Recherche avancée
Affichage des résultats 61 à 80 sur 1547 au total
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Pitfalls and uses of lab studies in predicting ecological effects of chemicals in the field - my research career as a backflip artist
It has long been argued that single species laboratory tests do not necessary predict the ecological effects of chemicals in the field. By ecological effects is used to mean effects on populations, communities and ecosystems. However ecotoxicologists have continued to use single species laboratory tests. My short research career has involved a number of change in direction - or backflips - in my attitude to these tests and I will illustrate this with examples of the effect of increased salinity on stream invertebrates, insecticides and fungicides on stream invertebrates and herbicides on benthic diatoms. I will discuss how such simple test systems combined with more complicated test systems can potential serve as models to test hypothesises as to how chemical stressors effect ecological systems.
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Wolf Re-Introduction in the Northern Rockies, USA: From Population and Predation Trends to Policy and Economics
Conflicts between wolves and livestock have continued to escalate since wolf re-introduction in the Northern Rockies, USA. We will provide an overview wolf re-introduction, including trends in populations and predation rates. We will also review how wolves have (or have not) affected livestock management practices and ranch profitability. We will then review the legal framework for wolf control in Wyoming, including predation compensation policies. Compensation policies have attempted to reduce the impact of wolf-livestock conflicts by compensating producers for lost livestock. Compensation schemes, however, focus only on direct predation (i.e., confirmed losses) despite a growing body of evidence that predation pressure also have indirect effects on prey, particularly domesticated livestock (e.g., slower weight gain, higher disease rates, or lower reproduction rates). We will then discuss our research, which uses an economic model of livestock production to estimate the economic impact of both direct and indirect effects of wolf predation. Our results suggest that short-run (i.e., year-to-year) financial impacts of wolf indirect effects may be as large as or larger than the direct effects. Including indirect effects implies that the compensation ratio (i.e., number of calves compensated per confirmed depredation) necessary to fully offset the financial impacts of wolves would need to be two to three times larger than current 7:1 compensation ratio used in Wyoming.
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Le système immunitaire des invertébrés est-il "spécifique" ou "non-spécifique"?
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Modelling competition and dispersal in a statistical phylogeographic framework
Competition between organisms influences the processes governing the colonization of new habitats. As a consequence, species or populations arriving first at a suitable location may prevent secondary colonization. While adaptation to environmental variables (e.g., temperature, altitude, etc.) is essential, the presence or absence of certain species at a particular location often depends on whether or not competing species co-occur. For example, competition is thought to play an important role in structuring mammalian communities assembly. It can also explain spatial patterns of low genetic diversity following rapid colonization events or the ``progression rule'' displayed by phylogenies of species found on archipelagos. Despite the potential of competition to maintain populations in isolation, past quantitative analyses have largely ignored it because of the difficulty in designing adequate methods for assessing its impact. We present here a new model that integrates competition and dispersal into a Bayesian phylogeographic framework. Extensive simulations and analysis of real data show that our approach clearly outperforms the traditional Mantel test for detecting correlation between genetic and geographic distances. But most importantly, we demonstrate that competition can be detected with high sensitivity and specificity from the phylogenetic analysis of genetic variation in space.Joint work with L. Ranjard, D. Welch and M. Paturel.
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A quantitative genetic signature of senescenece in plants
The evolution of senescence (the physiological decline of organisms with age) poses an apparent paradox because it represents a failure of natural selection to increase the survival and reproductive performance of organisms. The paradox can be resolved if natural selection becomes less effective with age, because the death of postreproductive individuals should have diminished effects on Darwinian fitness. A substantial body of empirical work is consistent with this prediction for animals. However, such evidence is still scarce in plants. I will discuss the plausible reasons why the genetic basis of senescence in plants was not studied from an evolutionary perspective in the past. I will also present our experimental results on the quantitative genetic basis of senescence in the short-lived perennial plant Silene latifolia and their contribution to our understanding of the evolution of senescence in plants.
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Heredity in evolution & evolution of heredity
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The genomics of adaptation in threespine sticklebacks
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Importance des microbiontes intestinaux dans les interactions socio-sexuelles
Les interactions qu'elles soient sociales ou sexuelles régissent un grand nombre de comportements et stratégies développés par les animaux pour maximiser leur valeur adaptative. Qu'elles soient conflictuelles ou symbiotiques, elles sont un puissant générateur d'évolution. Je suis une biologiste évolutive intéressée par les conflits sociaux et sexuels et comment ceux-ci sont résolus. Mes travaux de thèse et de premier post-doctorat ont porté sur l'étude phénotypique, génétique et chimique de la reconnaissance de parentèle chez les insectes parasitoïdes. Lors d'un second post-doctorat, je me suis intéressée à l'évolution des systèmes de reproduction (monoandrie et polyandrie) chez les drosophiles : conflits mâles/femelles, reconnaissance du partenaire sexuel et investissement reproducteur. A l'heure actuelle, j'ai intégré un troisième niveau dans mes recherches : les microbiontes intestinaux et comment les variations des communautés de microbiontes influencent les systèmes de reconnaissance et les interactions sexuelles chez les drosophiles
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Utilisation de phylogénies d'haplotypes pour l'identification de facteurs génétiques de risque
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A Tale of Two Insect Sterilizing Viruses
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Finding new partners in signaling pathways with message-passing algorithms
After a brief introduction to algorithmic complexity and some examples of graph problems in biology, I will present the formalism and algorithm we developed for the large-scale reconstruction of a signalling network, based on protein-protein interaction and transcriptomics data. The model we developed in consisted in modeling this reconstruction as a combinatorial optimization problem called the "Prize-collecting Steiner tree problem", and our algorithm, was applied to the reconstruction of the pheromone pathway in S. cerevisiae, with results that we were able to verify experimentally.
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Endosymbiosis in trypanosomatid protozoa: an eternal love affair
Some trypanosomatids harbor a symbiotic bacterium, which maintains a close association with the host, constituting an excellent model to study organelle origin and cellular evolution. Molecular data show that all endosymbiont containing trypanosomatids are grouped together in a single phylogenetic branch. Endosymbionts of different species are similar, being classified in the beta division of Proteobacteria, thus suggesting that a single evolutionary event gave rise to the symbiosis in the Trypanosomatidae family. The bacterium is enclosed by two unit membranes and presents a reduced peptidoglycan layer, which is essential for cell division and morphological maintenance. Regarding the protein composition, the number of intramembrane particles in the endosymbiont envelope is similar to that described for Gram-negative bacteria. Lipid analyses of purified endosymbionts show absence of sterols and indicate phosphatidylcholine as a major component of the envelope, as described in other intracellular bacteria. The endosymbiont promotes ultrastructural and physico-chemical alterations in the trypanosomatid and its presence influences the protozoan interaction with the insect host and mammalian cells. Symbiont-containing trypanosomatids are able to infect and to replicate inside fibroblasts and macrophages, whose microbicidal activity was deactivated by HIV-1 infection. The symbiosis in trypanosomatids is characterized by intensive metabolic exchanges; the bacterium contains enzymes and metabolic precursors that complete essential biosynthetic pathways of the protozoan. Conversely, the symbiont is capable of obtaining part of the required energetic molecules from the host glycosomes. Taken together, data suggest that the endosymbiont in trypanosomatids represents an intermediate evolutionary step between bacteria and eukaryotic cell organelles..
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Coûts et bénéfices dans les modèles mutualistes : le problème des marchés biologiques
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Modélisation de l'effet du dépistage du cancer du sein sur la mortalité à partir de données françaises: retour d'expérience
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multispecies coalescent and its use in population genetic analysis of genomic sequence data
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Comparing gene expression between Drosophila species: sex, embryos and spotted wings
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Early environmental effects on adult performance and the rate of senescence
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"Widespread signals of convergent adaptation to high altitude in Asia and america"
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Emergence of global patterns in bacterial growth: from single cells to communities
Understanding how phenomenological behaviors observed in biological systems emerge from molecular interactions of many individual unit and how these interactions shape the response of living systems to a changing environment are challenging questions which lie at the interface between multiple disciplines. In this talk I will draw an example from the human gut microbiome, the full consortium of microbes living in association with the human gut. Recent developments in DNA sequencing have made it possible to monitor how the compositions of microbial species change in time. Analysis of healthy adults under antibiotic treatment showed that the gut microbiota could take several weeks to recover after treatment cessation. This suggests that the combination of inter-species and host-microbe interactions and external perturbations could lead to hysteresis phenomena. We investigate this possibility and propose an out of equilibrium stochastic model able to explain this phenomenon. Our study reveals the importance of noise-activated dynamics in the recovery from antibiotic-perturbed states.
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Apport des modèles mécanistes pour l'évaluation des interventions dans l'infection par le virus de l'immunodéficience humaine (VIH)
Les modèles mathématiques basés sur des systèmes d'équations différentielles ont permis des avancées majeures dans l'infection par le VIH au milieu des années 1990 notamment en quantifiant la production et la disparition du virus et des cellules infectées. Depuis des progrès ont été réalisés dans l'estimation des paramètres de ce type de modèle. Concomitamment, la prise en charge des patients infectés par le VIH avec des traitements antirétroviraux et des immuno-interventions est en constante amélioration. Nous présenterons les nouveaux développements et les applications en cours notamment pour l'optimisation des traitements antirétroviraux et le développement clinique des immuno-interventions dont l'interleukine 7.