Study On The Geographical Distribution Pattern Of Acrolejeunea Sandvicensis

With the change of global climate and the worsening of ecological environment,the protection of biodiversity has been paid more and more attention by all countries.Conservation focuses on endemic and endangered species.The endemic species is easily endangered due to its narrow distribution and small population in the wild.Therefore,a deeper understanding of biologically endemic phenomena is essential for biodiversity conservation.Globally,bryophytes have a relatively low endemic rate compared to angiosperms.The latest view holds the idea that the endemic phenomenon of bryophytes is a short process due to high dispersal ability.However,there are two different views on the dispersal ability of bryophytes.One view holds that bryophytes have efficient long-distance dispersal ability,while the analysis based on global bryophyte distribution data believes that the ocean is the barrier of long-distance dispersal of bryophytes.Therefore,understanding the dispersal ability of bryophytes is the first thing to do before protection,and the study of the disjunction is an important means to understand dispersal ability.Acrolejeunea sandvicensis is widely distributed in east Asia,and disjuncted in Hawaii and the South Pacific,which means it has strong dispersal ability.However,it has not been distributed to America,Europe and Africa.Given the relatively close plant relationship between east Asia and North America,dispersal seems to be the main cause of this distribution pattern.Therefore,the Study on the geographical distribution pattern of A.sandvicensis will be helpful to understand the dispersal ability of bryophytes.We used A.sandvicensis as research material,firstly determined the current geographical distribution of the species based on the morphology and the re-identification of the historical specimens and then carried out a comprehensive molecular sampling.Using chloroplast gene trn L-trn F,trn G and nuclear gene ITS,phylogenetic trees were constructed by ML and BI methods,and the species status of this species was determined.The origin and migration routes of A.sandvicensis were explored by ancestral area reconstraction and divergency time estimate method.Through the prediction of the global potential area and the test of dispersal ability,the cause of the current geographical distribution pattern of the species was explained and its dispersal ability was understood.The main research results are as follows:1.According to the re-identification of specimen from 10 countries collected in BM,NICH and PC history museum,we ruled out the distribution sites in Cambodia,Malaysia,Tahiti,new caledonia,determine the current distribution of the species,mainly including China,India,Bhutan,Sikkim,Nepal,Pakistan,Japan,South Korea,Thailand,northern Vietnam and Hawaii.2.According to the phylogeny evidence,the Hawaiian population is inside the east Asian population and is closely related to the Guangxi and Hainan populations,indicating that although the Hawaiian population is distributed far away,it does not show strong genetic differentiation and possible cryptic species phenomenon.PCo A and Mantel tests were used to analyze the relationship between genetic distance,morphology and geographical distance,and it was found that there was no correlation among them.3.The result of ancestral area reconstraction and divergency time estimates based on the ITS,trn L-trn F,trn G show that the orgin of the species is Holarctic,and the species became extinct in large parts of its range during the glaciations.Then spread to mid-latitude area(23 ° 26 '~30 °N)36.50 million years ago,and in 1.12 million years the mid-latitude(23 ° 26'~30 °N)population or the high-latitude area(30°~66°34?N)long distance diapersal to Hawaii;The result of the haplotype network based on trn L-trn F,trn G were basically consistent with the branches of the divergency time tree,and the ancestral haplotype was Shared by populations in Shandong,Yunnan,Zhejiang,Shaanxi,Jiangxi,Hubei,Fujian,Anhui,Guangdong and Hunan.4.Based on the prediction of the global potential sites of the species,it was found that the species had suitable habitats in Asia,America,Africa and Oceania,and had the highest suitability in China.Therefore,it was speculated that the current global distribution pattern of the species was caused by the limitation of its dispersal ability.5.It was detected that A.sandvicensis showed low genetic diversity in the global scale based on trn L-trn F and trn G.The haplotype polymorphism h of the 23 populations was 0.8744,and the nucleotide polymorphism was 0.00273,Nm=0.2.In addition,AMOVA analysis of molecular variation showed that the species had a high level of intergroup differentiation worldwide,reaching 58.41%.The genetic differentiation coefficient between the populations was Fst=0.5841,and Nst=0.6308 > Gst=0.5435(P<0.01),indicating significant geographical isolation and weak dispersal ability.When island and foreign populations were removed,the genetic differentiation coefficient between the populations of this species was Fst=0.4955,and Nst=0.4939 > Gst=0.4287(P<0.01),showing higher dispersal ability.According to the data analysis of the morphology,found that in different latitudes of China,width with leaves,lobe width,the size of spores and the number of spores almost had no significant difference,but the island's spores are significantly bigger than mainland spores and has less spores.Showing weak dispersal ability among islands and strong one inside lands.Study on the geographical distribution pattern of Acrolejeunea sandvicensis combined with a fossil,it was found that although this species appeared to have strong long-distance dispersal ability,it was not so.The ocean is the barrier of long-distance dispersal of bryophytes,which further indicated that the spores of liverworts were difficult to dispersal for a long distance due to their weak resistance to ultraviolet rays.