Genetic Structure And Gene Flow In Hybrid Zone Of Hippophae Goniocarpa As Revealed By SSR Markers

Differences in the genetic structure of natural populations of plants are animportant manifestation of the genetic diversity. Distance isolation is the most directfactors influencing the spatial genetic structure of populations. An evolutionarypotential and the ability to withstand adverse environmental nature of species dependson not only the size of the genetic variation within species, but also depends on thegenetic structure of populations. Hybridization is the most important driving force ofthe plant evolution and the important way for the formation of new species. Hybridspeciation, in particular with the study of hybrid zone in recent years has become thefocus of plant evolutionary studies. Genetic composition and gene flow situation ofhybrid zone provides a good platform for research to clarify the isolation mechanismbetween species. In recent years, the rapid development and wide application of DNAmolecular markers such as SSR provides a powerful means and opportunities toresearch gene flow and population genetic structure. Based on previous work, severalhybrid zone of Hippophae goniocarpa and the populations of H. rhamnoides ssp.sinnesis and H. neurocarpa with different geographic isolation at the hybrid zone andsome neighboring sites in Qilian, Qinghai province were selected, and the geneticstructure and gene flow levels between populations of the same species as well as thatbetween different species in same hybrid zone were detected using SSR markers.The aims are1) to compare genetic structure and gene flow between populations of H.rhamnoides ssp. sinnesis and H. neurocarpa with different geographic isolation andbetween different species in same hybrid zone, and2) to investigate the function ofgeographic isolation in the hybrid zone of Hippophae and the maintaining mechanismof the hybrid zone. The main results and conclusions are as follows:1. Genetic structure and gene flow among four populations of H. rhamnoides ssp.sinnesis with different geographic distance at hybrid zone in Qilian, Qinghai (patch1of Gongbeiwan、patch2of Gongbeiwan、Rixucun and Xiaodongsuo) were detectedusing SSR markers. Genetic diversity at subspecies and population level are both high.Coefficient of gene differentiation（Gst）was0.1338from POPGENE, lower than themean value of outcrossing plant, showed that most of the variation existed within populations. The gene flow among populations of H. rhamnoides ssp. sinnesis inQilian(Nm=3.2379) is lower than the mean of other wind-pollinated, outcrossinglong-lived woody plants. Correlation test among gene flow and genetic distances andgeographical isolation distance of four populations indicated that gene flow andgenetic distances have nothing to do with the geographical isolation distance betweenpopulations. UPGMA cluster of individuals of H. rhamnoides ssp. sinnesis showedthat individuals within a population not fully together, indicates that a certain amountof gene flow occurred among populations.2. Genetic structure and gene flow among four populations of H. Neurocarpa(patch1of Gongbeiwan、patch2of Gongbeiwan、Rixucun and Xiaodongsuo) and twopure populations (Arouxiang and Binggou) nearby distributed with differentgeographic distance at hybrid zone in Qilian, Qinghai were detected using SSRmarkers. Genetic diversity at subspecies and population level are both high.Coefficient of gene differentiation（Gst）was0.1880from POPGENE, slightly lowerthan the mean value of outcrossing plant, showed that most of the variation existedwithin populations. The gene flow among populations of H. Neurocarpa inQilian(Nm=2.1589) is lower than the mean of other wind-pollinated, outcrossinglong-lived woody plants. Correlation test among gene flow and genetic distances andgeographical isolation distance of six population indicated that gene flow and geneticdistances have nothing to do with the geographical isolation distance betweenpopulations.UPGMA cluster of individuals of H. Neurocarpa showed that individualswithin a population not fully together,indicates that a certain amount of gene flowoccurred among populations.3.Genetic structure and gene flow of the hybrid zone of Hippophae goniocarpain Qilian, Qinghai (Gongbeiwan and Rixucun)were detected using SSR markers.Coefficient of gene differentiation（Gst）among species was0.2251and0.2102,respectively from POPGENE, both slightly higher than the mean value of outcrossingplant, but the genetic variation among species only accounted for22.51%and21.02%of total variance, respectively. Nm of hybrid zone of Gongbeiwan (1.7210) andRixucun (1.8792) are both lower than that among H. rhamnoides ssp. sinnesis populations and H. neurocarpa populations. However, the results also show that thereis still a certain degree of gene flow between parents and hybrids and parents inhybrid zone.4.Genetic distance and gene flow of H. rhamnoides ssp. sinnesis populations andH. neurocarpa populations in hybrid zone has nothing to do with the geographicalisolation distance among populations. However, hybridization only occurs in the areawhere parents mixed distribution, it is suggested that the pollen transmission distanceis limited and the long-distance seed dispersal may responsible for their geneticstructure formation. Test of interspecific gene flow of two hybrid zone (Gongbeiwanand Rixucun) explain that constantly hybridization events between H. rhamnoides ssp.sinnesis and H. neurocarpa maybe occur frequently, and the frequent hybridization islikely to maintain the relatively stable of hybrid zone along with natural selection.