Genetic variation, polyploidy and hybridization in Scandinavian Anthericum ramosum and A. liliago (Anthericaceae)
Sammanfattning: In this thesis, I investigate the differences in breeding system, levels of genetic variation and hierarchical structure of genetic diversity between Anthericum ramosum and A. liliago. The two species differ in ploidy level and flowering time, but have similar habitat preferences, reproductive biology and geographic distributions in Scandinavia. I also assess the potential for hybridization and gene flow between the two species, and explore the auto- or allopolyploid origin of tetraploid A. liliago. Isozyme analyses revealed fixed heterozygosity in A. liliago, which indicates an allopolyploid origin. This finding, combined with previous cytological data, suggest that A. ramosum represents one of its diploid progenitors. Crossing experiments provided no evidence for agamospermy, self-incompatibility or high levels of automatic self-pollination, in the two Anthericum species. Selfing in the diploid A. ramosum resulted in early inbreeding depression (low fruit and seed set), while no such effect was found in the tetraploid A. liliago. The geographic structure of isozyme variation in the tetraploid A. liliago could be interpreted in terms of the species' migration history. A higher number of alloalleles in the southwestern part of Scandinavia compared to the easternmost part, indicates a post-glacial immigration from the southwest. No such geographic pattern of genetic variation was found in the diploid A. ramosum. Isozyme data indicate that the genetic diversity in this species has been more strongly affected by recent population fragmentation. Experimental hybridizations and chromosome counts demonstrated a great potential for hybridization and a variable frequency of triploid individuals in Scandinavian populations. The hybrids have intermediate flowering time and flowers that failed to set fruit after cross-pollination. However, the pollen fertility may be sufficiently high to allow introgression of genes from the triploid cytotype to the tetraploid individuals of A. liliago, that overlap in flowering time. Isozyme analyses revealed several triploid multilocus genotypes in one population, indicating repeated hybridizations between triploid and tetraploid cytotypes.
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