Phylogeography Of The Rare And Endangered Medicinal Plants Of The Genus Notopterygium Boissieu

Investigating the geographic distribution patterns of genetic variations of natural populations could help to reveal the population demographic history and phylogeographic structure of the current species responded to past geological environmental changes and the glacial climate fluctuations. The genus Notopterygium Boissieu is the perennially herbaceous plants, mainly distributed in west and middle part of the Qinghai-Tibet Plateau (QTP) and adjacent areas. In recent years, due to the demand of the genus Notopterygium in the market gradually increased, resulted in the dratmically reducing of wild resources. The genus Notopterygium has been listed in the "China Species Red List". In this project, we investigated the phylogeography of 409 individuals of 49 of Notopterygium (N. incisum, N. franchetii, N. oviforme and N. forrestii) based on the sequence variations of chloroplast microsatellite (cpSSR), chloroplast DNA(cpDNA) and ribosome transcribed spacer ITS fragment. In order to investigate the effects of past geological environmental changes and the glacial climate fluctuations on genetic structure and the population demographic history of this genus, and then infer the potential glacial refuges and retreat/colonization routes of the genus Notopterygium during postglacial periods. Our findings will provide a scientific basis to develop conservation strategies of this genus plants. The main conclusions are listed below:In this study, genetic variation of 10 populations of N. incisum and 11 populations N. franchetii were examined by 10 pairs of chloroplast microsatellites (cpSSR). Low genetic diversity was identified in N. incisum and N. franchetii populations, respectively. The percentages of polymorphic loci (PPL), Nei's gene diversities (h), and Shannon's indices (I) was 60.00%,0.025, and 0.059,for N. incisum, while PPL= 80.00%, h= 0.059,I= 0.126 for N. franchetii, respectively. AMOVA revealed that genetic differences mainly existed among populations of N. incisum and N. franchetii (54.78% for N. incisum; 52.74% for N. franchetii), respectively.The phylogenetic analysis of cpDNA sequences indicated that four species of Notopterygium formed a monophyletic clade with high bootstrap support, N. franchetii and N. oviforme constituting the same clade. Our results infer that species already took place hybridization or introgression in chloroplast DNA, due to their characteristics of the parapatric distribution. Then N. incisum and N. forrestii formed an individual clade with high bootstrap support. The phylogenetic analysis of ITS region revealed that four species of Notopterygium have also formed a monophyletic clade and this four species formed an individual clade with high bootstrap support, and we concluded that the nrITS region with higher species resolution ratio in plant species.Molecular dating revealed that four species of Notopterygium origined 4.21-9.6Mya while the four species diverged 1.24-3.4Mya, which was concerned with the early Pleistocene climatic oscillations and uplift of the QTP. We proposed that the climatic oscillations and the uplift of plateau might have drived the divergence of the genus Notopterygium.Geographic distribution of cpDNA and ITS haplotypes analysis indicated that N. incisum and N. franchetii might have obviously occurred the expansion events during the Last Interglacial (LIG) and the Last Glacial Maximum (LGM) periods. Combined with the coalescence theory and mismatch analysis found that the expansion of N. incisum occurred around 0.28-0.85Mya. N. incisum and N. franchetii have experienced a bottleneck events, which may be affected by climatic conditions and human activities.Based on the geographical distribution of cpDNA haplotypes and geneic diversity analysis indicated that the southeast part of QTP, Qilian mountain areas and the Sichuan, Gansu and Qinghai areas with high genetic diversity and of much more private haplotypes, we concluded that these regions may be the potential refuges for N. incisum, and the southeast part of QTP, Qilian mountain area and Xinglong mountain area with high genetic diversity and much more private haplotypes, and which may be the potential refuges for N. franchetii. In addition, geographic distribution pattern cpDNA haplotypes analysis indicated that the northwestern part of Sichuan, southeastern part of Qinghai, central Gansu are the most suitable survival area for N. incisum and N. franchetii. Finally, we put forward some protection strategies according to the result of phylogeography of Notopterygium species.