Genome-wide analysis of speciation and adaptation in closely related plant species

This project is devoted to one of the most enduring questions in biology / how do species form. The most recent development in our understanding of the speciation process, the genic view of speciation, suggests that different genes may have different capacities to cross the species boundaries and introgress into closely related species. The genes under positive selection are expected to spread across many closely related species even if hybridization of such species is very rare. Such 'sharing' of adaptive alleles by several closely related species may significantly accelerate the adaptation process. On the other hand, genes under diversifying selection (i.e. different alleles are advantageous in different species) are not expected to introgress and may result in formation of so called 'genomic speciation islands' / regions of the genome that are closely linked to genes under diversifying selection and that do not introgress between species. Thus, under the genic speciation model the species boundaries are regarded as semi-permeable or 'porous'. However, the generality of such a view of speciation is not clear, as we do not know how 'porous' the species boundaries are. Using the latest genomic sequencing technology we will study the genetic basis of differences between two closely related plant species, Silene latifolia and S. dioica (Caryophillaceae). These species are widely distributed in Europe; their ranges broadly overlap and they are known to often form hybrids in areas of contact. However, the two species remain distinct despite the fact that they exchange genes. This project will specifically focus on the maintenance of species boundaries in face of on-going gene flow between S. latifolia and S. dioica. We will use a high-throughput genomic sequencer to determine the protein-encoding sequence in 15 individuals of each species sampled from wild populations. This dataset will include a significant proportion of genes in the genome, which will allow us to analyse what proportion of genes is undergoing introgression and what proportion stays separate between the two species. We will also identify genes under positive selection in either or both species and will test whether these genes are more or less prone to interspecific introgression between the species. The dataset will also be used to study genome-wide expression differences between the species. The genome-wide analysis of DNA polymorphism and divergence in the protein-coding regions will allow us to test modern theories of adaptation and speciation.