The Maintenance Of The Hybrid Zone By Contemporary Pollen Flow In Hybrid Zone Of Hippophae Goniocarpa And Historical Gene Flow Of Populations

According to the theory of hybridization, the precise balance between selection and gene flow is the necessary condition for the maintenance of the hybrid zone.Analysis of natural hybridization with contemporary and historical levels of gene flow can provide important clues and basis for further study on maintenance of hybrid zone.In this paper, to discuss the effect of gene flow on the maintenance of hybrid zone of Hippophae goniocarpa, we analyzed the current pollen flow and history gene flow of populations in the natural hybrid zone. Firstly, the open pollinated progeny of Hippophae goniocarpa which is hybrid and Hippophae rhamnoides ssp. sinensis and Hippophae neurocarpa which are parental species in hybrid zone of H.goniocarpa were paternity analysis using SSR molecular marker,to study the pollination pattern,distribution proportion of pollen contribution and interspecific pollen flow of three Hippophae female as the center. The pollen flow of the other four patches and the main patch in the population were also explored. Secondly, the historical gene flow and genetic structure between patches in GBW population were analyzed,consistenting with the result of pollen flow by the paternity analysis. Finally, we analyzed the gene flow and genetic structure of 5 populations of Hippophae in Qilian,Qinghai, including three hybrid populations and two H. neurocarpa populations,and compared interspecific and intraspecific gene flow for each population. The results of this study provide important clues for further study on the contemporary and historical gene flow, thus providing a theoretical basis for the maintenance of the hybrid zone.The final conclusion has the following several:1. The open pollinated progeny of two female parent of H. rhamnoides ssp.sinnesis and two of H. neurocarpa and a H.goniocarpa in GBW natural hybrid zones was studyed by paternity analysis method to explore the pollen flow and pollination pattern, obtained the pollen dispersal distance in path was 3~71m. There was no significant difference between the average pollen source distance of H. rhamnoides ssp. sinnesis and H. neurocarpa, but paternal origin of H. neurocarpa outside of 30 m was significantly more than that of H. rhamnoides ssp. sinnesis.2. Paternity analysis results show the pollen flow of H. rhamnoides ssp. sinnesisand H. neurocarpa is mainly in the intraspecific pollen flow, but the bidirectional interspecific pollen flow were also detected. The pollen contribution rate of the H.rhamnoides ssp. sinnesis from H. neurocarpa is 14.84%, and the contribution rate of H. neurocarpa from H. rhamnoides ssp. sinnesis is 9.13%, which indicates the pollen flow between the two species, but H. rhamnoides ssp. sinnesis as female parent receiving pollen from H. neurocarpa have greater proportion. The paternity analysis of H. neurocarpa's offspring detected pollen from H. goniocarpa, which shows the occurrence of backcross. Paternity analysis results of H. goniocarpa show pollen contribution rate from H. neurocarpa is higher than it from H. rhamnoides ssp.sinnesis.3. Pollination between 5 patches of GBW is estimated that long-distance pollination distance of H. rhamnoides ssp. sinnesis and H. neurocarpa may be greater than 200 m. The paternity analysis shows that patch 1 can detect the pollen sources from patche 2,3,4, and the pollen flow of patch 2 was the strongest. Patch 3 and patch4 have weak pollen flow to patch 1. The patch 5, which is the most distant from the patch 1, was not detected in the pollen contribution to patch 1.Genetic structure and gene flow were analyzed in 5 patches of GBW, which results showed that the overall genetic diversity of the 5 patches was rich(He=0.304, I=0.531), the level of genetic differentiation among populations was low, and the gene flow between patches was more than 1, and the gene exchange level was high. Genetic distance was significantly positively correlated with geographical distance, and gene flow was negatively correlated with geographical distance.4. Genetic structure and historical gene flow were analyzed in 5 populations of Hippophae in Qilian area of Qinghai. The results showed the genetic variation among populations was high, and the level of gene exchange was low, with an average of less than 1. The genetic distance between populations was not significantly positively correlated with the geographical distance, but the gene flow was negatively correlated with geographical distance. Comparison of intraspecific and interspecific gene flow showed that the level of gene exchange between populations in Qilian, Qinghai,which indicated that the degree of differentiation among populations in this region was large. Interspecific gene flow among different populations was generally lowerthan intraspecific gene flow, but there was still a certain degree of gene flow. In the analysis of interspecific gene flow in populations, interspecific gene flow in the GBW hybrid zone was large.The results of detection of historical gene flow and analysis of the contemporary pollen flow show that there is a certain degree of gene exchange between H.rhamnoides ssp. sinnesis and H. Neurocarpa, and the continuous occurrence of gene flow(pollen flow) plays an important role in the maintenance of the hybrid zone.