered via the symbiotic route. To better understand this pathway we combined genetic, molecular and physiological approaches to determine the specific functions of the two rice Pi transporters, PT11 and PT13, which are expressed only during AM symbiosis. The PT11 lineage of proteins is present in mono- and dicotyledons whereas PT13, while found across the Poaceae, is absent from dicotyledons. Surprisingly, mutations in either PT11 or PT13 affected fungal colonization and arbuscule formation demonstrating that both genes are essential for AM symbiosis between rice and Glomus intra.rad.ices. Importantly, for symbiotic Pi uptake, only PT11 is necessary and sufficient. We found that mycorrhizal rice, remarkably, received almost all Pi via the symbiotic route. Such dominating mycorrhizal Pi uptake was found in plants grown under controlled conditions as well as in field soils, suggesting that the AM symbiosis is relevant for the Pi nutrition of field grown rice. Development of smaller arbuscules in PT11 mutants suggested that symbiotic Pi signaling is required for fungal nourishment by the plant. However, co-culture of mutant with wild type nurse plants did not restore normal arbuscule size in mutant roots, indicating that other factors than malnutrition accounted for the altered arbuscule phenotype. Surprisingly, the loss of PT13 did not affect symbiotic Pi uptake although it impacted arbuscule morphology, suggesting that PT13 is involved in signaling during arbuscule development. However, induction of PT13 was not only monitored in arbusculated cells but also in inner cortex cells of non-inoculated roots of plants grown under high Pi fertilization conditions. According to preliminary observations, PT13 localized at the tonoplast in arbusculated and non-arbusculated cells, suggesting that it might be involved in transporting Pi into the vacuole, possibly for maintaining cellular Pi homeostasis. The further investigation showed that fungal colonization level was significantly affected in the crown roots of two ptlS mutant alleles, but not in large lateral roots, implying the possible role of PT13 for maintaining Pi homeostasis in the crown roots. - L'acquisition de phosphate (Pi) par les plantes cultivées s'effectue grâce à une symbiose mycorhizienne arbasculaire (AM). L'étude de cette symbiose devient fondamentale puisque d'une part, les réserves en phosphate minéral sont limitées, et, d'autre part, la demande pour une agriculture écologiquement soutenable se renforce. La machinerie d'absorption symbiotique du phosphate n'est cependant pas encore élucidée chez les plantes monocotylédones. Parmi celles-ci, le riz occupe une place primordiale. Aliment de base pour plus de la moitié de la population mondiale, il revêt de ce fait une dimension essentielle en termes de sécurité alimentaire. Pourtant, l'importance de la symbiose AM chez le riz dans le processus d'acquisition du phosphate n'est, encore de nos jours, que peu comprise. Dans cette étude, nous montrons que 70% du phosphate acquis par le riz est mis à disposition de la plante grâce à la symbiose AM. Afin de mieux comprendre ce mécanisme, nous avons employé des approches physiologiques et génétiques nous permettant de déterminer les fonctions spécifiques de deux transporteurs de Pi, PT11 et PT13, présents chez le riz et exprimés uniquement durant la symbiose AM. La famille de gènes à laquelle appartient PT11 est présente chez les monocotylédones ainsi que chez les dicotylédones tandis que PT13, bien que retrouvé au sein des Poaceae, est absent chez les dicotylédones. Etonnamment, des versions mutées de PT11 ou de PT13 affectent la colonisation par le champignon endo-mycorhizien ainsi que la formation d'arbuscules, démontrant l'importance de ces deux gènes dans la symbiose AM entre le riz et Glomus intraradices. Il est à noter que seul PT11 se révèle nécessaire et suffisant pour l'apport de Pi grâce à la symbiose. Nous avons observé que la presque totalité du phosphate dont dispose le riz lors d'une symbiose AM provient du champignon. De telles proportions ont été observées tant chez des plantes cultivées en conditions contrôlées que chez des plantes cultivées dans les champs. Cela suggère l'importance de la symbiose AM dans le processus d'acquisition du Pi chez le riz cultivé à l'extérieur. Le développement d'arbuscules plus petits chez le mutant PT11 tend à montrer qu'une voie signalétique impliquant le Pi symbiotique est nécessaire pour l'entretien du champignon par la plante. Toutefois, une co-culture du mutant avec des plantes sauvages ne permet pas de restaurer des arbuscules de taille normale dans les racines du mutant. Ce résultat indique le rôle de facteurs autres que la malnutrition aboutissant à la formation d'arbuscules altérés. Si la perte de PT13 n'affecte pas l'acquisition de phosphate symbiotique, la morphologie de l'arbuscule est, quant à elle, modifiée. Ceci suggère un rôle de PT13 durant le développement de l'arbuscule. Or, l'induction de PT13 est non seulement détectée dans des cellules contenant des arbuscules mais également dans des cellules du cortex, ceci chez des plantes cultivées sans champignon mais dans des conditions de fortes concentrations en engrais phosphaté. En accord avec des observations précédentes, PT13 est localisé au niveau du tonoplaste des cellules contenant ou non des arbuscules. Ceci suggère que PT13 pourrait être impliqué dans le transport du Pi vers la vacuole, éventuellement pour maintenir une certaine homéostasie du phosphate. Dans cette étude, nous démontrons également que le niveau de colonisation par le champignon est affecté de manière significative dans les racines principales des deux allèles du mutants ptl3, mais pas dans les grosses racines latérales. Cela impliquerait un rôle possible de PT13 dans le maintien de l'homéostasie du phosphate dans les racines principales. RESUME POUR UN LARGE PUBLIC Le phosphate (Pi), l'un des éléments minéraux essentiel au développement des plantes, se trouve généralement en faible quantité dans le sol, limitant ainsi la croissance des plantes. Le rendement de la production agricole dépend dès lors de l'addition d'engrais contenant du phosphate inorganique (Pi), obtenu à partir de ressources minières riches en phosphate. Or, ces ressources devraient être épuisées d'ici la fin du siècle. Les racines des plantes possèdent des transporteurs de phosphate efficaces leur permettant d'acquérir rapidement le Pi présent dans le sol. Comme le Pi s'avère immobile dans le sol, l'absorption rapide par les racines crée des zones pauvres en Pi autour des systèmes racinaires. Pour surmonter cet obstacle, les plantes ont développé une symbiose avec des champignons endomycorhiziens, la symbiose mycorhizienne arbusculaire (AM). Cette association leur donne accès à d'autres ressources en phosphate puisque le mycélium de ces champignons se développe sur une surface 100 fois supérieure à celle des racines. Cela augmente considérablement la surface de nutrition, dépassant ainsi la zone appauvrie en Pi. Le phosphate, transporté grâce au champignon jusqu'à l'intérieur des racines, est fourni à la plante par le biais de structures établies à l'intérieur des cellules végétales, appelées arbuscules. De leur côté, les plantes possèdent des transporteurs spécifiques afin de recevoir le Pi fourni par les champignons. A l'heure actuelle, la machinerie nécessaire à cette absorption a été uniquement décrite chez des plantes dicotylédones. Or, comprendre l'apport de phosphate par les champignons mycorhiziens s'avère particulièrement pertinent dans le cas des espèces monocotylédones cultivées telles que les céréales. Ces dernières constituent en effet la majeure partie de l'alimentation humaine. Parmi les céréales, le riz demeure l'aliment de base de la population mondiale, d'où son importance en terme de sécurité alimentaire. Durant mon travail de thèse, j'ai identifié et caractérisé le transporteur du riz impliqué dans l'apport de phosphate par ce type de symbiose AM. J'ai également démontré que le riz, lorsqu'il vit en symbiose, bénéficie de la presque totalité du Pi transporté par le champignon. Environ 40% de la production globale de riz est cultivée dans des conditions permettant la symbiose avec des mycorhizes arbusculaires. Les variétés de riz adaptées à ces conditions aérobiques deviennent des alternatives favorables aux cultivars actuels nécessitant une forte irrigation. Elles se révèlent en effet plus tolérantes aux pénuries d'eau et permettent l'utilisation de pratiques agricoles moins intensives. Les données présentées dans cette étude enrichissent nos connaissances concernant l'absorption du phosphate chez le riz grâce à la symbiose AM. Ces connaissances peuvent s'avérer décisives pour le développement de cultivars du riz plus adaptés à une agriculture écologiquement soutenable.

Persistent unequal sex ratio in a population of grayling (salmonidae) and possible role of temperature increase.

In some fishes, water chemistry or temperature affects sex determination or creates sex-specific selection pressures. The resulting population sex ratios are hard to predict from laboratory studies if the environmental triggers interact with other factors, whereas in field studies, singular observations of unusual sex ratios may be particularly prone to selective reporting. Long-term monitoring largely avoids these problems. We studied a population of grayling (Thymallus thymallus) in Lake Thun, Switzerland, that has been monitored since 1948. Samples of spawning fish have been caught about 3 times/week around spawning season, and water temperature at the spawning site has been continuously recorded since 1970. We used scale samples collected in different years to determine the average age of spawners (for life-stage specific analyses) and to identify the cohort born in 2003 (an extraordinarily warm year). Recent tissue samples were genotyped on microsatellite markers to test for genetic bottlenecks in the past and to estimate the genetically effective population size (N(e) ). Operational sex ratios changed from approximately 65% males before 1993 to approximately 85% males from 1993 to 2011. Sex ratios correlated with the water temperatures the fish experienced in their first year of life. Sex ratios were best explained by the average temperature juvenile fish experienced during their first summer. Grayling abundance is declining, but we found no evidence of a strong genetic bottleneck that would explain the apparent lack of evolutionary response to the unequal sex ratio. Results of other studies show no evidence of endocrine disruptors in the study area. Our findings suggest temperature affects population sex ratio and thereby contributes to population decline. Persistencia de Proporción de Sexos Desigual en una Población de Tímalos (Salmonidae) y el Posible Papel del Incremento de la Temperatura.

Conservation of the Eurasian Lynx (Lynx lynx) in a fragmented landscape - habitat models, dispersal and potential distribution

Abstract: The expansion of a recovering population - whether re-introduced or spontaneously returning - is shaped by (i) biological (intrinsic) factors such as the land tenure system or dispersal, (ii) the distribution and availability of resources (e.g. prey), (iii) habitat and landscape features, and (iv) human attitudes and activities. In order to develop efficient conservation and recovery strategies, we need to understand all these factors and to predict the potential distribution and explore ways to reach it. An increased number of lynx in the north-western Swiss Alps in the nineties lead to a new controversy about the return of this cat. When the large carnivores were given legal protection in many European countries, most organizations and individuals promoting their protection did not foresee the consequences. Management plans describing how to handle conflicts with large predators are needed to find a balance between "overabundance" and extinction. Wildlife and conservation biologists need to evaluate the various threats confronting populations so that adequate management decisions can be taken. I developed a GIS probability model for the lynx, based on habitat information and radio-telemetry data from the Swiss Jura Mountains, in order to predict the potential distribution of the lynx in this mountain range, which is presently only partly occupied by lynx. Three of the 18 variables tested for each square kilometre describing land use, vegetation, and topography, qualified to predict the probability of lynx presence. The resulting map was evaluated with data from dispersing subadult lynx. Young lynx that were not able to establish home ranges in what was identified as good lynx habitat did not survive their first year of independence, whereas the only one that died in good lynx habitat was illegally killed. Radio-telemetry fixes are often used as input data to calibrate habitat models. Radio-telemetry is the only way to gather accurate and unbiased data on habitat use of elusive larger terrestrial mammals. However, it is time consuming and expensive, and can therefore only be applied in limited areas. Habitat models extrapolated over large areas can in turn be problematic, as habitat characteristics and availability may change from one area to the other. I analysed the predictive power of Ecological Niche Factor Analysis (ENFA) in Switzerland with the lynx as focal species. According to my results, the optimal sampling strategy to predict species distribution in an Alpine area lacking available data would be to pool presence cells from contrasted regions (Jura Mountains, Alps), whereas in regions with a low ecological variance (Jura Mountains), only local presence cells should be used for the calibration of the model. Dispersal influences the dynamics and persistence of populations, the distribution and abundance of species, and gives the communities and ecosystems their characteristic texture in space and time. Between 1988 and 2001, the spatio-temporal behaviour of subadult Eurasian lynx in two re-introduced populations in Switzerland was studied, based on 39 juvenile lynx of which 24 were radio-tagged to understand the factors influencing dispersal. Subadults become independent from their mothers at the age of 8-11 months. No sex bias neither in the dispersal rate nor in the distance moved was detected. Lynx are conservative dispersers, compared to bear and wolf, and settled within or close to known lynx occurrences. Dispersal distances reached in the high lynx density population - shorter than those reported in other Eurasian lynx studies - are limited by habitat restriction hindering connections with neighbouring metapopulations. I postulated that high lynx density would lead to an expansion of the population and validated my predictions with data from the north-western Swiss Alps where about 1995 a strong increase in lynx abundance took place. The general hypothesis that high population density will foster the expansion of the population was not confirmed. This has consequences for the re-introduction and recovery of carnivores in a fragmented landscape. To establish a strong source population in one place might not be an optimal strategy. Rather, population nuclei should be founded in several neighbouring patches. Exchange between established neighbouring subpopulations will later on take place, as adult lynx show a higher propensity to cross barriers than subadults. To estimate the potential population size of the lynx in the Jura Mountains and to assess possible corridors between this population and adjacent areas, I adapted a habitat probability model for lynx distribution in the Jura Mountains with new environmental data and extrapolated it over the entire mountain range. The model predicts a breeding population ranging from 74-101 individuals and from 51-79 individuals when continuous habitat patches < 50 km2 are disregarded. The Jura Mountains could once be part of a metapopulation, as potential corridors exist to the adjoining areas (Alps, Vosges Mountains, and Black Forest). Monitoring of the population size, spatial expansion, and the genetic surveillance in the Jura Mountains must be continued, as the status of the population is still critical. ENFA was used to predict the potential distribution of lynx in the Alps. The resulting model divided the Alps into 37 suitable habitat patches ranging from 50 to 18,711 km2, covering a total area of about 93,600 km2. When using the range of lynx densities found in field studies in Switzerland, the Alps could host a population of 961 to 1,827 residents. The results of the cost-distance analysis revealed that all patches were within the reach of dispersing lynx, as the connection costs were in the range of dispersal cost of radio-tagged subadult lynx moving through unfavorable habitat. Thus, the whole Alps could once be considered as a metapopulation. But experience suggests that only few disperser will cross unsuitable areas and barriers. This low migration rate may seldom allow the spontaneous foundation of new populations in unsettled areas. As an alternative to natural dispersal, artificial transfer of individuals across the barriers should be considered. Wildlife biologists can play a crucial role in developing adaptive management experiments to help managers learning by trial. The case of the lynx in Switzerland is a good example of a fruitful cooperation between wildlife biologists, managers, decision makers and politician in an adaptive management process. This cooperation resulted in a Lynx Management Plan which was implemented in 2000 and updated in 2004 to give the cantons directives on how to handle lynx-related problems. This plan was put into practice e.g. in regard to translocation of lynx into unsettled areas. Résumé: L'expansion d'une population en phase de recolonisation, qu'elle soit issue de réintroductions ou d'un retour naturel dépend 1) de facteurs biologiques tels que le système social et le mode de dispersion, 2) de la distribution et la disponibilité des ressources (proies), 3) de l'habitat et des éléments du paysage, 4) de l'acceptation de l'espèce par la population locale et des activités humaines. Afin de pouvoir développer des stratégies efficaces de conservation et de favoriser la recolonisation, chacun de ces facteurs doit être pris en compte. En plus, la distribution potentielle de l'espèce doit pouvoir être déterminée et enfin, toutes les possibilités pour atteindre les objectifs, examinées. La phase de haute densité que la population de lynx a connue dans les années nonante dans le nord-ouest des Alpes suisses a donné lieu à une controverse assez vive. La protection du lynx dans de nombreux pays européens, promue par différentes organisations, a entraîné des conséquences inattendues; ces dernières montrent que tout plan de gestion doit impérativement indiquer des pistes quant à la manière de gérer les conflits, tout en trouvant un équilibre entre l'extinction et la surabondance de l'espèce. Les biologistes de la conservation et de la faune sauvage doivent pour cela évaluer les différents risques encourus par les populations de lynx, afin de pouvoir rapidement prendre les meilleuresmdécisions de gestion. Un modèle d'habitat pour le lynx, basé sur des caractéristiques de l'habitat et des données radio télémétriques collectées dans la chaîne du Jura, a été élaboré afin de prédire la distribution potentielle dans cette région, qui n'est que partiellement occupée par l'espèce. Trois des 18 variables testées, décrivant pour chaque kilomètre carré l'utilisation du sol, la végétation ainsi que la topographie, ont été retenues pour déterminer la probabilité de présence du lynx. La carte qui en résulte a été comparée aux données télémétriques de lynx subadultes en phase de dispersion. Les jeunes qui n'ont pas pu établir leur domaine vital dans l'habitat favorable prédit par le modèle n'ont pas survécu leur première année d'indépendance alors que le seul individu qui est mort dans l'habitat favorable a été braconné. Les données radio-télémétriques sont souvent utilisées pour l'étalonnage de modèles d'habitat. C'est un des seuls moyens à disposition qui permette de récolter des données non biaisées et précises sur l'occupation de l'habitat par des mammifères terrestres aux moeurs discrètes. Mais ces méthodes de- mandent un important investissement en moyens financiers et en temps et peuvent, de ce fait, n'être appliquées qu'à des zones limitées. Les modèles d'habitat sont ainsi souvent extrapolés à de grandes surfaces malgré le risque d'imprécision, qui résulte des variations des caractéristiques et de la disponibilité de l'habitat d'une zone à l'autre. Le pouvoir de prédiction de l'Analyse Ecologique de la Niche (AEN) dans les zones où les données de présence n'ont pas été prises en compte dans le calibrage du modèle a été analysée dans le cas du lynx en Suisse. D'après les résultats obtenus, la meilleure mé- thode pour prédire la distribution du lynx dans une zone alpine dépourvue d'indices de présence est de combiner des données provenant de régions contrastées (Alpes, Jura). Par contre, seules les données sur la présence locale de l'espèce doivent être utilisées pour les zones présentant une faible variance écologique tel que le Jura. La dispersion influence la dynamique et la stabilité des populations, la distribution et l'abondance des espèces et détermine les caractéristiques spatiales et temporelles des communautés vivantes et des écosystèmes. Entre 1988 et 2001, le comportement spatio-temporel de lynx eurasiens subadultes de deux populations réintroduites en Suisse a été étudié, basé sur le suivi de 39 individus juvéniles dont 24 étaient munis d'un collier émetteur, afin de déterminer les facteurs qui influencent la dispersion. Les subadultes se sont séparés de leur mère à l'âge de 8 à 11 mois. Le sexe n'a pas eu d'influence sur le nombre d'individus ayant dispersés et la distance parcourue au cours de la dispersion. Comparé à l'ours et au loup, le lynx reste très modéré dans ses mouvements de dispersion. Tous les individus ayant dispersés se sont établis à proximité ou dans des zones déjà occupées par des lynx. Les distances parcourues lors de la dispersion ont été plus courtes pour la population en phase de haute densité que celles relevées par les autres études de dispersion du lynx eurasien. Les zones d'habitat peu favorables et les barrières qui interrompent la connectivité entre les populations sont les principales entraves aux déplacements, lors de la dispersion. Dans un premier temps, nous avons fait l'hypothèse que les phases de haute densité favorisaient l'expansion des populations. Mais cette hypothèse a été infirmée par les résultats issus du suivi des lynx réalisé dans le nord-ouest des Alpes, où la population connaissait une phase de haute densité depuis 1995. Ce constat est important pour la conservation d'une population de carnivores dans un habitat fragmenté. Ainsi, instaurer une forte population source à un seul endroit n'est pas forcément la stratégie la plus judicieuse. Il est préférable d'établir des noyaux de populations dans des régions voisines où l'habitat est favorable. Des échanges entre des populations avoisinantes pourront avoir lieu par la suite car les lynx adultes sont plus enclins à franchir les barrières qui entravent leurs déplacements que les individus subadultes. Afin d'estimer la taille de la population de lynx dans le Jura et de déterminer les corridors potentiels entre cette région et les zones avoisinantes, un modèle d'habitat a été utilisé, basé sur un nouveau jeu de variables environnementales et extrapolé à l'ensemble du Jura. Le modèle prédit une population reproductrice de 74 à 101 individus et de 51 à 79 individus lorsque les surfaces d'habitat d'un seul tenant de moins de 50 km2 sont soustraites. Comme des corridors potentiels existent effectivement entre le Jura et les régions avoisinantes (Alpes, Vosges, et Forêt Noire), le Jura pourrait faire partie à l'avenir d'une métapopulation, lorsque les zones avoisinantes seront colonisées par l'espèce. La surveillance de la taille de la population, de son expansion spatiale et de sa structure génétique doit être maintenue car le statut de cette population est encore critique. L'AEN a également été utilisée pour prédire l'habitat favorable du lynx dans les Alpes. Le modèle qui en résulte divise les Alpes en 37 sous-unités d'habitat favorable dont la surface varie de 50 à 18'711 km2, pour une superficie totale de 93'600 km2. En utilisant le spectre des densités observées dans les études radio-télémétriques effectuées en Suisse, les Alpes pourraient accueillir une population de lynx résidents variant de 961 à 1'827 individus. Les résultats des analyses de connectivité montrent que les sous-unités d'habitat favorable se situent à des distances telles que le coût de la dispersion pour l'espèce est admissible. L'ensemble des Alpes pourrait donc un jour former une métapopulation. Mais l'expérience montre que très peu d'individus traverseront des habitats peu favorables et des barrières au cours de leur dispersion. Ce faible taux de migration rendra difficile toute nouvelle implantation de populations dans des zones inoccupées. Une solution alternative existe cependant : transférer artificiellement des individus d'une zone à l'autre. Les biologistes spécialistes de la faune sauvage peuvent jouer un rôle important et complémentaire pour les gestionnaires de la faune, en les aidant à mener des expériences de gestion par essai. Le cas du lynx en Suisse est un bel exemple d'une collaboration fructueuse entre biologistes de la faune sauvage, gestionnaires, organes décisionnaires et politiciens. Cette coopération a permis l'élaboration du Concept Lynx Suisse qui est entré en vigueur en 2000 et remis à jour en 2004. Ce plan donne des directives aux cantons pour appréhender la problématique du lynx. Il y a déjà eu des applications concrètes sur le terrain, notamment par des translocations d'individus dans des zones encore inoccupées.

Early Iron Age Pottery: A Quantitative Approach. Proceedings of the International Round Table organized by the Swiss School of Archaeology in Greece (Athens, Novembre 28-30, 2008).

Quantitative approaches in ceramology are gaining ground in excavation reports, archaeological publications and thematic studies. Hence, a wide variety of methods are being used depending on the researchers' theoretical premise, the type of material which is examined, the context of discovery and the questions that are addressed. The round table that took place in Athens on November 2008 was intended to offer the participants the opportunity to present a selection of case studies on the basis of which methodological approaches were discussed. The aim was to define a set of guidelines for quantification that would prove to be of use to all researchers. Contents: 1) Introduction (Samuel Verdan); 2) Isthmia and beyond. How can quantification help the analysis of EIA sanctuary deposits? (Catherine Morgan); 3) Approaching aspects of cult practice and ethnicity in Early Iron Age Ephesos using quantitative analysis of a Protogeometric deposit from the Artemision (Michael Kerschner); 4) Development of a ceramic cultic assemblage: Analyzing pottery from Late Helladic IIIC through Late Geometric Kalapodi (Ivonne Kaiser, Laura-Concetta Rizzotto, Sara Strack); 5) 'Erfahrungsbericht' of application of different quantitative methods at Kalapodi (Sara Strack); 6) The Early Iron Age sanctuary at Olympia: counting sherds from the Pelopion excavations (1987-1996) (Birgitta Eder); 7) L'aire du pilier des Rhodiens à Delphes: Essai de quantification du mobilier (Jean-Marc Luce); 8) A new approach in ceramic statistical analyses: Pit 13 on Xeropolis at Lefkandi (David A. Mitchell, Irene S. Lemos); 9) Households and workshops at Early Iron Age Oropos: A quantitative approach of the fine, wheel-made pottery (Vicky Vlachou); 10) Counting sherds at Sindos: Pottery consumption and construction of identities in the Iron Age (Stefanos Gimatzidis); 11) Analyse quantitative du mobilier céramique des fouilles de Xombourgo à Ténos et le cas des supports de caisson (Jean-Sébastien Gros); 12) Defining a typology of pottery from Gortyn: The material from a pottery workshop pit, (Emanuela Santaniello); 13) Quantification of ceramics from Early Iron Age tombs (Antonis Kotsonas); 14) Quantitative analysis of the pottery from the Early Iron Age necropolis of Tsikalario on Naxos (Xenia Charalambidou); 15) Finding the Early Iron Age in field survey: Two case studies from Boeotia and Magnesia (Vladimir Stissi); 16) Pottery quantification: Some guidelines (Samuel Verdan).

The role of vectors in the epidemiology of avian malaria

Studies on host-parasite relationships have commonly reported that parasitized hosts undergo changes in their behavioural and life history traits. How do these changes affect the fitness of the hosts? What are the ecological and evolutionary drivers of these changes? These open questions are crucial to predict the parasite spread amongst hosts. Surprisingly, mosquito vectors of diseases to humans and animals have long been seen as passive parasite transporters, being unaffected by the infection though they also function as hosts. Natural parasite-vector interactions are therefore poorly documented in the literature. In this thesis, we seek to address the role of wild vectors in the epidemiology of avian Plasmodium, the etiological agents of malaria in birds. We first conducted avian malaria surveys in field-caught mosquitoes to identify the natural vectors in our temperate study area. We report that ornithophilic Culex pipiens primarily act as a vector for Plasmodium vaughani in spring, this parasite species being progressively replaced by P. relictum along with the season. Season-related factors may thus shape the mosquitoes' vectorial capacity. We then used experimental approaches to determine the effect of avian malaria on wild, naturally infected C. pipiens. We show that infected mosquitoes incur unavoidable physiological costs associated with parasite exploitation, these costs being expressed as a reduced survival under nutritionally stressed conditions only. These results are of significant importance for the epidemiology of avian malaria since seasonal changes in climate may likely influence food quality and quantity available to the mosquitoes. The host-selection preferences of the vectors with respect to the malaria-infection status of their bird hosts largely determine the disease spreading. In a second laboratory experiment, we thus offered wild C. pipiens the opportunity to choose between uninfected and naturally infected great tits, Parus major. We show that host-seeking mosquitoes have innate orientation preferences for uninfected birds. This suggests that avian malaria parasites exert strong selective pressures on their vectors, pushing them to evolve anti-parasite behaviours. We lastly investigated the links between malaria-associated symptoms in birds and resulting attractiveness to the mosquitoes. We show that experimentally malaria-infected canaries, Serinus canaria, suffer severe haematocrit reduction at peak parasitaemia and reduced basal metabolic rate later in the course of the infection. However, no links between infection and bird attractiveness to the mosquitoes were shown in an experiment using canaries as live bait for mosquito trap in the field. These links may have been masked by confounding environmental factors. Using a system where the vectors, parasites and hosts co-occur in sympatry, this thesis illustrates that vectors are not always Plasmodium permissive, which opposes to the traditional view that malaria parasites should have little effect on their vectors. The way that the vectors respond to the parasite threat is largely determined by the environmental conditions. This may have major implications for the epidemiology of avian malaria. - Les études portant sur les relations hôtes-parasites mentionnent souvent que les hôtes parasités subissent des modifications de leurs traits d'histoire de vie ou bien comportementaux. Comment ces changements affectent-ils la valeur sélective des hôtes et celle de leurs parasites ? Quels sont les déterminants de ces modifications ? Ces questions sont d'un grand intérêt en épidémiologie. Pour autant, les moustiques vecteurs de maladies infectieuses ont longtemps été perçus comme de simples transporteurs de parasites, n'étant pas affectés par ces derniers. Cette thèse porte sur le rôle des vecteurs dans l'épidémiologie des Plasmodium aviaires, agents étiologiques de la malaria chez les oiseaux. Dans le but d'identifier les vecteurs naturels de malaria aviaire dans notre zone d'étude, nous avons tout d'abord collecté des moustiques sur le terrain, puis déterminé leur statut infectieux. Nous rapportons que les moustiques Culex pipiens sont principalement impliqués dans la transmission de Plasmodium vaughani au printemps, cette espèce de parasite étant progressivement remplacée par P. relictum au fil de la saison de transmission. Nous avons ensuite conduit une expérience visant à déterminer l'effet de la malaria aviaire sur des C. pipiens sauvages, naturellement infectés. Nous montrons que des coûts sont associés à l'infection pour les moustiques. Ces coûts occasionnent une diminution de la survie des vecteurs seulement lorsque ceux-ci sont privés de ressources nutritionnelles. Des changements saisonniers de climats pourraient affecter la quantité et la qualité des ressources disponibles pour les vecteurs et donc, leur aptitude à transmettre l'infection. Les traits comportementaux des moustiques vecteurs, tels que la recherche et le choix d'un hôte pour se nourrir, sont d'une importance majeure pour la dispersion de la malaria. Pour cela, nous avons offert à des C. pipiens sauvages l'opportunité de choisir simultanément entre une mésange charbonnière (Parus major) saine et une autre naturellement infectée. Nous montrons que les moustiques s'orientent préférentiellement vers des mésanges saines. Les Plasmodium aviaires exerceraient donc de fortes pressions de sélection sur leurs vecteurs, favorisant ainsi l'évolution de comportements d'évitement des parasites. Enfin nous avons cherché à identifier de potentiels liens entre symptômes de l'infection malarique chez les oiseaux et attractivité de ces derniers pour les moustiques. Nous montrons que des canaris (Serinus canaria) expérimentalement infectés sont fortement anémiés au moment du pic infectieux et que leur métabolisme basai diminue plus tard au cours de l'infection. Toutefois, aucun lien entre le statut infectieux et l'attractivité des canaris pour les moustiques n'a pu être montré lors d'une expérience réalisée en nature. Il se peut que ces liens aient été masqués par des facteurs environnementaux confondants. Dans son ensemble, cette thèse illustre que, contrairement aux idées reçues, les vecteurs de malaria aviaire ne sont pas toujours permissifs avec leurs parasites. L'environnement apparaît aussi comme un facteur déterminant dans la réponse des vecteurs face à la menace d'infection malarique. Cela pourrait fortement affecter l'épidémiologie de la malaria aviaire.

Gender and Security Sector Reform: Gendering Differently?

Recent efforts to implement gender mainstreaming in the field of security sector reform have resulted in an international policy discourse on gender and security sector reform (GSSR). Critics have challenged GSSR for its focus on 'adding women' and its failure to be transformative. This article contests this assessment, demonstrating that GSSR is not only about 'adding women', but also, importantly, about 'gendering men differently' and has important albeit problematic transformative implications. Drawing on poststructuralist and postcolonial feminist theory, I propose a critical reading of GSSR policy discourse in order to analyse its built-in logics, tensions and implications. I argue that this discourse establishes a powerful 'grid of intelligibility' that draws on gendered and racialized dualisms to normalize certain forms of subjectivity while rendering invisible and marginalizing others, and contributing to reproduce certain forms of normativity and hierarchy. Revealing such processes of discursive in/exclusion and marginalized subjectivities can serve as a starting point to challenge and transform GSSR practice and identify sites of contestation.