CONGRATULATIONS TO OUR NEW DOCTOR, Sandrine ADIBA who graduated with the Very honorable grade !
Sandrine ADIBA presented her PhD defense on December 13th 2010 in the Auditorium de Jussieu UPMC.
PhD title : "Natural selection and genetic drift effects on neutral polymorphism"
Members of the Jury :
Pierre Cosson, Genève, rapporteur
Christine Paillard, Brest, rapporteur
Delphine Sicard, Le moulon, examinateur
Amaury Lambert, UPMC, examinateur
Minus van Baalen, UPMC/ENS, directeur de thèse
Frantz Depaulis, ENS, co-directeur de thèse
Diversity is essential for all living organisms, it provides the basis for the species evolvability and their ability to adapt to environmental variations. Determining the factors contributing at the origin, the maintenance of the genetic variance observed remain central and fundamental research issues. The aim of this study was to understand evolutionary factors maintaining neutral polymorphism. The influence of the natural selection and genetic drift processes being complex, we developed complementary experimental and theoretical approaches to disentangle selective and drift contribution.
Using the biological model Escherichia coli and Dictyostelium discoideum, we first studied the natural variability of interactions between the two species. In the second part, we tested for bacterial traits involved in this natural variability. We found that bacteria carrying virulence genes were resistant to the amoeba grazing. This result was in agreement with the coincidental evolution hypothesis of virulence factors.
We then focus on population genetics aspects of our biological system. In our coevolution experiments, we followed bacterial allele frequency variations during 300 bacterial generations and in four environmental conditions: with or without biotic factor and with or without spatial structure. Our results did not depart from genetic drift predictions. The theoretical model developed addressed demographic stochasticity effects on neutral allele fixation probability and time to fixation. We found that the fixation probability and the time to fixation were affected by the demographic stochasticity compared to a model with a population of constant size (Moran model).
Key words: natural selection, genetic drift, polymorphism, coevolution, virulence, bacteria, amoeba, fixation.
Ecole doctorale : Frontières du Vivant ED474 Liliane Bettencourt