环境信号诱导发育的可塑性

有关环境因素作为影响发育的信号导致产生表观多型性的研究,属于遗传学、发育生物学、进化生物学和生态学研究领域的热点问题,在长期的积淀和拓展中形成了一门新的交叉学科——生态发育生物学。该学科以发育的可塑性为理论基础,研究多种环境因子诱导机体在发育中产生表观多型性的机制,包括非遗传多型性和应激性多型性。对于环境、发育和进化三者关系的研究尤为重视。本文介绍了该学科形成的背景,并对其研究主题进行分析和归纳,重点讨论了不同环境因子导致动物表观多型性的机制,包括季节和捕食者诱导的非遗传多型性,营养和激素调节社会性昆虫的品级分化,温度依赖型性别决定中的基因、酶与激素,动物对环境的适应与进化,机体的免疫应答与神经元的可塑性、环境污染物的致畸作用等。并对生态学与发育生物学结合的未来研究前景做了展望。     

蚜虫的表型可塑性及其遗传基础

表型可塑性(phenotypic plasticity)是有机体在适应生物或非生物环境时呈现不同表型的能力,并且有遗传基础。蚜虫是农林业的重要经济害虫,易受外部环境因素和自身遗传因素的影响而表现出表型的可塑性。本文综述了外部环境因素（如寄主植物、温度、光照、天敌等）的变异对蚜虫表型的影响。总体来说,蚜虫表型会因寄主植物的种类、品系以及发育阶段和营养状况的不同而有所差异; 温度变化对不同蚜虫种类的生殖力、生存力以及有翅蚜产生与否有极大影响。研究人员利用RAPD-PCR、微卫星等分子遗传标记确认寄主植物和温度是造成蚜虫种群遗传分化的重要因素。就内部因素而言,不同的蚜虫种类以及同一种蚜虫的不同克隆系在表型和遗传进化上也有不同程度的差异,在蚜虫受外界条件影响的不同虫态以及不同体色克隆系、不同生活周期的类群之间, 其生物学、生态学和遗传学都有所差异。分析上述各个因素对蚜虫表型可塑性的影响,对于蚜虫的生态进化研究和有效治理蚜害均有重要意义。本文在最后讨论了还有必要深入研究的诸多问题,如表观遗传调控,包括DNA甲基化、基因所在的核小体上的组蛋白的共价修饰和染色质重塑、siRNA介导的基因沉默以及微RNA（microRNA 或 miRNA）调控的基因表达变化等,又如有翅蚜的表型和遗传学研究,以及全球气候变化对蚜虫的生态进化的影响等问题。     

昆虫翅型分化的表型可塑性机制

翅多型现象在昆虫中广泛存在,是昆虫在飞行扩散和繁殖能力之间权衡的一种策略,对种群的环境适应性进化具有重要的意义。目前在植食性昆虫中研究较多,有关寄生蜂的翅型分化鲜见报道。综述了昆虫翅型分化的表型可塑性机制。遗传因素和环境因素均对昆虫翅的发育产生影响,基因型对翅型的决定具有显著作用,外界环境条件,包括温度、光周期、食物质量、自身密度、外源激素等因素对昆虫翅的发育也产生重要的调节作用,从而产生翅的非遗传多型性现象。此外,天敌的寄生或捕食作用可能会诱导某些昆虫的翅型产生隔代表型变化。对昆虫产生翅多型现象的生态学意义及其在生物进化过程中的作用进行了讨论,并探讨了寄生性昆虫翅型分化机制在生物防治上的可能应用途径。功能基因组学和表观遗传学的进一步发展可望为彻底揭示昆虫翅型分化机制提供新的机遇和技术手段。     

鸟鸣及其鸣唱控制系统发育可塑性研究进展

鸟类的鸣唱控制系统已成为研究神经系统与学习、行为和发育相关的一个重要模型。鸣禽鸣唱学习行为的神经基础为脊椎动物复杂习得行为的解剖学功能定位提供了一个范例。它也可为我们研究人类语言学习记忆提供借鉴,对近年来在鸟类鸣唱及其呜唱控制系统发育可塑性方面的研究进展进行了综述。     

木槿叶片结构的发育可塑性研究

对4个木槿种下类群叶片结构的发育可塑性进行了比较研究。(1)木槿 4 个种下类群的叶片在栅栏组织厚度、下表皮厚度、上表皮气孔密度、上下表皮气孔密度比,叶片厚度以及中脉维管组织等性状上均表现出较大的发育可塑性,这种可塑性对叶片适应植株光热综合因子的时空异质性具有重要意义。(2)木槿 4 个种下类群的同类型叶片在解剖学性状上的变异很小,即性状具有很大的稳定性。针对这一特点,对 4 个木槿种下类群一年生茎初生叶片结构的比较研究表明,紫花单瓣木槿和白花重瓣木槿之间的亲缘关系较近,雅致木槿和牡丹木槿亦存在较近的亲缘关系。研究结果支持将牡丹木槿和紫花单瓣木槿提升为亚种等级,并建议将白花重瓣木槿和雅致木槿分别看作紫花单瓣木槿和牡丹木槿的变型。     

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。     

进化发育生物学--发育、进化和遗传的再联合

发育生物学和进化生物学,以及遗传学历史上曾一度是彼此不分的统一体,后来由于各自研究重点的不同和相应研究手段的独立发展彼此分道扬镳了。如今,由于分子遗传学研究手段的革新使得基因序列测定成为分析发育机理、区分物种和评估种间亲缘关系的常规手段,三者又在基因水平上再度统一起来了,并形成一门被称为进化发育生物学（ｅｖｏｌｕｔｉｏｎａｒｙ ｄｅｖｅｌｏｐｍｅｎｔａｌ ｂｉｏｌｏｇｙ）的新学科。     

披针叶茴香对变化光环境的表型可塑性

植物对变化光环境的表型可塑性大小影响其在林下生境中分布、生长和更新。为探讨披针叶茴香在不同光环境下的整体表型可塑性及其适应机制,采用遮荫试验模拟5种光照条件(100%、52%、33%、15%和6%相对光照强度),研究了不同光环境下披针叶茴香叶片形态、生理、解剖结构、根系形态以及生物量分配等的变化。结果表明:叶生物量在5种光照处理之间差异不显著,但叶面积和比叶面积均随光照强度减弱显著增加。遮荫处理增加了叶绿素a、叶绿素b和类胡萝卜素的含量,但叶绿素a/b比值随光照强度减弱而降低。遮荫降低了非结构性碳水化合物(淀粉和可溶性糖)和可溶性蛋白的含量,增加了叶片氮和磷含量,对叶片氮/磷比影响较小。在52%和33%相对光照处理下,叶片中硝酸盐含量最低,而在100%和6%相对光照处理下硝酸盐积累较多。根生物量、细根和粗根的长度、表面积以及比根长和比根表面积在5种光照处理之间均没有显著差异,根系氮含量在低光环境(15%和6%相对光照处理)中显著降低。随光照强度减弱,披针叶茴香采取保守生存策略,并没有增加叶生物量的分配,而是分配较多的生物量给枝条和树干,储存能量。综合来看,披针叶茴香具有较宽的光生态幅,在6%—100%光照强度下均能正常生长,遮荫有利于披针叶茴香地上和总生物量的积累,52%的相对光照条件下生长最佳。变化光环境下根系性状和整体结构的可塑性相对较低,叶片生理性状的可塑性在披针叶茴香适应光环境变化过程中发挥了主要作用。     

干旱胁迫对欧李幼苗表型可塑性的影响

该研究以欧李为材料,探讨了干旱胁迫对欧李表型可塑性的影响。结果表明:(1)随着干旱胁迫的加剧,欧李根生物量、枝叶生物量、植株总生物量积累、根冠比和根冠比胁迫指数均呈现先升高后降低的趋势,在T1处理下达到最大值,并显著高于其他处理(α=0.05)。(2)随土壤含水量的降低,欧李根的生物量分配指数呈现先增加后降低的趋势,叶生物量与之相反,在T1处理下根的生物量分配指数最大,枝叶的最小(α=0.05)。(3)在水分供应为60%～80%时,欧李的株高、冠幅、基径、二级分枝数、主根长、主根直径及侧根数量均达到最大值(α=0.05),对一级分枝数的生长没有显著影响。(4)随着水分胁迫的加剧,叶片长从T2处理开始下降,叶片宽、单片叶面积及比叶面积均呈现先增加后减少的趋势(α=0.05)。综上可得,欧李通过调整形态特性和各器官生物量积累及其分配对不同干旱胁迫条件产生了较强的可塑性。     

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。     

Phenotypic plasticity: Eco-Devo and evolution

Phenotypic plasticity refers to the ability of an organism to alter its physiology/morphology/behavior in response to changes in environmental conditions. Although encompassing various phenomena spanning multi-ple levels of organization, most plastic responses seem to take place by altering gene expression and eventually altering ontogenetic trajectory in response to environmental variation. Epigenetic modifications provide a plausi-ble link between the environment and alterations in gene expression, and the alterations in phenotype based on environmentally induced epigenetic modifications can be inherited transgenerationally. Even closely related species and populations with different genotypes may exhibit differences in the patterns and the extents of plastic responses, indicating the wide existence of plasticity genes which are independent of trait means and directly respond to environmental stimuli by triggering phenotypic changes. The ability of plasticity is not only able to affect the adaptive evolution of species significantly, but is also an outcome of evolutionary processes. Therefore, phenotypic plasticity is a potentially important molder of adaptation and evolution.     

Phenotypic plasticity in development and evolution: facts and concepts

This theme issue pursues an exploration of the potential of taking into account the environmental sensitivity of development to explaining the evolution of metazoan life cycles, with special focus on complex life cycles and the role of developmental plasticity. The evolution of switches between alternative phenotypes as a response to different environmental cues and the evolution of the control of the temporal expression of alternative phenotypes within an organism''s life cycle are here treated together as different dimensions of the complex relationships between genotype and phenotype, fostering the emergence of a more general and comprehensive picture of phenotypic evolution through a quite diverse sample of case studies. This introductory article reviews fundamental facts and concepts about phenotypic plasticity, adopting the most authoritative terminology in use in the current literature. The main topics are types and components of phenotypic variation, the evolution of organismal traits through plasticity, the origin and evolution of phenotypic plasticity and its adaptive value.     

Phenotypic lability and the evolution of predator-induced plasticity in tadpoles

The hypothesis that predator-induced defenses in anuran larvae are maintained by divergent selection across multiple predation environments has not been fully supported by empirical results. One reason may be that traits that respond slowly to environmental variation experience a fitness cost not incorporated in the standard adaptive model, due to a time lag between detecting the state of the environment and expressing the phenotypic response. I measured the rate at which behavior and morphology of Rana temporaria tadpoles change when confronted with a switch in the predation environment at two points in development. Hatchling tadpoles that had been exposed during the egg stage to Aeshna dragonfly larvae were not phenotypically different from those exposed as eggs to predator-free conditions, and both responded similarly to post-hatching predator treatments. When 25-day-old tadpoles from treatments with and without dragonflies were subjected to a switch in the environment, their activity budgets reversed completely within 24-36 h, and their body and tail shape began changing significantly within 4 days. The behavioral response was conservative: Tadpoles switched from high-risk to predator-free treatments were slower to adjust their activity. The study confirmed that behavioral traits are relatively labile and exhibit strong plasticity, but it did not reveal such a pattern at the level of individual traits: Morphological traits that developed slowly did not show the least plasticity. Thus, I found that differences in lability of traits were useful for predicting the magnitude of plasticity only for fundamentally different kinds of characters.     

Phenotypic plasticity can facilitate adaptive evolution in gene regulatory circuits

Background  

Many important evolutionary adaptations originate in the modification of gene regulatory circuits to produce new gene activity phenotypes. How do evolving populations sift through an astronomical number of circuits to find circuits with new adaptive phenotypes? The answer may often involve phenotypic plasticity. Phenotypic plasticity allows a genotype to produce different - alternative - phenotypes after non-genetic perturbations that include gene expression noise, environmental change, or epigenetic modification.     

Phenotypic plasticity and social environment

Summary When individual organisms can differ phenotypically in ways that do not depend on the existence of genotypic differences among the individuals, they are said to be phenotypically plastic. Enhanced individual reproductive success in physically variable and/or uncertain environments is the conventional explanation for evolution of genetically based phenotypic plasticity. But this conventional wisdom seems inadequate in view of theoretical models demonstrating that individual ability to change sex, reproductive strategy, or location can evolve by natural selection in a stable, saturated, physically uniform habitat. I generalize these results to include the case of phenotypic plasticity. My models show that phenotypic plasticity can be evolutionarily stable in physically unvarying habitats as a consequence of social interactions. This approach to phenotypic plasticity challenges the accepted view that plasticity of phenotypes is non-adaptive or an adaptation to physical factors alone, and that natural selection cannot normally affect the mode of maintenance of phenotypic variation. The models may also offer additional perspectives on the evolution of sexual reproduction.     

Phenotypic plasticity across 50 MY of evolution: Drosophila wing size and temperature

We studied the response in wing size to rearing at different temperatures of nine strains of Drosophila representing six species. The species varied in their natural habitats from tropical to temperate and one cosmopolitan. The evolutionary divergence of the species spans 50 million years. While some quantitative differences were found, all species responded to temperature very similarly: females increased an average of ∼11% and males ∼14% when reared at 19 °C compared to 25 °C. The phenotypic plasticity in wing size in response to temperature appears to be a fixed trait in Drosophila across long evolutionary time and diverse ecological settings. This likely reflects the close relationship between wing area (and thus wing loading) and insect body mass that is a crucial factor for flight regardless of ecology and is, thus, maintained across long evolutionary time.     

Phenotypic plasticity in Phlox

Summary Three species of Phlox (Polemoniaceae) were grown in 6 greenhouse treatments. A variety of traits were recorded and the correlations among them were computed for each treatment. The phenotypic correlations between characters are significantly altered when plants are grown under different environmental conditions. These changes in correlation structure result from the differential phenotypic plasticity of traits. Partial correlations between flower production and other traits are also environment-dependent. Such changes can alter the intensity of, and possibly the response to, selection on traits correlated with fitness in natural plant populations.     

Phenotypic plasticity: an evolving plant character

Phenotypic plasticity is an important mode of adaptation to temporal and spatial environmental variability, particularly in plants. Although data are available concerning interspecific differences in the sizes and shapes of characters, there is little information concerning differences between taxa for the plastic responses of those characters. We have measured: (1) the mean value of a character, (2) the amount of character plasticity, and (3) the pattern of phenotypic plasticity for species in five genera, and calculated the divergences among species for each of these three measures. We compared the divergences of these measures to address the question of whether there is a relationship between the evolution of the character means of species and the evolution of the plasticities of those characters. We found that the evolutionary divergence of character plasticities could be independent of the interspecific divergence of character means. There was, however, a tendency for the divergence of amounts and patterns of plasticity to be related.     

Phenotypic plasticity and diversity in insects

Phenotypic plasticity in general and polyphenic development in particular are thought to play important roles in organismal diversification and evolutionary innovation. Focusing on the evolutionary developmental biology of insects, and specifically that of horned beetles, I explore the avenues by which phenotypic plasticity and polyphenic development have mediated the origins of novelty and diversity. Specifically, I argue that phenotypic plasticity generates novel targets for evolutionary processes to act on, as well as brings about trade-offs during development and evolution, thereby diversifying evolutionary trajectories available to natural populations. Lastly, I examine the notion that in those cases in which phenotypic plasticity is underlain by modularity in gene expression, it results in a fundamental trade-off between degree of plasticity and mutation accumulation. On one hand, this trade-off limits the extent of plasticity that can be accommodated by modularity of gene expression. On the other hand, it causes genes whose expression is specific to rare environments to accumulate greater variation within species, providing the opportunity for faster divergence and diversification between species, compared with genes expressed across environments. Phenotypic plasticity therefore contributes to organismal diversification on a variety of levels of biological organization, thereby facilitating the evolution of novel traits, new species and complex life cycles.