Rapid adaptation: a new dimension for evolutionary perspectives in ecology

Although the study of adaptation is central to biology, two types of adaptation are recognized in the biological field: physiological adaptation (accommodation or acclimation; an individual organism’s phenotype is adjusted to its environment) and evolutionary–biological adaptation (adaptation is shaped by natural selection acting on genetic variation). The history of the former concept dates to the late nineteenth and early twentieth centuries, and has more recently been systemized in the twenty-first century. Approaches to the understanding of phenotypic plasticity and learning behavior have only recently been developed, based on cellular–histological and behavioral–neurobiological techniques as well as traditional molecular biology. New developments of the former concepts in phenotypic plasticity are discussed in bacterial persistence, wing di-/polymorphism with transgenerational effects, polyphenism in social insects, and defense traits for predator avoidance, including molecular biology analyses. We also discuss new studies on the concept of genetic accommodation resulting in evolution of phenotypic plasticity through a transgenerational change in the reaction norm based on a threshold model. Learning behavior can also be understood as physiological phenotypic plasticity, associating with the brain–nervous system, and it drives the accelerated evolutionary change in behavioral response (the Baldwin effect) with memory stock. Furthermore, choice behaviors are widely seen in decision-making of animal foragers. Incorporating flexible phenotypic plasticity and learning behavior into modeling can drastically change dynamical behavior of the system. Unification of biological sciences will be facilitated and integrated, such as behavioral ecology and behavioral neurobiology in the area of learning, and evolutionary ecology and molecular developmental biology in the theme of phenotypic plasticity.     

Hormone signaling and phenotypic plasticity in nematode development and evolution

Phenotypic plasticity refers to the ability of an organism to adopt different phenotypes depending on environmental conditions. In animals and plants, the progression of juvenile development and the formation of dormant stages are often associated with phenotypic plasticity, indicating the importance of phenotypic plasticity for life-history theory. Phenotypic plasticity has long been emphasized as?a crucial principle in ecology and as facilitator of phenotypic evolution. In nematodes, several examples of phenotypic plasticity have been studied at the genetic and developmental level. In addition, the influence of different environmental factors has been investigated under laboratory conditions. These studies have provided detailed insight into the molecular basis of phenotypic plasticity and its?ecological and evolutionary implications. Here, we review recent studies on the formation of dauer larvae in Caenorhabditis elegans, the evolution of nematode parasitism and the generation of a novel feeding trait in Pristionchus pacificus. These examples reveal a conserved and co-opted role of an endocrine signaling module involving the steroid hormone dafachronic acid. We will discuss how hormone signaling might facilitate life-history and morphological evolution.     

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 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.     

Evolution and molecular mechanisms of adaptive developmental plasticity

Aside from its selective role in filtering inter-individual variation during evolution by natural selection, the environment also plays an instructive role in producing variation during development. External environmental cues can influence developmental rates and/or trajectories and lead to the production of distinct phenotypes from the same genotype. This can result in a better match between adult phenotype and selective environment and thus represents a potential solution to problems posed by environmental fluctuation. The phenomenon is called adaptive developmental plasticity. The study of developmental plasticity integrates different disciplines (notably ecology and developmental biology) and analyses at all levels of biological organization, from the molecular regulation of changes in organismal development to variation in phenotypes and fitness in natural populations. Here, we focus on recent advances and examples from morphological traits in animals to provide a broad overview covering (i) the evolution of developmental plasticity, as well as its relevance to adaptive evolution, (ii) the ecological significance of alternative environmentally induced phenotypes, and the way the external environment can affect development to produce them, (iii) the molecular mechanisms underlying developmental plasticity, with emphasis on the contribution of genetic, physiological and epigenetic factors, and (iv) current challenges and trends, including the relevance of the environmental sensitivity of development to studies in ecological developmental biology, biomedicine and conservation biology.     

Stem cell plasticity, cell fusion, and transdifferentiation

One of the most contentious issues in biology today concerns the existence of stem cell plasticity. The term "plasticity" refers to the capacity of tissue-derived stem cells to exhibit a phenotypic potential that extends beyond the differentiated cell phenotypes of their resident tissue. Although evidence of stem cell plasticity has been reported by multiple laboratories, other scientists have not found the data persuasive and have remained skeptical about these new findings. This review will provide an overview of the stem cell plasticity controversy. We will examine many of the major objections that have been made to challenge the stem cell plasticity data. This controversy will be placed in the context of the traditional view of stem cell potential and cell phenotypic diversification. What the implications of cell plasticity are, and how its existence may modulate our present understanding of stem cell biology, will be explored. In addition, we will examine a topic that is usually not included within a discussion of stem cell biology--the direct conversion of one differentiated cell type into another. We believe that these observations on the transdifferentiation of differentiated cells have direct bearing on the issue of stem cell plasticity, and may provide insights into how cell phenotypic diversification is realized in the adult and into the origin of cell phenotypes during evolution.     

Developmental phenotypic plasticity: Where ecology and evolution meet molecular biology

The plastic response of phenotypic traits to environmental change is a common research focus in several disciplines - from ecology and evolutionary biology to physiology and molecular genetics. The use of model systems such as the flowering plant Arabidopsis thaliana has facilitated a dialogue between developmental biologists asking how plasticity is controlled (proximate causes) and organismal biologists asking why plasticity exists (ultimate causes). Researchers studying ultimate causes and consequences are increasingly compelled to reject simplistic, ‘black box’ models, while those studying proximate causes and mechanisms are increasingly obliged to subject their interpretations to ecological ‘reality checks.’ We review the successful multidisciplinary efforts to understand the phytochrome-mediated shade-avoidance and light-seeking responses of flowering plants as a pertinent example of convergence between evolutionary and molecular biology. In this example, the two-way exchange between reductionist and holist camps has been essential to rapid and sustained progress. This should serve as a model for future collaborative efforts towards understanding the responses of organisms to their constantly changing environments.     

蚜虫基因组及功能基因组研究进展

蚜虫作为刺吸式昆虫和植物病毒的传播者,已经成为严重威胁农业生产发展的重要害虫之一。近几年随着分子生物学的发展,尤其是基因组测序技术的进步,蚜虫基因组学和功能基因组学取得了重大突破,使我们对蚜虫特殊的生物学特征有了深层次的认识。本文就蚜虫与内共生菌关系、表型可塑性、发育和生殖、系统进化、解毒酶基因家族以及唾液腺方面在基因组和功能基因组水平上的研究进展进行了综述。     

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。     

Phenotypic Plasticity Contributes to Maize Adaptation and Heterosis

Plant phenotypic plasticity describes altered phenotypic performance of an individual when grown in different environments. Exploring genetic architecture underlying plant plasticity variation may help mitigate the detrimental effects of a rapidly changing climate on agriculture, but little research has been done in this area to date. In the present study, we established a population of 976 maize F₁ hybrids by crossing 488 diverse inbred lines with two elite testers. Genome-wide association study identified hundreds of quantitative trait loci associated with phenotypic plasticity variation across diverse F₁ hybrids, the majority of which contributed very little variance, in accordance with the polygenic nature of these traits. We identified several quantitative trait locus regions that may have been selected during the tropical-temperate adaptation process. We also observed heterosis in terms of phenotypic plasticity, in addition to the traditional genetic value differences measured between hybrid and inbred lines, and the pattern of which was affected by genetic background. Our results demonstrate a landscape of phenotypic plasticity in maize, which will aid in the understanding of its genetic architecture, its contribution to adaptation and heterosis, and how it may be exploited for future maize breeding in a rapidly changing environment.     

No genetic diversity at molecular markers and strong phenotypic plasticity in populations of Ranunculus nodiflorus, an endangered plant species in France

BACKGROUND AND AIMS: Although conservation biology has long focused on population dynamics and genetics, phenotypic plasticity is likely to play a significant role in population viability. Here, an investigation is made into the relative contribution of genetic diversity and phenotypic plasticity to the phenotypic variation in natural populations of Ranunculus nodiflorus, a rare annual plant inhabiting temporary puddles in the Fontainebleau forest (Paris region, France) and exhibiting metapopulation dynamics. METHODS: The genetic diversity and phenotypic plasticity of quantitative traits (morphological and fitness components) were measured in five populations, using a combination of field measurements, common garden experiments and genotyping at microsatellite loci. KEY RESULTS: It is shown that populations exhibit almost undetectable genetic diversity at molecular markers, and that the variation in quantitative traits observed among populations is due to a high level of phenotypic plasticity. Despite the lack of genetic diversity, the natural population of R. nodiflorus exhibits large population sizes and does not appear threatened by extinction; this may be attributable to large phenotypic plasticity, enabling the production of numerous seeds under a wide range of environmental conditions. CONCLUSIONS: Efficient conservation of the populations can only be based on habitat management, to favour the maintenance of microenvironmental variation and the resulting strong phenotypic plasticity. In contrast, classical actions aiming to improve genetic diversity are useless in the present case.     

Phenotypic plasticity of the maize root system in response to heterogeneous nitrogen availability

Mineral nutrients are distributed in a non-uniform manner in the soil. Plasticity in root responses to the availability of mineral nutrients is believed to be important for optimizing nutrient acquisition. The response of root architecture to heterogeneous nutrient availability has been documented in various plant species, and the molecular mechanisms coordinating these responses have been investigated particularly in Arabidopsis, a model dicotyledonous plant. Recently, progress has been made in describing the phenotypic plasticity of root architecture in maize, a monocotyledonous crop. This article reviews aspects of phenotypic plasticity of maize root system architecture, with special emphasis on describing (1) the development of its complex root system; (2) phenotypic responses in root system architecture to heterogeneous N availability; (3) the importance of phenotypic plasticity for N acquisition; (4) different regulation of root growth and nutrients uptake by shoot; and (5) root traits in maize breeding. This knowledge will inform breeding strategies for root traits enabling more efficient acquisition of soil resources and synchronizing crop growth demand, root resource acquisition and fertilizer application during crop growing season, thereby maximizing crop yields and nutrient-use efficiency and minimizing environmental pollution.     

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 opposes species invasions by altering fitness surface

Understanding species invasion is a central problem in ecology because invasions of exotic species severely impact ecosystems, and because invasions underlie fundamental ecological processes. However, the influence on invasions of phenotypic plasticity, a key component of many species interactions, is unknown. We present a model in which phenotypic plasticity of a resident species increases its ability to oppose invaders, and plasticity of an invader increases its ability to displace residents. Whereas these effects are expected due to increased fitness associated with phenotypic plasticity, the model additionally reveals a new and unforeseen mechanism by which plasticity affects invasions: phenotypic plasticity increases the steepness of the fitness surface, thereby making invasion more difficult, even by phenotypically plastic invaders. Our results should apply to phenotypically plastic responses to any fluctuating environmental factors including predation risk, and to other factors that affect the fitness surface such as the generalism of predators. We extend the results to competition, and argue that phenotypic plasticity's effect on the fitness surface will destabilize coexistence at local scales, but stabilize coexistence at regional scales. Our study emphasizes the need to incorporate variable interaction strengths due to phenotypic plasticity into invasion biology and ecological theory on competition and coexistence in fragmented landscapes.     

Evolution and maintenance of the environmental component of the phenotypic variance: benefit of plastic traits under changing environments

How environmental variances in quantitative traits are influenced by variable environments is an important problem in evolutionary biology. In this study, the evolution and maintenance of phenotypic variance in a plastic trait under stabilizing selection are investigated. The mapping from genotypic value to phenotypic value of the quantitative trait is approximated by a linear reaction norm, with genotypic effects on its phenotypic mean and sensitivity to environment. The environmental deviation is assumed to be decomposed into environmental quality, which interacts with genotypic value, and residual developmental noise, which is independent of genotype. Environmental quality and the optimal phenotype of stabilizing selection are allowed to randomly fluctuate in both space and time, and individuals migrate equally before development and reproduction among different niches. Analyses show that phenotypic plasticity is adaptive within variable environments if correlations have become established between the optimal phenotype and environmental quality in space and/or time. The evolved plasticity increases with variances in optimal phenotypes and correlations between optimal phenotype and environmental quality; this further induces increases in mean fitness and the environmental variance in the trait. Under certain circumstances, however, the environmental variance may decrease with increase in variation in environmental quality.