Testing specialization hypothesis on a stress gradient

Specialization can allow plants to perform well in their home environments at the expense of poor performance in other habitats. A great difference in performance across habitats is observed as high phenotypic plasticity in performance traits and a by‐product of selection. However, phenotypic plasticity (particularly adaptive plasticity) can be an active response to the selection by allowing the maintenance of performance. Therefore, specialization and adaptive plasticity delineate two opposing strategies. The specialization hypothesis presents a non‐adaptive interpretation of plasticity and predicts that phenotypic plasticity of performance traits is greater in specialization to good habitats, whereas bad habitat specialists express low plasticity in performance traits. We tested the specialization hypothesis using plants adapted to extremely stressful mine‐site habitats (sites with highly acidic soil and heavy metal contamination). Seeds of five herbaceous species were collected from high stress (mine site) and low stress habitats. We established a glasshouse experiment where seedlings from high and low stress habitats were grown under near neutral pH and acid soil treatments. We compared performance trait plasticity (e.g. biomass) from high stress and low stress populations and found that there was no significant difference in performance traits between high and low stress populations across treatments. The overall result did not support the specialization hypothesis. Moreover, our results suggest that the species invaded the mine sites are either extreme generalists or the surrounding populations retain some stress tolerant genotypes that are capable of invading the mine sites.     

克隆植物对种间竞争的适应策略

克隆植物种群因其寿命的持久性、空间上的可移动性和繁殖方式的多样化等特征与非克隆植物有很大区别, 在自然生态系统中占有重要地位, 甚至成为优势种或者建群种。该文通过归纳有关克隆植物的种间竞争适应策略研究案例, 阐述了克隆植物的竞争能力差异和影响竞争力的因素; 论述了克隆植物在构件形态、克隆构型、繁殖对策等方面对种间竞争的响应, 以及生理整合作用与种间竞争的关系; 分析了导致某些同类研究的结论不一致的原因, 认为实验对象差异、实验设计、生境条件与克隆植物形态及生理上的时空动态变化等都可能影响实验结果; 提出了全球变化背景下的克隆植物种间竞争及其分子生态学机制等可能是今后需要重点关注的问题。     

竹类植物对异质生境的适应——表型可塑性

竹类植物是一类以木本为主的克隆植物,凭借表型可塑性的优势,对异质生境具有很强适应能力。然而,目前对竹类植物表型可塑性的实现方式及其异质生境适应对策未见系统总结,从而在一定程度上限制了竹类生态学的发展。从形态可塑性、选择性放置、克隆整合和克隆分工等4个方面对竹类植物的表型可塑性研究进行分析和梳理,结果表明:竹类植物在异质生境中具有明显的表型可塑反应,主要采用形态可塑性、选择性放置和克隆整合来适应异质生境,而克隆分工的普遍性仍有待验证;目前侧重于研究构件形态和生物量分配格局,而很少深入探讨形态、生理和行为等可塑性机理。今后竹类植物表型可塑性研究重点在于:1)克隆整合的格局与机理;2)克隆整合对生态系统的影响;3)克隆分工的形成及其与环境关系;4)表型可塑性的等级性及环境影响;5)不同克隆构型的表型可塑性特征及其内在机制。     

克隆植物的表型可塑性与等级选择

表型可塑性是指生物个体生长发育过程中遭受不同环境条件作用时产生不同表型的能力。进化的发生有赖于自然选择对种群遗传可变性产生的效力以及各基因型的表型可塑性。有足够的证据说明表型可塑性的可遗传性,它实际上是进化改变的一个成分。一般通过优化模型、数量遗传模型和配子模型来研究表型可塑性的进化。植物的构型是相对固定的,并未完全抑制表型可塑性。克隆植物因其双构件性而具有更广泛的、具有重要生态适应意义的表型可塑性。构件性使克隆植物具有以分株为基本单位的等级结构,从而使克隆植物的表型选择也具有等级性。构件等级一般包含基株、克隆片段或分株系统以及分株3个典型水平。目前认为克隆植物的自然选择有两种模式,分别以等级选择模型和基因型选择模型表征。等级选择模型认为:不同的等级水平同时也是表型选择水平,环境对各水平具有作用,各水平之间也有相互作用,多重表型选择水平的净效应最终通过繁殖水平——分株传递到随后的世代中。基因型选择模型指出:克隆生长引起分株的遗传变异,并通过基株内分株间以及基株间的非随机交配引起种子库等位基因频率的改变,产生微进化。这两种选择模式均突出强调了分株水平在自然选择过程中的变异性以及在进化中的重要性,强调了克隆生长和种子繁殖对基株适合度的贡献。基因型选择模型包含等级选择模型的观点,是对等级选择模型的重要补充。克隆植物的表型可塑性表现在3个典型等级层次上,由于各层次对自然选择压力具有不同的反应,其表型变异程度一般表现出“分株层次>分株片段层次>基株层次”的等级性反应模式。很多证据表明,在构件有机体中构件具有最大的表型可塑性,植物的表型可塑性实际上是构件而非整个遗传个体的反应。这说明克隆植物的等级反应模式可能具有普适性。如果该反应模式同时还是构件等级中不同“个体”适应性可塑性反应的模式,那么可以预测:1)在克隆植物中,分株层次受到的自然选择强度也最大,并首先发生适应性可塑性变化,最终引起克隆植物微进化;2)由于较弱的有性繁殖能力,克隆植物在进化过程中的保守性可能大于非克隆植物。克隆植物等级反应模式的普适性亟待验证。     

异质生境中水生植物表型可塑性的研究进展

水生植物是一类以草本植物为主、与水紧密相关的生态类群, 大多数具有克隆性。面对水环境的变化, 水生植物在形态、行为和生理上表现出多样化的表型可塑性, 对异质生境具有很强的适应能力。表型可塑性研究已在陆生植物的多个类群展开, 然而目前对异质生境下水生植物的生态适应对策, 尤其是表型可塑性的研究尚重视不够。本文在阐明克隆植物表型可塑性主要实现方式及其关系、水生环境异质性及其特点的基础上, 重点从形态可塑性、觅食行为、克隆整合、克隆分工和风险分摊等5个方面讨论了水生植物如何通过表型可塑性适应异质性水生环境。在今后的水生植物表型可塑性研究中, 建议着重探讨以下问题: (1)表型可塑性的变化规律及机理; (2)克隆整合对群落和生态系统的影响; (3)克隆整合与克隆片段化的权衡; (4)不同克隆构型的表型可塑性及其内在机制; (5)表型可塑性的适应性进化; (6)水生植物与其他类群/营养级物种的关系; (7)水生生态系统对全球变化的响应。     

Clonal plants—What is their role in succession?

Fifteen successional seres from man-made habitats in central Europe were compared and the occurrence of clonal species assessed on the basis of cover data. The effects of soil moisture and nitrogen (expressed using Ellenberg indicator values) on the performance of clonal plants were also considered. Clonal species formed the dominant component of vegetation cover in the majority of the seres studied. In moist sites, their dominance was more pronounced and the peak in their relative cover occurred earlier in succession. The relative importance of species with guerilla type growth tended to increase with time in most seres and after 10 years these were mostly more important than those exhibiting phalanx type growth. The prevalence of guerilla species after 10 years was more obvious in moist seres. Clonal species were able to become dominant regardless of soil conditions, whereas the dominance of non-clonal species tended to be restricted to very wet and nutrient-poor sites. Clonal plant species appeared to maintain their dominance for a longer period than non-clonal plants.     

Clonal Growth in Plants in Relation to Resource Heterogeneity:Foraging Behavior

In nature, essential resources for organisms, such as food for animals and light, water and nutrients for plants, are usually heterogeneously distributed, even at very small scale. As a result, all organisms, particularly plants mostly sessile, have a difficulty in acquiring essential resources from their environments. Animals express various types of foraging behavior to capture heterogeneously distributed essential foods. Clonal growth ( a vegetative reproductive process where by more than one individual of identical genetic composition is formed ) provides clonal plant not only with many "mouths" at different spatial positions, but also with a large spacial movability. As a clonal plant grows in environments characterized by a small-scale resource heterogeneity, its inter ramet connection permits a resource-sharing among the connected tamers. In addition, it may also allow certain ramets to respond locally and non-locally to resousce heterogeneity. This may lead to a division of labor among the connected ramets and a selective placement of ramets in favorable micro-habitats. Together these may enhance exploitation of resource heterogeneity by clonal plants, and in turn greatly contribute to maintenance or improvement of fitness. Such a behavior of clonal plants, expressed in heterogeneous environments, is to a large extent comparable to that of animals. Therefore, it has been considered as foraging behavior in clonal plants. More recently, it has been observed that phenotypic plasticity of clonal plants, which is relevant to foraging behavior, varies among species, types of genet architecture as well as among types of plants habitats. Foraging in clonal plants and its diversity have been receiving increasingly intensive investigations.     

On the evolution of clonal plant life histories

Clonal plant life histories are special in at least four respects: (1) Clonal plants can also reproduce vegetatively, (2) vegetative reproduction can be realised with short or long spacers, (3) and it may allow to plastically place vegetative offspring in benign patches. (4) Moreover, ramets of clonal plants may remain physically and physiologically integrated. Because of the apparent utility of such traits and because ecological patterns of distribution of clonal and non-clonal plants differ, adaptation is a tempting explanation of observed clonal life-history variation. However, adaptive evolution requires (1) heritable genetic variation and (2) a trait effect on fitness, and (3) it may be constrained if other evolutionary forces are overriding selection or by constraints, costs and trade-offs. (1) The few studies undertaken so far reported broad-sense heritability for clonal traits. Variation in selectively neutral genetic markers appears as pronounced in populations of clonal as non-clonal plants. However, neutral markers may not reflect heritable variation of life-history traits. Moreover, clonal plants may have been sampled at larger spatial scales. Empirical information on the contribution of somatic mutations to heritable variation is lacking. (2) Clonal life-history traits were found to affect fitness. However, much of this evidence stems from artificial rather than natural environments. (3) The relative importance of gene flow, inbreeding, and genetic drift, compared with selection, in the evolution of clonal life histories is hardly explored. Benefits of clonal life-history traits were frequently studied and found. However, there is also evidence for constraints, trade-offs, and costs. In conclusion, though it is very likely, that clonal life-history traits are adaptive, it is neither clear to which degree this is the case, nor which clonal life-history traits constitute adaptations to which environmental factors. Moreover, evolutionary interactions among clonal life-history traits and between clonal and non-clonal ones, such as the mating system, are not well explored. There remains much interesting work to be done in this field – which will be particularly interesting if it is done in the field.     

克隆植物对异质生境的适应对策研究进展

生境异质性是自然生态系统的基本特征,植物生长的必需资源和环境胁迫因子均存在着复杂的时间和空间异质性。克隆植物是指在自然条件下具有克隆特性的植物,即可通过与母株相连的芽、根茎、分蘖或枝条等繁殖体产生无性繁殖的植物,这些繁殖体一旦定居便可成为潜在的独立个体。克隆植物具有独特的生境适应策略(如形态可塑性、克隆整合、克隆分工、觅食行为、风险分摊等),面对异质性的生境条件,它可以通过调整自身的生理和形态结构来适应异质生境。目前,对于克隆植物在异质生境适应行为的研究已有很多报道,然而系统性的归纳和总结尚有欠缺。综述了克隆植物在不同资源异质生境(光照、养分、水分)和不同胁迫生境(盐碱胁迫、风沙胁迫、重金属胁迫)下独特的适应对策。最后,针对克隆植物对异质生境的适应对策,进行了总结并对未来的重点研究方向提出建议：(1)时间异质性尺度上的考量;(2)异质性生境中生物因子的调控作用;(3)克隆植物入侵机制;(4)克隆植物在生态修复中的应用潜力。     

表型可塑性与外来植物的入侵能力

外来植物的入侵能力与其性状之间的关系是入侵生态学中的基本问题之一。成功的入侵种常常能占据多样化的生境,并以广幅的环境耐受性为特征。遗传分化(包括生态型分化)和表型可塑性是广布性物种适应变化、异质性生境的两种不同但并不矛盾和排斥的策略。越来越多的实验证据表明,表型可塑性具有确定的遗传基础,本身是一种可以独立进化的性状。许多入侵种遗传多样性比较低,但同时又占据了广阔的地理分布区和多样化的生境,表型可塑性可能在这些物种的入侵成功和随后的扩散中起到了关键作用。本文首先介绍表型可塑性的含义,简述表型可塑性和生物适应的关系,然后从理论分析和实验证据两个方面论述了表型可塑性与外来植物入侵能力的相关性,最后针对进一步的研究工作进行了讨论。当然,并非所有入侵种的成功都能归因于表型可塑性,作者认为对于那些遗传多样性比较低同时又占据多样化生境的入侵种,表型可塑性和入侵能力的正相关可能是一条普遍法则,而非特例。     

Do clonal growth form and habitat origin affect resource-induced plasticity in Tibetan alpine herbs?

To investigate how growth form and habitat origin affect phenotypic plasticity to resource supply in the Tibetan alpine herbs, the phalanx-type species Stipa capillacea and the guerilla-type species Carex montis-everestii were sampled from two different habitats (alpine steppe and alpine scrubland) and grown under three levels of light intensity and two levels of nutrient supply. Interspecific differences in light-induced plasticity were detected only in number of ramets, specific leaf area and leaf sheath length. Plasticity in plant biomass, number of ramets and rhizome length in response to light intensity differed between the two habitats. Stipa plants were more plastic than Carex plants in number of ramets and specific leaf area in response to light intensity. Carex plants from the alpine scrubland expressed greater light-induced plasticity in plant biomass and number of ramets than those from the alpine steppe, and Stipa plants showed less interhabitat differences in plasticity, which may be closely related to their contrasting growth forms. Clonal growth form and habitat origin affected nutrient-induced plasticity in none of the measured traits. It may be the guerilla growth form that makes Carex plants more efficiently adapted to highly heterogeneous light conditions in scrubland, and less habitat-dependent plasticity contributes to success of the phalanx-type Stipa plants in alpine habitats. The results are discussed in the context of foraging for heterogeneously distributed essential resources and adaptation to habitat origin.     

Two types of division of labour in clonal plants: benefits, costs and constraints

Clonal plants spread vegetatively within their habitats by forming rooted ramets on stolons or rhizomes. Each of these ramets is capable of an independent existence after establishment. Nevertheless, ramets remain physically connected by stolon or rhizome internodes for variable periods of time, thereby allowing for resource movement and signal transduction within clones.Interconnected ramets of clonal plants, though potentially independent and totipotent, can specialize functionally in the performance of limited numbers of tasks such as the uptake of resources from above- vs below-ground sources, carbohydrate storage, vegetative spread and sexual reproduction. Such specialization and cooperation is comparable to a division of labour in economic systems or in colonies of social animals. The ecological significance of division of labour in clonal plants may be found in the increased efficiency of entire clones in exploiting their environments.Two different types of division of labour in clonal plants will be discussed in this review. The first type is an environmentally-induced specialization of ramets in the uptake of locally abundant resources (plastic division of labour), which can be found in several stoloniferous species. Evidence exists that this response increases resource uptake in spatially heterogeneous environments. The second type of division of labour, which occurs mainly in rhizomatous species, relates to a developmentally-programmed specialization and cooperation between interconnected ramets. This response pattern is thought to enhance plant performance by restricting the number of tasks for individual ramets and thereby significantly increasing the efficiency of task performance. In some plants, such an inherent division of labour is likely to contribute to nutrient extraction from poor and unpredictably variable sources.In this article not only benefits but also potential costs and constraints on division of labour in clonal plants are shown. The aim is to provide a review of existing knowledge and to develop concepts and hypotheses for future research.     

GENERALISTS,SPECIALISTS, AND THE EVOLUTION OF PHENOTYPIC PLASTICITY IN SYMPATRIC POPULATIONS OF DISTINCT SPECIES

The evolution of phenotypic plasticity is studied in a model with two reproductively isolated “species” in a coarse-grained environment, consisting of two types of habitats. A quantitative genetic model for selection was constructed, in which habitats differ in the optimal value for a focal trait, and with random dispersal among habitats. The main interest was to study the effects of different selection regimes. Three cases were investigated: (1) without any limits to plasticity; (2) without genetic variation for plasticity; and (3) with a fitness cost for phenotypically plastic reactions. In almost all cases a generalist strategy to exploit both habitats emerged. Without any limits to plasticity, optimal adaptive reactions evolved. Without any genetic variation for plasticity, a compromise strategy with an intermediate, fixed phenotype evolved, whereas in the presence of costs a plastic compromise between the demands of the habitats and the costs associated with plasticity was found. Specialization and phenotypic differentiation was only found when selection within habitats was severe and optimal phenotypes for different habitats were widely different. Under soft selection (local regulation of population numbers in each habitat) the specialists coexisted; under hard selection (global regulation of population numbers) one specialist outcompeted the other. The prevalent evolutionary outcome of compromises rather than specialization implies that costs or constraints are not necessarily detectable as local adaptation in transplantation or translocation experiments.     

The contribution of phenotypic plasticity to adaptation in Lacerta vivipara

Correlation between intraspecific phenotypic variability and variation of environmental conditions could reflect adaptation. Different phenotypes may result from differential expression of a genotype in different environments (phenotypic plasticity) or from expression of different genotypes (genetic diversity). Populations of Lacerta vivipara exhibit larger adult body length, lower age at maturity, higher fecundity, and smaller neonatal size in humid habitats compared to dry habitats. We conducted reciprocal transplants of juvenile L. vivipara to test for the genetic or plastic origin of this variation. We captured gravid females from four populations that differed in the relative humidity of their habitats, and during the last 2 to 4 weeks of gestation, we manipulated heat and water availability under laboratory conditions. Juveniles were released into the different populations and families were divided to compare growth rate and survival of half-sibs in two environments. Growth rate and survival were assessed using capture-recapture techniques. Growth rate was plastic in response to postnatal conditions and did not differ between populations of origin. Survival differed between populations of origin, partially because of differences in neonatal body length. The response of juvenile body length and body condition to selection in the different habitats was affected by the population of origin. This result cannot be simply interpreted in terms of adaptation; however, phenotypic plasticity of fecundity or juvenile size most probably resulted in adaptive reproductive strategies. Adaptation to the habitat by means of genetic specialization was not detected. Further investigation is needed to discriminate between genetic and long-term maternal effects.     

The consequences of phenotypic plasticity for ecological speciation

We use an individual-based numerical simulation to study the effects of phenotypic plasticity on ecological speciation. We find that adaptive plasticity evolves readily in the presence of dispersal between populations from different ecological environments. This plasticity promotes the colonization of new environments but reduces genetic divergence between them. We also find that the evolution of plasticity can either enhance or degrade the potential for divergent selection to form reproductive barriers. Of particular importance here is the timing of plasticity in relation to the timing of dispersal. If plasticity is expressed after dispersal, reproductive barriers are generally weaker because plasticity allows migrants to be better suited for their new environment. If plasticity is expressed before dispersal, reproductive barriers are either unaffected or enhanced. Among the potential reproductive barriers we considered, natural selection against migrants was the most important, primarily because it was the earliest-acting barrier. Accordingly, plasticity had a much greater effect on natural selection against migrants than on sexual selection against migrants or on natural and sexual selection against hybrids. In general, phenotypic plasticity can strongly alter the process of ecological speciation and should be considered when studying the evolution of reproductive barriers.     

Plasticity in salt tolerance traits allows for invasion of novel habitat by Japanese knotweed s. l. (Fallopia japonica and F.xbohemica, Polygonaceae)

Japanese knotweeds are among the most invasive organisms in the world. Their recent expansion into salt marsh habitat provides a unique opportunity to investigate how invasives establish in new environments. We used morphology, cytology, and AFLP genotyping to identify taxa and clonal diversity in roadside and salt marsh populations. We conducted a greenhouse study to determine the ability to tolerate salt and whether salt marsh populations are more salt tolerant than roadside populations as measured by the efficiency of PSII, leaf area, succulence, height, root-to-shoot ratio, and total biomass. Clonal diversity was extremely low with one F. japonica clone and five F. ×bohemica genotypes. The two taxa were significantly different in several traits, but did not vary in biomass or plasticity of any trait. All traits were highly plastic in response to salinity, but differed significantly among genets. Despite this variation, plants from the salt marsh habitats did not perform better in the salt treatment, suggesting that they are not better adapted to tolerate salt. Instead, our data support the hypothesis that plasticity in salt tolerance traits may allow these taxa to live in saline habitats without specific adaptation to tolerate salt.     

林下和林窗内绢毛匍匐委陵菜的克隆生长和克隆形态

 为了验证绢毛匍匐委陵菜(Potentilla reptans var. sericophylla)林窗和林下种群间的行为差异是完全由表型可塑性引起,还是局部分化的结果,将生长在北京东灵山油松（Pinus tabulaeformis）林林窗和林下的绢毛匍匐委陵菜,进行生境间的交互移植-重植野外生态实验。研究结果表明,实验植物的叶片长度、叶片宽度、叶柄长度和匍匐茎节间长度等克隆形态特征在两生境间无差异。两个来源的植株,其基株生物量、基株分株数和基株匍匐茎总长度等克隆生长特征在林下生境中都比在林窗生境中小,表现出显著的可塑性。所研究的克隆形态特征和克隆生长特征及其可塑性在不同生境来源的实验植物间没有差异。绢毛匍匐委陵菜克隆形态特征和克隆生长特征及其可塑性在林下和林窗生境间没有发生局部分化,林窗为其较适生境,克隆生长特征的可塑性对绢毛匍匐委陵菜利用生境异质性可能具有重要意义     

Trait plasticity,not values,best corresponds with woodland plant success in novel and manipulated habitats

Aims The clustering of plants with similar leaf traits along environmental gradients may arise from adaptation as well as acclimation to heterogeneous habitat conditions. Determining the forces that shape plant leaf traits requires both linking variation in trait morphology with abiotic gradients and linking that trait variation with plant performance under varying abiotic conditions. Across the spectrum of plant types, shade-tolerant evergreen herbs are relatively low in trait plasticity, compared to deciduous and sun-adapted species. These plants employ stress-tolerant strategies for survival, which coincide with relatively static trait morphologies, slow growth and hence a lower ability to adjust to changing environmental conditions.Methods We investigate how the survival of two ecologically similar understory evergreen species, Asarum arifolium and Hepatica nobilis, corresponds with variation in six commonly measured functional traits (leaf area, specific leaf area, plant height, leaf number, leaf length and shoot mass) along natural and experimental abiotic gradients. We examine temporal (the period 2007–9) and spatial (100 km) variations in these traits after (i) translocating 576 plants across a span from the southern Appalachian Mountains in NC, USA, to the Piedmont, GA, USA, which includes north- and south-facing slope habitats and (ii) the experimental manipulation of diffuse light and soil moisture.Important findings We find that when translocated into a novel habitats, with novel environmental conditions that often are more extreme than the source habitat, both species appear capable of considerable morphological acclimation and generally converge to similar trait values. Hepatica nobilis does not exhibit mean trait values particularly different from those of A. arifolium, but it demonstrates much greater phenotypic plasticity. These results indicate that relatively conservative plant species nonetheless acclimate and survive across heterogeneous environmental conditions.     

Small-scale heterogeneity in soil quality influences photosynthetic efficiency and habitat selection in a clonal plant

BACKGROUND AND AIMS: In clonal plants, internode connections allow translocation of photosynthates, water, nutrients and other substances among ramets. Clonal plants form large systems that are likely to experience small-scale spatial heterogeneity. Physiological and morphological responses of Fragaria vesca to small-scale heterogeneity in soil quality were investigated, together with how such heterogeneity influences the placement of ramets. As a result of their own activities plants may modify the suitability of their habitats over time. However, most experiments on habitat selection by clonal plants have not generally considered time as an important variable. In the present study, how the foraging behaviour of clonal plants may change over time was also investigated. METHODS: In a complex of environments with different heterogeneity, plant performance was determined in terms of biomass, ramet production and photosynthetic activity. To identify habitat selection, the number of ramets produced and patch where they rooted were monitored. KEY RESULTS: Parent ramets in heterogeneous environments showed significantly higher maximum and effective quantum yields of photosystem II than parents in homogeneous environments. Parents in heterogeneous environments also showed significantly higher investment in photosynthetic biomass and stolon/total biomass, produced longer stolons, and had higher mean leaf size than parents in homogeneous environments. Total biomass and number of offspring ramets were similar in both environments. However, plants in homogeneous environments showed random allocation of offspring ramets to surrounding patches, whereas plants in heterogeneous environments showed preferential allocation of offspring to higher-quality patches. CONCLUSIONS: The results suggest that F. vesca employs physiological and morphological strategies to enable efficient resource foraging in heterogeneous environments and demonstrate the benefits of physiological integration in terms of photosynthetic efficiency. The findings indicate that short-term responses cannot be directly extrapolated to the longer term principally because preferential colonization of high-quality patches means that these patches eventually show reduced quality. This highlights the importance of considering the time factor in experiments examining responses of clonal plants to heterogeneity.     

克隆植物的无性与有性繁殖对策

许多植物同时具有克隆生长与有性繁殖,两种繁殖方式间的平衡在不同物种间以及同一物种内不同种群间变化很大。旺盛的克隆生长可能会从多方面影响生活史进化。首先,许多克隆植物的有性繁殖与更新程度都很低,甚至有一些植物由于克隆生长而几乎完全放弃了有性过程,从而影响到克隆植物对局域环境的适应和地理范围进化。其次,克隆生长增大花展示进而增加了对传粉者的吸引,同时也增加了同株异花授粉的风险,而同株异花授粉往往会导致植物雄性和雌性适合度的下降。因此,克隆植物的空间结构与交配方式间可能存在着协同进化关系。最后,克隆生长与有性繁殖间可能存在着权衡关系:对克隆生长的资源投入将会减少对有性繁殖的资源投入。这种权衡关系可能是由环境条件、竞争力度、植物寿命和遗传等因素决定的。如果不同的繁殖方式是植物在不同环境下采取的适应性对策,那么我们可以预期:在波动和竞争力度大的生境中,植物应将大部分的繁殖资源分配给有性繁殖;而在相对稳定的环境中,克隆繁殖应该占据优势地位。但是自然选择对两种繁殖方式的选择结果是什么,以及控制这两种方式间平衡的生态和遗传因子究竟有哪些,到底是克隆生长单向地影响了植物的有性繁殖,还是与有性过程相伴随的选择压力同时塑造了植物的克隆习性?目前尚不清楚。同时从无性与有性繁殖两个方面综合考察克隆植物的繁殖对策是今后亟待加强的工作。