Conservation Genetics Of Endangered Plant Hopea Hainanensis In Hainan Island

Hopea hainanensis Merrill&Chun（Dipterocarpaceae）is an endangered tree species mainly distributed in Hainan Island,China and Northern Vietnam.It is a representative species of the tropical gully rainforest in Hainan Island.In this study,the main contents of conservation genetics（including distribution of genetic variation,genetic structure and mating system,etc.）of its existing population were studied by SSR technique,in order to reveal its endangered internal causes.The main findings were as follows:（1）According to next generation sequencing data,twenty-six microsatellite markers were developed,of which twelve markers were polymorphic in H.hainanensis and could be used for subsequent analysis.We used both Geno Dive and Polygene to calculate the level of genetic diversity.It was found that there was little difference between the two results.Geno Dive analyses showed that the number of alleles ranged from 2 to 6 per locus,and the observed and expected heterozygosity varied from 0 to0.755 and from 0.259 to 0.779,respectively.（2）Primer transferability was tested with H.chinensis Hand.-Mazz.and H.reticulata Tardieu.Three and seven markers were polymorphic,respectively.H.reticulata and H.hainanensis had similar levels of genetic diversity.The 12 polymorphic microsatellite markers could be applied to study genetic diversity,genetic differentiation,mating system and so on.（3）Genetic diversity and genetic structure were assessed using 12 SSR markers for10 populations sampled across Hainan Island.Compared to non-threatened Hopea species,H.hainanensis exhibited reduced overall genetic diversity（N_a=2.46;The mean H_e value of the population calculated by Polygene was 0.409,and the Genodive estimate was 0.427）and increased population differentiation(AMOVA:F_ST=0.23).A Mantel test found there was no correlation between genetic and geographical distances（r=0.040,p=0.418）.Bayesian model-based clustering and principal coordinate analysis consistently assigned H.hainanensis individuals into three genetic groups,which were found to be widespread and overlapping geographically.The observed genetic structure suggests that long-distance gene flow occurred among H.hainanensis populations prior to habitat fragmentation.Qualitative and graphical methods are used to determine the potential bottleneck of H.hainanensis populations.Compared with the other three species of Dipterocarpaceae,the frequency distribution of alleles in H.hainanensis was obviously distorted.This aberration of allele frequency distribution pattern is a characteristic of the bottleneck population,and the bottleneck effect may lead to the rapid loss of genetic diversity and the increase of population differentiation.（4）The preliminary analysis of the mating system found that the genetic composition of the female parent and the offspring were the same,indicating that the population may be apomixis rather than sexual.The emergence of apomixis may be the result of the mutual adaptation of plant reproductive methods and the environment,and at least provides a kind of reproductive guarantee.In addition,the existence of apomixis also provides an explanation for the current low genetic diversity of the H.hainanensis populations.Based on the study of the genetics and mating system of H.hainanensis,some suggestions for the protection were put forward.In situ protection of all populations is necessary.Ex-situ protection of H.hainanensis is also of great significance.The populations with high levels of genetic diversity may be used as material sources for ex situ conservation,while the populations with low levels of genetic diversity need special attention to prevent the effects of stress factors.The establishment of seed resource bank is beneficial to the recovery and reintroduction of H.hainanensis population in the future.