珠芽蓼种群克隆多样性及克隆结构的初步研究

珠芽蓼(Polygonum viviparum)是青藏高原东缘广泛分布的克隆植物,具有有性和无性(根状茎和珠芽)两种生殖方式。该研究采用RAPD技术对分布于不同海拔的珠芽蓼7个自然种群进行了克隆结构和克隆多样性(是单克隆种群还是多克隆种群)以及克隆多样性与海拔因子之间的相关性研究,为了解高山克隆植物对环境的适应性策略及揭示克隆植物的繁殖和分布特点提供科学依据。研究结果表明:1)采用13条RAPD引物对珠芽蓼7个种群共140个样本进行扩增分析,共扩增到117个位点,其中多态性位点84个,多态位点百分率PPL达到71.79%,检测到43个基因型,且全部为局限型基因型;2)与Ellstrand和Roose(1987)总结的克隆植物的克隆多样性平均值相比(PD=0.17,D=0.62),珠芽蓼种群克隆多样性水平稍高,Simpson指数平均为0.639,基因型比率PD平均为0.307;3)克隆结构分析表明,珠芽蓼种群内克隆之间的镶嵌明显,这可能与珠芽蓼过渡型的克隆构型有关。研究中珠芽蓼种群的构型有游击型、密集型以及这两者之间的过渡类型;4)采用SPSS软件对珠芽蓼种群的克隆多样性与海拔高度进行相关性分析,结果显示它们之间并无明显的相关性。     

Floral distribution,clonal structure,and their effects on pollination success in a self-incompatible <Emphasis Type="Italic">Convallaria keiskei</Emphasis> population in northern Japan

In plant species, when clonal growth produces a patchy structure and flowering ramets are clustered, the amount of pollen contributing to reproductive success is often regulated by pollinator efficiency and geitonogamy. The spatial population structure may influence reproductive success. We examined the clonal structure, the spatial ramet distribution, and their combined effects on fruit set in a natural population of the insect-pollinated, self-incompatible clonal herb, Convallaria keiskei, in northern Japan. The number of shoots, flowers, and fruits in 1-m² quadrats were counted at every 5 m grid point in an established 100 × 90-m study plot. From all the quadrats where shoots existed, leaf samples were collected for allozyme analysis. Using the two spatial parameters of flowering ramet densities and genotypes, we then constructed individual-based fruit-set models. A total of 236 quadrats contained shoots, and 135 contained flowering ramets, which indicated expanded distribution of this plant throughout the study plot, while shoots, flowers and fruits all showed clustering distributions. Allozyme analysis of 282 samples revealed 94 multilocus genotypes. The largest clone extended to more than 40 m, whereas 56 genotypes were detected in only one sample. Several large clones and many small clones were distributed close to each other. Fine-scale spatial modelling revealed that the neighbouring flower numbers of different genotypes, compared with local genet or flower diversity, more influenced fruit set, in which the range of the neighbour was 14.5 m. These findings indicate that the compatible pollen dispersed by insect pollinators has a significant effect on sexual reproduction, in this C. keiskei population. Consequently, the spatial structure, which includes both genet distribution and clonal expansion by ramets, had a significant effect on pollination success.     

High genotypic diversity and strong spatial structure in populations of Trifolium alpestre with low seed production

Studies on clonal plants indicate that the proportion between clonal and sexual reproduction can be variable, depending on local habitat conditions and the biological characteristics of the species. In the present study, we assessed this question in Trifolium alpestre by assaying genetic diversity and spatial genotypic structure of natural populations with the use of allozyme markers. Populations revealed high genetic diversity as well as strong spatial structure of multilocus genotypes. The values of genetic diversity were moderately high. Spatially aggregated, identical genotypes spread up to 15 m along linear transects and across 4‐m² plots indicate extensive clonal propagation within populations. However, the existence of numerous unique and small‐sized clones reflects significant contribution from sexual reproduction. Spatially and temporarily stochastic soil disturbances have evidently opened new opportunities for the successful sexual recruitment from the permanent soil seed bank and thus counteracted losses of genetic and genotypic diversity. Seed production in all populations during the three study years was low, in average up to 1.5–2.4 seeds per shoot. The almost total lack of seed set for 57 bagged flower heads on genotypes grown in a common garden indicates that T. alpestre needs pollinators for seed production.     

Microscale variation in alpine grasslands: AFLPs reveal a high level of genotypic diversity in Primula minima (Primulaceae)

The microscale variation and spatial genetic structure of the alpine plant species Primula minima L. was analysed using AFLPs. AFLP analysis based on three primer combinations and 123 fragments revealed no identical genotypes among the 86 studied samples from a 300 × 300 cm plot. Variation within the study plot was high: Nei's gene diversity was 0.22, Shannon's information index 0.33 and the percentage of polymorphic bands was 60.9. Cluster analysis revealed four main groups of genetically similar individuals and mapping these individuals resulted in a clear spatial pattern, with samples from the same group often located close together. The observed microscale structure was corroborated using a Mantel test, which revealed significant correlation of genetic and spatial distances, and by the results of a spatial autocorrelation analysis that indicated a high level of similarity between adjacent samples. An analysis of molecular variance revealed clear differentiation (18%) between the spatial groups. Overall gene flow within the plot was 1.11 and ranged from 0.33 between the spatially most distant groups to 2.33 between directly neighbouring groups. The extraordinary level of diversity detected in this study indicates an unexpectedly strong relevance of reproduction by seed for the species P. minima in alpine grasslands. The strong microscale variation suggests, however, that there is limited dispersal of seeds. Clonal reproduction is of subsidiary importance to sexual reproduction and seems to occur only over very small distances.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 549–556.     

Clonal and fine-scale genetic structure in populations of a restricted Korean endemic, Hosta jonesii (Liliaceae) and the implications for conservation

BACKGROUND AND AIMS: In plant populations the magnitude of spatial genetic structure of apparent individuals (including clonal ramets) can be different from that of sexual individuals (genets). Thus, distinguishing the effects of clonal versus sexual individuals in population genetic analyses could provide important insights for evolutionary biology and conservation. To investigate the effects of clonal spread on the fine-scale spatial genetic structure within plant populations, Hosta jonesii (Liliaceae), an endemic species to Korea, was chosen as a study species. METHODS: Using allozymes as genetic markers, spatial autocorrelation analysis of ramets and of genets was conducted to quantify the spatial scale of clonal spread and genotype distribution in two populations of H. jonesii. KEY RESULTS: Join-count statistics revealed that most clones are significantly aggregated at < 3-m interplant distance. Spatial autocorrelation analysis of all individuals resulted in significantly higher Moran's I values at 0-3-m interplant distance than analyses of population samples in which clones were excluded. However, significant fine-scale genetic structure was still observed when clones were excluded. CONCLUSIONS: These results suggest that clones enhance the magnitude of spatial autocorrelation due to localized clonal spread. The significant fine-scale genetic structure detected in samples excluding clones is consistent with the biological and ecological traits exhibited by H. jonesii including bee pollination and limited seed dispersal. For conservation purposes, genetic diversity would be maximized in local populations of H. jonesii by collecting or preserving individuals that are spaced at least 5 m apart.     

GENETIC STRUCTURE OF COEXISTING SEXUAL AND CLONAL SUBPOPULATIONS IN A FRESHWATER SNAIL (POTAMOPYRGUS ANTIPODARUM)

We examined clonal diversity and the distribution of both clonal and sexual genotypes in a single population of freshwater snails (Potamopyrgus antipodarum) in which diploid sexual individuals and triploid parthenogens coexist. A genetic analysis of individuals from three habitat zones in Lake Alexandrina, New Zealand revealed extremely high clonal diversity: 165 genotypes among 605 clonal individuals. The frequency of triploid clonal individuals increased with increasing depth in the lake, and most of the individual clones were habitat specific, suggesting that differences among habitats are important in structuring the clonal subpopulation. There were also high levels of clonal diversity within habitats, suggesting frequent origins of habitat-specific clones. In contrast, diploid sexual individuals were proportionately more common in the shallow regions of the lake (where infection by trematode larvae is highest), and there was no significant spatial structure in the sexual subpopulation. We suggest that habitat specialization by clones, as well as parasite-mediated selection against common clones, are important factors affecting the structure of this mixed population of sexual and clonal snails.     

Long-term persistence in a changing climate: DNA analysis suggests very old ages of clones of alpine Carex curvula

Carex curvula is a very slow-growing rhizomatous sedge that forms extensive stands in the European an alpine belt. The recruitment of sexual progeny is extremely rare and propagation occurs predominantly through clonal growth. The randomly amplified polymorphic DNA (RAPD) technique was used to analyse clonal structure in a small patch (2.0x0.4 m sampling transect plus some additional samples) of a high-alpine population of the species. Amplification of the DNA of 116 tiller samples from the patch with eight ten-base primers yielded a total of 95 bands, of which 73 were polymorphic. Based on the RAPD amplification profiles a total of 15 multilocus genotypes (putative clones) were identified. Due to the high number of polymorphic loci the number of genetic markers delineating individual clones was high (range: 16–39 markers) which suggests that our estimates of clonal diversity are precise. More than half of the sampled tillers were identified as belonging to a single clone which formed a relatively homogeneous disc intermingling with other clones only at its margin. Based on the maximum diameter of this large clone of more than 7000 tillers and estimates of annual expansion growth of rhizomes (0.4 mm year^-1), the age of the clone was calculated to be around 2000 years. This demonstrates that clones of C. curvula may persist on a single spot over long periods with quite diverse alpine climates ranging from rather mild periods in the Middle Ages to cool periods during the so called little ice age in the last century. Our results suggest caution with plant migration scenarios based on shifting isotherms where late-successional clonal species, which dominate the alpine vegetation all over the world, are concerned.     

佛坪国家级自然保护区秦岭箭竹克隆结构的SSR分析

利用SSR分子标记技术分析了佛坪国家级自然保护区秦岭箭竹(Fargesia qinlingensis)的克隆多样性和克隆结构,以探讨小尺度范围内秦岭箭竹自然居群遗传变异的分布特征,对该种开花特性、高山地区生态环境维护和大熊猫的保护提供重要依据。结果表明7对SSR引物共扩增出79个位点,其中多态性位点77个,多态位点百分率(PPB)为97.47%。秦岭箭竹的142个分株共形成107个克隆,最大克隆可达5 m。克隆多样性略高于其他克隆植物的平均值(D=0.62,G/N=0.17,E=0.68),基因型比率(G/N)、Simpson指数(D)、平均克隆大小(N/G)和Fager均匀性指数(E)分别为0.7535、0.9680、1.3271和0.5109。克隆空间结构分析表明秦岭箭竹的克隆构型为密集型,各克隆呈镶嵌性分布,同一克隆的分株排列紧密。克隆聚类分析表明各克隆之间聚类不明显,总体上来自同一样地的克隆被聚为一类。空间自相关分析显示在空间距离为36 m范围内,分株比基株有更显著的空间遗传结构,空间自相关系数r的取值范围分别为0.084—0.626和0.024—0.288,说明克隆繁殖在一定程度上限制了空间遗传结构的范围。样地内秦岭箭竹个体在空间距离小于44 m时存在显著的正相关空间结构,特别是在4 m处表现出最大的空间自相关系数(r=0.626),表明空间距离相距4 m内的个体最有可能属于同一克隆,4 m比5 m更能表现出清晰的克隆结构,X-轴截距为52.280,代表了秦岭箭竹不规则克隆的平均最小长度。秦岭箭竹的克隆多样性和克隆结构与初始苗补充、花粉散播方式和微环境差异有关。     

Clonal diversity and structure within a population of the pondweed Potamogeton pectinatus foraged by Bewick's swans

Clonal diversity within plant populations is affected by factors that influence genet (clone) survival and seed recruitment, such as resource availability, disturbance, seed dispersal mechanism, propagule predation and the age of the population. Here we studied a population of Potamogeton pectinatus, a pseudo-annual aquatic macrophyte. Within populations reproduction appears to be mainly asexually through subterranean propagules (tubers), while recruitment via seeds is believed to be relatively unimportant. RAPD markers were used to analyse clonal diversity and genetic variation within the population. Ninety-seven genets were identified among 128 samples taken from eight plots. The proportion of distinguishable genets (0.76) and Simpson's diversity index (0.99) exhibited high levels of clonal diversity compared to other clonal plants. According to an analysis of molecular variance (amova) most genetic variation occurred between individuals within plots (93-97%) rather than between plots (8-3%). These results imply that sexual reproduction plays an unexpectedly important role within the population. Nevertheless, autocorrelation statistics revealed a spatial genetic structure resulting from clonal growth. In contrast to genetic variation, clonal diversity was affected by several ecological factors. Water depth and silt content had direct negative effects on clonal diversity. Tuber predation by Bewick's swans had an unexpected indirect negative effect on clonal diversity through reducing the tuber-bank biomass in spring, which on its turn was positively correlated to clonal diversity. The disturbance by swans, therefore, did not enhance seed recruitment and thus clonal diversity; on the contrary, heavily foraged areas are probably more prone to stochastic loss of genets leading to reduced clonal diversity.     

Within-population spatial genetic structure, neighbourhood size and clonal subrange in the seagrass Cymodocea nodosa

Abstract The extent of clonality within populations strongly influences their spatial genetic structure (SGS), yet this is hardly ever thoroughly analysed. We employed spatial autocorrelation analysis to study effects of sexual and clonal reproduction on dispersal of the dioecious seagrass Cymodocea nodosa. Analyses were performed both at genet level (i.e. excluding clonal repeats) and at ramet level. Clonal structure was characterized by the clonal subrange, a spatial measure of the linear limits where clonality still affects SGS. We show that the clonal subrange is equivalent to the distance where the probability of clonal identity approaches zero. This combined approach was applied to two meadows with different levels of disturbance, Cadiz (stable) and Alfacs (disturbed). Genotypic richness, the proportion of the sample representing distinct genotypes, was moderate (0.38 Cadiz, 0.46 Alfacs) mostly due to dominance of a few clones. Expected heterozygosities were comparable to those found in other clonal plants. SGS analyses at the genet level revealed extremely restricted gene dispersal in Cadiz (Sp = 0.052, a statistic reflecting the decrease of pairwise kinship with distance), the strongest SGS found for seagrass species, comparable only to values for selfing herbaceous land plants. At Cadiz the clonal subrange extended across shorter distances (20-25 m) than in Alfacs (30-35 m). Comparisons of sexual and vegetative components of gene dispersal suggest that, as a dispersal vector within meadows, clonal spread is at least as important as sexual reproduction. The restricted dispersal and SGS pattern in both meadows indicates that the species follows a repeated seedling recruitment strategy.     

A contribution to characterisation of genetic variation in some natural Polish populations of Elymus repens (L.) Gould and Elymus hispidus (Opiz) Melderis (Poaceae) as revealed by RAPD markers*

To determine the relative importance of clonal growth and sexual reproduction, the Randomly Amplified Polymorphic DNA (RAPD) method was used to study genetic diversity and clonal structure of six populations of Elymus repens and four populations of Elymus hispidus from Poland. These outbreeding species are virtually self‐sterile and form widely spreading and long‐lived rhizomes. Using 12 primers, a total of 150 unambiguous RAPD fragments were amplified and scored. Results of AMOVA showed no significant genetic distinction between morphologically distinguished varieties of E. repens and E. hispidus. E. repens had slightly higher intra‐specific genetic polymorphism than E. hispidus; the percentage of polymorphic bands per population ranged from 38 to 49 and from 19 to 38 respectively. Clonal diversity measured using the Simpson diversity index (D) indicated different contributions of clonal reproduction in particular populations of E. repens (D: 0.20–0.72). Populations of E. hispidus were dominated by one or a few clones, which were generally restricted to a single population (D: 0.00–0.22). RAPD revealed that most genetic diversity resided within populations of the two studied species, suggesting that, despite their clonal character, propagation by seeds contributes considerably to reproduction of E. repens and E. hispidus.     

CLONAL STRUCTURE,GENOTYPIC DIVERSITY,AND SEED PRODUCTION IN POPULATIONS OF FILIPENDULA RUBRA (ROSACEAE) FROM THE NORTHCENTRAL UNITED STATES

Queen of the prairie, Filipendula rubra (Rosaceae), is a clonal plant species inhabiting calcareous fens and wet meadows of the northcentral United States. F. rubra reproduces asexually by underground rhizomes and sexually by seed. While many studies have explored genotype diversity in clonal species with limited sexual reproduction, fewer have been conducted on clonal species with the potential for extensive sexual reproduction. We studied the relationship between the extent of sexual reproduction and genotype diversity. Although genotype diversity in F. rubra was double that reported by others for 27 nearly obligate clonal plant species, it was still quite low. For 25 populations studied, the mean number of genotypes was 5.5 (range = 1–15; SE = 0.964) and the average proportion of distinguishable genotypes was 0.38 (range = 0.03–1.00; SE = 0.07). The production of viable seed was quite variable among populations (mean proportion of viable seeds = 0.242; range = 0.002–0.565; SE = 0.04). Considering that some inflorescences can produce over 5,000 seeds, the potential for recruitment of sexually produced individuals is very large. No correlation was found between seed production and genotype diversity as was expected in a self-incompatible species in which one-third of the populations possessed a single genotype. It was hypothesized that the low genotype diversity found in numerous populations may be due to competition limiting recruitment of new seedlings.     

Reproductive strategy, clonal structure and genetic diversity in populations of the aquatic macrophyte Sparganium emersum in river systems

Many aquatic and riparian plant species are characterized by the ability to reproduce both sexually and asexually. Yet, little is known about how spatial variation in sexual and asexual reproduction affects the genotypic diversity within populations of aquatic and riparian plants. We used six polymorphic microsatellites to examine the genetic diversity within and differentiation among 17 populations (606 individuals) of Sparganium emersum, in two Dutch-German rivers. Our study revealed a striking difference between rivers in the mode of reproduction (sexual vs. asexual) within S. emersum populations. The mode of reproduction was strongly related to locally reigning hydrodynamic conditions. Sexually reproducing populations exhibited a greater number of multilocus genotypes compared to asexual populations. The regional population structure suggested higher levels of gene flow among sexually reproducing populations compared to clonal populations. Gene flow was mainly mediated via hydrochoric dispersal of generative propagules (seeds), impeding genetic differentiation among populations even over river distances up to 50 km. Although evidence for hydrochoric dispersal of vegetative propagules (clonal plant fragments) was found, this mechanism appeared to be relatively less important. Bayesian-based assignment procedures revealed a number of immigrants, originating from outside our study area, suggesting intercatchment plant dispersal, possibly the result of waterfowl-mediated seed dispersal. This study demonstrates how variation in local environmental conditions in river systems, resulting in shifting balances of sexual vs. asexual reproduction within populations, will affect the genotypic diversity within populations. This study furthermore cautions against generalizations about dispersal of riparian plant species in river systems.     

贺兰山丁香自然居群克隆生长格局及遗传多样性的ISSR分析

运用ISSR分子标记技术,通过制定挖掘采样、"+"形采样及"垂直"采样3种采样方案,对贺兰山丁香(Syringa pinnatifolia var.alanshanica)不同居群的克隆多样性、克隆生长格局及其遗传多样性进行了分析.克隆多样性分析表明:挖掘采样方式采到的3个克隆系内,各自所包含的单株间具有完全相同的基因型;"垂直"采样及"+"形采样的7个居群、 239个样品表现出136个不同的基因型或克隆,显示贺兰山丁香具有较高的克隆多样性(D=0.994)及基因型分布均匀性(E=0.985).克隆生长空间格局分析表明,贺兰山丁香为密集型克隆植物.每个居群都由多克隆组成,克隆生长只发生在同一丛内,多数基株只含有1个分株,最多可达8个.物种水平上的平均克隆大小(N_C)和平均基因型比例(PD)分别为1.757和0.569.对贺兰山丁香遗传多样性分析的结果显示,在居群水平和物种水平上都保持着较高的遗传多样性,其遗传变异主要存在于居群内;但居群间分化程度较低(G_ST=0.320),表明自然居群间基因交流有限.     

Sex after all: high levels of diversity detected in the arctic clonal plant Saxifraga cernua using RAPD markers

Arctic plants in general and arctic clonal plants in particular have often been assumed to contain low levels of genetic diversity. We used RAPDs (random amplified polymorphic DNAs) to investigate genetic diversity in the arctic-alpine Saxifraga cernua , which mainly reproduces clonally via bulbils, at three spatial scales in Svalbard: (i) 'macroscale', between two sites 11 km apart; (ii) 'mesoscale', along two crossing transects at each site; and (iii) 'microscale', within a 3 × 3 m square at each site. Thirteen putative clones (RAPD phenotypes) were distinguished among 93 ramets based on 38 RAPD markers. The genetic diversity ( D ; mean 0.52, range 0.10–0.81) and evenness ( E ; mean 0.42, range 0.00–0.82) were at the same level as in clonal plants in general. However, the diversity strongly depended on site and spatial scale. Several clones were highly divergent and clustered independently of site in UPGMA and PCO analyses. In an analysis of molecular variance ( AMOVA ), most of the variation (59%) was found within sites. Mantel tests revealed no correlation between spatial and genetic distance within sites. Our results suggest that occasional sexual reproduction as well as clonal migration via bulbil dispersal play a significant role in the treeless arctic environment, where S. cernua is widespread and locally very abundant. In contrast, Bauert et al. ( Molecular Ecology 7, 1519–1527) found no genetic variation within populations or regions of the Alps, where the species has highly isolated occurrences.     

Unexpectedly high genetic variation in large unisexual clumps of the subdioecious plant Honckenya peploides (Caryophyllaceae)

Honckenya peploides is a subdioecious dune plant that reproduces both sexually and by clonal growth. In northwest Spain this species was found to exhibit an extreme spatial segregation of the sexes, and our objective was to investigate genetic variation in unisexual clumps. Genetic variation was studied in six unisexual clumps of H. peploides, three of them exclusively composed of males and three exclusively female. In total, 193 samples were analysed using isozyme analysis and 80 samples were analysed using two AFLP primer combinations. Both techniques revealed considerably high genetic diversity (average proportion of distinguishable genotypes: 0.22 for isozymes and 0.36 for AFLP; average Simpson’s D: 0.65 for isozymes and 0.68 for AFLP). Our results show that, in spite of clonal growth, each unisexual clump consists of different genotypes. Genetic diversity within clumps is similar for both sexual morphs. Reasons for unisexuality of the clumps are discussed.     

Impact of clonal growth on effective population size in Hymenoxys herbacea (Asteraceae)

By influencing the proliferation of different genotypes, clonal growth can affect the maintenance of genetic variability and magnitude of genetic drift within plant populations. However, estimates of effective population size rarely incorporate the contribution of both asexual and sexual reproduction. We estimated effective size (Ne) for two populations of the clonal, self-incompatible plant, Hymenoxys herbacea, using a stage-structured demographic model for organisms with asexual and sexual recruitment and then examined the impact of reproductive strategy using an elasticity analysis. Plant rosettes monitored in two successive years had high survival rates in both populations (mean 0.94). The mean number of sexually derived recruits per initial ramet was 0.041 (SE 0.039), whereas the mean number of clonal recruits was 0.61 (SE 0.90). Effective size was 1642 and 5769 in the two populations and the Ne/N ratio averaged 0.34, comparable to values for other clonal species. Elasticity analysis indicated that increases in both clonal and sexual recruitment cause an increase in Ne while increasing the variance reduced Ne. However, Ne was more sensitive to changes in the mean and variance of asexual recruitment than sexual recruitment. These results highlight the importance of considering asexual modes of reproduction when examining the role of genetic stochasticity in populations.     

Population genetic structure of Yushania niitakayamensis (Bambusoideae, Poaceae) in Taiwan

Yushania niitakayamensis is distributed in Taiwan, south-west China and northern Philippines. In Taiwan, the species occurs in the central mountain ranges from 1500 to 3500 m in altitude. Morphological variation, especially in terms of plant height, is large, with plants ranging from 10 cm to 5 m in height. The species appears to spread mainly by rhizomes and flowers rarely, leading to the prediction that most populations are comprised of a single or a few clonal genotypes and that the observed morphological variation is primarily due to phenotypic plasticity. The purpose of the present study was to investigate the genetic structure of this species on Mt Hohuan in central Taiwan. Ten plants from a single clone and ten plants of unknown genetic background were surveyed at one site in order to select RAPD primers useful for clone identification. Plants at a second site were collected at 1-m intervals across a 50-m transect through the population. Plants at one extreme (exposed portion) of the transect were approximately 15–30 cm in height, whereas plants up to 410 cm in height were found at the other shaded end of the transect. Comparison of amplification profiles for 12 primers revealed that in contrast to our predictions of genetic uniformity, many samples had reproducibly different RAPD amplification profiles, with the 51 samples representing 31 clones. These data imply that the clone size is relatively small, and the population is actually highly diverse genetically. The genetic variation in this population may be due to a higher frequency of sexual reproduction during the evolutionary history of the species and/or a high somatic mutation rate for RAPD loci in clones of Yushania.     

Genetic diversity of the expansive grass Brachypodium pinnatum in a changing landscape: Effect of habitat age

Perennial grasses constitute a major group of species showing a dramatic decline of biodiversity in successional plant communities. Using AFLP markers, we examined 12 populations of the expansive grass Brachypodium pinnatum differing in habitat age (30–50, ca. 100 and >300 years old) in order to determine whether clonal diversity of populations, genetic variation, and the relative importance of clonal propagation versus sexual reproduction change with grassland age. Five AFLP primer combinations gave a total of 517 bands, 79% of which were polymorphic. 314 different multilocus lineages were distinguished among the 453 samples analyzed. The number of genotypes (G) and clonal richness (R) decreased with habitat age, while the distribution of the frequency of genets changed from many clones of similar size to dominance by one or a few large clones. We consider these results to give evidence of significant role of sexual reproduction in the early phases of colonization and prevalence of clonal growth and competitive exclusion of less adapted genotypes in the later ones. However, habitat age had only marginal effect on genetic diversity, as percentage of polymorphic loci (PPL) within all the populations analyzed was similar, viz. 38.6–43.5%.