Chloe Zhang
In genetics, the term plastic is used to describe the concept of phenotypic plasticity, which refers to an organism's ability to exhibit different phenotypes (traits) in response to changes in its environment. This means that an organism with phenotypic plasticity can alter its behaviour, morphology, and physiology to adapt to new environmental conditions. Phenotypic plasticity is particularly important for species with long generation times, as it allows them to cope with rapid climate change and other environmental challenges within their lifetime. While the genome was once believed to be stable and unchanging, it is now understood to possess a certain level of plasticity, with genes being dynamic and constantly evolving. This genetic plasticity enables organisms to respond to environmental variations and facilitates evolutionary novelty and diversity.
| Characteristics | Values |
|---|---|
| Definition | In genetics, "plastic" refers to the ability of an organism to exhibit phenotypic plasticity, which is the capacity to produce different phenotypes (observable characteristics or traits) in response to different environmental conditions, even though their genotype (genetic makeup) remains the same. |
| Key Concept | Phenotypic Plasticity |
| Example | The classic example is the water flea, Daphnia, which can produce protective helmet-like structures (called "helmets" or "neckteeth") in response to the presence of predators. This is a plastic response, as the presence or absence of a trait is determined by the environment, not genetics. |
| Types | Plasticity can be categorized as normative, which is beneficial and adaptive, or non-normative, which can be maladaptive. |
| Advantage | Phenotypic plasticity allows organisms to adapt to changing environments without needing genetic changes, which are slower and often irreversible. |
| Influence | The environment plays a critical role in triggering plastic responses, and these responses can vary based on factors like temperature, nutrient availability, population density, and more. |
| Study Field | Epigenetics is the study of how environmental factors influence gene expression and phenotype, which is closely tied to phenotypic plasticity. |
| Flexibility | Plastic traits can be continuously variable (infinite variation) or discretely variable (limited forms of variation). |
| Trade-offs | Plasticity can come with trade-offs, such as reduced performance in one trait to benefit another or costs associated with producing certain plastic traits. |
| Genetic Influence | While plasticity is an environmental response, there is some genetic influence on the capacity for plasticity, and certain genotypes may be more or less responsive to environmental cues. |
| Research Areas | Plasticity is studied in a variety of fields, including behavioral ecology, evolutionary biology, and developmental biology, to understand how organisms adapt and the mechanisms underlying these responses. |
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What You'll Learn
Phenotypic plasticity
One of the key questions surrounding phenotypic plasticity is whether it promotes or hinders evolution. Some researchers, like Williams (1966) and Charlesworth et al. (1982), argue that plasticity hinders evolution by obstructing the development of underlying traits. They emphasize selection as the primary force guiding phenotypic evolution. On the other hand, proponents of phenotypic plasticity suggest that it facilitates evolutionary novelty and diversity. They propose the "plasticity-first evolution" or "flexible stem hypothesis", which suggests that environmentally responsive traits can lead to evolutionary changes.
To support the role of phenotypic plasticity in evolution, several predictions need to be fulfilled. Firstly, the origin of novelty often arises from environmentally responsive and developmentally plastic traits. Secondly, environmental responsiveness necessitates developmental reprogramming through developmental switch genes. Lastly, pulses of plasticity are restricted in evolutionary time, eventually becoming genetically encoded through processes like canalization, genetic accommodation, or genetic assimilation.
The significance of phenotypic plasticity is evident in the context of climate change. For example, the winter moth-great tit predator-prey system illustrates how warmer spring temperatures influence the timing of caterpillar abundance. The great tits, a bird species, respond to these environmental changes by adjusting their breeding times to synchronize with the peak caterpillar availability. This phenotypically plastic response showcases how organisms can adapt to variable breeding times due to climate change.
However, it is important to note that phenotypic plasticity does not always perfectly match an organism's phenotype with its environment. In the case of great tits in the Netherlands, the timing of reproduction is phenotypically plastic, but the shift in phenology was insufficient to match the breeding time with the availability of their food source. This highlights the limitations of phenotypic plasticity and the complex interplay between environmental cues and trait expression.
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Genetic variation
Phenotypic plasticity is a significant aspect of genetic variation, as it involves organisms producing distinct phenotypes in response to environmental changes. While phenotypic plasticity can help alleviate the negative consequences of environmental changes, it does not always ensure adaptation. Genetic variation for phenotypic plasticity can be inferred through specific models and plots.
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Plasticity and evolution
The term "plasticity" in genetics refers to phenotypic plasticity, which is the property of organisms to produce distinct phenotypes in response to environmental variation. This can include changes in an organism's behaviour, morphology, and physiology. Phenotypic plasticity is important for an organism's ability to cope with environmental variation, and it encompasses all types of environmentally induced changes that may or may not be permanent throughout an individual's lifespan.
Phenotypic plasticity has been proposed to play a significant role in evolution and the origin of novelty. However, this idea has been contentious, with some arguing that plasticity hinders evolution. One of the challenges in studying plasticity is distinguishing whether observed phenotypic variation results from plasticity in response to the environment or from genetic polymorphisms.
To support the role of plasticity in evolutionary novelty and diversity, three predictions must be fulfilled. Firstly, novelty often originates from environmentally responsive and developmentally plastic traits, referred to as "plasticity-first evolution" or the "flexible stem hypothesis". Secondly, environmental responsiveness requires developmental reprogramming in the form of developmental switch genes. Finally, pulses of plasticity are restricted in evolutionary time and become genetically encoded through processes such as canalization, genetic accommodation, or genetic assimilation.
Plastic responses to novel environments can be described by a ""plasticity vector", which quantifies the change in mean phenotypic trait values between two environments. These responses have high evolutionary potential when there is ample genetic variation underlying phenotypic variance and the plastic response aligns with the major axis of genetic variation in the new environment.
While plasticity can enable organisms to adapt and survive in a changing world, it can also retard adaptation by shielding genes from natural selection. The interplay between genetic variation and phenotypic plasticity in responses to climate change is still not fully understood, and it is unclear whether plasticity facilitates or hinders evolutionary rescue.
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Plasticity vectors
Phenotypic plasticity is defined as the property of organisms to produce distinct phenotypes in response to environmental variation. It is fundamental to the way in which organisms cope with environmental variation and encompasses all types of environmentally induced changes (e.g. morphological, physiological, behavioural, phenological) that may or may not be permanent throughout an individual's lifespan. Phenotypic plasticity always involves a change in gene expression or gene-product use.
Plastic responses can be described by a "plasticity vector" that quantifies the change in mean phenotypic trait values between two environments, expressed as the distance between the multivariate phenotype means. The plasticity vector is a powerful tool to understand how organisms adapt to their environments. It provides a quantitative measure of the plastic response of an organism to a novel environment, by comparing the multivariate mean phenotype in the original and novel environments.
The arrows connecting the centroids of non-novel (green) and novel (orange) environments are the plasticity vectors that describe the change in multivariate mean phenotype between the two environments. These vectors can be visualised in a reaction norm plot, which shows the relationship between an organism's phenotype and the environment it encounters. The plasticity vector can also be used to determine the evolutionary potential of plastic phenotypic responses. If there is ample genetic variation underlying the phenotype and the vector of the plastic response is well-aligned with the major axis of genetic variation in the novel environment, then the evolutionary potential is high. On the other hand, if there is limited genetic variation underlying the phenotype and the vector of the plastic response is not aligned with the major axis of genetic variation in the novel environment, then the evolutionary potential is low.
The concept of plasticity vectors is particularly relevant when studying the effects of environmental factors on leaf shape and size in plants. Leaves are very plastic, and their growth and shape can be altered by light levels and other environmental factors. For example, leaves grown in direct light tend to be thicker, which maximises photosynthesis, while those grown in the shade tend to be thinner and have a larger surface area to capture more light. Phenotypic plasticity allows plants to respond to environmental cues without changing their location, which is especially important for sessile organisms like plants.
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Genetic accommodation
The term "plastic" in genetics refers to phenotypic plasticity, which is the property of organisms to produce distinct phenotypes in response to environmental variation. This phenomenon has been observed in various domains of life, including insects, fish, plants, snails, and frogs.
Now, genetic accommodation is a mechanism by which novel phenotypes are produced and become established in a population. It is related to the concept of genetic assimilation, which refers to the process of selection where phenotypes that were originally expressed only after an environmental stimulus become genetically fixed. Genetic accommodation and genetic assimilation are both considered major forces in the origin and evolution of phenotypes.
The idea of genetic accommodation can be further understood through Waddington's concept of "canalization." He compared embryonic development to a ball rolling down a slope in an "epigenetic landscape," where each point represents a possible state of the organism. As a particular developmental pathway becomes entrenched or "canalized," it becomes more stable and likely to occur, even with environmental changes. However, major perturbations like heat shock or certain mutations can cause the system to explore other pathways. If these new pathways are selected for, they can become the new "canalized" route, even after the perturbation is discontinued.
In summary, genetic accommodation is a process where novel phenotypes emerge and become established in a population through the interplay of plasticity and environmental variation. It challenges the notion of static phenotypes and highlights the dynamic nature of genotype-phenotype relationships. By understanding genetic accommodation, we gain insights into the complex mechanisms that drive evolutionary change and the diverse range of phenotypes observed in nature.
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Frequently asked questions
Phenotypic plasticity is the property of organisms to produce distinct phenotypes in response to environmental variation. It involves a change in gene expression or gene-product use. Phenotypic plasticity is fundamental to the way organisms cope with environmental variation.
Phenotypic plasticity is found in all domains of life. Some examples include the pitcher plant mosquito, which has changed genetically in response to a longer growing season; the North American red squirrel, which has advanced its mean lifetime parturition date in response to an increase in temperature; and the Acyrthosiphon pisum of the aphid family, which can interchange between asexual and sexual reproduction.
Plasticity in genetics refers to the flexibility of the genome. The genome is not static but rather dynamic and constantly evolving. It is like a puzzle made up of parts that can move from one position to another, generating new combinations of elements with different functions and expression patterns.
