Fine Scale Genetic Structures And Gene Flow Of A Refugial Population Of Ginkgo Biloba In Tianmu Mountain:Evidence From Nuclear And Chloroplast Microsatellites

Ginkgo biloba, the sole extant representative of Ginkgoaceae, is a famous "living fossil" all over the world. Previous studies at range-widescale were focused on glacial refugia, genetic structure and human-mediated distribution history, but we still knew little about the genetic diversity, genetic structure and the cause of formation in a natural Ginkgo population at fine-scale levels. In this study,14biparental inherited nuclear microsatellites (nSSRs) and eight newly developed maternally inherited chloroplast microsatellites (cpSSRs) were used for a deep population gentic study of Ginkgo biloba in the Tianmu refugia located in the east of China. We analyzed genetic diversity, population (spatial) gentic structure, demographichistory, historical pollen and seed flow, and patterns of contemporary pollen and seed flow. We discussed the influence of different human disturbance on the population genetic variety and genetic structure and further analysis the possible factors that may play a role especially the gene flow. Based on the current conservation situation of the natural reserve and our results, we proposed an applicable protection strategy.High level of genetic diversity was shown both in the nSSR and cpSSR data in TM population. Significant genetic differentiation was detected among populations and lower genetic diversity was found in population which is far away from the protection zone. Significant spatial genetic structure was detected in BHQ population based on both nSSR and cpSSR. Limited gene flow resulting from population fragmentation and some other factors may be the main reason for the fine scale spatial gentic structure. Population demographic history showed a population decline in79433(19953-316228) yra, consistent to the time of late Pleistocene when the glacial attacked the northern hemisphere. We didn’t find any evidence of recent bottlenecks in all populations. Past climate changes played an important role in the formation of the current population patterns of a wind-pollinated, long-lived tree.A fat-tailed distribution of pollen and seed dispersal was shown in the results of paternity and parentage analysis. The farthest and mean pollen dispersal distance was22.75km and5.32km respectively.46%of effective dispersal events happened within1km. Pollen dispersal distance was negatively related to the density of male trees. Seed dispersal mainly concentrated in short distance (mean0.78m,74%within20m). Long distance of seed dispersal was also found (11%farther than1km, farthest16.42km). These results indicated that seeds were mainly gravity dispersed and animals and human beings can serve as secondary seed dispersers. The long dispersal distance and high frequency of gene flow may be an important mechanism for the pollen-pollinated, long-lived trees to buffer the influence of habitant fragmentation.From conservation perspectives, we suggest (1) collecting pollen manually according to the genotype of male trees and their spatial distribution, artificial insemination to avoid the possibility of inbreeding, keeping the distance of males and neighboured females further than400m;(2) collecting seeds from mother trees (especially with different haplotypes), artificially breeding, recruiting the seedlings to the natural population, strengthening the continuity among populations and balancing the sex ratio, keeping the distance of males and neighboured females less than1300m, changing the age structure of the population, keepingthe potential of natural reproduction and maintenace;(3) more attention to the study of the behavioral ecology of seed dispersal and natural renewal of seedlings, reveal the limited factors for the effective reproduction of Ginkgo in the whole life history.