GENETIC VARIATION IN TRAGOPOGON SPECIES: ADDITIONAL ORIGINS OF THE ALLOTETRAPLOIDS T. MIRUS AND T. MISCELLUS (COMPOSITAE)

Abstract

Genetic diversity in the introduced diploids Tragopogon dubius, T. porrifolius, and T. pratensis and their neoallotetraploid derivatives T. mirus and T. miscellus was estimated to assess the numbers of recurrent, independent origins of the two tetraploid species in the Palouse region of eastern Washington and adjacent Idaho. These tetraploid species arose in this region, probably within the past 50–60 yr, and provide one of the best models for the study of polyploidy in plants. The parental species of both T. mirus and T. miscellus have been well documented, and each tetraploid species has apparently formed multiple times. However, a recent survey of the distributions of these allotetraploids revealed that both tetraploid species have expanded their ranges considerably during the past 50 yr, and several new populations of each species were discovered. Therefore, to evaluate the possibility that these recently discovered populations are of recent independent origin, a broad analysis of genetic diversity in T. mirus, T. miscellus, and their diploid progenitors was conducted. Analyses of allozymic and DNA restriction site variation in all known populations of T. mirus and T. miscellus in the Palouse and several populations of each parental diploid species revealed several distinct genotypes in each tetraploid species. Four isozymic multilocus genotypes were observed in T. mirus, and seven were detected in T. miscellus. Tragopogon mirus possesses a single chloroplast genome, that of T. porrifolius, and two distinct repeat types of the 18S‐26S ribosomal RNA genes. Populations of T. miscellus from Pullman, Washington, have the chloroplast genome of T. dubius; all other populations of T. miscellus have the chloroplast DNA of T. pratensis. All populations of T. miscellus combine the ribosomal RNA repeat types of T. dubius and T. pratensis, as demonstrated previously. When all current and previously published data are considered, both T. mirus and T. miscellus appear to have formed numerous times even within the small geographic confines of the Palouse, with estimates of five to nine and two to 21 independent origins, respectively. Such recurrent polyploidization appears to characterize most polyploid plant species investigated to date (although this number is small) and may contribute to the genetic diversity and ultimate success of polyploid species.

Gene loss and silencing in Tragopogon miscellus (Asteraceae): comparison of natural and synthetic allotetraploids

“…Homoeologous recombination seems to have caused loss of chromosome fragments in re-synthesised Brassica allopolyploids (Song et al, 1995;Gaeta et al, 2007). Ownbey (1950) observed multivalent formation in early generations of natural T. miscellus, and the patterns of isozyme variation in T. miscellus are consistent with homoeologous recombination (Soltis et al, 1995). More recently, Lim et al (2008) and Tate et al (in press) reported multivalent formation in both natural and synthetic Tragopogon allopolyploids, along with unisomy, trisomy and reciprocal translocations in natural Tragopogon allopolyploids.…”

“…These parents are phylogenetically divergent (Mavrodiev et al, 2005;Buggs et al, 2008); therefore, homoeologues in T. miscellus can be distinguished by sequence differences (for example, Tate et al, 2006). The species formed repeatedly in different localities from separate populations of the diploid progenitors (reviewed in Soltis et al, 1995Soltis et al, , 2004a, giving replicated independent natural allopolyploid lines. In addition, we now have multiple, reciprocal synthetic allopolyploid lines of the species (Tate et al, in press).…”

Evolution and Expression of Homeologous Loci in Tragopogon miscellus (Asteraceae), a Recent and Reciprocally Formed Allopolyploid

“…2613) and T. pratensis (Moscow, ID; Soltis and Soltis collection no. 2608), which represent the most likely progenitor genotypes for these T. miscellus populations (Soltis et al 1995), were also sampled.…”

“…Following the introduction of three diploid (2n ¼ 12) species (Tragopogon dubius, T. pratensis, and T. porrifolius) from Europe to western North America during the early 1900s, two allotetraploid species (T. mirus and T. miscellus) formed (Ownbey 1950). The ancestries of both allotetraploids were confirmed through flavonoid, isozymic, and DNA studies (Ownbey andMcCollum 1953, 1954;Brehm and Ownbey 1965;Roose and Gottlieb 1976;Soltis and Soltis 1989;Soltis et al 1995;Cook et al 1998). Molecular data indicate that T. miscellus and T. mirus have formed repeatedly, perhaps as many as 21 and 13 times, respectively, in just the past 80 years (reviewed in Soltis et al 2004).…”

Molecular evidence for an extinct parent of the tetraploid species Microseris acuminata and M. campestris (Asteraceae, Lactuceae)

“…Molecular data provide new sources of evidence for polyploid evolution (Doyle et al 1990;Soltis & Soltis 1993;Soltis et al 1995;Lowe & Abbott 1996). This investigation was designed to use molecular data to determine the exact parentage of M. acuminata and M. campestris including evidence for a unique origin or a repeated local origin.…”