Phylogeography And Evolutionary Relationship Of Stipa Grandis In Northern Grassland Of China

Stipa grandis is a perennial and gramineous forage grass which is widely distributed in the Eurasian steppe.Stipa grandis often appears as constructive species.The phylogeography not only explores the distribution patterns of species’genetic diversity,but also reveals the formation and evolution mechanism and history dynamic of species.There is no study about the phylogeography of Stipa grandis.Our present work investigated the phylogeography and evolutionary relationship of Stipa grandis including thirty-six populations from different geographic regions in northern grassland.The analysis was carried out based on Amplified Fragment Length Polymorphism（AFLP）.Genetic diversity within and between populations,population genetic structure and evolutionary relationships of Stipa grandis were detected,and it provided a theoretical basis for the deepening of molecular ecology theory.A total of 714 individuals from thirty-six populations from different geographic regions in northern grassland were investigated.Genetic diversity indexes and genetic structure analysis showed that ten primer combinations produced 967 reproducible and distinct fragments,among which 95.76%were polymorphic.Low genetic diversity was detected in 27-D₁ population（H=0.0204）,while high genetic diversity was detected in 38-D1 population（H=0.0848）and 31-D1 population（H=0.0840）.High genetic differentiation（80.23%）among populations was detected with Gst=0.8023.Low gene flow among populations was detected with Nm=0.1232.Analysis of molecular variance（AMOVA）showed that the variation among Stipa grandis populations from different geographic regions（80%）was greater than the variation within populations（20%）,which revealed that genetic variation in Stipa grandis populations from different geographic regions was mainly from among populations,and the genetic variation was significant（P<0.05）.Mantel test result showed that there was significant correlation between genetic distance and geographic distance among Stipa grandis populations from different geographic regions.The trees of evolutionary relationship constructed by UPGMA method and Neighbour-Joining method showed that the thirty-six Stipa grandis populations from different geographic regions were distributed according to the certain geographical rules,and formed a obvious pedigree geographical structure.The evolutionary pathway of Stipa grandis populations from different geographic regions in this study was like that Stipa grandis populations of 57-D1,58-D₁ were the original populations,and gradually spread to the typical distribution of Stipa grandis（e.g.,the diffusion populations 59-D1,56-D1 and 48-D1）.Since then,Stipa grandis continued spread to the west and formed diffusion populations（e.g.,52-D₁,46-D₁,47-D₁,50-D₁,61-D₁,44-D₁,45-D₁,54-D₁,43-D₁,39-D₁,41-D₁,42-D₁,40-D₁,33-D₁,34-D₁,35-D₁,36-D₁,37-D₁,29-D₁,30-D₁,31-D₁,32-D₁,38-D₁,27-D₁,28-D1,25-D1 and 12-D1）.Eventually,Stipa grandis formed the current distribution pattern.Overall,the evolutionary route of Stipa grandis in northern grassland was roughly followed by the direction from east to west.Genotypic diversity analysis showed that 395 genetypes were detected from a total of 714 individuals from thirty-six populations,which indicated Stipa grandis populations had abundant genotypes.Every individual was an independent genotype in 25-D1,31-D1,36-D1 and 56-D1 populations（G=20）,while there was only one genotype in 61-D1 population（G=1）.The percentage of genptype（G/N）ranged from0.05 to 1,the mean value was 0.55,which belonged to moderate level.The distribution of eve was uniform in 25-D1,31-D1,36-D1,56-D1 and 61-D1populations（eve=1）.High genotypic diversity was detected in 25-D1,31-D1,36-D1,and 56-D1 populations（div=1,shw=1.301）,while low genotypic diversity was detected in 61-D1 population（div=0,shw=0）.The correlation analysis between genetic diversity indexes and ecological factors showed that there was no significant correlation between genetic diversity indexes and the latitude,longitude,mean annual precipitation,and aridity in Stipa grandis populations from the different geographic regions（P>0.05）.The correlation analysis between genotypic diversity indexes and ecological factors showed that there was no significant correlation between the number of genotypes（G）,the percentage of genptype（G/N）and latitude,longitude respectively,while there was significant correlation between the number of genotypes（G）,the percentage of genptype（G/N）and mean annual precipitation,and aridity respectively.There was significant correlation between genotypic diversity（div）,shannon-wiener index（shw）,uncorrected genotypic diversity（diu）and longitude,mean annual precipitation,and aridity respectively,while there was no significant correlation between genotypic diversity（div）,shannon-wiener index（shw）,uncorrected genotypic diversity（diu）and latitude.