植物表型可塑性研究进展

表型可塑性已成为生态进化发育生物学的核心概念,很大程度上由于植物可塑性研究的主要贡献,但人们仍远未完全了解表型可塑性的原因和结果。从整体角度理出表型可塑性研究发展的基本脉络,介绍研究内容、途径和简史,聚焦于几个主要方面的研究进展及发展方向。现代可塑性研究的兴盛始于关于可塑性的进化学重要性的一篇综述,从现象的描述、对其遗传基础和可塑性本身进化的讨论,发展到探索其背后的发育机制、植物生长与适应策略、生态学影响等。未来可塑性研究应在重新理解和评价表型可塑性及其适应性的基础上,更关注自然条件下环境因子和可塑响应的复杂性。表型可塑性的生态-进化学意义仍将是未来研究的重点。     

Toward a population genetic framework of developmental evolution: the costs,limits, and consequences of phenotypic plasticity

Adaptive phenotypic plasticity allows organisms to cope with environmental variability, and yet, despite its adaptive significance, phenotypic plasticity is neither ubiquitous nor infinite. In this review, we merge developmental and population genetic perspectives to explore costs and limits on the evolution of plasticity. Specifically, we focus on the role of modularity in developmental genetic networks as a mechanism underlying phenotypic plasticity, and apply to it lessons learned from population genetic theory on the interplay between relaxed selection and mutation accumulation. We argue that the environmental specificity of gene expression and the associated reduction in pleiotropic constraints drive a fundamental tradeoff between the range of plasticity that can be accommodated and mutation accumulation in alternative developmental networks. This tradeoff has broad implications for understanding the origin and maintenance of plasticity and may contribute to a better understanding of the role of plasticity in the origin, diversification, and loss of phenotypic diversity.     

Environmental Heterogeneity and Population Differentiation in Plasticity to Drought in <Emphasis Type="Italic">Convolvulus Chilensis</Emphasis> (Convolvulaceae)

Plant populations may show differentiation in phenotypic plasticity, and theory predicts that greater levels of environmental heterogeneity should select for higher magnitudes of phenotypic plasticity. We evaluated phenotypic responses to reduced soil moisture in plants of Convolvulus chilensis grown in a greenhouse from seeds collected in three natural populations that differ in environmental heterogeneity (precipitation regime). Among several morphological and ecophysiological traits evaluated, only four traits showed differentiation among populations in plasticity to soil moisture: leaf area, leaf shape, leaf area ratio (LAR), and foliar trichome density. In all of these traits plasticity to drought was greatest in plants from the population with the highest interannual variation in precipitation. We further tested the adaptive nature of these plastic responses by evaluating the relationship between phenotypic traits and total biomass, as a proxy for plant fitness, in the low water environment. Foliar trichome density appears to be the only trait that shows adaptive patterns of plasticity to drought. Plants from populations showing plasticity had higher trichome density when growing in soils with reduced moisture, and foliar trichome density was positively associated with total biomass. Co-ordinating editor: F. Stuefer     

植物的表型可塑性、异速生长及其入侵能力

表型可塑性是指同一个基因型对不同环境响应产生不同表型的特性,特定性状的可塑性本身可以遗传,也可以接受选择而发生进化。植物个体的异速生长是指生物体某一特征的相对生长速率不等于第二种特征的相对生长速率的特性,该特性是由物种的遗传性决定的一种固定特征,植物往往朝着最佳的异速生长曲线进化。植物特定基因型在不同环境下,诸如生物量分配和种群几何学上的一些表型差异,既可由异速生长造成,也可由表型可塑性造成。植物本身的异速生长是一种"外观可塑性",而异速生长曲线的改变才是真正的可塑性。植物的表型可塑性、异速生长对于入侵植物的适应具有重要意义。干扰等异质性生境下表型可塑性成为物种生存扩散的有利性状,表型可塑性强的物种更有可能成为广布种。植物本身的异速生长特性或其异速生长曲线的改变都能影响其入侵能力。     

Constraints on the evolution of adaptive phenotypic plasticity in plants

The high potential fitness benefit of phenotypic plasticity tempts us to expect phenotypic plasticity as a frequent adaptation to environmental heterogeneity. Examples of proven adaptive plasticity in plants, however, are scarce and most plastic responses actually may be 'passive' rather than adaptive. This suggests that frequently requirements for the evolution of adaptive plasticity are not met or that such evolution is impeded by constraints. Here we outline requirements and potential constraints for the evolution of adaptive phenotypic plasticity, identify open questions, and propose new research approaches. Important open questions concern the genetic background of plasticity, genetic variation in plasticity, selection for plasticity in natural habitats, and the nature and occurrence of costs and limits of plasticity. Especially promising tools to address these questions are selection gradient analysis, meta-analysis of studies on genotype-by-environment interactions, QTL analysis, cDNA-microarray scanning and quantitative PCR to quantify gene expression, and two-dimensional gel electrophoresis to quantify protein expression. Studying plasticity along the pathway from gene expression to the phenotype and its relationship with fitness will help us to better understand why adaptive plasticity is not more universal, and to more realistically predict the evolution of plastic responses to environmental change.     

Phenotypic plasticity in gene expression contributes to divergence of locally adapted populations of Fundulus heteroclitus

We examine the interaction between phenotypic plasticity and evolutionary adaptation using muscle gene expression levels among populations of the fish Fundulus heteroclitus acclimated to three temperatures. Our analysis reveals shared patterns of phenotypic plasticity due to thermal acclimation as well as non‐neutral patterns of variation among populations adapted to different thermal environments. For the majority of significant differences in gene expression levels, phenotypic plasticity and adaptation operate on different suites of genes. The subset of genes that demonstrate both adaptive differences and phenotypic plasticity, however, exhibit countergradient variation of expression. Thus, expression differences among populations counteract environmental effects, reducing the phenotypic differentiation between populations. Finally, gene‐by‐environment interactions among genes with non‐neutral patterns of expression suggest that the penetrance of adaptive variation depends on the environmental conditions experienced by the individual.     

Signal perception, differential expression within multigene families and the molecular basis of phenotypic plasticity

Abstract. This Introduction to the Special Issue of Plant, Cell and Environment on 'Sensing the Environment'is concerned with the molecular mechanisms that may link the perception of environmental signals with the evocation of those specific developmental responses that collectively are known as phenotypic plasticity. The significance of phenotypic plasticity at the evolutionary, developmental and ecological levels is outlined, and it is argued that the extent of an individual's adaptability to environmental conditions must be a reflection of the extent and sophistication of the controls over the synthesis and action of specific proteins. Reviewing evidence from a selected range of plant enzymes and regulatory proteins, it is proposed that differential regulation of the expression of members of multigene families may represent the molecular basis of phenotypic plasticity.     

泡沙参复合体（桔梗科）的物种生物学研究：Ⅰ表型的可塑性

表型可塑性是生物变异中由环境引起的一种变异,是植物适应的一种重要方式。对沙参属这样一个形态上复杂多变、分类上很难处理的类群,研究其表型可塑性不仅为探讨性状变异、判断其系统学意义及选择可靠的分类性状提供了有益的资料,而且有助于揭示沙参属植物变异、适应和进化的机制。本文从泡沙参复合体中选择了6个居群,利用播种和移栽试验,通过对不同个体和居群在一致条件下的表现及野外和移栽后的对比,对根、茎、叶、花和果等形态性状的表型可塑性进行了初步的观测分析。结果表明,一些叶片、花部和果实性状具有较大的发育可塑性,尤其是叶形、花萼裂片不仅发育变化大,而且随发育过程定向变化。环境可塑性较大的性状主要是根、茎、花序分枝等性状,而叶片、花部、果实和种子性状的环境饰变能力都较小。最后,对泡沙参复合体形态性状的变异从发育可塑性和环境可塑性的角度进行了讨论。     

Avoiding extinction under nonlinear environmental change: models of evolutionary rescue with plasticity

Rapid environmental changes are putting numerous species at risk of extinction. For migration-limited species, persistence depends on either phenotypic plasticity or evolutionary adaptation (evolutionary rescue). Current theory on evolutionary rescue typically assumes linear environmental change. Yet accelerating environmental change may pose a bigger threat. Here, we present a model of a species encountering an environment with accelerating or decelerating change, to which it can adapt through evolution or phenotypic plasticity (within-generational or transgenerational). We show that unless either form of plasticity is sufficiently strong or adaptive genetic variation is sufficiently plentiful, accelerating or decelerating environmental change increases extinction risk compared to linear environmental change for the same mean rate of environmental change.     

Low genetic diversity contrasts with high phenotypic variability in heptaploid Spartina densiflora populations invading the Pacific coast of North America

Species can respond to environmental pressures through genetic and epigenetic changes and through phenotypic plasticity, but few studies have evaluated the relationships between genetic differentiation and phenotypic plasticity of plant species along changing environmental conditions throughout wide latitudinal ranges. We studied inter‐ and intrapopulation genetic diversity (using simple sequence repeats and chloroplast DNA sequencing) and inter‐ and intrapopulation phenotypic variability of 33 plant traits (using field and common‐garden measurements) for five populations of the invasive cordgrass Spartina densiflora Brongn. along the Pacific coast of North America from San Francisco Bay to Vancouver Island. Studied populations showed very low genetic diversity, high levels of phenotypic variability when growing in contrasted environments and high intrapopulation phenotypic variability for many plant traits. This intrapopulation phenotypic variability was especially high, irrespective of environmental conditions, for those traits showing also high phenotypic plasticity. Within‐population variation represented 84% of the total genetic variation coinciding with certain individual plants keeping consistent responses for three plant traits (chlorophyll b and carotenoid contents, and dead shoot biomass) in the field and in common‐garden conditions. These populations have most likely undergone genetic bottleneck since their introduction from South America; multiple introductions are unknown but possible as the population from Vancouver Island was the most recent and one of the most genetically diverse. S. densiflora appears as a species that would not be very affected itself by climate change and sea‐level rise as it can disperse, establish, and acclimate to contrasted environments along wide latitudinal ranges.     

The timescale of environmental fluctuations determines the competitive advantages of phenotypic plasticity and rapid evolution

Organisms can respond to fluctuating environments by phenotypic plasticity and rapid evolution, both occurring on similar timescales to the environmental fluctuations. Because each adaptation mechanism has been independently studied, the effects of different adaptation mechanisms on ecological dynamics are not well understood. Here, using mathematical modeling, we compared the advantages of phenotypic plasticity and rapid evolution under conditions where the environment fluctuated between two states on various timescales. The results indicate that the advantages of phenotypic plasticity under environmental fluctuations on different timescales depend on the cost and the speed of plasticity. Both the speed of plastic adaptation and the cost of plasticity affect competition results, while the quantitative effects of them vary depending on the timescales. When the environment fluctuates on short timescales, the two populations with evolution and plasticity coexist, although the population with evolution is dominant. On moderate timescales, the two populations also coexist; however, the population with plasticity becomes dominant. On long timescales, whether the population with phenotypic plasticity or evolution is more advantageous depended on the cost of plasticity. Moreover, our results indicate that the mechanisms resulting in the dominance of the plastic population over the population with evolution are different depending on the timescales of environmental fluctuations. Therefore, the timescales of environmental fluctuations deserve more attention if we are to better understand the detailed competition results underlying phenotypic variation.     

The combined effects of temporal autocorrelation and the costs of plasticity on the evolution of plasticity

Adaptive phenotypic plasticity is an important source of intraspecific variation, and for many plastic traits, the costs or factors limiting plasticity seem cryptic. However, there are several different factors that may constrain the evolution of plasticity, but few models have considered costs and limiting factors simultaneously. Here we use a simulation model to investigate how the optimal level of plasticity in a population depends on a fixed maintenance fitness cost for plasticity or an incremental fitness cost for producing a plastic response in combination with environmental unpredictability (environmental fluctuation speed) limiting plasticity. Our model identifies two mechanisms that act, almost separately, to constrain the evolution of plasticity: (i) the fitness cost of plasticity scaled by the nonplastic environmental tolerance, and (ii) the environmental fluctuation speed scaled by the rate of phenotypic change. That is, the evolution of plasticity is constrained by the high cost of plasticity in combination with high tolerance for environmental variation, or fast environmental changes in combination with slow plastic response. Qualitatively similar results are found when maintenance and incremental fitness costs of plasticity are incorporated, although a larger degree of plasticity is selected for with an incremental cost. Our model highlights that it is important to consider direct fitness costs and phenotypic limitations in relation to nonplastic environmental tolerance and environmental fluctuations, respectively, to understand what constrains the evolution of phenotypic plasticity.     

Phenotypic plasticity is not affected by experimental evolution in constant,predictable or unpredictable fluctuating thermal environments

The selective past of populations is presumed to affect the levels of phenotypic plasticity. Experimental evolution at constant temperatures is generally expected to lead to a decreased level of plasticity due to presumed costs associated with phenotypic plasticity when not needed. In this study, we investigated the effect of experimental evolution in constant, predictable and unpredictable daily fluctuating temperature regimes on the levels of phenotype plasticity in several life history and stress resistance traits in Drosophila simulans. Contrary to the expectation, evolution in the different regimes did not affect the levels of plasticity in any of the traits investigated even though the populations from the different thermal regimes had evolved different stress resistance and fitness trait means. Although costs associated with phenotypic plasticity are known, our results suggest that the maintenance of phenotypic plasticity might come at low and negligible costs, and thus, the potential of phenotypic plasticity to evolve in populations exposed to different environmental conditions might be limited.     

不同坡向川西亚高山林木竞争与叶片表型可塑性的关系研究

表型可塑性是植物生长响应外界环境变化的重要表现形式,体现了植物个体在环境胁迫下的适合度。但是关于植物表型可塑性的驱动机制仍然存在很多争议。为了探讨植物表型可塑性的影响因素,以四川省阿坝藏族羌族自治州位于同一海拔梯度但坡向相反的天然次生林为研究对象,分析了不同坡向竞争强度与10种树木叶片功能性状表型可塑性的关系的差异。研究发现：(1)研究样地中阴坡水分和养分资源优于阳坡;(2)阴坡上林木平均种内和种间竞争强度高于阳坡,阴坡上林木种内竞争强度随着树木个体大小的增加而显著性减少,阳坡上林木种内竞争强度却随着个体大小的增加而增加;(3)阴坡上叶片表型可塑性高于阳坡,表型可塑性随着个体大小的增加而增加,在阳坡上却随着个体大小增加而降低。这些结果表明阴坡上水分等资源环境条件优于阳坡,林木生长受到环境资源限制较少。在林木生长过程中,较高的竞争强度引起的资源重叠加剧,尤其是种内竞争强度的变化,从而导致了阴坡上较高的叶片表型可塑性。因为较高的竞争强度,随着林木个体大小的增加,树木需要更高的可塑性赢得竞争优势来获取更多的资源支持生长。但是在阳坡上,资源相对缺乏,环境资源对树木生长的限制降低了叶片表型的可塑...     

Animal learning as a source of developmental bias

As a form of adaptive plasticity that allows organisms to shift their phenotype toward the optimum, learning is inherently a source of developmental bias. Learning may be of particular significance to the evolutionary biology community because it allows animals to generate adaptively biased novel behavior tuned to the environment and, through social learning, to propagate behavioral traits to other individuals, also in an adaptively biased manner. We describe several types of developmental bias manifest in learning, including an adaptive bias, historical bias, origination bias, and transmission bias, stressing that these can influence evolutionary dynamics through generating nonrandom phenotypic variation and/or nonrandom environmental states. Theoretical models and empirical data have established that learning can impose direction on adaptive evolution, affect evolutionary rates (both speeding up and slowing down responses to selection under different conditions) and outcomes, influence the probability of populations reaching global optimum, and affect evolvability. Learning is characterized by highly specific, path‐dependent interactions with the (social and physical) environment, often resulting in new phenotypic outcomes. Consequently, learning regularly introduces novelty into phenotype space. These considerations imply that learning may commonly generate plasticity first evolution.     

Strong and parallel salinity‐induced phenotypic plasticity in one generation of threespine stickleback

Phenotypic plasticity is a major factor contributing to variation of organisms in nature, yet its evolutionary significance is insufficiently understood. One example system where plasticity might have played an important role in an adaptive radiation is the threespine stickleback (Gasterosteus aculeatus), a fish that has diversified after invading freshwater lakes repeatedly from the marine habitat. The parallel phenotypic changes that occurred in this radiation were extremely rapid. This study evaluates phenotypic plasticity in stickleback body shape in response to salinity in fish stemming from a wild freshwater population. Using a split‐clutch design, we detected surprisingly large phenotypically plastic changes in body shape after one generation. Fish raised in salt water developed shallower bodies and longer jaws, and these changes were consistent and parallel across families. Although this work highlights the effect of phenotypic plasticity, we also find indications that constraints may play a role in biasing the direction of possible phenotypic change. The slopes of the allometric relationship of individual linear traits did not change across treatments, indicating that plastic change does not affect the covariation of traits with overall size. We conclude that stickleback have a large capacity for plastic phenotypic change in response to salinity and that plasticity and evolutionary constraints have likely contributed to the phenotypic diversification of these fish.     

The fitness costs of developmental canalization and plasticity

Organisms are capable of an astonishing repertoire of phenotypic responses to the environment, and these often define important adaptive solutions to heterogeneous and unpredictable conditions. The terms ‘phenotypic plasticity’ and ‘canalization’ indicate whether environmental variation has a large or small effect on the phenotype. The evolution of canalization and plasticity is influenced by optimizing selection‐targeting traits within environments, but inherent fitness costs of plasticity may also be important. We present a meta‐analysis of 27 studies (of 16 species of plant and 7 animals) that have measured selection on the degree of plasticity independent of the characters expressed within environments. Costs of plasticity and canalization were equally frequent and usually mild; large costs were observed only in studies with low sample size. We tested the importance of several covariates, but only the degree of environmental stress was marginally positively related to the cost of plasticity. These findings suggest that costs of plasticity are often weak, and may influence phenotypic evolution only under stressful conditions.     

Environmental stress and the costs of whole-organism phenotypic plasticity in tadpoles

Costs of phenotypic plasticity are important for the evolution of plasticity because they prevent organisms from shaping themselves at will to match heterogeneous environments. These costs occur when plastic genotypes have relatively low fitness regardless of the trait value expressed. We report two experiments in which we measured selection on predator-induced plasticity in the behaviour and external morphology of frog tadpoles (Rana temporaria). We assessed costs under stressful and benign conditions, measured fitness as larval growth rate or competitive ability and focused analysis on aggregate measures of whole-organism plasticity. There was little convincing evidence for a cost of phenotypic plasticity in our experiments, and costs of canalization were nearly as frequent as costs of plasticity. Neither the magnitude of the cost nor the variation around the estimate (detectability) was sensitive to environmental stress.