Weed versus wildflower : mating system ecology in a taraxacum native-exotic contact zone

Closely related plant species often exhibit differences in ploidy level, mode of reproduction, and traits related to reproduction. Differences in ploidy levels are often associated with mating system differentiation, especially in genera capable of clonal seed production through apomixis, which are derived from ancestral sexual lineages. The evolution of apomixis and associated changes in ploidy level contributes to niche differentiation and geographic separation between closely related plant species. Incomplete reproductive isolation between sexual and apomict taxa can lead to introgression of apomictic genotypes into sexual populations, and also to possible reproductive interference following cross-pollination. Furthermore, the evolution of apomixis relaxes selection on traits subject to sexual selection in sexual lineages, eventually leading to distinct phenotypes in closely related sexual and apomict species. Niche differentiation among species of different ploidy levels could also lead to the evolution of distinct secondary metabolites. ... Taken together, these studies demonstrate a new mechanism by which exotic species may negatively impact native plants- through induced inbreeding depression accompanied by hybridization. Furthermore, my research sheds new light on how pollen morphology evolves within and between taxa, and sets the stage for future studies on the physical mechanisms and genetic pathways underlying pollen transfer. Differences in pollen morphology between sexual and apomictic taxa provide an additional barrier to reproductive interference, hybridization, and introgression of apomictic genotypes into sexual populations. Overall, Taraxacum provides a great system for research in species interactions and ecology, and additionally is amenable for use in teaching and outreach activities