Repeated range expansions and inter-/postglacial recolonization routes of Sargentodoxa cuneata (Oliv.) Rehd. et Wils. (Lardizabalaceae) in subtropical China revealed by chloroplast phylogeography.

Most plant phylogeographic studies in subtropical China have stressed the importance of multiple refugia and limited admixture among refugia. Little attention has been paid to range expansion and recolonization routes in this region. In this study, we implemented a phylogeographic survey on Sargentodoxa cuneata, a widespread woody deciduous climber in subtropical China to determine if it conforms to the expansion-contraction (EC) model during the Pleistocene. Sequence variation of two chloroplast intergenic spacers (IGSs) in 369 individuals from 54 populations of S. cuneata was examined. Twenty-six chloroplast haplotypes were recovered. One of these (H5) occurred across the range of S. cuneata and was absent from only 13 populations. Sixteen of the 26 haplotypes were connected to H5 by one mutation and displayed a star-like pattern in the haplotype network. All chloroplast haplotypes clustered into two lineages (A and B) in a Bayesian tree, and most haplotypes (18 out of 26) originated during the mid-Pleistocene (0.63-1.07Ma). Demographic analyses detected a recent range expansion that occurred at 95.98ka (CI: 61.7-112.53ka) for Lineage A. The genetic signature of an ancient range expansion after the Middle Pleistocene Transition (MPT) was also evident. Three recolonization routes were identified in subtropical China. The results suggest that temperate plants in subtropical China may conform to the EC model to some extent. However, the genetic signature from multiple historical processes may complicate the phylogeographic patterns of organisms in the region due to the mild Pleistocene climate. This study provides a new perspective for understanding the evolutionary history of temperate plants in subtropical China.