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

Abstract

SummaryTragopogon 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.

Pure polyploidy: Closing the gaps in autopolyploid research

“…Allopolyploidy is frequently associated with rapid change throughout the genome, including aneuploidy and chromosomal translocations, which occur relatively quickly after WGD (Xiong et al, 2011;Chester et al, 2012;Zhang et al, 2013). Although older allopolyploid genomes are typically characterized by chromosomal additivity, or near-additivity, with respect to their diploid parental species, they also frequently reveal evidence of past chromosomal rearrangements through the presence of fixed homoeologous translocations (Pontes et al, 2004;Udall et al, 2005;Berkman et al, 2012;Mavrodiev et al, 2015). Allopolyploids also experience widespread gene loss, changes in levels of gene expression, gene silencing, changes to histone modification and DNA methylation, and transposon activation (Madlung et al, 2002;Comai et al, 2003;Adams & Wendel, 2005;Chen & Tian, 2007;Buggs et al, 2009Buggs et al, , 2011Parisod et al, 2010a).…”

Present‐day sympatry belies the evolutionary origin of a high‐order polyploid

“…Xiong et al, 2011;Chester et al, 2012). However, the extent to which these immediate genomic changes persist remains largely unknown (Lim et al, 2007;Mavrodiev et al, 2015). As many aspects of genome rearrangements can lead to discordance between genes in phylogenetic signatures, the extent and duration of such changes affect the inference of polyploid origins.…”

Partial interfertility between independently originated populations of the neo-allopolyploid Mimulus peregrinus

“…Although there is ample genetic evidence of multiple origins across a variety of allopolyploid taxa (e.g. Wyatt et al 1988;Ashton and Abbott 1992;Franzke and Mummenhoff 1999;Segraves et al 1999;Soltis et al 2004;Beck et al 2012;Mavrodiev et al 2015;Servick et al 2015;Vallejo-Marín et al 2015), fewer studies have experimentally compared the interfertility of independently originated populations. For instance, Modliszewski and Willis (2012) investigated the interfertility of populations of independent origin of the allotetraploid Mimulus sookensis (2n = 4x = 56), which is the polyploid derivative of hybrids between M. guttatus and M. nasutus (2n = 28) (Benedict et al 2012).…”

“…Wyatt et al 1988;Soltis and Soltis 1991;Ashton and Abbott 1992;Doyle et al 1999;Segraves et al 1999;Beck et al 2012;Modliszewski and Willis 2012;Sampson and Byrne 2012;Mavrodiev et al 2015;Servick et al 2015;Vallejo-Marín et al 2015). Although each instance of polyploid formation may result in limited genetic diversity, mating between independently generated polyploids may introduce genetic variation into the nascent lineage and create new genetic combinations .…”