Altitudinal variations in flower and bulbil production of an alpine perennial, Polygonum viviparum L. (Polygonaceae)

Two opposite views exist regarding sexual versus asexual reproductive performance of Polygonum viviparum . One suggests that increasing altitude favors flower production, while the other suggests that increasing altitude increases bulbil production. In this study, we present an investigation of the reproductive performance of 13 populations of P. viviparum on the Qinghai–Tibet Plateau (QTP). Our results show that, with increasing altitude, the height of inflorescence and total number of flowers and bulbils decrease significantly, but there is no significant effect on bulbil and flower number. In addition, there is a weak correlation between the proportion of flowers per population and altitude in our study sites due to the exception population 12, which is in a disturbed habitat. We conclude that more resources might be allocated to flowers in populations at higher altitudes, indicating the importance of sexual reproduction over asexual reproduction in alpine plants of QTP.     

Causes of variation in sexual and asexual reproduction in diploid and triploid populations of <Emphasis Type="Italic">Allium scorodoprasum</Emphasis>

Allium scorodoprasum is a bulbous geophyte that reproduces by seeds, aerial bulbils, and subterranean daughter bulbs. This research represents the analysis of intraspecific variations in sexual and asexual reproduction in relation to ploidy levels and the environmental conditions from 11 diploid and 24 triploid populations in Lithuania. The results showed that the seed production was extremely rare and occurred only in diploid populations. The numbers of flowers and aerial bulbils per plant as well as mean mass of one bulbil were the characteristics in which differences between ploidy levels were the biggest. The diploids on average produced more (61.9), but smaller (mean mass = 29.6 mg) bulbils and more flowers (16.7), while triploids produced less (41.7), but larger (mean mass = 45.9 mg) bulbils and fewer (5.2) flowers. The study revealed that the main determinant of intracytotypic variation in quantity of both sexual and asexual structures was light availability.     

Vivipary in Polygonum viviparum: an adaptation to cold climate?

Populations of Polygonurn viviparurn were investigated in the Swiss Alps at 14 sites, ranging from 450 m to 2530 m above sea level. The average length of stems and the mean number of reproductive organs (flowers + bulbils) decreased significantly with increasing altitude. On average, the ratio of flowers to bulbils per inflorescence also declined so that at high altitudes, bulbil production was more pronounced. Increased allocation to vegetative reproduction is discussed as an adaptation to cold climate. It is suggested that enhanced vegetative reproduction might be controlled by incornplete floral induction in high altitudes. In addition variability within and between populations was investigated by isozyme electrophoresis and the examination of bulbil colours. A considerable amount of variability was found in alpine populations. The demonstrated genetic variability showed that in P. viviparum it is likely that minor sexual reproduction is maintained even under alpine conditions. This is reflected in different enzyme phenotypes and different bulbil colours.     

不同生境下珠芽蓼（蓼科）的繁殖策略比较

在青藏高原横断山区以海拔相同的高山流石滩和高寒草甸中的珠芽蓼（Polygonum viviparum）居群为研究对象,探讨该物种在不同生境条件下的繁殖策略以及无性繁殖和有性繁殖间的关系。结果发现,流石滩居群的珠芽蓼植株高度和珠芽数量显著低于高寒草甸居群,而珠芽和花总数量、花数量和每个花序上的花比例却显著高于高寒草甸居群。研究结果表明珠芽蓼在环境更为恶劣的高山流石滩生境中增加了对繁殖器官和花资源的投资,说明在高山植物中繁殖优先于营养生长,且有性繁殖比无性繁殖具有更为重要的作用。而对每个植株上花数量和珠芽数量的统计结果表明,两者呈显著的负相关关系,进一步证明了同一植株内无性繁殖和有性繁殖的权衡关系。     

Aspects of sexual failure in the reproductive processes of a rare bulbiliferous plant,<Emphasis Type="Italic"> Titanotrichum oldhamii</Emphasis> (Gesneriaceae), in subtropical Asia

Titanotrichum oldhamii produces both flowers and asexual bulbils on its inflorescences. However, field observations and herbarium collections indicate that seed set is infrequent and that most reproduction is from vegetative bulbils. We have investigated the failure of sexual reproduction and identified four major causes: (1) in the wild, the seed:ovule ratio for open pollination was only 1.9%, in contrast to 10.1% for artificial cross-pollination, implying poor pollinator services. (2) The overall reproductive success was 5–10 times greater in glasshouse pollination treatments compared to field treatments. This suggests suboptimal environmental conditions for seed set in natural habitats, which may eliminate natural seed set completely. (3) Pollination experiments showed that outcrossed populations set significantly more seed and had higher germination rates than intra-populational and self crosses, in both field and glasshouse experiments. T. oldhamii thus appears to benefit from wide outcrossing. Pollen transfer between populations, however, seems to be infrequent because of the rarity and scattered distribution of Titanotrichum populations. (4) Flowers near the apex of the inflorescence are less likely to set seed, especially late in the season when inflorescences convert to bulbil production. In these late flowers, pollen tubes showed poor guidance as they approach the micropyle of the ovules. Even under optimal glasshouse conditions, the average outcrossing success was only 0.229. Almost one-half of the ovules remained undeveloped and 13.5% of ovules aborted after pollination, indicating a strong shift of resource allocation toward vegetative bulbils and rhizome development. Efficient reproduction from asexual bulbils may thus have released Titanotrichum from strong selection for efficient sexual reproduction. However, occasional seed set observed in the wild may be very important for maintaining some genetic diversity in populations, and promoting overall fitness.     

Biology of the polyploid geophyte Allium oleraceum (Amaryllidaceae): Variation in size,sexual and asexual reproduction and germination within and between tetra-, penta- and hexaploid cytotypes

It has been proposed that plant species cytotypes commonly exhibit altered morphology, reproduction, geographic and ecological distributions. We studied phenotypic variation in height, sexual (flowers, seeds) and asexual (aerial bulbils) reproduction in natural populations and in the conditions of a common garden of three cytotypes (2n = 4x, 5x, 6x) of the bulbous geophyte Allium oleraceum in the Czech Republic. Additionally, we compared the germination and dormancy of seeds and bulbils to determine whether propagules have different ecological roles. The pattern of morphological differentiation observed between cytotypes under natural conditions was similar to that observed under common garden conditions, suggesting that variability in morphological characteristics appears to be associated with ploidy levels. We revealed differences in size and sexual and asexual production between A. oleraceum cytotypes, but with wide overlap among cytotypes, suggesting a limited possibility of the studied traits to reliably distinguish between cytotypes. Tetraploids and pentaploids were rather similar; they were taller and produced more flowers than hexaploids, which were mostly flowerless (mean <0.7 flower/plant). All cytotypes were able to produce viable seeds, but their numbers were extremely low, usually less than 3 seeds per inflorescence; clonal reproduction via aerial bulbils dominates in all cytotypes (flower:bulbil ratio <0.5), with tetraploids producing more but lighter bulbils than other cytotypes. The seed: ovule ratio was low (<0.1) in all cytotypes, although hexaploids reached higher values than other cytotypes. Bulbils germinated better (means >80%) than seeds in all cytotypes, with pentaploid bulbils showing the highest germination (mean 90.5%). The cytotypes did not differ in seed germination (range of means 73.4%–76.3%). About 6% of seeds did not germinate but were still viable at the end of the experiment, while all non-germinated bulbils of all cytotypes had rotten away. Seeds, but not bulbils, can likely form a short-term persistent propagule soil bank. We found no evidence of a phenotypic trade-off between the production of flowers (seeds) and the production of bulbils within the inflorescence of all studied cytotypes. Together, inter-cytotypic differences in fitness-related traits cannot completely explain the different geographic and ecological distributions of cytotypes in the Czech Republic found by previous research.     

Trade-offs between sexual and clonal reproduction in an aquatic plant: experimental manipulations vs. phenotypic correlations

That trade-offs result from the allocation of limited resources is a central concept of life history evolution. We quantified trade-offs between sexual and clonal reproduction in the aquatic plant, Butomus umbellatus, by experimentally manipulating sexual investment in two distinct nutrient environments. Increasing seed production caused a significant but nonlinear trade-off. Pollinating half of all flowers strongly reduced clonal bulbil production, but pollinating the remaining flowers did not cause any further trade-off. Trade-offs were not stronger under low nutrient conditions that clearly limited plant growth. Experimentally induced trade-offs were not reflected in negative phenotypic correlations between sexual and clonal allocation among plants within eight populations grown in a uniform greenhouse environment. Diminishing effects of increased sexual allocation plus a lack of accord between experimental manipulations and phenotypic correlations suggest that trade-offs between sexual and clonal reproduction are unlikely to constrain the evolution of reproductive strategy in this species.     

The effect of pollination on resource allocation among sexual reproduction,clonal reproduction,and vegetative growth in <Emphasis Type="Italic">Sagittaria potamogetifolia</Emphasis> (Alismataceae)

In order to evaluate the effects of pollination on resource allocation in the marsh herb Sagittaria potamogetifolia, experimental manipulation of pollination efficiency on the pattern of resource allocation was accessed by the proportion of dry weight measurements of sexual, vegetative, and clonal organs. In trials where half of the flowers were pollinated, a significant increase of resource allocated to sexual production and decrease to vegetative production resulted compared to plants that received no pollination. In trials where pollination was 100%, these two reproductive components showed the same trend, but less dramatically. This may support the idea that the trade-offs would be more pronounced when the resource was scarce. Besides, a higher inflorescence production with a lower fruit reproduction occurred as a consequence of decreased pollination level. This increased inflorescence production may be a mechanism to promote outcrossing by enhancing floral attraction or by synchronizing reproductive activity with insect pollinators. Examination for possible trade-offs in resource allocation revealed that there was also a trade-off caused by pollination between fruits plus flowers and bulbils production, which might have detrimental effects on the survival of individuals and populations, but promotes outcrossing and genetic variability.     

Genetic variation, disequilibrium and natural selection on reproductive traits in Allium vineale

Bulbils and seeds collected from Allium vineale plants from natural populations were grown under uniform conditions. The bulbil-derived offspring represented the parental generation, whereas the seed-derived offspring represented the sexually produced offspring generation. Molecular markers were used to identify maternal genets. Variation in traits determining the allocation to sexual and asexual reproduction was partitioned among genets and ramet families in the parental and offspring generations. From observations of a release of genetic variation and slippage in the mean phenotype in the offspring generation, we inferred that there exists extensive genetic disequilibrium for reproductive traits in A. vineale populations, that most of the genetic variance is because of dominance effects, and that natural selection favours a reduced allocation to sexual reproduction. No genetic correlation between sexual and asexual allocation traits was found. We discuss the implications of these results with respect to the evolution of a mixed reproductive system in A. vineale.     

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.     

Does the silver moss Bryum argenteum exhibit sex-specific patterns in vegetative growth rate,asexual fitness or prezygotic reproductive investment?

Background and Aims

Expected life history trade-offs associated with sex differences in reproductive investment are often undetected in seed plants, with the difficulty arising from logistical issues of conducting controlled experiments. By controlling genotype, age and resource status of individuals, a bryophyte was assessed for sex-specific and location-specific patterns of vegetative, asexual and sexual growth/reproduction across a regional scale.

Methods

Twelve genotypes (six male, six female) of the dioecious bryophyte Bryum argenteum were subcultured to remove environmental effects, regenerated asexually to replicate each genotype 16 times, and grown over a period of 92 d. Plants were assessed for growth rates, asexual and sexual reproductive traits, and allocation to above- and below-ground regenerative biomass.

Key Results

The degree of sexual versus asexual reproductive investment appears to be under genetic control, with three distinct ecotypes found in this study. Protonemal growth rate was positively correlated with asexual reproduction and sexual reproduction, whereas asexual reproduction was negatively correlated (appeared to trade-off) with vegetative growth (shoot production). No sex-specific trade-offs were detected. Female sex-expressing shoots were longer than males, but the sexes did not differ in growth traits, asexual traits, sexual induction times, or above- and below-ground biomass. Males, however, had much higher rates of inflorescence production than females, which translated into a significantly higher (24x) prezygotic investment for males relative to females.

Conclusions

Evidence for three distinct ecotypes is presented for a bryophyte based on regeneration traits. Prior to zygote production, the sexes of this bryophyte did not differ in vegetative growth traits but significantly differed in reproductive investment, with the latter differences potentially implicated in the strongly biased female sex ratio. The disparity between males and females for prezygotic reproductive investment is the highest known for bryophytes.     

养分供应对3种舞花姜属植物繁殖方式的影响

该研究选用的3种舞花姜属植物中,毛舞花姜(Globba barthei)和双翅舞花姜(G. schomburgkii)自然条件下开花不结实,以珠芽进行繁殖;异果舞花姜(G. racemosa)则同时以种子和珠芽进行繁殖。在人工栽培条件下,高养分处理显著增加毛舞花姜的珠芽干重((1.11±0.10) g vs. (3.08±0.69) g,p=0.010 7)、珠芽数量((30.58±2.92) vs. (74.74±9.73),p=0.000 4)、珠芽大小((10.5±1.48) mg vs. (53.50±11.42) mg,p=0.001 5)、植株营养体重((3.99±0.23) g vs. (9.67±1.17) g,p=0.000 2)和双翅舞花姜的珠芽数量((51.74±3.64) vs. (108.71±21.52),p=0.018 1)。不同养分条件下两种舞花姜的开花数量无显著差异。人工去除珠芽、花对两种舞花姜植株当年生花和珠芽的数量无显著影响(p<0.05)。自然条件下异果舞花姜不同居群间珠芽大小、珠芽数、珠芽重、果实重、种子数和营养体重等均存在极显著差异(p<0.001)。异果舞花姜各居群植株珠芽数和营养体重(r=0.901,p<0.05)、珠芽重和珠芽大小 (r=0.849,p<0.05) 呈显著正相关;果实重和种子数(r=0.998,p<0.05) 呈显著正相关。土壤因子主成分分析表明前3个主成分提供的信息量分别为50.575%、18.204% 和11.883%,其中第一主成分中的全氮(0.959)、速效氮(0.885)和有机质(0.821)负荷量最大,第二主成分中土壤速效磷(0.824)负荷量最大。植株营养体重和土壤速效磷极显著正相关(r=0.906,p<0.01),珠芽大小与全氮(r=0.798)、速效氮(r=0.780)和有机质(r=0.821)均呈显著正相关(p<0.05)。果实重和种子数与土壤因子相关性不显著(p<0.05)。3种舞花姜的无性繁殖器官更易受到养分供应的影响,有性繁殖器官对养分供应变化响应不显著,有性和无性繁殖之间似不存在补偿关系。     

Evolution of Rotifer Life Histories

When compared to most other multicellular animals, rotifers are all relatively small, short-lived and fast-reproducing organisms. However among and within different rotifer species there is a large variation in life history patterns. This review accounts for such variation in rotifers, with a strong focus on monogonont rotifers. As the life cycle of monogonont rotifers involves both asexual and sexual reproduction, life history patterns can be examined on the level of the genetic individual, which includes all asexual females, sexual females and males that originated from one resting egg. This concept has been applied successfully in many areas, for example in predicting optimal levels of mictic reproduction or sex allocation theory. The benefits and implications of the view of the genetic individual are discussed in detail. Rotifer life histories can also be viewed on the level of physiological individuals. A large part of this review deals with the life histories of individual amictic females and addresses life history traits like body size, egg size and resource allocation patterns. It asks which trade-offs exist among those traits, how these traits change under the influence of environmental factors like food availability or temperature, and whether these changes can be interpreted as adaptive.     

Sexual and vegetative reproduction in the aboveground part of a dioecious clonal plant, <Emphasis Type="Italic">Dioscorea japonica</Emphasis> (Dioscoreaceae)

In dioecious clonal plants, the reproductive effort required to set seeds will be responsible for the larger investment in sexual reproduction by females. If there will be a trade-off in resource allocation between sexual and clonal reproduction, this differential sexual reproduction will lead to sexual differentiation in the relative amount of clonal reproduction. To test this prediction, we studied differences between the sexes in their phenologies and investments in sexual and vegetative reproduction (clonal reproduction by means of bulbils) with respect to ramet size in a dioecious clonal plant, Dioscorea japonica Thunb. The period of bulbil production overlapped the period during which infructescences developed. Females flowered later, produced heavier inflorescences, and fewer flowers per inflorescence than did males. Regression analysis using the size of the individual plants demonstrated that large females made smaller investments in inflorescences and larger investments in sexual reproduction than did large males. In contrast, females invested fewer resources in vegetative reproduction than did males. However, the total investments in sexual and vegetative reproduction did not differ between the sexes. These results supported our hypothesis on the sexual differentiation in sexual and clonal reproduction.     

Short-term consequences of reproductive mode variation on the genetic architecture of energy metabolism and life-history traits in the pea aphid

Cyclically parthenogenetic animals such as aphids are able alternating sexual and asexual reproduction during its life cycle, and represent good models for studying short-term evolutionary consequences of sex. In aphids, different morphs, whether sexual or asexual, winged or wingless, are produced in response to specific environmental cues. The production of these morphs could imply a differential energy investment between the two reproductive phases (i.e., sexual and asexual), which can also be interpreted in terms of changes in genetic variation and/or trade-offs between the associated traits. In this study we compared the G-matrices of energy metabolism, life-history traits and morph production in 10 clonal lineages (genotypes) of the pea aphid, Acyrthosiphon pisum, during both sexual and asexual phases. The heritabilities (broad-sense) were significant for almost all traits in both phases; however the only significant genetic correlation we found was a positive correlation between resting metabolic rate and production of winged parthenogenetic females during the asexual phase. These results suggest the pea aphid shows some lineage specialization in terms of energy costs, but a higher specialization in the production of the different morphs (e.g., winged parthenogenetic females). Moreover, the production of winged females during the asexual phase appears to be more costly than wingless females. Finally, the structures of genetic variance-covariance matrices differed between both phases. These differences were mainly due to the correlation between resting metabolic rate and winged parthenogenetic females in the asexual phase. This structural difference would be indicating that energy allocation rules changes between phases, emphasizing the dispersion role of asexual morphs.     

Meristem fate and bulbil formation in Titanotrichum (Gesneriaceae)

Titanotrichum oldhamii (a monotypic genus from Taiwan, Okinawa, and adjacent regions of China) has inflorescences bearing either showy yellow flowers or asexual bulbils. Asexual reproduction by bulbils is important in natural populations, and bulbil production increases in August and September at the end of the flowering season (which runs from June to the end of September). The bulbils are small (～1-2.5 mm long) and numerous. They consist of a small portion of stem (bract-stem) topped by opposite storage bracts that enclose a minute apical meristem. A secondary root develops from the side of the bract-stem. The floral meristem of T. oldhamii has three possible fates: (1) bulbil formation, (2) flower formation, or (3) bracteose proliferation. Bracteose proliferation rarely occurs and appears to be a developmental transition between the bulbiliferous and racemose inflorescence forms. It is strongly reminiscent of the floricaula and squamosa mutants of Antirrhinum. In the bulbiliferous form a single floral primordium, which would normally produce one flower, gives rise to ～50-70 bulbils by repeated subdivision of the meristem. This form of bulbil production appears to be unique to Titanotrichum. Occasionally a floral meristem divides, but the subdivision forms multiflowered units of up to four flowers rather than bulbils, suggesting that meristem fate is reversible up to the first or second meristem subdivision. In Titanotrichum, therefore, primordium fate is apparently not determined at inception but becomes irreversibly determined shortly after the appearance of developmental characteristics of the floral or bulbil pathway.     

The ecology of flower and bulbil production in Polygonum viviparum

Polygonum viviparum produces inflorescences which bear both sexual flowers and asexual bulbils in highly variable proportions. This paper investigates the proportion of flowers and bulbils per inflorescence at 12 sites in central Norway. It is shown that there is a 'trade—off between flowers and bulbils so that one cannot be increased without reducing the other'. On average, the balance is tilted in favour of bulbils, but there are significant differences in the proportion of bulbils per inflorescence among sites and among quadrats within 11 of the sites. Of these 11 sites there are 6 in which the proportion of bulbils per inflorescence is correlated with factors of the biotic environment. The factors include: (1) the amount of vascular plant cover, which is negatively correlated with the proportion of bulbils at 2 sites; (2) the cover of P. viviparum , which is positively correlated at 1 site; (3) the number of P. viviparum inflorescences, which is negatively correlated at 3 sites. The results suggest that both intra– and inter–specific factors of the biotic environment play a role in the control of bulbil and flower production in P. viviparum.     

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.     

青藏高原东缘块茎堇菜鳞茎分配的个体大小依赖性

块茎堇菜(Viola tuberifera)为青藏高原特有两型闭锁花植物,属多年生草本,具独特的混和交配系统,既可通过早春开放花异花受精和夏季地上地下闭锁花自花受精有性繁殖,还可通过秋季新鳞茎无性繁殖产生后代。高山环境下,异花受精常因花粉限制而无法正常进行,自花受精和克隆繁殖成为保障植物种群正常繁衍的不二之选,而克隆繁殖更能在植株资源消耗最小的情况下保障子代的存活。该文以青藏高原东缘高寒草甸的混合繁育植物块茎堇菜为研究对象,探索其生长期内鳞茎分配的个体大小依赖性,以及植株如何权衡鳞茎的资源分配以适应个体大小的变化。结果表明：块茎堇菜生活史阶段的鳞茎分配具有个体大小依赖性,鳞茎分配与个体大小呈极显著负幂指数相关关系(P<0.01),个体越大,鳞茎分配越小;反之,个体越小,鳞茎分配越高。即块茎堇菜对鳞茎的资源投入受个体大小的制约,通过鳞茎分配比例的高低响应植株自身资源状况的变化,保障在高寒环境下植物种群的生存和繁衍。该研究结果为高山植物克隆繁殖的生活史进化提供了依据。     

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.