Chloe Zhang
Phenotypic plasticity is the ability of organisms to produce distinct phenotypes in response to environmental variation. This allows animals to respond to changes in their environment by developing appropriate morphological, physiological, or behavioural traits that better suit the new conditions. For example, animals with a plastic digestive system can adapt to changes in dietary nutrient composition, diet quality, and energy requirements. Phenotypic plasticity is particularly important for immobile organisms, but mobile organisms such as animals also exhibit some degree of plasticity. For instance, spadefoot toads can produce alternative tadpole morphs – a slower-developing omnivore morph and a more rapid carnivore morph.
| Characteristics | Values |
|---|---|
| Definition | Phenotypic plasticity is the property of organisms to produce distinct phenotypes in response to environmental variation |
| Usefulness | Phenotypic plasticity is more important for immobile organisms, but mobile organisms like animals also have at least some degree of plasticity |
| Examples | Water fleas (Daphnia magna) have shown phenotypic plasticity in response to the heat stress of warmer, urban pond waters; Nestling house sparrows (Passer domesticus) transition from an insect diet to a seed-based diet, accompanied by an increase in the activity of the enzyme maltase; Spadefoot toads in the genus Spea produce alternative tadpole morphs |
| Benefits | Allows individual organisms to develop appropriate morphological, physiological, or behavioral traits that better fit a particular environment; Can be useful for population growth in varying environments |
| Costs | Extended development period, unexpected environmental changes, and trade-offs with other fitness-related traits |
| Evolution | The evolution of plasticity is influenced by factors such as the potential costs associated with maintaining the sensory and regulatory mechanisms needed for plastic responses |
| Genetic Variation | Cryptic genetic variation refers to genetic variation that does not contribute to phenotypic variation under standard conditions but can modify the phenotype following changes in the environment or genetic context |
| Temporal Plasticity | A type of phenotypic plasticity where organisms change their phenotype in response to short-term environmental changes; Animals respond with reversible physiological and behavioral changes |
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What You'll Learn
Digestive system plasticity
Phenotypic plasticity is defined as the property of organisms to produce distinct phenotypes in response to environmental variation. It is fundamental to the way organisms cope with environmental variation, encompassing all types of environmentally induced changes that may or may not be permanent throughout an individual's lifespan.
Phenotypic plasticity of the digestive system allows some animals to respond to changes in dietary nutrient composition, diet quality, and energy requirements. Changes in the nutrient composition of the diet (the proportion of lipids, proteins, and carbohydrates) may occur during development or with seasonal changes in the abundance of different food types. These diet changes can elicit plasticity in the activity of particular digestive enzymes on the brush border of the small intestine. For example, nestling house sparrows (Passer domesticus) transition from an insect diet, high in protein and lipids, to a seed-based diet that contains mostly carbohydrates; this diet change is accompanied by a twofold increase in the activity of the enzyme maltase, which digests carbohydrates. Acclimatizing animals to high-protein diets can increase the activity of aminopeptidase-N, which digests proteins.
In the case of migratory birds, phenotypic flexibility in the digestive system allows them to respond to increased energy demands. For example, when acclimated to extremely low temperatures, migratory birds can increase their feeding rate by approximately 126% compared to when they are at benign temperatures.
Phenotypic plasticity in the digestive system can also be influenced by infection. For instance, various species of non-human primates infected with intestinal worms engage in leaf-swallowing, which physically dislodges parasites from the intestine. The leaves also irritate the gastric mucosa, promoting the secretion of gastric acid and increasing gut motility, effectively flushing parasites from the system.
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Thermal variation adaptation
Phenotypic plasticity is an organism's ability to express multiple phenotypes from the same genome in response to environmental variation. It is an important mechanism for animals to adapt to thermal variations in their environment.
For example, spadefoot toads in the genus Spea produce alternative tadpole morphs in response to their environment. In favourable conditions, they produce a rapid-developing carnivorous tadpole that specialises in preying on animals such as fairy shrimp. In less favourable conditions, they produce a slower-developing omnivorous tadpole morph.
Another example is the African butterfly, which expresses distinct phenotypes in dry and wet seasons. These seasonal phenotypes show pervasive gene expression differences, indicating a lack of genetic variation for plasticity, which may limit their evolutionary responses to climate change.
Phenotypic plasticity allows animals to maximise their fitness by tracking predictable cycles of contrasting ecological conditions. This can include the timing of breeding in birds, the diapause decision in multivoltine insects, and seasonal wing patterns in butterflies.
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Temporal plasticity
The majority of plasticity studies rely on reaction norms, which describe the amplitude of changes in traits across gradients of environmental conditions. However, reaction norms often fail to capture the temporal dynamics of plasticity, especially the speed at which it occurs. By integrating the temporal component into how we describe, quantify, and conceptualize phenotypic plasticity, we can gain a deeper understanding of its diversity, evolution, and consequences.
Phenotypic plasticity can be either adaptive or maladaptive, depending on the environmental cues present. For example, freshwater snails alter their shell shape and reduce growth in the presence of a predator, making them more crush-resistant. However, they cannot distinguish between predatory and non-predatory sunfish, so they may exhibit these defensive changes inappropriately, making them more susceptible to other predators when no threat is present.
Overall, temporal plasticity is an important aspect of phenotypic plasticity, allowing animals to respond to short-term environmental changes and increase their fitness in variable and predictable environments. By studying the rate of phenotypic plasticity and integrating the temporal dynamics into our understanding of this concept, we can gain valuable insights into its evolutionary significance and its role in helping organisms cope with environmental changes.
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Polyphenism
Phenotypic plasticity is the capacity of a single genotype to exhibit a variety of phenotypes in response to environmental variation. It is more important for immobile organisms, such as plants, than mobile organisms, like most animals, because mobile organisms can often move away from unfavourable environments. However, animals do exhibit some degree of phenotypic plasticity. For example, the digestive system of some animals can respond to changes in dietary nutrient composition, diet quality, and energy requirements.
There are several types of polyphenism in animals. For example, the sex of some animals is determined by the environment, such as in crocodiles, where variations in nest temperature determine the sex of the offspring. Other examples of polyphenism in animals include the castes of honey bees and other social insects, seasonal polyphenisms, such as in some butterflies which have different patterns during the year, and predator-induced or resource polyphenisms, which allow animals to exploit variations in their environment.
Polyphenic mechanisms are not entirely stable, and it is still unclear to what extent such switches are continuously reinforced after the completion of development. However, polyphenisms are generally considered threshold traits, exhibiting two discrete alternative morphologies induced by two different environments. When polyphenic species are raised in laboratory conditions that are intermediate to those found in nature, they often produce intermediate forms, suggesting that the two forms found in nature are not due to a binary switch-like developmental process.
The study of polyphenism provides a window into gene-environment interactions and phenotypic plasticity. It is hypothesized that homeostatic and robustness mechanisms facilitate the evolution of novel traits and life history strategies, and understanding the regulation of polyphenic traits may offer insights into how novel phenotypes arise and evolve over time.
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Genetic assimilation
Phenotypic plasticity is the ability of an organism to produce distinct phenotypes in response to environmental variation. It is more important for immobile organisms, such as plants, than mobile organisms, like most animals, as they can move away from unfavourable environments. However, animals do exhibit some degree of phenotypic plasticity. For example, nestling house sparrows transition from a high-protein insect diet to a seed-based diet after hatching, which is accompanied by an increase in the activity of the enzyme maltase, which digests carbohydrates.
Initially, a population occupies one environment (A), with an unexpressed capacity for plasticity. If the environment changes (B), the pre-existing reaction norm allows the population to persist by producing a novel phenotype with no initial genetic change. If natural selection continues to operate in the new environment (C), the novel phenotype may become genetically fixed (assimilated), and the original reaction norm may lose plasticity.
The concept of genetic assimilation has sparked debates in evolutionary literature, with some arguing that it challenges the Modern Synthesis paradigm. However, there is also interest in its potential evolutionary significance and the mechanisms underlying it.
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Frequently asked questions
Phenotypic plasticity is the ability of an organism to exhibit different characteristics in response to changes in its environment.
Phenotypic plasticity allows animals to develop traits that are better suited to their environment, increasing their chances of survival.
Water fleas (Daphnia magna) have shown phenotypic plasticity in response to heat stress in their environment. They have also been known to grow large helmets and spikes in defense against predators.
Environmental cues can trigger the expression of specific phenotypes that are better adapted to the environment. These cues can be reliable indicators of the environment the organism will encounter as an adult.
Phenotypic plasticity can be costly if the development period is extended or if the environment changes unexpectedly, rendering the expressed phenotype maladaptive. There may also be trade-offs between plasticity and other fitness-related traits, such as growth rate.
