Phylogeography And Speciation Of Ostryopsis

The climatic oscillations and geological events usually changed the original ranges of organisms that resulted in adaptive evolutions of these species, and sometimes lead to origins of the new species. The temperate regions at the high and middle latitudes during the Quaternary period may have experienced recurrent climatic oscillations and the species occurring there must have retained more genetic signatures in response to such a climatic change. However, little is known of this effect on the Chinese temperate plants. Where were refuges of the temperate plants in China during the Quaternary glacial period? How did they change their original ranges? Was there adaptive speciation during such a distributional change? In this thesis, an endemic genus was chosen as a proxy to answer these questions.Ostryopsis is a small genus of Betulaceae with only two species, i.e., O. davidiana Decne and O. nobilis Balf. f. et W.W.Sm. Chloroplast DNA is maternally inherited in most angiosperms, and the variation of cpDNA is extensively used to study genetic signatures of plants due to the climatic fluctuation. In this study, three chloroplast DNA regions (trnV-trnM, trnL-trnF and psbA-trnH) were sequenced for 451 individuals of 29 populations covering the total range of the two species. A total of 13 haplotypes were identified. Three of them were found in Xiaowutai Mountain and four in Zhongdian. The genetic diversity of these two regions suggests that they might have served as important glacial refuges of two species respectively and the postglacial recolonization starts. The ancestral haplotypes in the southeast Gansu and the north Sichuan of O. davidiana, in southwest Sichuan of O. nobilis also suggest these regions might be glacial refuge of two species. However, the low genetic diversity of these regions suggests that populations there might have undergone intensive bottleneck effects.Additionally, the speciation between O. davidiana and O. nobilis probably is a progenitor-derivative type because the haplotypes of the former clustered within the latter. It is possible that a few individuals of O. nobilis colonized the north during the interglacial stages and the following isolations during the following glacial stages resulted in the formation of the former. This speciation should have occurred at the early glacial stage of the Quaternary because the genetic patterns of the former obviously suggest that all current populations might have experienced genetic bottlenecks because of the climatic oscillations.