If you have ever been near a river, or even a puddle, there is a good chance you might have seen a tadpole. Gray treefrog tadpoles have the ability to change their phenotype depending on the environment they are growing. If there are many predators in the environment, then the tadpoles will produce a phenotype that allows them to escape detection. Conversely, if there are no predators present in the environment, they will produce a phenotype that allows them to grow quickly!
It is amazing how tadpoles have such phenotypic plasticity! What does this mean, though? You'll have to keep reading to find out!
Phenotypic plasticity definition
First, let's take a look at the definition of phenotypic plasticity. In essence, phenotypic plasticity occurs when individuals with the same genotype exhibit different phenotypes in different environments.
Phenotypic plasticity refers to the change in phenotype caused by environmental factors.
In other words, an organism that exhibits phenotypic plasticity can alter its phenotype based on its environment.
Phenotypes are the observable traits of an organism.
Figure 1. Phenotypic plasticity, Isadora Santos - StudySmarter Originals.
Different phenotypes can be expressed by organisms with phenotypic plasticity depending on the environment, and this is achieved by regulatory genes that switch on structural genes in response to specific stimuli.
For example, some trees can produce shade and sun leaves. These leaves differ in shape, and the genes that determine leaf shape are light-sensitive.
The phenotypic changes that are associated with organisms vary considerably and can include traits like body mass, size, shape, the anatomical structure of parts and organs, behavior, metabolism, and even sex expression.
There are many environmental factors that can trigger phenotypic plasticity, and one of them is temperature.
In some turtles, the temperature at which embryos develop determines the sex! At cooler temperatures, the embryo will develop into a male. At warmer temperatures, egg incubation will produce females.
Other environmental factors include seasonal changes, nutrition, chemical signaling, and the presence of predators (as seen in gray tree frog tadpoles).
Snowshoe hares, a species of rabbit, have their color influenced by seasonal changes.
Organisms can also be influenced by nutrition.
For example, people with calcium deficiency may develop short stature.
A chemical signal can be produced by other organisms in the environment and affect the behavior of another organism.
As an example, yeast secretes pheromones to communicate with yeasts of the opposite sex about their presence and readiness to mate.
Adaptive phenotypic plasticity
Adaptive phenotypic plasticity is also known as acclimation. This type of plasticity is mostly seen in animals that grow thicker fur during the winter, or in some plants producing smaller leaves during the dry season!
Acclimation is referred to as a physiological adjustment to a change in an environmental factor.
Basically, acclimation is a way for plants and animals to adapt to seasonal changes or other persistent changes in the environment.
Importance of phenotypic plasticity
So, why would it be important for organisms to have phenotypic plasticity? Two words: phenotypic fitness!
An organism that possesses the phenotype that is most suited to that environment will have higher fitness. Therefore, plastic organisms might have a higher fitness across multiple environments (compared to organisms with fixed phenotypes).
Fitness is the ability to survive, reproduce and contribute to the future gene pool.
Phenotypic plasticity also has some important practical applications. To reduce its effects, researchers have been studying plasticity.
For example, in crops, reducing plasticity in crops ensures that high yields are always achieved even if environmental conditions change!
In humans and other animals, the ability to understand plasticity might give scientists more insight into some abnormalities that are caused by environmental factors.
Phenotypic plasticity examples
Let's take a look at some common examples involving phenotypic plasticity: flower color based on soil pH, and the effect of increased UV on melanin production in animals.
The color of hydrangea flowers when growing in soils with different pH values. Hydrangeas grown in acidic soils had a blue color, whereas hydrangeas grown in pH around 7 had more of a deep pink color!
Arctic animals such as snowshoe hares change their fur color according to the weather! During the summer, snowshoe hares tend to be brown or gray due to the majority of their habitat being brown or gray. However, when it gets snowy and everything turns white, their fur color changes to white as well.
This color change is linked to how much light they receive during the day.
Phenotypic plasticity in humans
Phenotypic plasticity can also happen in humans. Think about identical twins for a second. Although they might have the same genotype and similar phenotypes, their phenotype will not be 100% identical because of the effects that the environment has on them!
Under different environmental conditions, humans can have different weights too!
For example, a person's weight will most likely change depending on diet and exercise.
Environmental factors such as nutrition can also influence human phenotypic expression.
Phenylketonuria is an autosomal recessive genetic disorder that is characterized by high levels of phenylalanine. Individuals with this disorder are not able to metabolize the amino acid phenylalanine, so as it accumulates, it causes the brain cells to die, leading to death. The good news is that, if the person sticks to a diet to reduce phenylalanine levels to a minimum, the disorder can be controlled!
Another example involves UV radiation. In humans, melanin production is affected by UV rays. Melanin is a pigment produced by melanocytes to protect DNA from UV radiation. So, if there is an increase in exposure to UV rays, pigmentation production also increases!
Have you ever heard of neuronal plasticity? Neuronal plasticity occurs when synaptic connections strengthen or weaken over time, in response to the level of activity at the synapse! Scientists believe that a defect in neuronal plasticity could be an underlying cause of autism, which is characterized by impaired communication and social interaction.
Polyphenism vs. phenotypic plasticity
Now that we discussed phenotypic plasticity, let's look at phenotypic plasticity in organisms that exhibit polyphenism, also known as discrete plasticity.
Polyphenism is when discrete phenotypes arise from a single genotype due to differences in environmental conditions.
Genotype is the genetic makeup of an organism.
A great example of polyphenism is seen in female honeybees. In this case, food is the cause of phenotypic plasticity, and their larval diet will determine whether it becomes a queen or a worker!
Testing for phenotypic variation
Lastly, let's take a look at how researchers test if the phenotypic variation is due to genotype or environment. The general equation for phenotypic variance is as follows:
$$ \text{Phenotypic variance = Genetic variance + Environmental variance} $$
A reciprocal transplant experiment is a common method of investigating differences between populations, and it involves moving individuals with alternative phenotypes among alternative environments. There will be similar reaction norms between populations when the differences are attributed to environmental factors (phenotypic plasticity).
A reaction norm is a type of graph that shows the pattern of phenotypes an organism may develop upon exposure to different environments.
Phenotypic Plasticity - Key takeaways
- Phenotypic plasticity refers to an organism's ability to change its phenotype depending on its environment.
- Phenotypic changes associated with the environment can occur in organisms in a variety of ways, including changes in body mass, size, shape, anatomical structure, behavior, metabolism, and even gender.
References
- Relyea, R., ECOLOGY : the economy of nature, 2021.
- Dewitt, T. J., & Scheiner, S. M., Phenotypic plasticity : functional and conceptual approaches, 2004.
- Mary Jane West-Eberhard, Developmental plasticity and evolution, 2003.
- Freeman, J. C., Evolutionary Analysis, 2020.
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