Affichage des résultats 741 à 760 sur 1226 au total
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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Chemical risk assessment is, to date, predominantly focussed on “single species – single compound” toxicity testing of short-lived species. This approach cannot practically be used to assess all possible wildlife-pollutant combinations, and particularly falls short when assessing risk for species with life histories that do not suit laboratory experimentation. Long-lived species such as sea turtles and crocodiles are one example. In this seminar, we will present ongoing work on the exposure and accumulation of organic pollutants in sea turtles and crocodiles, and the application of computer models that integrate ecology, physiology and ecotoxicology as a basis for risk assessment for such long-lived species.
The distributions of the Trans-Himalayan large herbivores are fragmented, engendering a spatial heterogeneity in their species-richness. We capitalised on this natural-experiment situation to understand the niche dynamics of herbivores in relation to the number of sympatric species. We used the blue sheep Pseudois nayaur, a relatively widely distributed mountain ungulate, as a model species to address the issue. We selected three discrete valleys in three protected areas with almost similar environmental features but varying wild ungulate species richness, and studied the species' diet and habitat utilization in them. Habitat variables were observed in the field and microhistological faecal analysis was carried out to determine the habitat and diet widths of the animal in the three areas with different ungulate species richness. The habitat- and diet-niche widths were determined using the Shannon's H' Index. The results showed that habitat width of blue sheep has a negative relationship with the number of sympatric species. However, contrary to our expectation, there was a hump-shaped relationship between blue sheep's diet width and the sympatric species richness, with the diet width being narrower in areas of allopatry as well as in areas with greater number of sympatric species, and the widest diet spectrum in areas with moderate species richness. We suspect that the narrow diet width in allopatry is out of choice, while it is out of necessity in areas with greater number of sympatric species due to resource partitioning. We suggest that interactions with sympatric species lead to niche adjustment of mountain ungulates, and underscore the importance of including biotic interactions in species distribution models, which have often been neglected.
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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.
Deux équipes présentent des résultats ou des questions qui leurs sont propres afin de favoriser de nouvelles discussions au sein du laboratoire.
Deux équipes présentent des résultats ou des questions qui leurs sont propres afin de favoriser de nouvelles discussions au sein du laboratoire.
Deux équipes présentent des résultats ou des questions qui leurs sont propres afin de favoriser de nouvelles discussions au sein du laboratoire.«Telling metabolic stories to explore metabolomics data: A case study on the Yeast response to cadmium exposure» Cecilia Coimbra Klein et«Sénescence et sélection sexuelle chez les populations naturelles de vertébrés» Jean-Francois Lemaitre
Deux équipes présentent des résultats ou des questions qui leurs sont propres afin de favoriser de nouvelles discussions au sein du laboratoire.
Deux équipes présentent des résultats ou des questions qui leurs sont propres afin de favoriser de nouvelles discussions au sein du laboratoire.
Deux équipes présentent des résultats ou des questions qui leurs sont propres afin de favoriser de nouvelles discussions au sein du laboratoire.
Papers evaluating measures of explained variation, or similar indices, invariably use independence from censoring as the most important criterion. And they invariably end up suggesting that some measures meet this criterion, and some don't, leading to a conclusion that the first are better than the second. As a consequence, users are offered measures that cannot be used with time-dependant covariates and effects, not to mention extensions to repeated events or multi state models. We explain in this paper that the above mentioned criterion is of no use in studying such measures, since it simply favours those that make an implicit assumption of a model being valid everywhere. Measures not making such an assumption are disqualified, even though they are better in every other respect. We show that if these, allegedly inferior, measures are allowed to make the same assumption, they are easily corrected to satisfy the `independent-from-censoring' criterion. Even better, it is enough to make such an assumption only for the times greater than the last observed failure time $tau$. Which, in contrast with the `preferred' measures, makes it possible to use all the modelling flexibility up-to $tau$, and assume whatever one wants after $tau$. As a consequence, we claim that measures being proffered as better in the existing reviews, are exactly those that are inferior
Research in the lab focuses on the evolution and ecology of associations between hosts (mostly insects!) and the organisms that infect them, from parasites and pathogens to obligate mutualists, from nematodes and parasitoids to inherited bacterial endosymbionts. Interests also include selfish genetic elements, disease ecology and evolution, unusual genetic systems and life histories, and insects in general.https://perlmanlab.weebly.comet un article récent décrivant un remarquable système de distorsion du sexe et autres bizarreries génétiques chez les « booklice » :https://www.sciencedirect.com/science/article/pii/S0960982218313642
In the absence of a clear understanding of its genetic basis, Cytoplasmic Incompatibility (CI) has so far been conceptualized using a simple toxin-antitoxin model. Under this model, a symbiont's ³compatibility type² is determined by the specific interaction between two components: a modification factor (mod, expressed in sperm) and a rescue factor (resc, expressed in the eggs). Here we confront this model to a well studied, complex and puzzling CI study system: the mosquito Culex pipiens. We show that a more elaborate model is required to account for the observed pattern, including multiple mod and resc genes, and possibly quantitative variation in gene products. We develop such a model and fit its parameters to the data using a parsimony approach. We thereby produce explicit predictions with regards to the genetic architecture of CI; namely, we infer that at least five mod / resc pairs are required to explain the data. These predictions provide a starting point for future genetic and genomic analyses of CI and will hopefully contribute to the decryption of its molecular basis.