Multiple origins of the allotetraploid Tragopogon mirus (Compositae): rDNA evidence
1991
Soltis, P.S. | Soltis, D.E.
Tragopogon mirus is one of only a few polyploids whose time of origin is known with a high degree of certainty. Previous studies of morphological, karyotypic, and electrophoretic variation suggested multiple origins of allotetraploidy in T. mirus from the Palouse region of eastern Washington and adjacent Idaho. Restriction site analysis of the 17S-25S ribosomal RNA genes (rDNA) was used to test for multiple origins of T. mirus. The rDNA restriction profiles of six populations of T. mirus were compared with those of eight populations of T. dubius and six of T. porrifolius, the diploid progenitors. Populations of T. mirus combine the rDNAs of T. dubius and T. porrifolius, confirming the proposed origin of the tetraploid. Furthermore, the incorporation of restriction site polymorphisms of T. porrifolius into different populations of T. mirus demonstrates at least two independent origins of T. mirus. Although T. mirus often occurs with its diploid progenitors, these mixed populations do not necessarily reflect sites of origin of the tetraploid. In the three mixed populations examined, the diploids could not have produced the tetraploid plants found at the same site. Extensive dispersal of the tetraploid and fluctuating population sizes coupled with local extinctions and subsequent recolonization could explain the discordance between rDNA genotypes and their distributions. Thus, population dynamics in Tragopogon may obscure the sites of independent origin of T. mirus. Finally, although multiple origins of polyploid species have been reported frequently, few studies have demonstrated multiple polyploidization events on a geographic scale of a few kilometers.
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