The impacts of polyploidy, geographic and ecological isolations on the diversification of Panax (Araliaceae). Issue 1 (December 2015) - Shi, Feng-Xue
Abstract Background Panax L. is a medicinally important genus within family Araliaceae, where almost all species are of cultural significance for traditional Chinese medicine. Previous studies suggested two independent origins of the East Asia and North America disjunct distribution of this genus and multiple rounds of whole genome duplications (WGDs) might have occurred during the evolutionary process. Results We employed multiple chloroplast and nuclear markers to investigate the evolution and diversification ofPanax . Our phylogenetic analyses confirmed previous observations of the independent origins of disjunct distribution and both ancient and recent WGDs have occurred withinPanax . The estimations of divergence time implied that the ancient WGD might have occurred before the establishment ofPanax . Thereafter, at least two independent recent WGD events have occurred withinPanax, one of which has led to the formation of three geographically isolated tetraploid speciesP. ginseng, P. japonicus andP. quinquefolius . Population genetic analyses showed that the diploid speciesP. notoginseng harbored significantly lower nucleotide diversity than those of the two tetraploid speciesP. ginseng andP. quinquefolius and the three species showed distinct nucleotide variation patterns at exon regions. Conclusion Our findings based on the phylogenetic and population genetic analyses, coupled with the species distribution patterns ofPanax, suggested that the two rounds of WGD along with the geographic and ecological isolations might have together contributed to the evolution and diversification of this genus.