Tangled Bank Seminar
Tangled Bank Seminar by Sylvain Glémin (University of Rennes) on "Dynamics of mating system evolution and its genomic consequences in wheat relatives (Aegilops/Triticum)" and Johanna Leppälä (Umeå University) on "Postzygotic reproductive isolation at different levels of genetic divergence".
Dynamics of mating system evolution and its genomic consequences in wheat relatives (Aegilops/Triticum)
ECOBIO Lab, CNRS, University of Rennes
The evolution of selfing from outcrossing is one of the most frequent transitions in flowering plants. Although potentially ecologically successful on the short term, selfing is supposed to be an evolutionary dead-end on the long term because of its negative genetic consequences. Theory predicts that selfing increases genetic drift and genetic linkage, reducing genetic diversity and the efficacy of selection. In addition, selfing species are more prone to extinction/recolonization dynamics, which increases further genetic drift. Selfing species are thus supposed to have a reduced adaptive potential and to accumulate weakly deleterious mutations. In several species, genomic signatures of the negative effects of selfing have been found. However, the pace at which selfing impacts genome evolution and the relative roles of demographic versus linked selection effects remain unclear. To address these questions we sequenced the transcriptome of two to 20 individuals for all 13 diploid species of the Aegilops/Triticum genus (wheat relatives) that presents a wide range of mating systems, from self-incompatible to highly selfing species. Phylogenomic analyses revealed a complex history with past hybridizations and pointed to a self-incompatible ancestor with several evolutions to different degrees of selfing. We found a strong and continuous effect of mating system on patterns of polymorphism and selection efficacy. We also used recombination maps to estimate the effect of linked selection on patterns of polymorphism. Our results showed that both linked selection and demography played a role. Finally, the comparison of polymorphism and divergence patterns suggested a (very) recent origin of selfing habit, hence a potentially rapid turnover of selfing species, raising the question of the underlying causes of high extinction rates in selfers.
I’m an evolutionary biologist interested in the evolution of life-history traits, especially reproductive systems, and their genomic consequences. I use population genetics modelling and sequence data analyses approaches (phylogeny, population genomics) on several groups of plants and animals.
Postzygotic reproductive isolation at different levels of genetic divergence
Department of Ecology and Environmental Science
Umeå University, Sweden
For new species to arise, reproductive isolation has to develop between diverging populations of an existing species, to the point where gene flow ceases. To identify barriers that are involved in speciation process itself, rather than barriers that have evolved after reproductive isolation is complete, barriers need to be studied already within species. The only irreversible barrier to gene flow is intrinsic postzygotic isolation: inviability or sterility of hybrid offspring independent of their environment. Therefore, we have focused our study to mostly intrinsic postzygotic reproductive barriers between outcrossing Arabidopsis species, A. arenosa, A. halleri and A. lyrata, as well as between populations of A. lyrata. The project has identified postzygotic reproductive barriers between different levels of genetic divergence and compared strength of reproductive isolation and genetic distance. We found that within species, the first barrier that evolves is hybrid male fertility, whereas between species a strong seed developmental barrier exists, in addition to hybrid male fertility reduction. The correlation between genetic distance and the strength of the different postzygotic reproductive barriers is variable. As reduction of hybrid male fertility was identified to be the first barrier emerging already within species, additional experiments have been conducted to understand mechanism of failure in hybrid pollen development. As hybrid dysfunction is assumed to result from negative interactions between genes, so called Dobzhansky-Muller incompatibilities, quantitative trait locus (QTL) mapping experiments have been conducted between the closest and most distant pairs of populations/species of the study. Ultimate aim is to understand which forces drive development of reproductive isolation by analysis of DNA sequences of the identified genes.
I am an evolutionary geneticist interested in development of reproductive barriers during speciation. My research has focused on reduction of hybrid pollen fertility as it is one of the first barriers to emerge already between populations of outcrossing Arabidopsis. In addition, I am interested in evolution of cytoplasmic male sterility (CMS) and correlation between ecological divergence and reproductive isolation. In my on-going work, I also wish to explore genetics of clonal growth and how does it affect survival and sexual reproduction.