Phylogeography And Speciation Of Picea Likiangensis Complex And Closely Related Species

The climatic oscillations during the Quaternary,not only resulted in the change of distribution range of all species,but also promoted adaptive evolution and origin of new species.The Qinghai-Tibetan Plateau is sensitive to the climatic oscillations due to its complex topology with the high altitude.In order to reveal how this oscillation affected the distribution range and speciation of plants occurring there,the present dissertation studied the phylogeography and possible speciation pattern of Picea likiangensis complex and closely related species.The mitochondrial(mt)genomes are inherited matemally while chloroplast(cp)genomes are inherited paternally in Pinaceae,and their respective variations are important for detecting gene flows mediated respectively by seeds and pollens,and having the great advantages of elucidating species divergence and following hybridization introgression.A total of 678 individuals of 67 populations,representing five taxa of three assumed species were collected and their morphological variations were illustrated.A total of five fragments from mt and cpDNA were sequenced for all individuals.No mixed population was found for P.wilsonii and P.purpurea.A few populations are morphologically pure for each of three varieties of P likiangensis (var.likiangensis,var.rubescens and Var.linzhiensis)in their allopatric distribution regions.However,these three taxa and Picea purpurea were morphologically mixed in many populations with two and/or more taxa within their parapatric distribution regions.Three cpDNA fragments(trnS-trnG,trnL-trnF and ndhK/C)identified seven chlorotypes and they clustered into two clades with one mainly occurring in the P. wilsonii-P,purpurea lineage.Two mtDNA fragments(nadl and nad5)identified 11 mitotypes and they grouped into three tentative clades.The earliest diverged one was mainly found in the P.wilsonii-P,purpurea lineage.All typical populations of both P. willsonii and P.purpurea fixed the same mitotype and chlorotype.However,each of three varieties of P.likiangensis contained two or more chlorotypes and mitotypes. According to the evolutionary relationships of haplotypes and their distributions, the following conclusions were drawn.(1)P.wilsonii-P,purpurea lineage diverged early and no differentiation was found between them possibly due to the late divergence between them or too frequent gene flow,which stopped the inter-specific mt and cpDNA differentiation although their morphological differentiation is distinct. (2)Var.linzhiensis should be recognized as a distinct species and its origin was involved three lineage through hybridization,including var.likiangensis,var. rubescens and P.wilsonii-P,purpurea lineage.(3)Frequent hybridizations were detected between most taxa.In contrast to the previous expectation that the long-dispersed pollens may result in the introgression,the present results suggested that the seed-mediated gene flow are more likely to result in the introgression of mtDNA genomes between closely related taxa.(4)Multiple refugia were retained for both var.likiangensis and var.rubescens during the glacial ages.Additionally,the final suggestion was also confirmed by the RAPD result.