Phylogeography of the genus Dasiphora (Rosaceae) in the Qinghai-Tibetan Plateau: divergence blurred by expansion

摘要

Plateau uprisings and climatic oscillations are considered to have caused extensive allopatric divergences that account for the rich species diversity of the Qinghai-Tibetan Plateau (QTP). However, secondary contact during range shifts in the Quaternary glacial cycles or inter-uplift stages may have restored the gene flow between species and so counteracted these divergences, particularly in rapidly-adapting dominant elements. We tested this hypothesis by determining the phylogeographical history of Dasiphora (Rosaceae), a genus of two species that are widely distributed on the QTP and co-exist in numerous localities. We sequenced two chloroplast DNA fragments (rbcL, trnT-L) for 559 individuals from 87 populations. Bayesian methods were used to identify phylogenetic relationships and to estimate divergence times. Demographic histories were inferred using neutrality tests, mismatch distribution analysis, and coalescent simulation. A total of 112 haplotypes that clustered into three major groups were identified. The formation of these groups and their subgroups was dated to between the Pliocene and the late Pleistocene. In addition, we found that some groups underwent multiple extensive expansions. Species-specific haplotypes were identified for each species, although these haplotypes phylogenetically intermixed. These results suggest that recent plateau uplifts and climatic oscillations might have caused the deep divergences observed within this genus. However, later range expansions probably blurred these divergences and possible species boundaries. Our results shed new light on the complex evolutionary history of the QTP alpine plants