Genetic Diversity And Population Dynamics Of Clematis Subsect. Acerifoliae

Clematis subsect.Acerifoliae W.T.Wang,including two small shrubby species:Clematis acerifolia Maxim.and Clematis elobata（S.X.Yan）S.X.Yan&L.Xie,is disjunctively distributed on the cliffs of southern and northern ends of the Taihang Mountains.Both species are restricted in their ranges with limited number and size of populations.Although it has high ornamental value,there are few basic studies of this subsection.Effective conservation of the vulnerable species requires a comprehensive understanding of their biological attributes,such as genetic diversity,phylogeny,ecology,etc.In this study,genetic diversity and population structure of C.subsect.Acerifoliae were carried out,the potential distributions of this subsection in contemporary and the past were assessed,the cause of the disjunctive distribution of this subsection was discussed,and some recommendations for effective conservation were provided,based on reduced-representation genome sequencing and ecological niche model.The main research results are as follows:1.Genetic diversityFirst of all,we carried out a comprehensive field investigation for C.subsect.Acerifoliae,and collected fresh plant leaves for subsequent experiments.Then,we performed reduced-representation genome sequencing on 49 individuals from 8 populations of C.acerifolia and 18 individuals from 4populations of C.elobata.A total of 212792 single nucleotide polymorphism loci（SNPs）were obtained,and 10,234 SNPs were gained for genetic diversity analysis when missing data was controlled below 10%.The genetic analysis showed that the genetic diversity of C.subsect.Acerifoliae was low,of which the genetic diversity of Clematis elobata（Pi=0.1767,Ho=0.1716）is slightly higher than that of Clematis acerifolia（Pi=0.1410,Ho=0.1235）,and the degree of genetic differentiation of Clematis elobata(F_ST=0.1253)is slightly lower than that of Clematis acerifolia(F_ST=0.1669).The genetic structure analysis and principal coordinate analysis（PCo A）showed that the population of C.subsect.Acerifoliae could be divided into three groups:Clematis elobata for a group,Clematis acerifolia from Mentougou district of Beijing for a group,and Clematis acerifolia from Fangshan district of Beijing and Hebei for another group.Genetic variation mainly exists between these three groups.There was significant correlation between genetic distance and geographical distance（r=0.7001525,p=0.006**;r=0.9888948,p=0.0415*）.2.Molecular datingWith Clematis fruicosa as the only outgroup,molecular clock analysis of this subsection showed that the origin of this subsection and the differentiation time of C.acerifolia and C.elobata were relatively early.The C.acerifolia populations began to divide into two groups in the early Pleistocene of Quaternary,and the populations within the two groups differentiated successively.However,the C.elobata populations differentiated relatively later than the C.acerifolia populations and began to divide in the middle Pleistocene.3.Niche modelingThe distribution of subsect Acerifoliae was simulated by using ensemble of small models framework in ECOSPAT R package.According to the simulation result,the potential high-suitable distribution area of C.acerifolia was mainly distributed in the Taihang Mountain and Yanshan Mountain of Beijing and Hebei under the current climate conditions,while the potential high-suitable distribution of C.elobata right now was mainly located in the Taihang Mountains at the border of Henan and Shanxi,which were both larger than the actual distribution areas.Meanwhile,the simulation of different climatic conditions in the past showed that since the Last Interglacial Glacial,the high-suitable area of C.acerifolia has been located in the northern end of the Taihang Mountains,indicating that the current distribution should be a refugia for C.acerifolia during the glacial period.However,the high-suitable area of C.elobata showed a trend of northward migration and expansion from the Last Interglacial Glacial to the present,suggesting that there may have a large range of distribution migration in the history of C.elobata.It is also possible that C.elobata may have been widely distributed,and had shrunk its range with several relic populations in southern Taihang Mountains.4.Gradient forest analysis and redundancy analysisAccording to the gradient forest analysis and redundancy analysis,the main bioclimatic factors affecting the genetic variation structure of C.acerifolia and C.elobata were slightly different.The most important environmental factors affecting the genetic structure of C.acerifolia were precipitation seasonality,mean diurnal range,slope and precipitation of driest month.The main bioclimatic factors contributig to the genetic structure of C.elobata were annual precipitation,slope and subsoil gravel content.Among these factors,the most significant correlation was found between precipitation variables and the genetic variation of this subsection,indicating that precipitation variables played a key role in the distribution,inheritance and differentiation of C.subsect.Acerifoliae.In addition,slope also had an important environmental effect on the genetic variation of C.subsect.Acerifoliae,the genetic variation of which accumulated with the increase of slope.5.Conservation issuesBased on our analyses and the filed investigations of C.subsect Acerifoliae,populations with high genetic diversity need to be protected in particular,such as the population in Nanshiyang Grand Canyon of Beijing for C.acerifolia and the population in Yuntaishan,Henan for C.elobata.On the basis of in situ conservation,human activities in the distribution area should be prohibited to reduce habitat destruction.At the same time,in order to restore and expand the wild populations,relevant experiments,such as assisted migration,artificial breeding,and reintroducing the seedlings into their suitable habitat,should be carried out actively.