Population Genetic Structure And Ecological Adaptive Characteristics Of Vitex Rotundifolia(Lamiaceae)

Vitex rotundifolia Linnaeus f.is an important specie in coastal flora with both ecological and medicinal values.However,there is little knowledge on the phylogeny and population genetics of V.rotundifolia,thus hampering the formulation of the conservation strategies for this endangering species.This study explored the genetic differentiation and genetic pattern of V rotundifolia to provide theoretical and data support for these species conservation protection based on multiple methods such as morphology,anatomy,pollination biology,population genetics and phylogeography.We conduct morphological and pollination biology studies based on samples in Jiaodong area.The results based on direct observation showed that the root system of V.rotundifolia is well developed,with adventitious roots distributed on the surface,the panicles are terminal with blue-purple corolla.The drupe is nearly round,and the seed setting rate in these samples are 85.2%.Observation of tissue sectioning of different plant organs through paraffin-making technology showed that the structure of the root,stem and leaf of V.rotundifolia had more parenchyma,which could improve its water retention capacity.In addition,a high degree of lignification of roots,stems and leaves were observed,by which V.rotundifolia becomes more strengthen.Collectively,these results showed that V.rotundifolia is highly adaptable to the sandy and saline environment.We found a low diversity of pollinating insects for rotundifolia in Jiaodong area,based both on treading method,circulation route method as well as standard strain all-day observation method.These insects can be grouped intothree families and two orders,i.e.Hymenoptera Vespidae,Apidae andApidae,Bombus;Sphingidae Lepidoptera.Among them,Vespidae is the main pollinating group,followed by Stellatarum species,and finally Apidae species;Bombus is the occasional species.They are consistent in the time-intensivevisits,that is at periods of 8:00-10:00 and 15:00-17:00,respectively,but the residence time of Hymenoptera insects is longer than other pollinating insects.According to the geographical distribution characteristics of V rotundifolia in China,this study adoptes a sampling strategy that spans 12 provinces and 23regions from south to north in multiple climate zones,on the basis of latitude.A total of 49 groups,including 23 groups in this study and 26 groups in previous studies,were analyzed in population genetics research,among which 43 groups are V rotundifolia and 6 groups are Vitex trifolia Linn.These groups mainly cover all the natural populations of V rotundifolia in China.In addition,our samples are also included 3 groups of South Korea and 3 groups of Japan.The samples genered 217 nrDNA sequences(ITS2)and 216 cpDNA(TrnH-psdA+TrnG-TrnS)sequences and data analyses showed that:(1)Calculation of the haplotypes and their numbers of both genes of V.rotundifolia and V trifolia and then construction of haplotype network map and geographical distribution map.The aligned sequences were analyzed by using DnaSP software,and results showed that V rotundifolia had four types of nrDNA haplotypes and 23 types of cpDNA haplotypes.By contrast,V trifolia had 7 types of nrDNA haplotypes and 5 types of cpDNA gene haplotypes.Both species shared the nrDNA haplotypes H1 and cpDNA haplotypes H16 and H17 in common.(2)The genetic diversity parameters of V rotundifolia were performed by Arlequin software and the results showed that genetic diversity of chloroplast genes(A=0.16-0.714,?=0.000000-0.006272,Hd=0.0000-0.9048)was significantly higher than that of nuclear genes(A=0.08-1.00,n=0.000000-0.004028,Hd=0.0000-1.0000);the former has a higher nucleotide diversity(?=0.050608)than the latter(?=0.038233)as well.(3)The Fst value of the chloroplast gene(Fst=0.184*,P<0.001)generated from AMOVA analysis indicates a significant genetic differentiation in the population,and the genetic differentiation within the V rotundifolia population was greater than that between the populations.(4)Mantel test showed that V rotundifolia chloroplast gene(r=-0.134,P=0.792)and nuclear gene(r=0.006,P=0.468),indicating that no significant correlation between genetic distance and geographical distance.Clearly,the geographical distance did not affect the gene flow between groups.(5)Population expansion test for the V.rotundifolia showed that it had recently expansion based on the result of nuclear gene mismatch distribution curve and neutral test Tajima's D=-0.66428,Fs=-1.2389.Based on the above population genetics research results,we found that the V.rotundifolia population had heterogeneous genetic differentiation.Combining the haplotype network map and geographical distribution map of these groups,we speculated that due to the influence of the Quaternary ice age,V.rotundifolia had at least two north and south refuges,which had a certain correlation with the location of the coast.V rotundifolia had undergone partly population expansion through the refuge after the Quaternary ice age,but the genetic differentiation is not obvious,as a result,V rotundifolia and V.trifolia are still conspecific.Our morphological and pollination studies also support that V.rotundifolia has adapted to sandy environments and local habitats,but the morphological differences between V.rotundifolia group and V trifolia group were obvious.These conclusions provid theoretical and data support for the conservation biology research of V rotundifolia.