Genetic variation and evolutionary trade-offs for sexual and asexual reproductive modes in Allium vineale (Liliaceae)

Populations of Allium vineale commonly include individuals with very different allocation patterns to three modes of reproduction: sexual flowers, aerially produced asexual bulbils, and belowground asexual offsets. If selection is currently acting to maintain these different allocation patterns there must be a genetic basis for variation in allocation to these three reproductive modes. In addition, negative genetic correlations between reproductive traits would imply evolutionary trade-offs among reproductive strategies. We evaluated the heritability of these allocation patterns by growing 16 clones from a single population in the greenhouse at two levels of fertilization. Bulb mass and the mass and number of bulbils, offsets, and flowers were used as response variables, in addition to the proportion allocated to each reproductive mode. We found evidence of substantial heritable variation in allocation to sexual reproduction and in allocation within the two modes of asexual reproduction, indicating high sensitivity of these allocation patterns to natural selection. We also found evidence of strong negative genetic correlations between bulbil and flower traits, as well as between bulbil and offset traits, with one group of genotypes allocating greater resources to aerial asexual bulbils and the second group allocating more resources to belowground asexual offsets and aerial flowers. Phenotypic plasticity in allocation to above- vs. belowground asexual reproduction and sexual vs. asexual aerial reproduction was limited, indicating that plants are unlikely to change reproductive mode in response to nutrient availability. Together, then, we have demonstrated strong heritability for, and trade-offs in, the reproductive allocation patterns within this plant population.     

The importance of sexual and asexual reproduction in the recent evolution of Allium vineale

In the weedy plant species Allium vineale (wild garlic), individuals may simultaneously produce sexually and asexually derived offspring, by seed and bulbils, respectively. In this study, genetic and genotypic diversity was determined in samples from 14 European A. vineale populations using nuclear (RAPD) and cytoplasmic (PCR-RFLP of cpDNA) markers to investigate the importance of the different reproductive modes. In the whole sample, 77 nuclear multilocus genotypes and four chloroplast haplotypes (chlorotypes) were found. Populations exhibited a high degree of subdivision for nuclear and cytoplasmic markers as estimated from hierarchical F-statistics; at the same time, identical chlorotypes could be found in populations separated by large distances. Genotypic diversity was significantly lower than expected under free recombination in almost all populations, indicating that recruitment into populations is mostly by asexually produced offspring. Nevertheless, within each chlorotype, the distribution of markers from pairs of nuclear loci was incompatible with a purely clonal structure, suggesting that many multilocus genotypes have originated by sexual recombination rather than by mutation within asexual lineages. It is argued that the weedy habit of A. vineale is likely to have favored bulbil reproduction, whereas sexually generated genotypes may have facilitated local adaptation during the species' expansion across Europe.     

Genetic and environmental factors affecting reproductive variation in Allium vineale

Traits related to allocation of resources to sexual and asexual reproduction, together with seed production, were scored on Allium vineale plants sampled from five sites in southern Sweden during a period of 4 years. In addition, random amplified polymorphic DNA (RAPD) fingerprinting of the sampled plants allowed the identification of genets. Integration of genetic and phenotypic data from field and greenhouse provided for the analysis of among‐year, among‐site, and among‐genet variance components. These variance components were taken to represent the influences of short‐term environmental changes, persistent site divergence, and within‐site genet differences, respectively. It was shown that differences among sites and among genets explained a large part of the phenotypic variation of allocation traits, whereas among‐year differences had a larger influence on the variation in seed production. Together, the results support the conclusions of a recent model on the evolution of mixed reproductive systems, that predicts a stable balance between sexual and asexual reproduction because of annual fluctuations in fecundity through the two modes.     

Anisogamy,sexual selection,and the evolution and maintenance of sex

Summary In the present paper we distinguish between two aspects of sexual reproduction. Genetic recombination is a universal features of the sexual process. It is a primitive condition found in simple, single-celled organisms, as well as in higher plants and animals. Its function is primarily to repair genetic damage and eliminate deleterious mutations. Recombination also produces new variation, however, and this can provide the basis for adaptive evolutionary change in spatially and temporally variable environments.The other feature usually associated with sexual reproduction, differentiated male and female roles, is a derived condition, largely restricted to complex, diploid, multicellular organisms. The evolution of anisogamous gametes (small, mobile male gametes containing only genetic material, and large, relatively immobile female gametes containing both genetic material and resources for the developing offspring) not only established the fundamental basis for maleness and femaleness, it also led to an asymmetry between the sexes in the allocation of resources to mating and offspring. Whereas females allocate their resources primarily to offspring, the existence of many male gametes for each female one results in sexual selection on males to allocate their resources to traits that enhance success in competition for fertilizations. A consequence of this reproductive competition, higher variance in male than female reproductive success, results in more intense selection on males.The greater response of males to both stabilizing and directional selection constitutes an evolutionary advantage of males that partially compensates for the cost of producing them. The increased fitness contributed by sexual selection on males will complement the advantages of genetic recombination for DNA repair and elimination of deleterious mutations in any outcrossing breeding system in which males contribute only genetic material to their offspring. Higher plants and animals tend to maintain sexual reproduction in part because of the enhanced fitness of offspring resulting from sexual selection at the level of individual organisms, and in part because of the superiority of sexual populations in competition with asexual clones.     

Evolutionary increase in sexual and clonal reproductive capacity during biological invasion in an aquatic plant Butomus umbellatus (Butomaceae)

To test the hypothesis that increased allocation to reproduction is selected during biological invasion, we compared germination, survival, growth, and reproduction of native vs. introduced populations of the invasive aquatic plant Butomus umbellatus in a common greenhouse environment. Although seedling emergence and establishment did not differ consistently, survival thereafter was twice as high for eight introduced North American than eight native European populations. As predicted, introduced plants were more likely to produce sexual inflorescences and clonal asexual vegetative bulbils, and they invested much more biomass in both reproductive modes. Higher reproductive investment was due to higher proportional allocation of biomass rather than larger plant size. These results are consistent with selection for increased reproduction during range expansion. However, population genetic surveys indicate that recruitment from seed rarely occurs in introduced populations. Hence increased sexual allocation is not an adaptive response to invasion. Although increased clonal reproduction may be advantageous in expanding populations, genetic evidence from introduced populations of B. umbellatus suggests that increased clonal allocation may have arisen via stochastic processes during long-distance transport or a selective filter right at introduction, rather than incremental natural selection during range expansion.     

Genetic Control of Contagious Asexuality in the Pea Aphid

Although evolutionary transitions from sexual to asexual reproduction are frequent in eukaryotes, the genetic bases of such shifts toward asexuality remain largely unknown. We addressed this issue in an aphid species where both sexual and obligate asexual lineages coexist in natural populations. These sexual and asexual lineages may occasionally interbreed because some asexual lineages maintain a residual production of males potentially able to mate with the females produced by sexual lineages. Hence, this species is an ideal model to study the genetic basis of the loss of sexual reproduction with quantitative genetic and population genomic approaches. Our analysis of the co-segregation of ∼300 molecular markers and reproductive phenotype in experimental crosses pinpointed an X-linked region controlling obligate asexuality, this state of character being recessive. A population genetic analysis (>400-marker genome scan) on wild sexual and asexual genotypes from geographically distant populations under divergent selection for reproductive strategies detected a strong signature of divergent selection in the genomic region identified by the experimental crosses. These population genetic data confirm the implication of the candidate region in the control of reproductive mode in wild populations originating from 700 km apart. Patterns of genetic differentiation along chromosomes suggest bidirectional gene flow between populations with distinct reproductive modes, supporting contagious asexuality as a prevailing route to permanent parthenogenesis in pea aphids. This genetic system provides new insights into the mechanisms of coexistence of sexual and asexual aphid lineages.     

Reproductive strategies in some arctic Saxifraga (Saxifragaceae), with emphasis on the narrow endemic S. svalbardensis and its parental species

Arctic saxifrages show conspicuous reproductive and chromosomal variation. We examined sexual and asexual traits in 43 phytotron-cultivated Svalbard populations of nine species, including the endemic, supposedly entirely asexual and aneupolyploid S. svalbardensis and its parental species, S. cernua and S. rivularis. All species were self-compatible hermaphrodites with low pollen/ovule ratios, including the strongly protandrous S. cernua , which previously has been reported as self-incompatible with an androdioecious mating system. Spontaneous selfing resulted in considerable seed set in several species and a few seeds in S. svalbardensis and S. cernua; hand-selfing and cross-pollination often increased seed set in the two latter species. Self-fertilized seeds of S. svalbardensis and S. cernua were viable and developed into normal, vigorous plants. Saxifraga rivularis and its close relative S. hyperborea were strongly autogamous. The bulbil-reproducing S. svalbardensis and S. cernua showed extreme variation in fertility, probably because of frequent aneuploidy. Many plants of S. cernua were fully fertile, suggesting that although natural seed set rarely has been observed, sexual reproduction is frequent enough to maintain its previously reported high levels of clonal diversity. Some plants of S. svalbardensis were also fairly fertile. This species may have considerable evolutionary potential; sexual events can lead to increasingly fertile genets with euploid chromosome numbers.     

Distance-dependent performance of asexual progeny in Allium vineale (Liliaceae)

Local adaptation within and among populations may have an impact on processes ranging from speciation to the evolution of mixed breeding systems and dispersal strategies. It is also one potential factor that could favor the production of asexual over sexual propagules. This field experiment tested whether asexually produced bulbils of Allium vineale demonstrate local adaptation to the parental microsite at the scale of natural dispersal from the parent (5, 25, 50, 100, and 1000 cm). Both "home' and randomly chosen "away' genotypes were planted at each location to determine the relative performance of the "home' genotype. Overall, bulbil performance declined with distance from the parent. In particular, "home' bulbils outperformed "away' bulbils at a distance of 25 cm from the parent, indicating that local adaptation has occurred at the scale of natural dispersal in this species. The variance in propagule performance also increased at farther distances from the parent, indicating that the predictability of offspring performance decreases with distance. Fine-scale local adaptation within the range of seed dispersal in this population may be one factor favoring asexual reproduction in Allium vineale.     

克隆和有性亲体效应及其调控机制

植物表型受自身基因型、所处环境及其亲体所经历环境的共同影响;其中,亲体环境对子代表型的影响被称为亲体效应。亲体效应不仅可通过有性繁殖产生的种子传递给后代(即有性亲体效应),也可以通过克隆生长等无性繁殖产生的分株传递给后代(即克隆亲体效应)。亲体效应对植物种群,特别是对有性繁殖受限、缺乏遗传变异的克隆植物种群的长期进化可能发挥着极其重要的作用,因此,对亲体效应研究进展的梳理非常必要。对克隆亲体效应和有性亲体效应的内涵进行了阐释,并论述了克隆和有性亲体效应对子代表型、适合度、种内/种间竞争能力以及种群/群落结构和功能的潜在影响;阐述了亲体效应的潜在调控机制,包括供给机制、代谢物质调控机制、表观遗传机制等;论述了克隆亲体效应在克隆植物适应进化中的作用。未来可以就克隆亲体效应的遗传稳定性及其对克隆生活史性状变异的贡献程度,以及克隆和有性亲体效应引起的表型多样性对种内/种间关系、种群/群落多样性及生态系统结构、功能和稳定性的影响开展深入研究。     

INBREEDING DEPRESSION VARIES WITH INVESTMENT IN SEX IN A FACULTATIVE PARTHENOGEN

The reproductive mode of facultative parthenogens allows recessive mutations that accumulate during the asexual phase to be unmasked following sexual reproduction. Longer periods of asexual reproduction should increase the accumulation of deleterious mutations within individuals, reduce population-level genetic diversity via competition and increase the probability of mating among close relatives. Having documented that the investment in sexual reproduction differs among populations and clones of Daphnia pulicaria , we ask if this variation is predictive of the level of inbreeding depression across populations. In four lake populations that vary in sex investment, we raised multiple families (mother, field-produced daughter, laboratory-produced daughter) on high food and estimated the fitness reduction in both sexually produced offspring relative to the maternal genotype. Inbred individuals had lower fitness than their field-produced siblings. The magnitude of fitness reduction in inbred offspring increased as population-level investment in sex decreased. However, there was less of a fitness reduction following sex in the field-produced daughters, suggesting that many field-collected mothers were involved in outcross mating.     

Asexual and sexual reproductive strategies in clonal plants

Most plants can reproduce both sexually and asexually (or vegetatively),and the balance between the two reproductive modes may vary widely between and within species.Extensive clonal growth may affect the evolution of life history traits in many ways.First,in some clonal species,sexual reproduction and sex ratio vary largely among populations.Variation in sexual reproduction may strongly affect plant's adaptation to local environments and the evolution of the geographic range.Second,clonal growth can increase floral display,and thus pollinator attraction,while it may impose serious constraints and evolutionary challenges on plants through geitonogamy that may strongly influence pollen dispersal.Geitonogamous pollination can bring a cost to plant fitness through both female and male functions.Some co-evolutionary interactions,therefore,may exist between the spatial structure and the mating behavior of clonal plants.Finally,a trade-off may exist between sexual reproduction and clonal growth.Resource allocation to the two reproductive modes may depend on environmental conditions,competitive dominance,life span,and genetic factors.If different reproductive modes represent adaptive strategies for plants in different environments,we expect that most of the resources should be allocated to sexual reproduction in habitats with fluctuating environmental conditions and strong competition,while clonal growth should be dominant in stable habitats.Yet we know little about the consequence of natural selection on the two reproductive modes and factors which control the balance of the two reproductive modes.Future studies should investigate the reproductive strategies of clonal plants simultaneously from both sexual and asexual perspectives.     

Nitrogen fertilizer and gender effects on the secondary metabolism of yaupon,a caffeine-containing North American holly

Females and males of sexually dimorphic species have distinct resource demands due to differential allocation to reproduction. Sexual allocation theory predicts that functional traits will diverge between sexes to support these demands. However, such dimorphism may be masked by the impact of current reproduction on source-sink interactions between vegetative and reproductive organs. We ask whether natural selection has led to genetic dimorphism in homologous physiological traits between sexes of the dioecious willow shrub, Salix glauca. In a common garden experiment we compared physiological responses to drought stress by male and female ramets in the absence of confounding demands from reproductive structures. Ramets experienced similar pre-dawn leaf water status (Ψ_l) as parental genets in flower within the natural population, indicating that experimental dry-down mirrored environmental conditions in nature. Male and female ramets achieved similar instantaneous water use efficiency, based on the ratio of carbon gain to water loss, under wet and dry conditions. However, female ramets experienced greater water stress (i.e., more negative Ψ_l) than males under dry conditions. Lower Ψ_l for female ramets may partly reflect the maintenance of conductance under drought; males, in contrast, maintain Ψ_l under drought by reducing conductance. Differences between sexes in terms of conductance and leaf water status of the vegetative ramets were absent in a concomitant comparison of parental flowering plants. Our results show (1) genetic divergence in physiology between sexes of S. glauca occurs in the absence of gender-specific reproductive sinks, (2) males are the more physiologically plastic sex with respect to water use, and (3) paradoxically, divergence in water relations between sexes is not detectable at sexual maturity under natural conditions.     

Daphnia females adjust sex allocation in response to current sex ratio and density

Cyclical parthenogenesis presents an interesting challenge for the study of sex allocation, as individuals’ allocation decisions involve both the choice between sexual and asexual reproduction, and the choice between sons and daughters. Male production is therefore expected to depend on ecological and evolutionary drivers of overall investment in sex, and those influencing male reproductive value during sexual periods. We manipulated experimental populations, and made repeated observations of natural populations over their growing season, to disentangle effects of population density and the timing of sex from effects of adult sex ratio on sex allocation in cyclically parthenogenetic Daphnia magna. Male production increased with population density, the major ecological driver of sexual reproduction; however, this response was dampened when the population sex ratio was more male‐biased. Thus, in line with sex ratio theory, we show that D. magna adjust offspring sex allocation in response to the current population sex ratio.     

Extreme genetic diversity in asexual grass thrips populations

The continuous generation of genetic variation has been proposed as one of the main factors explaining the maintenance of sexual reproduction in nature. However, populations of asexual individuals may attain high levels of genetic diversity through within‐lineage diversification, replicate transitions to asexuality from sexual ancestors and migration. How these mechanisms affect genetic variation in populations of closely related sexual and asexual taxa can therefore provide insights into the role of genetic diversity for the maintenance of sexual reproduction. Here, we evaluate patterns of intra‐ and interpopulation genetic diversity in sexual and asexual populations of Aptinothrips rufus grass thrips. Asexual A. rufus populations are found throughout the world, whereas sexual populations appear to be confined to few locations in the Mediterranean region. We found that asexual A. rufus populations are characterized by extremely high levels of genetic diversity, both in comparison with their sexual relatives and in comparison with other asexual species. Migration is extensive among asexual populations over large geographic distances, whereas close sexual populations are strongly isolated from each other. The combination of extensive migration with replicate evolution of asexual lineages, and a past demographic expansion in at least one of them, generated high local clone diversities in A. rufus. These high clone diversities in asexual populations may mimic certain benefits conferred by sex via genetic diversity and could help explain the extreme success of asexual A. rufus populations.     

The effects of reproductive specialization on energy costs and fitness genetic variances in cyclical and obligate parthenogenetic aphids

Organisms with coexisting sexual and asexual populations are ideal models for studying the consequences of either reproductive mode on the quantitative genetic architecture of life-history traits. In the aphid Rhopalosiphum padi, lineages differing in their sex investment coexist but all share a common parthenogenetic phase. Here, we studied multiple genotypes of R. padi specialized either for sexual and asexual reproduction and compared their genetic variation in fitness during the parthenogenetic phase. Specifically, we estimated maintenance costs as standard metabolic rate (SMR), together with fitness (measured as the intrinsic rate of increase and the net reproductive rate). We found that genetic variation (in terms of broad-sense heritability) in fitness was higher in asexual genotypes compared with sexual genotypes. Also, we found that asexual genotypes exhibited several positive genetic correlations indicating that body mass, whole-animal SMR, and apterous individuals production are contributing to fitness. Hence, it appears that in asexual genotypes, energy is fully allocated to maximize the production of parthenogenetic individuals, the simplest possible form of aphid repertoire of life-histories strategies.     

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.     

High variation in clonal vs. sexual reproduction in populations of the wild strawberry, Fragaria virginiana (Rosaceae)

Background and Aims

Many plants reproduce both clonally and sexually, and the balance between the two modes of reproduction will vary among populations. Clonal reproduction was characterized in three populations of the wild strawberry, Fragaria virginiana, to determine the extent that reproductive mode varied locally between sites. The study sites were fragmented woodlands in Cook County, Illinois, USA.

Methods

A total of 95 strawberry ramets were sampled from the three sites via transects. Ramets were mapped and genotyped at five variable microsatellite loci. The variability at these five loci was sufficient to assign plants to clones with high confidence, and the spatial pattern of genets was mapped at each site.

Key Results

A total of 27 distinct multilocus genotypes were identified. Of these, 18 genotypes were detected only once, with the remaining nine detected in multiple ramets. The largest clone was identified in 16 ramets. No genets were shared between sites, and each site exhibited markedly different clonal and sexual recruitment patterns, ranging from two non-overlapping and widespread genets to 19 distinct genets. Only one flowering genet was female; the remainder were hermaphrodites.

Conclusions

Local population history or fine-scale ecological differences can result in dramatically different reproductive patterns at small spatial scales. This finding may be fairly widespread among clonal plant species, and studies that aim to characterize reproductive modes in species capable of asexual reproduction need to evaluate reproductive modes in multiple populations and sites.Key words: Clonal structure, gynodioecy, Fragaria virginiana, microsatellites, population genetic structure     

Parental effects in Plantago lanceolata L. III. Measuring parental temperature effects in the field

To determine the evolutionary importance of parental environmental effects in natural populations, we must begin to measure the magnitude of these effects in the field. For this reason, we conducted a combined growth chamber-field experiment to measure parental temperature effects in Plantago lanceolata. We grew in the field offspring of controlled crosses of chamber-grown parents subjected to six temperature treatments. Each treatment was characterized by a unique combination of maternal prezygotic (prior to fertilization), paternal prezygotic, and postzygotic (during fertilization and seed set) temperatures. Offspring were followed for three years to measure the effects of treatment on several life-history traits and population growth rate, our estimate of fitness. Parental treatment influenced germination, growth, and reproduction of newborns, but not survival or reproduction of offspring at least one year old. High postzygotic temperature significantly increased germination and leaf area at 17 weeks by approximately 35% and 2%, respectively. Probability of flowering and spike production in the newborn age class showed significant parental genotype x parental treatment interactions. High postzygotic temperature increased offspring fitness by approximately 50%. The strongest contributors to fitness were germination and probability of flowering and spike production of newborns. A comparison of our data with previously collected data for chambergrown offspring shows that the influence of parental environment on offspring phenotype is weaker but still biologically meaningful in the field. The results provide evidence that parental environment influences offspring fitness in natural populations of P. lanceolata and does so by affecting the life-history traits most strongly contributing to fitness. The data suggest that from the perspective of offspring fitness, natural selection favors parents that flower later in the flowering season in the North Carolina Piedmont when it is warmer. Genotypic-specific differences in response of offspring reproductive traits to parental environment suggest that parental environmental effects can influence the rate of evolutionary change in P. lanceolata.     

Reproductive allocation between the sexes,across natural and novel habitats,and its impact on genetic diversity

Allocation to reproductive mode (sexual and asexual) can vary depending on environmental conditions but is often examined at the population level, whereas selection acts upon the individual. We examined individual variation in reproductive mode to identify how the interaction of sex and the environment affect population genetic diversity. Using the plant Marchantia inflexa, we tested whether reproductive allocation pattern varies consistently between males and females and among plants collected from different environments, and determined if morphological responses were the result of individual plasticity or genetic differences. We then quantified genetic variability between the different environments and between the sexes. Male and female plants were collected from two strikingly different habitats within the same region: along natural sites (rivers) and along novel human-modified sites (roadsides). Using a common garden approach, we found a strong sex by habitat interaction: male and female responses differed significantly by their source habitat. For females, relative to river-collected, road-collected plants had higher growth and asexual reproduction, while the pattern was reversed, although not significant, for males. Genetic differentiation was significant between the two habitats with no evidence of individual differences in plasticity for growth, but there was a genotype effect for asexual propagule production. Males and females did not differ genetically; but river-collected plants with lower sexual potential were more diverse than roadside-collected plants, possibly the result of founder events. These results show that individual variation in reproduction is controlled by the interaction of both the environment and genetics. Due to different selection pressures between natural and novel habitats, there are observable differences in life history traits with an associated evolutionary response to the novel habitat.     

Population genetic consequences of the reproductive system in the liverwort <Emphasis Type="Italic">Mannia fragrans</Emphasis>

Ecological factors affecting reproduction and dispersal are particularly important in determining genetic structure of plant populations. Polyoicous reproductive system is not rare in bryophytes; however, to date, nothing is known about its functioning and possible population genetic effects. Using the liverwort Mannia fragrans as a model species, the main aims of this study were to separate the relative importance of the components of the polyoicous reproductive system and to assess its consequences on the genetic structure of populations. High sex expression rates increasing with patch size and strongly female-biased sex ratios were detected. Additional input into clonal growth after production of sex organs was found in males compared to females. Similar clonal traits of the rare bisexual and asexual plants and preference toward newly colonized patches suggest that selection prefers colonizers that first develop organs of both sexes, hence ensuring sexual reproduction when no partner is present. Despite frequent spore production, ISSR markers revealed low genetic diversity, probably resulting from the effective clonal propagation of the species and frequent crossing between genetically identical plants. The presence of numerous rare alleles and unique recombinant haplotypes indicates occasional recombination and mutation. Effective spreading of new haplotypes is probably hampered however by large spore size. Since populations are small and isolated, such haplotypes are probably continuously eliminated by genetic drift. These results suggest that although both sexual and asexual reproductions seem to be effective, asexual components of the reproductive system play a greater role in shaping the genetic composition of the populations.