Effects of clonality on the genetic variability of rare,insular species: the case of Ruta microcarpa from the Canary Islands

Many plant species combine sexual and clonal reproduction. Clonal propagation has ecological costs mainly related to inbreeding depression and pollen discounting; at the same time, species able to reproduce clonally have ecological and evolutionary advantages being able to persist when conditions are not favorable for sexual reproduction. The presence of clonality has profound consequences on the genetic structure of populations, especially when it represents the predominant reproductive strategy in a population. Theoretical studies suggest that high rate of clonal propagation should increase the effective number of alleles and heterozygosity in a population, while an opposite effect is expected on genetic differentiation among populations and on genotypic diversity. In this study, we ask how clonal propagation affects the genetic diversity of rare insular species, which are often characterized by low levels of genetic diversity, hence at risk of extinction. We used eight polymorphic microsatellite markers to study the genetic structure of the critically endangered insular endemic Ruta microcarpa. We found that clonality appears to positively affect the genetic diversity of R. microcarpa by increasing allelic diversity, polymorphism, and heterozygosity. Moreover, clonal propagation seems to be a more successful reproductive strategy in small, isolated population subjected to environmental stress. Our results suggest that clonal propagation may benefit rare species. However, the advantage of clonal growth may be only short‐lived for prolonged clonal growth could ultimately lead to monoclonal populations. Some degree of sexual reproduction may be needed in a predominantly clonal species to ensure long‐term viability.     

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.     

Clonal diversity,spatial dynamics,and small genetic population size in the rare sunflower, <Emphasis Type="Italic">Helianthus verticillatus</Emphasis>

Knowledge of population size is an important step for identifying populations of immediate conservation concern. However, this task is difficult in plant species that exhibit clonal growth, since a simple “head count” may not be appropriate. Here, I determine the genetic population size and the extent of clonality in the four known populations of a rare sunflower, Helianthus verticillatus. Previous work in this species revealed high genetic diversity in all populations but significant fitness differences among them. In this study, populations exhibited high clonal diversity but consisted of far fewer genetic individuals than previously reported. Moreover, the clonal structure of populations was clumped, such that genotypes were highly clustered, which may promote selfing among genets. The results of this study are related to previously examined levels of genetic diversity and fitness, and findings are discussed in the context of the ecological and biological dynamics in clonal plant populations. Finally, the results of this study led to an upgrade in the priority status of this species for the Endangered Species List.     

Genetic variation and clonal structure of the rare,riparian shrub <Emphasis Type="Italic">Spiraea virginiana</Emphasis> (Rosaceae)

Genetic diversity is often considered important for species that inhabit highly disturbed environments to allow for adaptation. Many variables affect levels of genetic variation; however, the two most influential variables are population size and type of reproduction. When analyzed separately, both small population size and asexual reproduction can lead to reductions in genetic variation, although the exact nature of which can be contrasting. Genetic variables such as allelic richness, heterozygosity, inbreeding coefficient, and population differentiation have opposite predictions depending upon the trait (rarity or clonality) examined. The goal of this study was to quantify genetic variation and population differentiation in a species that resides in a highly stochastic environment and is both rare and highly clonal, Spiraea virginiana, and to determine if one trait is more influential genetically than the other. From populations sampled throughout the natural range of S. virginiana, we used microsatellite loci to estimate overall genetic variation. We also calculated clonal structure within populations, which included genotypic richness, evenness, and diversity. Gene flow was investigated by quantifying the relationship between genetic and geographic distances, and population differentiation (θ) among populations. Observed heterozygosity, genotypic richness, and inbreeding coefficients were found to be representative of high clonal reproduction (averaging 0.505, 0.1, and –0.356, respectively) and the number of alleles within populations was low (range = 2.0–3.6), being more indicative of rarity. Population differentiation (θ) among populations was high (average = 0.302) and there was no relationship between genetic and geographic distances. By examining a species that exhibits two traits that both can lead to reduced genetic variation, we may find an enhanced urgency for conservation. Accurate demographic counts of clonal species are rarely, if ever, possible and genetic exploration for every species is not feasible. Therefore, the conclusions in this study can be potentially extrapolated to other riparian, clonal shrubs that share similar biology as S. virginiana.     

Clonality in the Endangered <Emphasis Type="Italic">Ambrosia pumila</Emphasis> (Asteraceae) Inferred from RAPD Markers; Implications for Conservation and Management

Clonal plants have the ability to spread and survive over long periods of time by vegetative growth. For endangered species, the occurrence of clonality can have significant impacts on levels of genetic diversity, population structure, recruitment, and the implementation of appropriate conservation strategies. Here we␣examine clone structure in three populations of Ambrosia pumila (Nutt.) Gray (Asteraceae), a federally endangered clonal species from southern California. Ambrosia pumila is a perennial herbaceous species spreading from a rhizome, and is frequently found in dense patches of several hundred stems in a few square meters. The primary habitat for this species is upper terraces of rivers and drainages in areas that have been heavily impacted by anthropogenic disturbances and changing flood regimes. RAPD markers were employed to document the number and distribution of clones within multiple 0.25 m² plots from each of three populations. Thirty-one multi-locus genotypes were identified from the 201 stems sampled. The spatial distribution of clones was limited with no genotypes shared between plots or populations. Mean clone size was estimated at 9.10 ramets per genet. Genets in most plots were intermingled, conforming to a guerrilla growth form. The maximum genet spread was 0.59 m suggesting that genets can be larger than the sampled 0.25 m² plots. Spatial autocorrelation analysis found a lack of spatial genetic structure at short distances and significant structure at large distances within populations. Due to the occurrence of multiple genets within each population, the limited spread of genets, and a localized genetic structure, conservation activities should focus on the maintenance of multiple populations throughout the species range.     

Spatial structure and clonal distribution of genotypes in the rare Typha minima Hoppe (Typhaceae) along a river system

We studied the genetic diversity of the dwarf bulrush (Typha minima) along a 60 km section of the Isère river using AFLP markers. Total clonality was relatively low (proportion of distinguishable genotypes = 0.70) but extremely variable among populations with one monoclonal population and several populations where all sampled individuals were different. Genetic diversity was high (He = 0.129) and again variable among populations. Although no major genetic discontinuity could be detected, gene flow was found to be limited. Our results show a much higher diversity compared to Swiss populations. The high genetic diversity within most populations despite the species’ potentially important clonal growth indicates that populations are relatively young. This is in line with the fact that the species lives in open habitats created by high floods that erase river banks leading to a metapopulation dynamics. However the metapopulation dynamics is at least partly disturbed as gene flow appears to be restricted so that our populations are probably at risk if no action is taken to re-establish more natural river flow dynamics.     

Does the Reproductive Strategy Affect the Transmission and Genetic Diversity of Bionts in Cyanolichens? A Case Study Using Two Closely Related Species

Observed levels of population genetic diversity are often associated with differences in species dispersal and reproductive strategies. In symbiotic organisms, the genetic diversity level of each biont should also be highly influenced by biont transmission. In this study, we evaluated the influence of the reproductive strategies of cyanolichen species on the current levels of population genetic diversity of bionts. To eliminate any phylogenetic noise, we selected two closely related species within the genus Degelia, which only differ in their reproductive systems. We sampled all known populations of both species in central Spain and genotyped the fungal and cyanobacterial components of lichen samples using DNA sequences as molecular markers. We applied population genetics approaches to evaluate the genetic diversity and population genetic structure of the symbiotic components of both lichen species. Our results indicate that fungal and cyanobiont genetic diversity is highly influenced by the reproductive systems of lichen fungus. We detected higher bionts genetic diversity values in the sexual species Degelia plumbea. By contrast, the levels of fungal and cyanobiont genetic diversity in the asexual species Degelia atlantica were extremely low (almost clonal), and the species shows a high specificity towards its cyanobiont. Our results indicate that reproduction by vegetative propagules, in species of the genus Degelia, favors vertical transmission and clonality, which affects the species’ capacity for resources and competition, thereby limiting the species to restricted niches.     

Patterns of sex ratio variation and genetic diversity in the dioecious forest perennial <Emphasis Type="Italic">Mercurialis perennis</Emphasis>

In small populations of plant species with separate sexes, it can be expected that besides the local environment also stochastic events influence population sex ratios. Biased sex ratios may in turn negatively affect genetic diversity due to increased genetic drift and, in clonal plants, due to reduced sexual reproductive output. Empirical evidence for these processes is scarce, however. We investigated the pattern of sex ratio variation and the distribution of genetic variation of the dioecious clonal forest herb Mercurialis perennis using AFLP markers. Analysis of molecular variance indicated a pronounced genetic structure. Overall within-population genetic diversity was moderate and local sex ratios were slightly male biased. The proportion of male to female plants in large populations slightly increased with increasing light penetration to the herb layer. Small populations, on the contrary, displayed high variability in sex ratios, unrelated to the local light environment. Genotypic diversity decreased with more male-biased sex ratios. We conclude that stochastic events related to small population size and the local forest environment, related to canopy closure, affect the proportion of female plants and indirectly influence local genotypic diversity, likely through the degree of sexual reproduction. This is one of the first studies to report a clear association between gender proportions and genetic diversity of a dioecious plant species in a fairly large survey.     

Clonal diversity of populations of Calamagrostis epigejos in relation to environmental stress and habitat heterogeneity

The clonal diversity of four populations of the vegetatively propagating grass Calamagrostis epigejos was studied with isozyme markers From each population, 100 individuals were sampled within a 10 × 10 m gnd In two populations of unpolluted sites 5 and 10 clones were distinguished, respectively Higher levels of clonal diversity were found m the populations at an abandoned sewage farm (59 clones) and around a copper smelter (92 clones) The level of clonal diversity observed suggests that sexual recruitment is important for the genetic structure in this species On the unpolluted, presumably more suitable habitats, the clonal diversity was lower than on the habitats polluted with heavy metals The results are discussed in relation to environmental stress and habitat heterogeneity, with the conclusion that in the unpolluted habitats intraspecific competition results in low clonal diversity On the other hand, stressful conditions decrease the importance of competition and facilitate the coexistence of a great number of clones     

Three-gene identity coefficients demonstrate that clonal reproduction promotes inbreeding and spatial relatedness in yellow-cedar, Callitropsis nootkatensis

Asexual reproduction has the potential to promote population structuring through matings between clones as well as through limited dispersal of related progeny. Here we present an application of three-gene identity coefficients that tests whether clonal reproduction promotes inbreeding and spatial relatedness within populations. With this method, the first two genes are sampled to estimate pairwise relatedness or inbreeding, whereas the third gene is sampled from either a clone or a sexually derived individual. If three-gene coefficients are significantly greater for clones than nonclones, then clonality contributes excessively to genetic structure. First, we describe an estimator of three-gene identity and briefly evaluate its properties. We then use this estimator to test the effect of clonality on the genetic structure within populations of yellow-cedar (Callitropsis nootkatensis) using a molecular marker survey. Five microsatellite loci were genotyped for 485 trees sampled from nine populations. Our three-gene analyses show that clonal ramets promote inbreeding and spatial structure in most populations. Among-population correlations between clonal extent and genetic structure generally support these trends, yet with less statistical significance. Clones appear to contribute to genetic structure through the limited dispersal of offspring from replicated ramets of the same clonal genet, whereas this structure is likely maintained by mating among these relatives.     

High population differentiation and extensive clonality in a rare mallee eucalypt: Eucalyptus curtisii Conservation genetics of a rare mallee eucalypt

Microsatellite polymorphisms were analysed toassess the extent and pattern of geneticdiversity within and between isolatedpopulations of the rare mallee eucalypt, Eucalyptus curtisii. Twelve populations intotal were sampled throughout the 500 km rangeof the species in South-east Queensland.Results from analysis of 5 loci indicated ahigh degree of clonality within many of thesites, with two populations being comprised ofsingle genets. Estimates of radial growth ratessuggest that these clones may be between 4000and 9000 years old. Low overall levels ofgenetic diversity were recorded for thespecies, H _e = 0.54, however a highlysignificant amount of populationdifferentiation was observed, R _ST =0.22. There was no evidence of isolation bydistance and although there were morphologicaldifferences between some populations, this wasunrelated to molecular variation.The low level of genetic diversity and highproportion of interpopulation variation agreeswith the findings of other studies onregionally distributed eucalypts. The findingsindicate that previous estimates of theeffective population size of the species arelargely overestimated and that the individualpopulations are sufficiently differentiatedthat they should be treated as separatemanagement units. Further study is recommendedto elucidate the full extent of clonality inthe species and to conduct germination trialson seed collected from clonal populations.     

Clonality, genetic diversity and support for the diversifying selection hypothesis in natural populations of a flower-living yeast

Vast amounts of effort have been devoted to investigate patterns of genetic diversity and structuring in plants and animals, but similar information is scarce for organisms of other kingdoms. The study of the genetic structure of natural populations of wild yeasts can provide insights into the ecological and genetic correlates of clonality, and into the generality of recent hypotheses postulating that microbial populations lack the potential for genetic divergence and allopatric speciation. Ninety‐one isolates of the flower‐living yeast Metschnikowia gruessii from southeastern Spain were DNA fingerprinted using amplified fragment length polymorphism (AFLP) markers. Genetic diversity and structuring was investigated with band‐based methods and model‐ and nonmodel‐based clustering. Linkage disequilibrium tests were used to assess reproduction mode. Microsite‐dependent, diversifying selection was tested by comparing genetic characteristics of isolates from bumble bee vectors and different floral microsites. AFLP polymorphism (91%) and genotypic diversity were very high. Genetic diversity was spatially structured, as shown by amova (Φ_st = 0.155) and clustering. The null hypothesis of random mating was rejected, clonality seeming the prevailing reproductive mode in the populations studied. Genetic diversity of isolates declined from bumble bee mouthparts to floral microsites, and frequency of five AFLP markers varied significantly across floral microsites, thus supporting the hypothesis of diversifying selection on clonal lineages. Wild populations of clonal fungal microbes can exhibit levels of genetic diversity and spatial structuring that are not singularly different from those shown by sexually reproducing plants or animals. Microsite‐dependent, divergent selection can maintain high local and regional genetic diversity in microbial populations despite extensive clonality.     

Clonal and genetic diversity of Carex moorcroftii on the Qinghai-Tibet plateau

Carex moorcroftii Falc. ex Boott is a rhizomatous clonal sedge dominating vast alpine steppe and meadow vegetations in the hinterland of the Qinghai-Tibet plateau. To reveal the genetic and clonal structure of this species, nine populations were investigated using ten inter-simple sequence repeat (ISSR) markers. As compared to other rhizomatous Carex species, C. moorcroftii had lower genetic diversity (H_s = 0.10) at population level and higher genetic differentiation (G_st = 0.66) and lower gene flow (N_m = 0.26) between populations. Clonal diversity in C. moorcroftii in terms of Simpson index (D = 0.65) was comparable to that in other clonal species while lower than that in Carex species from the arctic and subarctic areas. The ratio of clonal diversity to genetic variation in C. moorcroftii was closely correlated with latitude, enabling a speculation about the northern migration of this species on this plateau.     

Spatial genetic structure in wild cherry (Prunus avium L.): I. variation among natural populations of different density

Conservation of forest genetic resources requires intensive knowledge of the spatial arrangement of genetic diversity. In this study, we used four natural Prunus avium stands in Germany with contrasting for densities to understand patterns of spatial genetic structure. To this end, we genotyped adults and saplings at eight microsatellite markers, 54 AFLP loci and at the gametophytic incompatibility locus. We estimated levels of clonal propagation, spatial genetic structure and gene dispersal. High mortality occurred among young clonal individuals, as depicted by the lower clonal diversity in saplings. Contrasting levels of spatial genetic structure were observed among markers, ontogenic stages and populations. AFLP were more efficient for detecting spatial autocorrelation but did not allow us to differentiate low and high density populations, while high density populations showed substantially stronger spatial genetic structure at microsatellite loci. Furthermore, kinship decreased with tree age only in low density stands. We discuss the present results in terms of population history, pollen and seed dispersal and population density. Although conspecific density seems to be an interesting indicator of genetic diversity for conservation programmes, we still need to disentangle the relative influence of clonal propagation and density on the strength of spatial genetic structure. Simulation studies are needed to further address this question.     

Clonality strongly affects the spatial genetic structure of the nurse species Aechmea nudicaulis (L.) Griseb. (Bromeliaceae)

Aechmea nudicaulis is a clonal bromeliad common to the Brazilian Atlantic forest complex and is found abundantly in the sandy coastal plain vegetation (restinga) on the north coast of Rio de Janeiro state, Brazil. This restinga site is structured in vegetation islands, and the species plays a key role as a nurse plant, much favoured by its clonality. We studied the clonal structure and consequences of clonality on the population spatial genetic structure (SGS) of this species using six nuclear microsatellites. Spatial autocorrelation analysis was performed to study the effects of sexual and clonal reproduction on the dispersal of A. nudicaulis. Analyses were performed at the genet (i.e. excluding clonal repeats) and ramet levels. Genotypic richness was moderate (R = 0.32), mostly as a result of the dominance of a few clones. The spatial distribution of genets was moderately intermingled, the mean clone size was 4.9 clonal fragments per genet and the maximum clonal spread was 25 m. Expected heterozygosities were high and comparable with those found in other clonal plants. SGS analyses at the genet level revealed significantly restricted gene dispersal (Sp = 0.074), a strong SGS compared with other herbaceous species. The clonal subrange extended across 23 m where clonality had a significant effect on SGS. The restricted dispersal and SGS pattern in A. nudicaulis, coupled with high levels of genetic diversity, indicated a recruitment at windows of opportunity (RWO) strategy. Moreover, the spatial distribution of genetic variation and the habitat occupation pattern in A. nudicaulis were dependent not only on the intrinsic biological traits of the species (such as spacer size and mating system), but also on biotic interactions with neighbouring species that determined suitable habitats for germination and the establishment of new genets. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178 , 329–342.     

Genetic and clonal diversity of the endemic ant-plant Humboldtia brunonis (Fabaceae) in the Western Ghats of India

Humboldtia brunonis (Fabaceae, Caesalpinioideae) is a dominant self-incompatible ant-plant or myrmecophyte, growing as an understorey tree in high-density patches. It is endemic to the biodiversity hotspot of the southern Western Ghats of India and, besides ants, harbours many endemic invertebrate taxa, such as bees that pollinate it as well as arboreal earthworms, within swollen hollow stem internodes called domatia. Using inter simple sequence repeat (ISSR) markers, three geographically separated populations were found to be multiclonal, characterized by high levels of clonal diversity. Values for the Simpson diversity index ranged between 0.764 and 0.964, and for Fager’s evenness index between 0.00 and 0.036 for neighbourhoods within populations. This myrmecophyte was found to combine sexual recruitment (66.7%) and clonal production (33.3%) as methods of reproduction. Moderate amounts of genetic diversity at the species level were observed, with 52.63% polymorphism, and moderate values of Shannon’s diversity index (0.1895) as well as of Nei’s gene diversity (0.1186). In each population, observed genotypic diversity was significantly lower than expected, indicating significant genetic structure. Neighbour-joining trees demonstrated that Agumbe, which is the most northern population examined and geographically twice as far away from the other two populations, grouped separately and with larger bootstrap support from a larger cluster consisting of the Sampaji and Solaikolli populations, which are closer to each other geographically. Some neighbourhoods within each population showed spatial genetic structure even at small spatial scales of <5 m. A combination of clonality and short-distance pollen movement by small pollinating bees (Braunsapis puangensis) coupled with primary ballistic seed dispersal, and possible secondary seed dispersal by rodents, may contribute to spatial genetic structure at such small scales. The clonality of H. brunonis may be a factor that contributes to its dominance in Western Ghat forests where it supports a rich diversity of invertebrate fauna.     

Standardizing methods to address clonality in population studies

Although clonal species are dominant in many habitats, from unicellular organisms to plants and animals, ecological and particularly evolutionary studies on clonal species have been strongly limited by the difficulty in assessing the number, size and longevity of genetic individuals within a population. The development of molecular markers has allowed progress in this area, and although allozymes remain of limited use due to their typically low level of polymorphism, more polymorphic markers have been discovered during the last decades, supplying powerful tools to overcome the problem of clonality assessment. However, population genetics studies on clonal organisms lack a standardized framework to assess clonality, and to adapt conventional data analyses to account for the potential bias due to the possible replication of the same individuals in the sampling. Moreover, existing studies used a variety of indices to describe clonal diversity and structure such that comparison among studies is difficult at best. We emphasize the need for standardizing studies on clonal organisms, and particularly on clonal plants, in order to clarify the way clonality is taken into account in sampling designs and data analysis, and to allow further comparison of results reported in distinct studies. In order to provide a first step towards a standardized framework to address clonality in population studies, we review, on the basis of a thorough revision of the literature on population structure of clonal plants and of a complementary revision on other clonal organisms, the indices and statistics used so far to estimate genotypic or clonal diversity and to describe clonal structure in plants. We examine their advantages and weaknesses as well as various conceptual issues associated with statistical analyses of population genetics data on clonal organisms. We do so by testing them on results from simulations, as well as on two empirical data sets of microsatellites of the seagrasses Posidonia oceanica and Cymodocea nodosa. Finally, we also propose a selection of new indices and methods to estimate clonal diversity and describe clonal structure in a way that should facilitate comparison between future studies on clonal plants, most of which may be of interest for clonal organisms in general.     

FREQUENT CLONALITY IN FUCOIDS (FUCUS RADICANS AND FUCUS VESICULOSUS; FUCALES,PHAEOPHYCEAE) IN THE BALTIC SEA1

Asexual reproduction by cloning may affect the genetic structure of populations, their potential to evolve, and, among foundation species, contributions to ecosystem functions. Macroalgae of the genus Fucus are known to produce attached plants only by sexual recruitment. Recently, however, clones of attached plants recruited by asexual reproduction were observed in a few populations of Fucus radicans Bergström et L. Kautsky and F. vesiculosus L. inside the Baltic Sea. Herein we assess the distribution and prevalence of clonality in Baltic fucoids using nine polymorphic microsatellite loci and samples of F. radicans and F. vesiculosus from 13 Baltic sites. Clonality was more common in F. radicans than in F. vesiculosus, and in both species it tended to be most common in northern Baltic sites, although variation among close populations was sometimes extensive. Individual clonal lineages were mostly restricted to single or nearby locations, but one clonal lineage of F. radicans dominated five of 10 populations and was widely distributed over 550 × 100 km of coast. Populations dominated by a few clonal lineages were common in F. radicans, and these were less genetically variable than in other populations. As thalli recruited by cloning produced gametes, a possible explanation for this reduced genetic variation is that dominance of one or a few clonal lineages biases the gamete pool resulting in a decreased effective population size and thereby loss of genetic variation by genetic drift. Baltic fucoids are important habitat‐forming species, and genetic structure and presence of clonality have implications for conservation strategies.     

Reproductive ecology and genetic variability in natural populations of the wild potato,Solanum kurtzianum

The cultivated potato (Solanum tuberosum ssp. tuberosum) has more than 200 related wild species distributed along the Andes, adapted to a wide range of geographical and ecological areas. Since the last century, several collection expeditions were carried out to incorporate genetic variability into the potato germplasm around the world. However, little is known about the reproductive ecology and genetic population structure of natural potato population from field studies. The aim of this work is to study, in the field, the genetic variability and reproductive strategies of populations of one of the most widely distributed potato species in Argentina, Solanum kurtzianum, growing in Mendoza province. AFLP markers showed that the genetic variability is mainly present among plants within populations, indicating that in the sampled populations, sexual reproduction is more relevant than clonal multiplication (by tubers). Additional evidence was obtained evaluating the genetic diversity in populations with a distribution in patches, where several genotypes were always detected. From a field study performed in the Villavicencio Natural Reserve, we found that the average number of plump seeds per fruit was 94.3, identified and calculated the foraging distance of four insect pollinators, and demonstrated the seed dispersal by storm water channels. We argue that the breeding system, the two modes of reproduction and the ecological interaction described here may have a prominent role in determining the genetic structure of S. kurtzianum populations, and discuss the importance of field studies on population genetics, reproductive biology and ecology to design collections and conservation strategies.     

Genetic structure of the clonal herb Tanakaea radicans (Saxifragaceae) at multiple spatial scales,revealed by nuclear and mitochondrial microsatellite markers

The genus Tanakaea is a plant genus that consists of one or two evergreen herbaceous species in Japan and China. As rithophytic plant species occur on shaded rocks, the populations are usually isolated and sporadically found in disjunct areas. To evaluate the genetic structure of the species at multiple spatial scales, 10 nuclear and mitochondrial microsatellite markers were developed. The novel markers showed high genetic variations (two to 15 alleles and H_e from 0.400 to 0.894). Clonal samples were identified with the probability of identity of 9.0E‐8. When evaluated with 11 populations in Japan, significant genetic differentiation between regional population groups was detected (F_ST = 0.313 between Shikoku and Honshu islands), suggesting they have long been isolated from each other. Overall, these markers will be useful for population genetic research to investigate clonal structure and genetic diversity and levels of genetic differentiation between the geographically isolated populations.