Analysis of genetic variation in rare endemic species Oxytropis chankaensis Jurtz. (Fabaceae) using RAPD markers

The method of polymerase chain reaction with random primers (RAPD) was used to assess genetic variation and population differentiation in the rare endemic plant Oxytropis chankaensis Jurtz. (Fabaceae). DNA samples from plants of two isolated populations were compared at 133 loci detected by use of ten primers. Both populations examined were characterized by high polymorphism levels (P95 = 72.9%, A = 1.92 and P95 = 74.4%, A = 1.88, respectively). They were also statistically significantly different in the frequencies of most of the amplicons. For each of the plants, unique multilocus RAPD phenotype was established using 17 to 20 RAPD markers. Diagnostic markers were not revealed. The populations were poorly differentiated. On average, the between-population component accounted for about 8% of the variation, while 92% of the variation was detected within populations. High variation along with the low degree of differentiation characteristic of two most geographically remote populations of O. chankaensis can have several explanations, among which a polyploid origin of the species seems to be most important.     

Reproductive biology and conservation genetics of Goodyera procera (Orchidaceae)

Goodyera procera is an endangered terrestrial orchid in Hong Kong. Information on its reproductive biology and pattern of genetic variation is needed to develop efficient conservation strategies. Pollination experiments showed that the species is self-compatible, but dependent on pollinators for fruit set. Bagged plants produced no fruits. Artificial pollinations resulted in 92% fruit set through selfing, 94% with geitonogamous pollination, and 95% following xenogamous pollination. Fruit set in the open-pollinated control was 75% at the same sites. Allozyme electrophoresis and random amplified polymorphic DNA (RAPD) were used to evaluate genetic variation and structure of 15 populations of Goodyera procera. Despite its outbreeding system, allozyme data revealed low variation both at the population (P = 21.78%, A = 1.22, and H = 0.073) and species (P = 33%, A = 1.33, and H = 0.15) levels, in comparison with other animal-pollinated outbreeding plant species. However, RAPD variation was relatively high (P = 55.13% and H = 0.18 at the population level, and P = 97.03% and H = 0.29 at the species level). G_ST estimates indicated high levels of genetic differentiation among populations (G_ST = 0.52 and I = 0.909 ± 0.049 based on allozyme data, and G_ST = 0.39 and I = 0.859 ± 0.038 based on RAPD data), much above the average for outcrossing species, suggesting that gene flow was limited in this species. Based on these data, suitable strategies were developed for the genetic conservation and management of the species.     

Genetic Differentiation of Pedunculate Oak Quercus robur L. in the European Part of Russia Based on RAPD Markers

Using randomly amplified polymorphic DNA markers (RAPD), genetic variation and differentiation in four populations of pedunculate oak Quercus robur L. were examined. The populations occupy a large part of the Quercus robur range in the European Russia (Voronezh and Novgorod oblasts; Republics of Mordovia and Bashkortostan). With each of six random primers (A02, A09, A17, B01, B08, B11), 96 DNA samples were analyzed by PCR. In all, 48 putative polymorphic RAPD loci were detected. We failed to reveal population-specific DNA fragments for any primer although the frequencies of 14 fragments were significantly different among populations. The oak populations studied exhibited high variability: 73–90% of genes were polymorphic and the effective allele number was about 1.4. The total genetic variation varied from 0.202 (Vor) to 0.245 (Nov), which corresponded to the estimates for populations of this species from Central and Western Europe. The populations examined showed low among-population differentiation (G _ST = 0.098); gene flow N _e m was 4.61. The proportion of among-population variation of the RAPD loci studied accounted for 7% of the total variability; more than 93% of the total variability was explained by individual and within-population variation.     

Detection of Low Genetic Variation in a Critically Endangered Chinese Pine, Pinus squamata, Using RAPD and ISSR Markers

With only 32 individuals in the northeastern corner of Yunnan Province, China, Pinus squamata is one of the most endangered conifers in the world. Using two classes of molecular markers, RAPD and ISSR, its very low genetic variation was revealed. Shannon's index of phenotypic diversity (I) was 0.030, the mean effective number of alleles per locus (A_e) was 1.032, the percentage of polymorphic loci (P) was 6.45, and the expected heterozygosity (H_e) was 0.019 at the species level based on RAPD markers. The results of ISSR were consistent with those detected by RAPD but somewhat higher (I = 0.048, A_e = 1.042, P = 12.3, H_e = 0.029). The genetic variation of the subpopulation on the southwest-facing slope was much higher than that of the subpopulation on the northeast-facing slope, which may be attributed to the more diverse environment on the southwest-facing slope. The genetic differentiation between the two subpopulations was very low. The between-subpopulation variabilities, Φ_ST, calculated from RAPD and ISSR data were 0.011 and 0.024. Because of the lack of fossil records and geological historical data, it was difficult to explain the extremely low genetic diversity of the species. We postulate that this ancient pine might have experienced strong bottlenecks during its long evolutionary history, which caused the loss of genetic variation. Genetic drift and inbreeding in post-bottlenecked small populations may be the major forces that contribute to low genetic diversity. Human activities such as logging may have accelerated the loss of genetic diversity in P. squamata.     

Polymorphism of RAPD,ISSR and AFLP markers of the <Emphasis Type="Italic">Panax ginseng</Emphasis> C. A. Meyer (Araliaceae) genome

The genus Panax (Araliaceae) is world-famous because many its members have important medicinal properties. Panax ginseng C. A. Meyer is more popular than other species of the genus because remedies prepared from this plant stimulate immunity, help to prevent diseases, and have antistress effects. In addition, the ginseng root extract is traditionally used as a means against aging. At present, this species is found in the wild only in Primorsky krai, Russia, but its populations are extremely exhausted and need to be restored. In this study, effectiveness of molecular DNA markers in detecting genetic variation and differentiation of the ginseng populations was tested. Genetic variation of ginseng, identified using RAPD (P = 4%; H _pop = 0.0130) and ISSR (P = 9.3%; H _pop = 0.0139) markers was low. The AFLP* approach, according to which amplicons are separated in polyacrylamide gel and visualized by means of silver staining, showed somewhat higher variability (P = 21.8%; H _pop = 0.0509), while its effectiveness in population differentiation was as low as that of RAPD and ISSR. The AFLP** technique, which included analysis of the fragments using genetic analyzer, revealed high genetic diversity of ginseng (P = 94.4%; H _pop = 0.3246). All populations examined using the AFLP** markers were statistically significantly differentiated based on the AMOVA results. Our result suggest effectiveness of AFLP** markers for characterization of the genetic structure and genetic relationships of the ginseng populations. These markers are recommended for use in large-scale population genetic studies of this species to develop measures of its conservation.     

Genetic diversity of insular natural populations of <Emphasis Type="Italic">Festuca pratensis</Emphasis> Huds.: RAPD analysis

In natural populations of Festuca pratensis Huds. from the islands of Onega Lake, the level of genetic diversity was evaluated. In three populations variability of 64 RAPD loci was tested. The level of genetic diversity (P _95% = 30.2; H _exp = 0.093) was low for a cross-pollinating plant species. Furthermore, genetic similarity between the plants from insular populations was found to be high (I _N = 0.887). It was demonstrated that genetic variation among the population accounted for at most 5.3% of total genetic diversity, which, however, was higher than the F _ST values for continental populations (F _ST = 0.022). It was suggested that specific features of the genetic structure of insular population, i.e., low gene diversity within the populations along with high differentiation among the populations, were caused by the gene flow attenuation, as a result of isolation, and intensification of inbreeding. These features had negative effect on total population adaptation.     

Inter-simple sequence repeat (ISSR) variation in forest coffee trees (Coffea arabica L.) populations from Ethiopia

Genetic variation of forest coffee trees (Coffea arabica L.) from four regions of Ethiopia was investigated using inter-simple sequence repeat (ISSR) markers. A total of 160 individuals representing 16 populations were sampled. Eleven ISSR primers amplified a total of 123 fragments of which 31 fragments (25%) were polymorphic. Estimate of total gene diversity (H _T), and the coefficient of genetic differentiation (G _ST) were 0.37 and 0.81, respectively. This indicates that most of the variability is between populations than within populations. The partitioning of genetic variation into within and between populations based on Shannon’s information index also revealed more differentiation between populations (0.80) than within populations (0.20). In the phenogram most of the coffee tree samples were clustered on the basis of their regions of origin but failed to cluster according to their respective populations, which could be attributed to the presence of substantial gene flow between adjacent populations in each region assisted by man in the process of transplantation or by wild animals such as monkeys, which eat the berries and defecate the seeds elsewhere. On the other hand, the inter-regional clustering of some coffee tree samples from Bale and Jimma regions could be due to the transport of coffee seeds across regions and their subsequent planting. Although ISSR markers detected lower polymorphic loci than previously reported results with random amplified polymorphic DNA (RAPD) markers on the same materials, it can be used as an alternative method for molecular characterization of C. arabica populations. The results may provide information to select sites for in situ conservation.     

Genetic diversity of Mexican brook lamprey <Emphasis Type="Italic">Lampetra (Tetrapleurodon) geminis</Emphasis> (Alvarez del Villar, 1966)

Lampreys are the only surviving representatives of the oldest known vertebrates. The Mexican lamprey L. geminis (nonparasitic), is particularly interesting, because it is an endemic, biogeographical relict, and a threatened species. RAPD markers were used to describe genetic diversity in L. geminis A total of 77 specimens were collected from five populations, three in the R'o Grande de Morelia-Cuitzeo basin and two in the R'o Duero-Lerma-Chapala basin, Mexico. Eighty-eight RAPD markers were obtained from eight primers. Genetic diversity within each population was estimated using Shannon's index (S), heterozygosity (H) and gene diversity (h). These estimates revealed significant variation within populations, although a variance homogeneity test (HOMOVA) showed no significant differences among populations or between basins. Nei genetic distance values indicate a low genetic differentiation among populations. Analysis of molecular variance (AMOVA) indicates that most of the genetic diversity occurs within populations (91.4%), but that a statistically significant amount is found among populations (P0.001). Principal coordinates and cluster analyses of RAPD phenotypes show that specimens are not grouped by geographical origin. The genetic diversity found within L. geminispopulations may be explained by its breeding system and an overlapping of generations. The scarce genetic differentiation among populations is likely to the low rate of DNA change that characterizes the lamprey group.     

High Polymorphism and Autotetraploid Origin of the Rare Endemic SpeciesOxytropis chankaensisJurtz. (Fabaceae) Inferred from Allozyme Data

Using starch electrophoresis, we examined 19 enzyme systems presumably controlled by 35 loci in the rare endemic tetraploid speciesOxytropis chankaensisJurtz. (Fabaceae). Electrophoretic patterns and their genetic interpretation are presented. The isozyme data suggest tetrasomic inheritance in O. chankaensis. Three or four alleles at a particular locus were found in a number of individual plants, which indicate the autotetraploid origin of this species. Seventeen loci were shown to be polymorphic. As reliable gene markers for population systems, we recommend highly active polymorphic systems showing good allozyme separation (Ce-2, Gpi-2, Gpt-2, Idh-2, Lap, Mdh-2, and Mdh-3). Parameters of allozyme variability proved to be very high for a rare species with a restricted range: P = 48.6%, A = 2, A _p = 3.06, H _ob = 0.173.     

Genetic variation in the endangered <Emphasis Type="Italic">Anisodus tanguticus</Emphasis> (Solanaceae), an alpine perennial endemic to the Qinghai-Tibetan Plateau

We used random amplified polymorphic DNA markers (RAPDs) to assess genetic variation between- and within-populations of Anisodus tanguticus (Solanaceae), an endangered perennial endemic to the Qinghai-Tibetan Plateau with important medicinal value. We recorded a total of 92 amplified bands, using 12 RAPD primers, 76 of which (P = 82.61%) were polymorphic, and calculated values of H_t and H_sp of 0.3015 and 0.4459, respectively, suggesting a remarkably high rate of genetic variation at the species level. The average within-population diversity also appeared to be high, with P, H_e and H_pop values of 55.11%, 0.1948 and 0.2918, respectively. Analyses of molecular variance (AMOVA) showed that among- and between-population genetic variation accounted for 67.02% and 32.98% of the total genetic variation, respectively. In addition, Nei’s coefficient of differentiation (G_ST) was found to be high (0.35), confirming the relatively high level of genetic differentiation among the populations. These differentiation coefficients are higher than mean corresponding coefficients for outbreeding species, but lower than reported coefficients for some rare species from this region. The genetic structure of A. tanguticus has probably been shaped by its breeding attributes, biogeographic history and human impact due to collection for medicinal purposes. The observed genetic variations suggest that as many populations as possible should be considered in any planned in situ or ex situ conservation programs for this species.     

Genetic variability and differentiation of <Emphasis Type="Italic">Caragana microphylla</Emphasis> populations as revealed by RAPD markers

Genetic variability in random amplified polymorphic DNA (RAPD) was studied in 90 individuals of Caragana microphylla, an outcrossing perennial shrub species, from five natural populations sampled in Inner Mongolia steppe of China on a small scale. Nineteen selected primers were used to amplify DNA samples, and totally 225 bands were detected. The percentage of polymorphic bands within populations ranged form 58.22% to 63.56%, with an average of 60% at the population level and 71.11% at the species level, indicating relatively high genetic variations in C. microphylla species. Shannon’s information index (l) and Nei’s gene diversity (h) showed the similar trend with each other. According to the analysis of Nei’s gene diversity, the percentage of genetic variation among populations was 7.13%, indicating a low level of genetic differentiation among populations. There existed a strong gene flow (N _m = 3.26) among populations. Although AMOVA analysis also revealed most variation was within populations (Φ_ST = 4.1%), a significant proportion was observed among populations (P < 0.001) in the present study, suggesting genetic differentiation occurred among populations at a certain extent. Based on Mantel’s tests and the results of previous studies, the genetic structure pattern of C. microphylla accorded with the isolation-by-distance model on a very large scale, however, on a small scale, the significant genetic differentiation among populations might be enhanced by the micro-environmental divergence among the sampling sites, rather than by geographic factors. Analysis of the genetic variations of C. microphylla populations provided useful information for the adaptive strategy of Caragana species.     

北沙柳群体遗传多样性和遗传结构分析

以内蒙古北沙柳(Salix psammophila)国家种质资源库内9个群体(P1~P9)288个无性系为实验材料,利用TP-M13-SSR技术,选取22对具有多态性EST-SSR北沙柳引物,采用毛细管电泳对PCR产物进行检测,分析北沙柳遗传多样性、分化程度和群体遗传结构,为北沙柳种质资源库遗传管理、无性系鉴定、品种选育、遗传改良和构建指纹图谱提供理论依据。结果显示:(1)22对EST-SSR引物共检测到222个等位基因,各位点平均等位基因数(A)为10,四倍体基因型丰富度(G)和特异基因型(G1)总和分别为1 460和802个,平均特异基因型比率(P1)和种质鉴别率(P2)分别为45.86%和13.21%。(2)9个群体平均等位基因数(A)为7.475,基因型丰富度(G)为15.586,观察杂合度(Ho)和期望杂合度(He)分别为0.577和0.638。以期望杂合度He为标准,北沙柳群体遗传多样性水平最低的是P1和P9。(3)北沙柳群体遗传分化系数仅为0.02,AMOVA分子变异分析显示,北沙柳群体大部分遗传变异来自群体内(97%),群体间变异仅为3%。(4)三维主成分、聚类和Structure群体遗传结构分析显示,9个群体被划分为2个组,Mantel检验表明北沙柳遗传距离与地理距离极显著相关(r=0.684 P0.001)。研究表明,北沙柳种质资源具有丰富的遗传多样性,这是其具有耐旱、耐寒、耐高温、耐沙埋和抗风蚀等适应性较强的分子基础;北沙柳的遗传变异集中在群体内;分布区群体呈现由中心向边缘群体扩张分化的趋势。     

A Study of Conservation Genetics in Cupressus chengiana,an Endangered Endemic of China,Using ISSR Markers

ISSR markers were used to analyze the genetic diversity and genetic structure of eight natural populations of Cupressus chengiana in China. ISSR analysis using 10 primers was carried out on 92 different samples. At the species level, 136 polymorphic loci were detected. The percentage of polymorphic bands (PPB) was 99%. Genetic diversity (H _e) was 0.3120, effective number of alleles (A _e) was 1.5236, and Shannon’s information index (I) was 0.4740. At the population level, PPB = 48%, A _e=1.2774, H _e=0.1631, and I=0.2452. Genetic differentiation (G _st) detected by Nei’s genetic diversity analysis suggested 48% occurred among populations. The partitioning of molecular variance by AMOVA analysis indicated significant genetic differentiation within populations (54%) and among populations (46%; P < 0.0003). The average number of individuals exchanged between populations per generation (N _m ) was 0.5436. Samples from the same population clustered in the same population-specific cluster, and two groups of Sichuan and Gansu populations were distinguishable. A significantly positive correlation between genetic and geographic distance was detected (r=0.6701). Human impacts were considered one of the main factors to cause the rarity of C. chengiana, and conservation strategies are suggested based on the genetic characters and field investigation, e.g., protection of wild populations, reestablishment of germplasm bank, and reintroduction of more genetic diversity.     

Evolutionary implications of allozyme and RAPD variation in diploid populations of dioecious buffalograss Buchloë dactyloides

Buffalograss, Buchloë dactyloides, is widely distributed throughout the Great Plains of North America, where it is an important species for rangeland forage and soil conservation. The species consists of two widespread polyploid races, with narrowly endemic diploid populations known from two regions: central Mexico and Gulf Coast Texas. We describe and compare the patterns of allozyme and RAPD variation in the two diploid races, using a set of 48 individuals from Texas and Mexico (four population samples of 12 individuals each). Twelve of 22 allozyme loci were polymorphic, exhibiting 35 alleles, while seven 10-mer RAPD primers revealed 98 polymorphic bands. Strong regional differences were detected in the extent of allozyme polymorphism: Mexican populations exhibited more internal gene diversity (H_e= 0.20, 0.19) than did the Texan populations (H_e= 0.08, 0.06), although the number of RAPD bands in Texas (n= 62) was only marginally smaller than in Mexico (n= 68). F-statistics for the allozyme data, averaged over loci, revealed strong regional differentiation (mean F_RT=+ 0.30), as well as some differentiation among populations within regions (mean F_PR=+ 0.09). In order to describe and compare the partitioning of genetic variation for multiple allozyme and RAPD loci, we performed an Analysis of Molecular Variance (AMOVA). AMOVA for both allozyme and RAPD data revealed similar qualitative patterns: large regional differences and smaller (but significant) population differences within regions. RAPDs revealed greater variation among regions (58.4% of total variance) than allozymes (45.2%), but less variation among individuals within populations (31.9% for RAPDs vs. 45.2% for allozymes); the proportion of genetic variance among populations within regions was similar (9.7% for RAPDs vs. 9.6% for allozymes). Despite this large-scale concordance of allozyme and RAPD variation patterns, multiple correlation Mantel techniques revealed that the correlations were low on an individual by individual basis. Our findings of strong regional differences among the diploid races will facilitate further study of polyploid evolution in buffalograss.     

Genetic variation within and among populations of a wild rice Oryza granulata from China detected by RAPD and ISSR markers

Genetic variation within and between five populations of Oryza granulata from two regions of China was investigated using RAPD (random amplified polymorphic DNA) and ISSR (inter-simple sequence repeat amplification) markers. Twenty RAPD primers used in this study amplified 199 reproducible bands with 61 (30.65%) polymorphic; and 12 ISSR primers amplified 113 bands with 52 (46.02%) polymorphic. Both RAPD and ISSR analyses revealed a low level of genetic diversity in wild populations of O. granulata. Furthermore, analysis of molecular variance (AMOVA) was used to apportion the variation within and between populations both within and between regions. As the RAPD markers revealed, 73.85% of the total genetic diversity resided between the two regions, whereas only 19.45% and 6.70% were present between populations within regions and within a population respectively. Similarly, it was shown by ISSR markers that a great amount of variation (49.26%) occurred between the two regions, with only 38.07% and 12.66% between populations within regions and within a population respectively. Both the results of a UPGMA cluster, based on Jaccard coefficients, and pairwise distance analysis agree with that of the AMOVA partition. This is the first report of the partitioning of genetic variability within and among populations of O. granulata at the DNA level, which is in general agreement with a recent study on the same species in China using allozyme analysis. Our results also indicated that the percentage of polymorphic bands (PPB) detected by ISSR is higher than that detected by RAPD. It seems that ISSR is superior to RAPD in terms of the polymorphism detected and the amplification reproducibility. Received: 29 March 2000 / Accepted: 15 May 2000     

High chloroplast haplotype diversity in the endemic legume <Emphasis Type="Italic">Oxytropis chankaensis</Emphasis> may result from independent polyploidization events

Oxytropis chankaensis Jurtz. (Fabaceae) is an endangered perennial tetraploid species endemic to the Khanka Lake coast. In Russia, O. chankaensis is distributed across a very restricted zone along the western shore of this lake. To characterise all known populations of this species, we assessed the genetic diversity of four noncoding regions of chloroplast DNA (cpDNA). Variable sites detected within the trnL–trnF, the petG–trnP, and the trnS–trnG regions allowed the identification of seven haplotypes. On the other hand, no variation was found in the trnH–psbA region. O. chankaensis exhibited an overall low level of nucleotide diversity (π = 0.00052) but a marked haplotype diversity (h = 0.718). A combination of three or four haplotypes was found in each population, and most of the cpDNA variation (above 90%) was distributed within populations. The level of genetic structure that we detected in O. chankaensis using maternal plastid DNA markers was much lower (G _ST = 0.037) than the average that is estimated for angiosperms. We found no evidence for isolation by distance or for phylogeographic structuring in O. chankaensis. Our data suggest that autopolyploidy has arisen more than once in the evolutionary history of this species. Repetitive expansion and contraction during past and ongoing demographic events both seem to be involved in shaping the current genetic structure of O. chankaensis. This study provides valuable information for developing the most appropriate strategy for conserving this endemic species with a narrow habitat range.     

Use of RAPD and ISSR Markers in Detection of Genetic Variation and Population Structure among Fusarium oxysporum f. sp. ciceris Isolates on Chickpea in Turkey

Genetic variation among the isolates of Fusarium oxysporum f. sp. ciceris, the causal agent of chickpea wilt worldwide, was analysed using pathogenicity tests and molecular markers – random amplified polymorphic DNA (RAPD) and inter‐simple sequence repeat (ISSR) polymorphism. Hundred and eight isolates were obtained from diseased chickpea plants in 13 different provinces of Turkey, out of which 74 isolates were assessed using 30 arbitrary decamer primers and 20 ISSR primers. Unweighted pair‐grouped method by arithmetic average cluster analysis of RAPD, ISSR and RAPD + ISSR datasets provided a substantially similar discrimination among Turkish isolates and divided into three major groups. Group 1, 2 and 3 consisted of 41, 18 and 15 isolates, respectively. These methods revealed a considerable genetic variation among Turkish isolates, but no correlation with regard to the clustering of isolates from different geographic regions. Analysis of molecular variance confirmed that most genetic variability resulted from the differences among isolates within regions. Our results also indicated that the low‐genetic differentiation (F_ST) and high gene flow (Nm) among populations had a significant effect on the emergence and evolutionary development of F. oxysporum f. sp. ciceris. This is the first report on genetic diversity and population structure of F. oxysporum isolates on chickpea in Turkey.     

Genetic Diversity Within and Among Lepidium draba Populations from Eastern Anatolia Based on RAPD Analysis

Genetic variation and structure of six natural populations of Lepidium draba L. from Eastern Anatolia were assessed using random amplified polymorphic DNA (RAPD) markers. For RAPD analysis, 12 primers generated 218 reproducible bands across the six populations analyzed, of which 73 bands (33.3%) were polymorphic. The mean Nei’s gene diversity value for all six populations was 0.1771. Shannon’s information index varied with population (0.2278–0.3082), averaging 0.2608. Analysis of molecular variance (AMOVA) showed that genetic diversity was greater within populations (58.66%) than among populations (30.68%). In addition, the variation between groups was 10.33%. The genetic differentiation among populations (G _ST) was 0.3210, indicating that most genetic diversity occurs within populations. Gene flow (Nm) was low, at only 0.5288.     

Analysis of DNA polymorphism in a relict Uralian species,large-flowered foxglove (<Emphasis Type="Italic">Digitalis grandiflora</Emphasis> Mill.), using RAPD and ISSR markers

Genetic polymorphism of the Uralian relict plant species, large-flowered foxglove Digitalis grandiflora Mill. (family Scrophulariaceae), was examined using RAPD and ISSR techniques. A total of 149 RAPD and 74ISSR markers were tested. The indices characterizing polymorphism and genetic diversity were calculated. The data obtained pointed to a high level of genetic variation of D. grandiflora (P ₉₅ = 65%). The cenopopulation examined was weakly differentiated with most of genetic diversity accounted by within-population differentiation.     

Genetic differentiation among populations ofArabis serrata (Brassicaceae) along its geographic distribution

Levels and distribution of genetic variation were investigated in ten populations of the perennialArabis serrata distributed along a latitudinal gradient throughout Japan. Populations of this endemic species occupy predominantly three types of habitats: limestone and derived soils, volcanic and disturbed sites. Previous studies showed that plants ofA. serrata are differentiated in morphological and ecological traits under both natural conditions and common garden experiments suggesting genetic differentiation among populations. To assess the degree of genetic differentiation under different habitats ofA. serrata populations, we analyzed the isozyme genetic structure. Ten populations, located in mountains of central and northern Honshu and Hokkaido, were analyzed by starch gel enzyme electrophoresis. Fourteen loci of eight enzymes were resolved and six loci were monomorphic for all the populations. Populations sampled maintain low levels of genetic variation (P=0.16;H=0.05;A=1.16) compared to that maintained by other outcrossing seed plants. In some cases, few or no heterozygous individuals were detected, and consequently, mean observed heterozygosity was zero or near zero. Six (29%) of the fixation indices,F, estimated deviated significantly from Hardy Weinberg genotypic expectations indicating a deficiency of heterozygotes in most of the cases. The mean genetic identity (Nei'sI) between population pairs was 0.852 and indicates a moderate level of genetic differentiation among populations.Arabis serrata has most of its genetic variation distributed among rather than within populations. The among-population component of the total genetic diversity (G _ST mean value) was 0.416, indicating genetic differentiation between populations. There groups of populations were recognized in an unrooted tree generated by the Neighbor-Joining method. These results suggest groups of populations differentiated regionally. Estimates of interpopulational gene flow (Nm) were very variable (range 0.049–3.718) with a meanNm=1.203 for all populations.