Mating systems and multiple origins in the North American polyploid Tragopogon complex

Polyploidy is a significant force in the evolution and diversification of the plant kingdom. Exploration of the mechanisms by which polyploid plants arise, and the consequences of their evolution, has been ongoing in the field of plant biology for decades. The work presented here addresses several questions pertaining to polyploid evolution: whether a polyploid species has a higher rate of self-fertilization than one of its diploid progenitors; whether polyploid species arise only once, through a single evolutionary event, or repeatedly, in essence re-creating the species; and whether members of the polyploid Tragopogon complex behave as biennials or annuals.;Outcrossing rates were assessed for both natural and artificial populations of diploid and tetraploid species of Tragopogon. The results suggest that there is greater variation in mating systems among populations within species than there is between diploid and tetraploid species. This result fails to support the hypothesis that polyploids might be expected to exhibit higher selfing rates than closely related diploids.;Using Random Amplified Polymorphic DNA markers, the number of separate origins of each of two polyploid Tragopogon species was assessed. The results show that each population of tetraploid surveyed bore a unique marker profile, suggesting that each had an independent origin. This means that these polyploid species have arisen repeatedly and are not the products of single, isolated evolutionary events.;Finally, wild seedlings of four species of Tragopogon were marked in the fall of one year, and the fate of those seedlings during the following summer was tracked. The results suggest that not all Tragopogon species exhibit the same life history, and that in some species there is a greater level of plasticity, with respect to life history, than is exhibited in other species.