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Abstract

Clonal species, such as seagrass Zostera marina, have two levels of “population”, an asexual population of ramets belonging to a single clone/genet, which is nested into the population of clones/genets, the “classical”, sexually reproducing population. Although earlier theoretical and conceptual work has repeatedly suggested that somatically generated variation plays an important role in modular species, population genetics of such species has been focused on the “classical” germline genetic variation. This thesis extends the knowledge on the multi-level genetic variation in the model seagrass species Z. marina using whole-genome resequencing. In Chapter 1, I studied the somatic genetic variation (SoGV) in a Z. marina meadow tracing back to one single sexual event. In chapter 2, I studied population genomics of Z. marina, based on the worldwide distribution of the “classical” germline genetic variation. In chapter 3, I proposed the concept of identity by heterozygosity (IBH), meaning that two diploid genomes are identically heterozygous at some genetic markers such as SNPs (single-nucleotide polymorphisms). This was used to detect ramets of the same clone/genet. In summary, two levels of SoGV, namely among cell populations, and among ramets/modules, are nested within “classical” germline genetic variation in clonal species, owing to somatic mutation and somatic genetic drift. This thesis opens up new avenues of studying multi-level genetic variation by using clonal species as model. Further modeling and theoretical work based on clonal species will broaden the current population genetics theory.