Multiple origins and chromosomal novelty in the allotetraploid Tragopogon castellanus (Asteraceae)

Tragopogon includes two classic examples of recently formed allopolyploid species in North America: T. mirus and T. miscellus. Older Tragopogon allotetraploids from Eurasia offer ideal taxa for comparing the longer term outcomes of allopolyploidy. To help resolve the ancestry of one of these older polyploids, phylogenetic analyses of multiple populations of the allotetraploid T. castellanus (2n = 24) and its putative diploid parents, T. crocifolius and T. lamottei, were conducted using sequences from nuclear (internal transcribed spacer, ITS; and alcohol dehydrogenase 1A, Adh) and plastid (trnT-trnL spacer, trnL intron, trnL-trnF spacer and rpl16 intron) loci. Fluorescence in situ hybridization (FISH) and genomic in situ hybridization (GISH) were used to investigate the chromosomal constitution of T. castellanus. Our data confirm that the widely distributed T. crocifolius and the Iberian endemic, T. lamottei, are the diploid parents of T. castellanus, and that this polyploid formed at least three times. One group of populations of T. castellanus is distinct in exhibiting two pairs of rearranged chromosomes. These data suggest that some of the chromosomal variants that originate in young polyploids (here, an intergenomic translocation) may become fixed in populations, contributing to novelty in older polyploid lineages. The geographical distributions of the allopolyploids and parents are also complex, with allotetraploid populations being disjunct from one or both of the most closely related diploid parental populations.