Molecular evidence of reticulate evolution in the subgenus Plantago (Plantaginaceae)

Abstract

Polyploidization is a frequent evolutionary event in plants that has a large influence on speciation and evolution of the genome. Molecular phylogenetic analyses of the taxonomically complex subgenus Plantago were conducted to elucidate intrasubgeneric phylogenetic relationships. A nuclear-encoding single-copy gene, SUC1 (1.0-1.8 kb), was sequenced in 24 taxa representing all five sections of the subgenus Plantago and two taxa from subgenus Coronopus as the outgroup. Fifteen known polyploids and one putative polyploid were sampled to examine polyploid origins and occurrence of reticulate evolution by cloning and sequence analysis of SUC1. Phylogenetic relationships were estimated using maximum parsimony, neighbor-joining, and Bayesian analyses. For the first time, our analysis provides a highly resolved phylogenetic tree. Subgenus Plantago formed a well-supported monophyletic clade. In contrast, alleles from polyploid species were scattered across the whole SUC1 phylogenetic tree, and some independent allopolyploids originated from hybridization between distant lineages. One reason for this taxonomic complexity can be attributed to reticulate evolution within the subgenus Plantago. Our results also suggest the possibility of two independent long-distance dispersals between the northern and southern hemispheres.

DNA sequences from three genomes reveal multiple long-distance dispersals and non-monophyly of sections in Australasian Plantago (Plantaginaceae)

“…These three species were more closely related to species from section Plantago, Virginica and Micropsyllium than to the Australasian species from sections Mesembrynia and Oliganthos (albeit with PP support values <95%). The topology of Ishikawa et al (2009) also agrees with this result. Although sampling of additional DNA markers and species of subgenus Plantago -particularly from southern hemisphere sections Oliganthos and Mesembrynia -is needed to confirm the origin and direction of these dispersal events, the present results are nevertheless unambiguous in supporting multiple dispersals of Plantago into New Zealand.…”

“…Interestingly, polyploidy does not appear to have played a major role in the evolutionary history outside of subgenus Plantago, so its importance within sections Oliganthos and Mesembrynia from the southern hemisphere (Rahn 1984) is of great interest. Ishikawa et al (2009) were able to show that, of the species they sampled within subgenus Plantago, one is of autopolyploid origin and 10 are of allopolyploid origin, including P. spathulata and P. raoulii. We are currently counting chromosomes to resolve several variable and unknown species in New Zealand (B. Murray, H. M. Meudt, P. J. GarnockJones and M. L. Tay, unpubl.…”

“…The topology of their phylogeny was similar to that in Rønsted et al (2002) although with higher resolution and support values (Ishikawa et al 2009). With respect to biogeography, both Rønsted et al (2002) and Ishikawa et al (2009) inferred that the distribution of these southern hemisphere species, and indeed of the genus as a whole, was largely influenced by long-distance dispersal.…”

“…The four species of section Mesembrynia sampled (P. debilis from Australia, P. raoulii and P. spathulata from New Zealand, and P. stauntonii from the Amsterdam & St Paul Islands) formed a highly supported monophyletic group in this clade, whereas the two sampled species from section Oliganthos (P. uniglumis and P. rigida from South America) were not monophyletic and were in unresolved positions near the section Virginica clade. A more recent study using a nuclear-encoding single-copy gene, SUC1 (Ishikawa et al 2009), sampled 18 of the 19 individuals of subgenus Plantago included in Rønsted et al (2002), plus four additional species including P. depressa and P. camtschatica, two Asian species of section Mesembrynia. The topology of their phylogeny was similar to that in Rønsted et al (2002) although with higher resolution and support values (Ishikawa et al 2009).…”

“…A more recent study using a nuclear-encoding single-copy gene, SUC1 (Ishikawa et al 2009), sampled 18 of the 19 individuals of subgenus Plantago included in Rønsted et al (2002), plus four additional species including P. depressa and P. camtschatica, two Asian species of section Mesembrynia. The topology of their phylogeny was similar to that in Rønsted et al (2002) although with higher resolution and support values (Ishikawa et al 2009). With respect to biogeography, both Rønsted et al (2002) and Ishikawa et al (2009) inferred that the distribution of these southern hemisphere species, and indeed of the genus as a whole, was largely influenced by long-distance dispersal.…”