I also found that species with monoicous and polyocious mating systems, high sporulation frequency and smaller spores that prefer poor habitats tend to produce more hybrids than other species. I showed that hybridisation is very common in the genus, but mostly takes the form of allopolyploid hybridisation, where two haploid species produce a diploid hybrid species. The combination of these features makes them an excellent model for studying the genomics of speciation in general, and the long-standing question of the evolutionary significance of introgression in particular.įirst, I explored the extent of gene flow in the genus and its relation to phylogenetic divergence and variation in key life-history traits of the hybridising species, based on the published literature. Peatmosses (Sphagnum) are described by recent rapid diversification, frequent hybridisation, ancient history, phenotypic and ecological plasticity, and huge ecological importance. In this thesis, speciation with gene flow is studied on the genomic level in a bryophyte genus of peatmosses. This remains challenging in non-model and nonvascular plants, where comprehensive genomic resources are lacking, and the role of gene flow for speciation remains poorly understood. Studying genomes of diversifying lineages enables the identification of the genomic footprints of gene flow, which facilitates disentangling its role for speciation from that of other evolutionary forces, such as selection and genetic drift. Gene flow is believed to be especially important for speciation in plants. Gene flow, or introgression, can bring genetic novelty into recipient species, and hence promote adaptation, while simultaneously being antagonistic to establishment of reproductive isolation between the hybridising species. Speciation is one of the most fundamental evolutionary processes, as it creates biodiversity.
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