Genetic variation, cytotype associations and geographical parthenogenesis in the subtropical grass genus Paspalum

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Polyploidy in flowering plants is one of the most significant spontaneous factors of evolutionary processes, promoting diversification via genome duplication and gene pool fragmentation. In polyploid complexes, the features of their reproductive modes, and pollination syndromes shape genetic variation and population structure. On the other hand, it is widely known that hybridization and polyploidization create a situation of genomic shock linked to changes in reproductive systems such as self-fertility (autogamy) or apomixis (asexually formed seeds). Breeding system character transitions are of particular interest because they affect the amount and distribution of genetic variation within species. Moreover, both self-fertility and apomixis are mechanisms that facilitate uniparental reproduction and enhance colonizing abilities where pollinators or partners for mating are limited (Baker's law). Reproductive assurance through self-fertilization and/or apomixis can promote range expansion outlining geographical cytotype diversity patterns (e.g. geographical parthenogenesis), however the benefit of reproductive assurance might be outweighed by seed discounting, loss of genetic diversity and in selfers, inbreeding depression. Other potential benefits to apomictic reproduction are partitioning of ecological niches and use of the resource space by broad arrays of clones (The Frozen Niche Variation Model) or the colonizing ability of clones with a broad ecological capacity (General Purpose Genotypes). To investigate the complex dynamics determining geographic distributions and cytotype associations in natural populations, we will take advantages of the model system Paspalum (ie. presence of sexual self-sterile / self-fertile diploids, sexual self-sterile / self-fertile tetraploids, apomictic self-fertile tetraploids), and analyse consequences of autogamy vs. allogamy, diploid vs. polyploid, sexual vs. apomictic state characters on genetic variation and cytotype diversity at population level. Ploidy levels and developmental pathways will be studied using flow cytometry. Genetic variation and structuring within and among populations will be assessed using Amplified Fragment Length Polymorphisms and microsatellite markers. The comparison of different cytotypes / reproductive systems will give insights into the importance of these factors for plant evolution and biogeography.