Chloroplast phylogeography of Terminalia franchetii (Combretaceae) from the eastern Sino-Himalayan region and its correlation with historical river capture events.

The reorganization of major river drainages in the Sino-Himalayan region of Southwest China was caused primarily by river separation and capture events following the most recent uplift of the Tibetan Plateau (≤ 3.4 Ma). Terminalia franchetii is a shrub or small tree species endemic to the river valleys of this region. Based on a range-wide sampling comprising 28 populations and 258 individuals, we investigated the relationship between the modern phylogeographic structure of T. franchetii and geological changes in drainage patterns, using chloroplast DNA sequences (trnL-F, petL-psbE). T. franchetii was found to harbor high haplotype diversity (h(T)=0.784) but low average within-population diversity (h(S)=0.124). Mismatch distribution and neutrality tests provided no evidence of recent demographic population growth. Two (out of five) population groups identified exhibited a disjunctive distribution of dominant haplotypes between northern and southern valleys, corresponding to the geography of past drainage systems. We conclude that the modern disjunctive distribution of T. franchetii, and associated patterns of cpDNA haplotype variation, result from vicariance caused by several historical river separation and capture events. Overall, our inferred timings of these events (mostly mid-to-late Pleistocene) agree with previous time estimates of drainage re-arrangements in the Sino-Himalayan region.