Institut de Mathématiques de Toulouse

Les événements de la journée


2 événements


  • Géométrie complexe

    Jeudi 6 décembre 10:30-11:30 - Stéphane Lamy - IMT

    Morphismes signature sur les groupes de Cremona de rang supérieur

    Résumé : (collaboration avec J. Blanc et S. Zimmermann) Le groupe de Cremona de rang n est le groupe des transformations birationnelles de l’espace projectif complexe de dimension n. En contraste avec le cas des surfaces, je décrirai comment obtenir de nombreux morphismes depuis ce groupe vers Z/2 dès que le rang est au moins 3. Je donnerai une idée des ingrédients de la preuve qui repose sur la théorie des modèles minimaux, via les travaux de A-S. Kaloghiros d’une part (relations dans le programme de Sarkisov), et ceux de C. Birkar d’autre part (résolution de la conjecture BAB sur la finitude des variétés Fano).

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  • Séminaire Mathématiques pour la biologie

    Jeudi 6 décembre 13:30-14:30 - Luis-Miguel Chevin - Centre d'Ecologie Fonctionnelle et Evolutive (Montpellier)

    "Evolution, phenotypic plasticity, and population growth in randomly changing environments"

    Résumé : Most natural environments vary randomly, beyond any trend such as global warming. These stochastic environmental fluctuations often are faster, and of larger magnitude, than environmental trends, making them one the biggest challenges that living organisms have to face in the wild. Furthermore the patterns of these fluctuations are themselves altered by global change. I will present results from our recent and ongoing research on the impacts of stochastic environmental fluctuations on the eco-evolutionary dynamics of populations. I will start with theoretical results about the interplay between phenotypic plasticity, adaptive evolution, and population growth/extinction risk in stochastic environments. One of the key predictions concerns the distribution of population size and extinction risk caused by a randomly fluctuating optimum for a polygenic, quantitative trait. This theoretical work highlights the prominent role of temporal autocorrelation in the environment, which determines the time scale of environmental predictability. I will then show how we can try and address similar questions through experimental evolution with the unicellular microalgae Dunaliella salina. This species is able to tolerate extremely high salinity (up to NaCl saturation) through plastic physiological mechanisms. Its natural environment includes shallow ponds, where salinity varies through time in connection to climatic conditions (precipitation, evaporation). We experimentally expose a large number of Dunaliella populations to random fluctuations in salinity with different levels of autocorrelation, and track their population sizes, tolerance curves, phenotypic plasticity, and (epi)genetic variation. Our results show some patterns consistent with theory, as well as novel, unexpected findings.

    Lieu : salle MIP, 1er étage bat 1R3

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