Institut de Biologie de l'École Normale Supérieure ENS . CNRS UMR8197 . Inserm U1024 Directeur : Pierre Paoletti

Experimental Evolutionary Genetics

Background

Outstanding problems in evolutionary genetics include: 1) understanding how pleiotropy of gene function are integrated across levels of biological organization; 2) understanding how associations among alleles within and between loci depend on mutation, segregation and recombination; 3) understanding how inbreeding and assortative mating impinges upon the genetic structure of a population. Our research aims to give insights to these problems in the context of adaptation to novel environments. The model organism used is the nematode Caenorhabditis elegans, which has been developed for experimental evolution by creating populations with standing genetic diversity and alternative reproduction systems. We have further developed a large recombinant inbred line panel for mapping quantitative trait loci.

Research highlights

One of the topics investigated is the origin and evolution of reproduction systems. As expected from theory, we have found that selfing hermaphrodites can invade outcrossing populations when there is reproductive assurance and little inbreeding depression. Male reproductive success, however, can determine rates of transitions from outcrossing to selfing and the extent to which selfing is maintained. This may be because C. elegans hermaphrodites are constrained in their allocation of developmental resources towards male, female and “selfing” functions but also because of the evolution of sexual conflicts. Populations evolving under partial selfing appear to gain the short-term benefits of selfing, in purging deleterious recessive alleles, but also the long-term benefits of outcrossing, in maintaining genetic diversity that may important for future adaptation.

Another topic we investigate is the evolution of phenotypic plasticity. Whenever individuals have information about the environment they will reproduce during develop, then within-generation phenotypic plasticity is expected to evolve. Otherwise, transgenerational phenotypic plasticity and within- and between-generation bet-hedging strategies will be favored by natural selection. We study the quantitative and population genetics of adaptation to changing and fluctuating environments, by testing for 1) the evolution of maternal effect strategies; 2) within- and between-individual evolution of locomotion bias; and 3) the impact of segregation and recombination on the probability of extinction.

One last venue of research is to describe the genetic architecture of phenotypes at several levels of organization. GxE, polygenicity and epistasis seem to dominate the genetics of fitness-related traits, but it is unclear if the same is true for locomotion or gene-expression traits unrelated to fitness. High-throughput phenotyping of locomotion and gene-expression also allows us to test for pleiotropy, dominance and epistatic effects.