Local forest environment largely affects below-ground growth, clonal diversity and fine-scale spatial genetic structure in the temperate deciduous forest herb Paris quadrifolia

Paris quadrifolia (herb Paris) is a long-lived, clonal woodland herb that shows strong differences in local population size and shoot density along an environmental gradient of soil and light conditions. This environmentally based structuring may be mediated by differences in clonal growth and seedling recruitment through sexual reproduction. To study the interrelationship between environmental conditions and spatial patterns of clonal growth, the spatial genetic structure of four P. quadrifolia populations growing in strongly contrasting sites was determined. In the first place, plant excavations were performed in order to (i) determine differences in below-ground growth of genets, (ii) investigate connectedness of ramets and (iii) determine total genet size. Although no differences in internode length were found among sites, clones in moist sites were much smaller (genets usually consisted of 1-3 interconnected shoots, most of them flowering) than genets in dry sites, which consisted of up to 15 interconnected shoots, the majority of which were vegetative. Further, amplified fragment length polymorphism (AFLP) markers were used. Clonal diversity was higher in populations located in moist and productive ash-poplar forests compared to those found in drier and less productive mixed forest sites (G/N: 0.27 and 0.14 and Simpson's D: 0.84 and 0.75, respectively). Patterns of spatial population genetic structure under dry conditions revealed several large clones dominating the entire population, whereas in moist sites many small genets were observed. Nevertheless, strong spatial genetic structure of the genet population was observed. Our results clearly demonstrate that patterns of clonal diversity and growth form of P. quadrifolia differ among environments. Limited seedling recruitment and large clone sizes due to higher connectedness of ramets explain the low clonal diversity in dry sites. In moist sites, higher levels of clonal diversity and small clone sizes indicate repeated seedling recruitment, whereas strong spatial genetic structure suggests limited seed dispersal within populations.     

Genetic variation within and among patches of the clonal species, Vaccinium stamineum L

Once thought to be dominated by a few genets, clonal plant populations can contain high levels of genetic diversity. Sexual reproduction and vegetative growth strategy affect the amount and distribution of genetic diversity within clonal plant populations. We determined the scale of genetic diversity in a population of Vaccinium stamineum, a clonal shrub that forms discrete patches. Using the random amplified polymorphic DNA (RAPD) technique, we surveyed the genetic diversity of V. stamineum within and among patches from a 1-ha site. We found 67 unique RAPD profiles among the 99 sampled individuals from 22 patches. In two patches, all the sampled individuals had the same RAPD profile. In seven patches, every individual sampled had a different RAPD profile. The remaining patches showed mixed RAPD profiles which suggested both clonal and sexual reproduction. Each unique RAPD profile was restricted to one patch (with one exception), which suggests that clonal growth occurs at the patch scale. High levels of genetic variation within some patches may be explained by somatic mutation; however, seedling recruitment is a more likely explanation.     

The effect of herbivores on genotypic diversity in a clonal aquatic plant

In clonal plants, vegetative parts may outcompete seeds in the absence of disturbance, limiting the build‐up of genotypic diversity through repeated seedling recruitment (RSR). Herbivory may provide disturbance and trigger establishment of strong colonizers (seeds) at the expense of strong competitors (clonal propagules). In the clonal aquatic fennel pondweed Potamogeton pectinatus, two distinct herbivore guilds may modify the dynamics of propagation. In winter, Bewick's swans may deplete patches of tubers, promoting seedling establishment in spring. In summer, seed consumption by waterfowl can reduce the density of viable seeds but grazing may also reduce tuber production and hence facilitate seedling establishment. This study is among the first to experimentally test herbivore impact on plant genotypic diversity. We assess the separate and combined effects of both herbivore guilds on genotypic diversity and structure of fennel pondweed beds. Using microsatellites, we genotyped P. pectinatus from an exclosure experiment and assessed the contribution of herbivory, dispersal and sexual reproduction to the population genetic structure. Despite the predominance of clonal propagation in P. pectinatus, we found considerable genotypic diversity. Within the experimental blocks, kinship among genets decreased with geographic distance, clearly identifying a role for RSR in the maintenance of genotypic diversity within the fennel pondweed beds. However, over a period of five years, none of the herbivory treatments affected genotypic diversity. Hence, sexual reproduction on a local scale is important in this putatively clonal plant and possibly sufficient to ensure a relatively high genotypic diversity even in the absence of herbivores. Although we cannot preclude a role of herbivory in shaping genotypic diversity of a clonal plant, after five years of exclusion of the two investigated herbivore guilds no measurable effect on genotypic diversity was detected.     

Clonal Diversity in Differently-Aged Populations of the Pseudo-Annual Clonal Plant Circaea lutetiana L.

Abstract: In many clonal plant species seedling recruitment is restricted to short colonization episodes early in the development of the population, and clonal diversity (i.e., genet diversity) in the population is expected to decrease with increasing population age. In established populations of the pseudo-annual Circaea lutetiana seedling recruitment has previously not been observed. Therefore, we expected established populations to have low clonal diversities. We analysed number and frequency of genets and spatial distribution of genets in six differently-aged C. lutetiana populations with the use of four informative RAPD primers. We found relatively low clonal diversities in young populations but very high clonal diversities in established populations. Therefore, the hypothesis was rejected that seedling recruitment does not occur in established populations. Moreover, we did not find large genet size asymmetries in established populations. Genet size differences can be caused by stochastic processes or by fitness related traits, such as differences in vegetative reproduction. Because vegetative propagation of ramets is dependent on ramet size, and the number of ramets and the size of each ramet determine genet size, we expected that large genets produced, on average, large ramets. However, this was not the case, suggesting that stochastic processes caused genet size differences. Genet size may also be bounded if spatial distribution of genets is affected by micro-habitat differences. For this we expected to find a clumped spatial distribution of ramets of the same genet. However, ramets of large genets were always found intermingled with ramets belonging to other genets.     

Genet structure and determinants of clonal structure in a temperate deciduous woodland herb, Uvularia perfoliata

1 We used isozyme variation to examine the genet structure of Uvularia perfoliata patches in gap and closed canopy habitats in a temperate deciduous forest in Maryland, USA.
2 A large patch in a gap habitat was composed of a small number of widely spread genets with many ramets, and a large number of genets with more restricted distribution and few ramets. Genets with many ramets were patchily distributed at a metre scale. Analysis of genet structure on a scale of square centimetres, however, revealed that the genets were highly intermingled with no clear boundaries between them. The presence at both scales of sampling of many genets with unique multilocus genotypes indicated continuing genet recruitment within the population.
3 In the closed canopy habitat, the patches examined were each composed of a single unique multilocus genotype, suggesting that each had developed by asexual propagation following the establishment of a single genet.
4 The clonal structure of U. perfoliata patches in both gap and closed canopy habitats therefore appears to depend on recruitment patterns of genets. Populations in closed canopy habitats are characterized by a 'waiting' strategy, in which asexual ramet production maintains populations until genet recruitment by seed production can occur under the more optimal conditions associated with canopy gaps. Extended sampling suggests that the genetic diversity of U. perfoliata populations is primarily controlled by the disturbance regime of the forest canopy.     

Genetic structure of the saxicole Pitcairnia geyskesii (Bromeliaceae) on inselbergs in French Guiana

South American inselbergs constitute singular and fragmented habitats in the tropical rain forest. Pitcairnia geyskesii is restricted to these habitats and exhibits both sexual and asexual reproduction. The genetic structure of populations on three inselbergs in French Guiana is examined by analysis of ten isozyme loci. All analyzed populations show high levels of genetic variation. On average, 63.3% of loci per population were polymorphic, with a mean number of 2.21 alleles per polymorphic locus, and mean observed and expected heterozygosities of 0.185 and 0.183, respectively. The analyses of genetic variability displayed at different levels (inselbergs, subpopulations, and mats) give different but complementary information. A significant multilocus disequilibrium was detected in one subpopulation, whereas none was observed within the whole populations sampled on the three inselbergs. Tests on spatial genetic structure indicate a patchy distribution of genotypes on two inselbergs. The data give some insights on the reproductive behavior of P. geyskesii. (1) Efficient sexual reproduction leads to seed recruitment at the level of the inselberg. (2) Both clonality and seed recruitment occur within mats. (3) Vegetative spread by fragmentation is involved in the establishment of new mats. There is substantial differentiation (F(ST) = 0.322) and low gene flow among inselbergs (Nm = 0.234). High genetic diversity within inselbergs appears as a consequence of the association of genet longevity induced by clonal replication and recruitment of new genets produced by sexual reproduction.     

Patterns of genotypic diversity suggest a long history of clonality and population isolation in the Australian arid zone shrub Acacia carneorum

For plants capable of both sexual and clonal reproduction, the relative frequency of these reproductive modes is influenced by genetic and ecological factors. Acacia carneorum is a threatened shrub from the Australian arid zone that occurs as a set of small, spatially isolated populations. Sexual reproduction appears to be very rare: despite regular flowering, only two populations set seed. It is not known whether this reflects an ancient pattern, or results from rapid land use changes following arrival of Europeans in the region 150 years ago. We assessed genotypic variation throughout the range of A. carneorum using AFLP markers, to elucidate the relative importance of clonal and sexual reproduction in this species’ history. Clonal diversity (CD) within populations ranged from 0 to 0.820 (mean CD = 0.270, SE = 0.094), but the relative abundances of genets were typically highly skewed. On average, the two fruiting populations had higher CD (mean CD = 0.590, SE = 0.265) than non-fruiting populations (mean CD = 0.179, SE = 0.077) (t = 2.315, p = 0.049), but most populations contained multiple genets. All genets were population-specific, and there was substantial divergence among populations (Φ _ST = 0.690), implying a long history of isolation. We conclude that clonality has predominated in A. carneorum populations, with occasional sexual recruitment, and that current failure of most populations to set seed likely reflects both a long history of asexual reproduction and effects of habitat disturbance. Conservation of this species may benefit from translocations to increase genotypic diversity within populations.     

Demographic and random amplified polymorphic DNA analyses reveal high levels of genetic diversity in a clonal violet

We performed demographic and molecular investigations on woodland populations of the clonal herb Viola riviniana in central Germany. We investigated the pattern of seedling recruitment, the amount of genotypic (clonal) variation and the partitioning of genetic variation among and within populations. Our demographic study was carried out in six violet populations of different ages and habitat conditions. It revealed that repeated seedling recruitment takes place in all of these populations, and that clonal propagation is accompanied by high ramet mortality. Our molecular investigations were performed on a subset of three of these six violet populations. Random amplified polymorphic DNA analyses using six primers yielded 45 scorable bands that were used to identify multilocus genotypes, i.e. putative clones. Consistent with our demographic results and independent of population age, we found a large genotypic diversity with a mean proportion of distinguishable genotypes of 0.93 and a mean Simpson's diversity index of 0.99. Using AMOVA we found a strong genetic differentiation among these violet populations with a PhiST value of 0.41. We suggest that a high selfing rate, limited gene flow due to short seed dispersal distances and drift due to founder effects are responsible for this pattern. Although Viola riviniana is a clonal plant, traits associated with sexual reproduction rather than clonality per se are moulding the pattern of genetic variation in this species.     

Sexual reproduction, clonal diversity and genetic differentiation in patchily distributed populations of the temperate forest herb Paris quadrifolia (Trilliaceae)

Clonal plant species have been shown to adopt different strategies to persist in heterogeneous environments by changing relative investments in sexual reproduction and clonal propagation. As a result, clonal diversity and genetic variation may be different along environmental gradients. We examined the regional and local population structure of the clonal rhizomatous forest herb Paris quadrifolia in a complex of forest fragments in Voeren (Belgium). Relationships between population size (the number of shoots), shoot density (the number of shoots per m²) and local growth conditions were investigated for 47 populations. Clonal diversity and genetic variation within and among 19 populations were investigated using amplified fragment length polymorphism markers. To assess the importance of sexual reproduction, seed set, seed weight and germination success were determined in 18 populations. As predicted, local growth conditions largely affected population distribution, size and density of P. quadrifolia. Populations occurring in moist and relatively productive sites contained significantly more shoots. Here, shoots were also much more sparsely distributed compared to populations occurring in dry and relatively unproductive sites, where shoots showed a strongly aggregated distribution pattern. Clonal diversity was relatively high, compared with other clonal species (G/N ratio = 0.43 and Simpson’s D=0.81). Clonal diversity significantly (P<0.01) decreased with increasing shoot density while molecular genetic variation was significantly (P<0.01) affected by population size and local environmental conditions. Lack of recruitment and out-competition of less-adapted genotypes may explain the decreased genetic variation in dry sites. Analysis of molecular variance revealed significant genetic variation among populations (Φ _ST=0.42, P<0.001), whereas pairwise genetic distances were not correlated to geographic distances, suggesting that gene flow among populations is limited. Finally, the number of generative shoots, the number of seeds per fruit and seed weight were significantly and positively related to population size and local growth conditions. We conclude that under stressful conditions populations of clonal forest plant species can slowly evolve into remnant populations characterized by low levels of genetic variation and limited sexual reproduction. Conservation of suitable habitat conditions is therefore a prerequisite for effective long-term conservation of clonal forest plant species.     

Genetic structure of a population of the clonal grass Setaria incrassata

We studied the genetic structure of a population of the clonal grass Setaria incrassata using isozyme electrophoresis to determine the extent of clone and gene diversity within and between three spatially isolated Setaria patches. High clone diversity and an even distribution of genets, which covered less than 0.25 m² on average, indicated that patch formation was dominated by propagation from seed. Gene diversity was high within the population and there was little genetic differentiation between patches. High levels of heterozygosity and polymorphism and strongly negative fixation indices indicated extensive recombination through outbreeding, despite the low number of alleles per locus. The synergistic effects of vegetative and sexual propagation may have contributed towards the unexpectedly high genetic diversity of this population. Genetic diversity in clonal populations may be preserved in the genotypes of clones and may therefore be increased by even rare recombination events.     

植物克隆多样性与生态系统功能

克隆繁殖产生基因型相同的个体。通常情况下,局域克隆多样性取决于Eriksson种苗补充机制,即已有基因型丧失和新基因型补充之间的平衡。但是,环境因素对克隆多样性也有着重要的作用,如干扰会通过提供种苗更新机会或影响幼苗生长来改变克隆多样性。以前的研究表明遗传变异程度确定进化潜力,最近的研究揭示出基因型多样性也有着即时效应。较高的基因型多样性可能会因含有抗性基因型概率较高的抽样效应和/或保险机制而提高稳定性。一些研究发现克隆多样性的提高可增加初级生产力、维持动物丰富度和多度,并影响生物地球化学过程。该文也讨论了克隆多样性与生态系统功能关系的机制。     

Polyploidy and microsatellite variation in the relict tree Prunus lusitanica L.: how effective are refugia in preserving genotypic diversity of clonal taxa?

Refugia are expected to preserve genetic variation of relict taxa, especially in polyploids, because high gene dosages could prevent genetic erosion in small isolated populations. However, other attributes linked to polyploidy, such as asexual reproduction, may strongly limit the levels of genetic variability in relict populations. Here, ploidy levels and patterns of genetic variation at nuclear microsatellite loci were analysed in Prunus lusitanica, a polyploid species with clonal reproduction that is considered a paradigmatic example of a Tertiary relict. Sampling in this study considered a total of 20 populations of three subspecies: mainland lusitanica (Iberian Peninsula and Morocco), and island azorica (Azores) and hixa (Canary Islands and Madeira). Flow cytometry results supported an octoploid genome for lusitanica and hixa, whereas a 16‐ploid level was inferred for azorica. Fixed heterozygosity of a few allele variants at most microsatellite loci resulted in levels of allelic diversity much lower than those expected for a high‐order polyploid. Islands as a whole did not contain higher levels of genetic variation (allelic or genotypic) than mainland refuges, but island populations displayed more private alleles and higher genotypic diversity in old volcanic areas. Patterns of microsatellite variation were compatible with the occurrence of clonal individuals in all but two island populations, and the incidence of clonality within populations negatively correlated with the estimated timing of colonization. Our results also suggest that gene flow has been very rare among populations, and thus population growth following founder events was apparently mediated by clonality rather than seed recruitment, especially in mainland areas. This study extends to clonal taxa the idea of oceanic islands as important refugia for biodiversity, since the conditions for generation and maintenance of clonal diversity (i.e. occasional events of sexual reproduction, mutation and/or seed immigration) appear to have been more frequent in these enclaves than in mainland areas.     

Genetics of cattails in radioactively contaminated areas around Chornobyl

Research on populations from radioactively contaminated areas around Chornobyl has produced ambiguous results for the presence of radiation effects. More studies are needed to provide information on whether radiation exposure at Chornobyl significantly affected genetic diversity in natural populations of various taxa. Eleven and nine variable microsatellite loci were used to test for differences in genetic diversity between reference and Chornobyl populations of two cattail species (Typha angustifolia and Typha latifolia, respectively) from Ukraine. Our purpose was to determine whether radiation had a significant impact on genetic diversities of the Chornobyl Typha populations, or if their genetic composition might be better explained by species demography and/or changes in population dynamics, mainly in sexual and asexual reproduction. Populations closest to the reactor had increased genetic diversities and high number of genets, which likely were due to factors other than radiation including increased gene flow among Chornobyl populations, enhanced sexual reproduction within populations, and/or origin of the genets from seed bank. Both Typha species also demonstrated small but significant effects associated with latitude, geographical regions, and watersheds. Typha's demography in Ukraine possibly varies with these three factors, and the small difference between Chornobyl and reference populations of T. latifolia detected after partitioning the total genetic variance between them is probably due primarily to these factors. However, the positive correlations of several genetic characteristics with radionuclide concentrations suggest that radiation may have also affected genetics of Chornobyl Typha populations but much less than was expected considering massive contamination of the Chornobyl area.     

Disturbance by mowing affects clonal diversity: the genetic structure of Ranunculus ficaria (Ranunculuaceae) in meadows and forests

To study the impact of disturbance by mowing on clonal variation, we compared the genetic structure of Ranunculus ficaria (Ranunculaceae) in meadows and forests located in southeast Germany. We applied random amplified polymorphic DNA (RAPD) analysis to investigate the clonal and genetic diversity and analysed a total of 117 samples from three study plots in each habitat type. Polymerase chain reaction with six primers resulted in 57 fragments. Clonal diversity differed clearly between the two analysed habitat types and was significantly higher in the study plots from meadows than in those from forests. The mean percentage of distinguishable genotypes (PD) was 0.80 in meadow plots and 0.36 in forest plots, and the detected genets were smaller in meadow plots than in forest plots. Mean genetic diversity measured as percentage of polymorphic bands, Shannon’s information index and Nei’s gene diversity was also higher in meadows (44.4, 0.22 and 0.14) than in forests (25.1, 0.09 and 0.05). The higher level of clonal diversity in meadow plots is most likely due to the effects of disturbance by mowing, which increases the dispersal of bulbils and promotes the establishment of new plants in meadows compared to forests.     

具混合繁殖策略的草本植物异果舞花姜的居群遗传结构

 居群遗传结构的形成受到各种因素的影响。其中, 繁殖方式可能对居群内遗传变异有极其重要的意义, 而距离隔离也是居群间变异产 生的主要原因之一。异果舞花姜(Globba racemosa)具有混合繁殖策略(以种子进行有性繁殖和以珠芽进行无性克隆繁殖)。调查分布于云南的7 个异果舞花姜居群间有性与无性克隆繁殖的差异。采用ISSR标记研究各个居群的遗传多样性与克隆多样性, 探讨繁殖方式和距离隔离对居群遗 传结构的影响。调查结果表明, 异果舞花姜各个居群存在一定的繁殖差异。ISSR结果显示, 该种在种水平上呈现较高水平的遗传变异 (PPB=71.19%), 大部分的变异来自于居群间(G_ST = 0.590 7)。同时, 异果舞花姜具有较高水平克隆多样性(G/N = 0.88)。遗传多样性和克隆多 样性与繁殖水平的变异间相关性不明显, 说明繁殖方式不是居群遗传结构形成的必要和决定性的因素。居群间的地理距离与遗传距离显著相关 (r = 0.68, p < 0.05), 表明距离隔离是居群间遗传变异形成的重要原因。其它因素(如少量新有性个体的补充、细胞突变、奠基效应等)也对 异果舞花姜居群遗传结构的形成和维持起到了重要作用。     

CONTRIBUTIONS OF SEXUAL AND ASEXUAL REPRODUCTION TO POPULATION STRUCTURE IN THE CLONAL SOFT CORAL,ALCYONIUM RUDYI

Numerous studies of population structure in sessile clonal marine invertebrates have demonstrated low genotypic diversity and nonequilibrium genotype frequencies within local populations that are monopolized by relatively few, highly replicated genets. All of the species studied to date produce planktonic sexual propagules capable of dispersing long distances; despite local genotypic disequilibria, populations are often panmictic over large geographic areas. The population structure paradigm these species represent may not be typical of the majority of clonal invertebrate groups, however, which are believed to produce highly philopatric sexual propagules. I used allozyme variation to examine the population structure of the temperate soft coral, Alcyonium rudyi, a typical clonal species whose sexually produced larvae and asexually produced ramets both have very low dispersal capabilities. Like other clonal plants and invertebrates, the local population dynamics of A. rudyi are dominated by asexual reproduction, and recruitment of new sexually produced genets occurs infrequently. As expected from its philopatric larval stage, estimates of genetic differentiation among populations of A. rudyi were highly significant at all spatial scales examined (mean θ = 0.300 among 20 populations spanning a 1100-km range), suggesting that genetic exchange seldom occurs among populations separated by as little as a few hundred meters. Mapping of multilocus allozyme genotypes within a dense aggregation of A. rudyi ramets confirmed that dispersal of asexual propagules is also very limited: members of the same genet usually remain within < 50 cm of one another on the same rock surface. Unlike most previously studied clonal invertebrates, populations of A. rudyi do not appear to be dominated by a few widespread genets: estimates of genotypic diversity (G_o) within 20 geographically distinct populations did not differ from expectations for outcrossing, sexual populations. Despite theoretical suggestions that philopatric dispersal combined with typically small effective population sizes should promote inbreeding in clonal species, inbreeding does not appear to contribute significantly to the population structure of A. rudyi. Genet genotype frequencies conformed to Hardy-Weinberg expectations in all populations, and inbreeding coefficients (f) were close to zero. In general, the population structure of A. rudyi did not differ significantly from that observed among outcrossing sexual species with philopatric larval dispersal. Age estimates suggest, however, that genets of A. rudyi live for many decades. Genet longevity may promote high genotypic diversity within A. rudyi populations and may be the most important evolutionary consequence of clonal reproduction in this species and the many others that share its dispersal characteristics.     

Genetic analysis of salt-marsh sedge Carex scabrifolia Steud. populations using newly developed microsatellite markers

Nine microsatellite loci were isolated and characterized from the clonal salt-marsh sedge Carex scabrifolia, and genetic diversities within four populations were analyzed. The number of alleles per locus ranged from 2 to 7, with an average of 4.7. The observed and expected heterozygosities ranged from 0.000 to 1.000 and 0.000 to 0.679, respectively. In two populations, almost all polymorphic loci showed a significant excess of heterozygotes due to their high clonal reproduction and low number of genotypes (genets) composing the populations. Thus, the number of identical genets varied greatly among populations and ranged from 1 to 28, irrespective of population size (i.e., population area and ramet number). When attempting to conserve and restore clonal plants such as C. scabrifolia, it is important to preserve sufficient genetic diversity within a population, which can be assessed using genetic markers such as the simple sequence repeat markers described here.     

Local genetic structure in a clonal dioecious angiosperm

We used seven microsatellite loci to characterize genetic structure and clonal architecture at three different spatial scales (from meters to centimetres) of a Cymodocea nodosa population. C. nodosa exhibits both sexual reproduction and vegetative propagation by rhizome elongation. Seeds remain buried in the sediment nearby the mother plant in a dormant stage until germination. Seed dispersal potential is therefore expected to be extremely restricted. High clonal diversity (up to 67% of distinct genotypes) and a highly intermingled configuration of genets at different spatial scales were found. No significant differences in genetic structure were found among the three spatial scales, indicating that genetic diversity is evenly distributed along the meadow. Autocorrelation analyses of kinship estimates confirmed the absence of spatial clumping of genets at small spatial scale and the expectations of a very restricted seed dispersal (observed dispersal range 1-21 m) in this species.     

Scaling of processes shaping the clonal dynamics and genetic mosaic of seagrasses through temporal genetic monitoring

Theoretically, the dynamics of clonal and genetic diversities of clonal plant populations are strongly influenced by the competition among clones and rate of seedling recruitment, but little empirical assessment has been made of such dynamics through temporal genetic surveys. We aimed to quantify 3 years of evolution in the clonal and genetic composition of Zostera marina meadows, comparing parameters describing clonal architecture and genetic diversity at nine microsatellite markers. Variations in clonal structure revealed a decrease in the evenness of ramet distribution among genets. This illustrates the increasing dominance of some clonal lineages (multilocus lineages, MLLs) in populations. Despite the persistence of these MLLs over time, genetic differentiation was much stronger in time than in space, at the local scale. Contrastingly with the short-term evolution of clonal architecture, the patterns of genetic structure and genetic diversity sensu stricto (that is, heterozygosity and allelic richness) were stable in time. These results suggest the coexistence of (i) a fine grained (at the scale of a 20 × 30 m quadrat) stable core of persistent genets originating from an initial seedling recruitment and developing spatial dominance through clonal elongation; and (ii) a local (at the scale of the meadow) pool of transient genets subjected to annual turnover. This simultaneous occurrence of initial and repeated recruitment strategies highlights the different spatial scales at which distinct evolutionary drivers and mating systems (clonal competition, clonal growth, propagule dispersal and so on) operate to shape the dynamics of populations and the evolution of polymorphism in space and time.     

Fine-scale clonal structure and diversity within patches of a clone-forming dioecious shrub, Ilex leucoclada (Aquifoliaceae)

BACKGROUND AND AIMS: The mode of reproduction (sexual vs. asexual) is likely to have important effects on genetic variation and its spatial distribution within plant populations. An investigation was undertaken of fine-scale clonal structure and diversity within patches of Ilex leucoclada (a clone-forming dioecious shrub). METHODS: Six patches were selected in a 1-ha plot previously established in an old-growth beech forest. Two of the selected patches were composed predominantly of stems with male flowers (male patch), and two contained stems with predominantly female flowers (female patch). The remaining two patches contained stems with male flowers and stems with female flowers in more or less equal proportions (mixed patch). Different genets were distinguished using random amplified polymorphic DNA (RAPD) markers. KEY RESULTS: One hundred and fifty-six genets with different RAPD phenotypes were identified among 1928 stems from the six patches. Among the six patches, the male patches had the lowest clonal diversity, and the mixed patches had the highest. Distribution maps of the genets showed that they extended downhill, reflecting natural layering that occurred when stems were pressed to the ground by heavy snow. In every patch, there were a few large genets with many stems and many small genets with a few stems. CONCLUSION: The differences in clonal diversity among patches may be due to differences in seedling recruitment frequencies. The skewed distribution of genet size (defined as the number of stems per genet) within patches may be due to differences in the timing of germination, or age (with early-establishing genets having clear advantages for acquiring resources) and/or intraspecific competition.