Phylogeography of an alpine aquatic herb Ranunculus bungei (Ranunculaceae) on the Qinghai-Tibet Plateau

Many phylogeographic studies of terrestrial plant species on the Qinghai-Tibet Plateau (QTP) have been carried out to elucidate the range shifts in response to climatic oscillations in the Quaternary. However, patterns of range shifts for aquatic plants following the climate change on the QTP are poorly understood. Here, we studied the historical range shifts of the aquatic herb Ranunculus bungei Steud. on the QTP using four chloroplast (cpDNA) non-coding spacers. We revealed low within-population genetic diversity (H-S=0.052) and high interpopulation genetic differentiation (G(ST)=0.914; N-ST=0.954). But the high population differentiation was not coupled with a distinct phylogeographic structure (N-ST>G(ST), P>0.05). Phylogenetic analyses revealed two main cpDNA haplotype lineages and the split between these two lineages can be dated back to the late Tertiary (3.84-11.90 Ma). Two independent range expansions within the two intraspecific lineages at approximately 0.15-0.46 and 0.17-0.50 Ma were revealed. Our results suggested that R. bungei survived the Last Glacial Maximum and/or previous glacial periods on the QTP. Colonization or recolonization during the repeated range expansions may have replaced the early haplotypes and the pre-existing genetic structure and could explain the non-significant phylogeographical structure.