Recherche avancée
Affichage des résultats 21 à 40 sur 1312 au total
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A Diversity of Conservation Dilemmas with Demographic Solutions
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Non-random inbreeding with respect to phenotype biases estimates of inbreeding depression
Animals often show substantial variation in dispersal behaviour and resident individuals are more likely to inbreed. At least part of the variation in dispersal behaviour may be phenotype-dependent, potentially leading to non-random inbreeding with respect to a particular phenotype. Here we show that non-random inbreeding in structured populations can have important implications for estimates of the effect of inbreeding (inbreeding depression). We do this using a long-term individual-based data set for a population of Eurasian dippers (Cinclus cinclus), a bird species living exclusively along streams and rivers. Extensive pedigree data show that close inbreeding is relatively common in this species. However, inbreeding birds are not a random subsample of the population but are smaller on average. Given the significant heritability of body size, inbred individuals are smaller due to both additive genetic and inbreeding effects. Importantly, the effects of inbreeding are overestimated if additive genetic effects are not accounted for. We show how estimating the effects of inbreeding within an animal model framework removes this bias, highlighting the importance of integrating quantitative genetics and animal behaviour when measuring the effects of inbreeding in the wild.
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Nouvelle formule de séminaires internes
Deux équipes présentent des résultats ou des questions qui leurs sont propres afin de favoriser de nouvelles discussions au sein du laboratoire.
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Dating phylogenies with incompletely preserved fossils
In recent years, evolutionary biologists have become increasingly interested in dating phylogenies. This is usually accomplished by calibrating interior nodes in the tree against the fossil record, an ad hoc approach with a considerable risk of mirepresenting the fossil information. I discuss an alternative approach, in which fossils are included along with extant taxa in a Bayesian total-evidence analysis. By coding morphological characters for both extant and extinct taxa, it is possible to explicitly integrate over the uncertainty in the placement of individual fossils, while using their ages to date the tree. In such a total-evidence analysis of the early radiation of the Hymenoptera (wasps, ants and bees), we showed that fossils contributed significantly to the estimation of divergence times, despite considerable uncertainty in their placement. The posterior distributions on divergence times were less sensitive to prior assumptions and tended to be more precise than in standard node dating. The total-evidence analysis also showed that four of the seven Hymenoptera calibration points used in node dating were based on erroneous or doubtful assumptions about fossil placement. One of the most important advantages of total-evidence dating over node dating is that it provides a better platform for further modeling of important aspects, such as the fossilization process and the sampling of extinct and extant taxa. We are currently exploring such extensions of the basic model.
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Heteroplasmy in human mitochondrial DNA: characteristics, transmission, and tissue-specificity.
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Choanoflagellates, animal evolution, and the role of microbial eukaryotes in global ocean ecology
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Nouvelle formule de séminaires internes
Deux équipes présentent des résultats ou des questions qui leurs sont propres afin de favoriser de nouvelles discussions au sein du laboratoire.
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Network-based approaches for the spatial spreading of communicable diseases
Mathematical and computational approaches based on network theory and complex system dynamics are increasingly showing their potential to address open problems on the spreading of communicable diseases on a spatially structured and heterogeneous human population. I will review my recent research work in this direction presenting studies on both fundamental problems and specific epidemic events. On the theoretical side, I will show how the mathematical formalism of reaction-diffusion processes and metapopulation networks can shed light on the impact of the complex features characterising individuals' mobility patterns on the propagation of emerging infections. How do traveling flows, journey duration and difference in travel frequency impact local mixing and transmission of influenza-like diseases? How do the mobility of individuals and their distribution in space determine dominance/co-dominance regimes in case of multiple interacting strains of the same pathogen? Besides these fundamental research questions, the same formalism can form the basis of data-driven computational models for the spatial spreading of real infection events. In case of an epidemic emergency, such models represent valuable tools for estimating in real time the transmission potential of the disease, providing assessment of the epidemic situation and projections of possible unfolding scenarios. I will discuss the two paradigmatic examples of the 2009 H1N1 pandemic and of the MERS-CoV outbreak.
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The Molecular Transformation of Evolutionary Biology.
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"Microevolution in Island Birds: Insights from white-eye colonisations of southwest Pacific islands »
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Apports de l'écotoxicologie dans la gestion de la qualité des eaux et des milieux aquatiques
Evaluer le bon état des masses d'eau, évaluer les impacts des activités humaines, détecter les polluants émergents à de très faibles doses, et évaluer leurs risques sur le long terme, etc., pour faire face à ces défis, de nouvelles connaissances et des technologies innovantes sont nécessaires. La gestion durable de la ressource en eau et des milieux aquatiques impose de s'appuyer sur des recherches finalisées de haut niveau. La loi sur l'eau et les milieux aquatiques (LEMA) a confié à l'Onema une mission explicite afin de renforcer l'utilisation des connaissances scientifiques et techniques pour éclairer la conception, la mise en œuvre et le suivi des politiques publiques dans le domaine de l'eau par une expertise de haut niveau. L'Onema conduit cette mission avec ses moyens propres et en construisant des partenariats avec les organismes nationaux de recherche. A travers plusieurs exemples de projets de recherche ou d'études menés dans le cadre des conventions partenariales de l'Onema, nous verrons dans quelle mesure les résultats de la recherche appliquée le domaine de l'écotoxicologie peuvent aider à la mise en œuvre de la directive cadre sur l'eau, notamment par le soutien à des travaux permettant de mieux comprendre les phénomènes de transfert des contaminants organiques hydrophobes dans les réseaux trophiques, le soutien à des travaux sur les effets des substances chimiques sur les écosystèmes soumis à des expositions chroniques et multiples pour en tirer des marqueurs d'effets utilisables sur le terrain, etc.
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Dynamic modelling of HPV transmission and cervical cancer natural history : implications for public health interventions
In the last three decades, the appreciation of the role of infections in cancer aetiology has greatly expanded. Among the 13 million new cancer cases that occurred worldwide in 2008, around 2 million (16%) were attributable to infections. Cervical cancer is a major example of infection-related cancer. The uncovering of a causal relationship between carcinogenic HPV infections and cervical cancer is shifting public heath intervention from cancer control to infection control paradigm. Worldwide, vaccination and detection of infected individuals play a increasingly crucial role in cervical cancer control. In support of this paradigm shift, the use of infection transmission models has entered the field of infection-related cancer epidemiology. These models are useful to understand the infection transmission processes, to estimate the key parameters that govern the spread of infection, and to project the potential impact of different preventive measures. This presentation, focused on HPV transmission and cervical cancer natural history, aims to concisely illustrate the main principles of transmission dynamics, the basic structure of infection transmission models, and their use in combination with empirical data
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De la délimitation moléculaire des espèces à l'étude de leur génome : l'hétérozygotie dans tous ses états
La co-occurrence dans un même individu de deux demi-génomes semblables mais différents (hétérozygotie) est une caractéristique générale des organismes diploïdes qui pose de gros problèmes techniques lors du séquençage : double pics, échec de l'assemblage des données,... En dépit de ces difficultés apparentes, les séquences d'organismes hétérozygotes apportent une mine d'informations très utiles à la délimitation des espèces et à l'analyse de leurs génomes. Après avoir montré comment reconstruire les allèles d'individus hétérozygotes par séquençage direct, sans cloner, j'introduirai une approche nouvelle pour la délimitation moléculaire des espèces basée sur l'analyse de l'hétérozygotie : cette approche, appelée "haplowebs", ne repose pas sur le critère de monophylie et surpasse pour cette raison les méthodes actuellement utilisées en barcoding (GMYC, ABGD,...). Dans la deuxième partie de mon exposé, je montrerai comment l'analyse récente de l'hétérozygotie d'un rotifère bdelloïde a permis de prouver son asexualité et de mettre en évidence l'importance des conversions géniques et des transferts horizontaux dans l'évolution de son génome.
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GENOMIC APPROACHES TO UNDERSTANDING STRUCTURAL COLOUR IN PLANTS
While we often think of colour as synonymous with pigment, many of the most spectacular colours in nature are caused by differential interference of different wavelengths of light as they are scattered by nano structured surface features. There are many famous examples of such structural colour in animals, such as the iridescent scales on morpho butterflies and peacock feathers, but structural colour is also common throughout the plant kingdom, from algae to numerous groups of flowering plants. Structural colour in flowers is thought to aid in pollinator attraction, but it is also common in leaves, where its functional significance is not well understood. We are investigating the genetic basis and functional significance of structural colour in a variety of plant species with a range of approaches including genomics. We are working with genome-wide transcription data for two distinct lineages of iridescent plants: the living fossil Selaginella, which produces blue iridescence in the l eaves and the flowering plant Spiloxene which has iridescent flowers. We have obtained RNAseq data for four different tissues for each of four Selaginella species exhibiting a range of iridescence intensities and for Spiloxene capensis. For each species, de novo transcriptome assemblies were produced and used for differential gene expression analysis. Between 14,000 and 26,000 gene families were found for each species, with between 150 and 250 gene families exhibiting significant differences in gene expression across the four tissues examined. We have identified several genes that code for cell wall modifying enzymes that are differentially expressed only in iridescent species as candidates for the generation of cell wall layering responsible for iridescence in Selaginella. We are also investigating differentially expressed photosynthesis genes to test the hypotheses that iridescence may play a role in increasing photosynthetic efficiency or in photoprotection. We hope that t he use of functional genomics, coupled with detailed anatomical and developmental studies and optical modelling that are ongoing in our lab, will help to unravel the evolutionary origins and ecological roles of plant structural colour.
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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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