Multiple Origins

For many reasons Tragopogon is a novel system that affords the opportunity to examine the early stages of polyploidization in nature. The natural populations of both allopolyploid species (T. miscellus and T. mirus) are approximately 80 years (40 generations old in these biennial plants)—this time frame, and the fact that they have experienced natural selection, provide a window into polyploidization that cannot be matched via the study of synthetic polyploids (e.g., crops, and genetic models). Furthermore, molecular studies suggest that there may be as many as 21 lineages of separate origin of T. miscellus and 11 of T. mirus just in the Palouse of eastern WA and adjacent ID (Soltis et al. 1995, 2004, 2009b; Symonds et al. 2010); the polyploids have also formed in AZ, MT, OR, and WY (Brown & Schaack, 1972; Ownbey & McCollum, 1954; Soltis & al., 2012a, b).  Studies employing microsatellite markers (Symonds et al. 2010) reveal multiple origins on a small geographic scale—even polyploid populations in different parts of the same small towns separated by only 1-2 kilometers have often originated independently. Given that multiple polyploidizations are common in plants (Soltis and Soltis 1993, 1999, 2000, 2009), Tragopogon represents in microcosm what occurs in other polyploids over much larger geographic areas and longer time frames. These repeated origins in a small geographic area and a narrow time frame also provide the unique opportunity to ask if evolution repeats itself across these many lineages.

Molecular studies not only confirmed the parentage of Tragopogon mirus and T. miscellus, but also showed that each allotetraploid formed repeatedly in the introduced range (e.g., Soltis & al., 2004, 2012a), but the tetraploids have not formed in Europe, probably because the diploid parents are largely isolated ecologically and geographically. Based on microsatellite markers and other lines of DNA evidence, there may be as many as 21 lineages of separate origin of T. miscellus and 11 of T. mirus just in the Palouse of WA and ID (Soltis & al., 1995, 2004, 2009; Symonds & al., 2010). The polyploids have also formed independently in Oregon, Arizona, Wyoming, and Montana (Brown & Schaack, 1972; Ownbey & McCollum, 1954; Soltis & al., 2012a, b). Multiple origins in some cases occurred on a very small geographic scale—polyploid populations in different parts of a single small city separated by only 1-2 kilometers originated independently (Soltis and Soltis 1989; Symonds & al., 2010).

Given that multiple polyploidizations are common in plants (Soltis and Soltis 1993, 1999, 2000, 2009), Tragopogon represents in microcosm what occurs in other polyploids over much larger geographic areas and longer time frames. These repeated origins in a small geographic area and a narrow time frame also provide the unique opportunity to ask if evolution repeats itself across these many lineages.