Evolution, Ecologie et Paléontologie
( Evo-Eco-Paléo )

Unité Mixte de Recherche UMR 8198





Diversity, measured by the number of currently existing species, is the result of a dynamic that combines processes generating new species (speciation events) and others that dwindle the number of taxa (extinctions). Contemporary extinction rates, as measured by the reduction in the number of species or by the ongoing reduction in population sizes, are found to be extremely high in both plants and animals, presumably as a consequence of ongoing global changes. Although the diversity of factors responsible for extinctions are beginning to be well understood, our knowledge on the mechanisms of speciation is less consolidated. Developing a detailed insight into the speciation process will require us to understand the various factors that cause reproductive isolation, i.e. the evolution of the so-called species barriers. Of particular importance are the specific barriers occurring at the origin of the reproductive isolation between diverging lineages, as their effects on hybrid viability or hybrid fertility determine the possibility of hybridization between diversifying lineages. We aim to study this process at various levels. First at the genomic level, by identifying some genomic factors explaining the local density in speciation genes. Some of the large chromosomal patterns are already well-identified: for instance, sex chromosomes strongly concentrate genes acting as barriers between species. Second, at the geographical level as isolation of populations will tend to facilitate the fixation of these species barriers, whereas migration may slow down differentiation and reverse incomplete species barriers. Secondary contact between two formerly isolated lineages with semi-permeable barriers may also increase the strength of isolation in hybrid zones by the reinforcement of reproductive isolation. Third, at the environmental level, as adaptive walks of populations in similar or different niches are expected to lead to the accumulation of mutations of different effects on the hybrid fitness. The main objectives of this new speciation group are to explore the contributions of genomic, geographic and environmental factors on the emergence of new species. To answer these questions on different evolutionary time scales, the group gathers researchers in paleontology, genetics, genomics, bioinformatics, phylogeny and quantitative morphology.

















Ongoing projects.

Use of allelic and phylogenetic diversity at the self-incompatibility locus of Brassicaceae as a marker of bottlenecks associated with speciation. X. Vekemans, C. Poux and C Roux.

In this project we compare allelic diversity and phylogenetic relationships among alleles at the self-incompatibility locus  within and between related species in order to identify possible bottlenecks associated with speciation events. This approach, using the phenomenon of increased conservation of ancestral polymorphism under the effect of strong balancing selection  at the self-incompatibility locus (cf. Castric et al. Plos Genetics, 2008) is complementary and will be compared to the historical demographic inference approach based on neutral polymorphism at the genome level.