Molecular Phylogeographic And Genetic Diversity Study On An Endangered Herb, Saruma Henryi Oliv.(Aristolochiaceae) Endemic To China

Saruma is an isolated relic genus within the family Aristolochiaceae, and comprises a single species, Saruma henryi Oliv., which is a perennial herb endemic to China (Hsu,2005). As a typical plant in Central China, S. henryi is of high phylogenetic, ecological and medicinal significances, thus has been listed as an endangered species by both local and central governments in China. With short lifecycles and sensitivity to environmental changes, herbaceous plants are good materials for molecular phylogeographic studies to reveal the evolutionary history of plants in Central China since the late Tertiary and throughout the Quaternary. Here we report our recent application of cpSSRs, sequencing of chloroplast DNA and ISSR markers to the populations of S. henryi. Our specific goals were to:(i) reveal the phylogeography of this species and propose possible explanations for the high diversity and endemism in Central China; (ii) understand the genetic diversity and structure of this species and provide essential references for the formulation of effective conservation strategies.In this study, chloroplast microsatellites (cpSSRs) and atpB-rbcL intergenic spacers were employed to reveal its genetic diversity and phylogeographic patterns. We detected high within-species genetic diversity (HT= 0.939 for cpSSR; HT= 0.862 for atpB-rbcL) and pronounced genetic differentiation (Hs= 0.182, GST= 0.811, RST= 0.09, FST= 0.93 for cpSSR; HS= 0.238, GST= 0.724, NST=0.758, FST= 0.79 for atpB-rbcL) with a strong phylogeographic pattern (RST＞GST, P＜0.01 for cpSSR; NST＞GST, U= 0.25 for atpB-rbcL). Eleven haplotypes were distinguished by cpSSRs and atpB-rbcL intergenic spacers, respectively. The molecular phylogenetic data, together with the geographic distribution of the haplotypes, suggested the existence of several localized refugia during the last glaciation from which the present-day distribution may be derived. Nested clade analysis (NCA) identified the limited gene flow (caused by low dispersal capacity and complex topography of its habitats) as the main factor responsible for the strong population differentiation and phylogeographic pattern. All populations experienced allopatric fragmentation and past fragmentation, which were more obvious in the populations south of Yangtze River. In addition, contiguous range expansions occurred in western Mt. Qinling and eastern Mt. Bashan, and there existed a migration trend from southeastern to northwestern China.Inter simple sequence repeats (ISSR) markers were employed to study genetic diversity and genetic differentiation in forteen populations of Samura henryi Oliv.. High genetic diversity in species lever (ppb=73.71,h=0.2658,I=0.3928) and high genetic differentiation (GsT=0.63) were found among populations, while genetic diversity at population level were low (ppb=23.45, h=0.0831,I=0.134). Analysis of molecular variance (AMOVA) showed that most of the ISSR variation (FST= 0.6718) in Samura henryi Oliv occurred among populations. Gene flow was very limited with the value of 0.29. Mating system and genetic drift resulted from environmental fragment may responsible for the present genetic structure of the species. In situ conservation strategies were proposed based on the information revealed by the experiment.