Phenotypic Plasticity

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.

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.

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.

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!

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).

Phenotypic plasticity also has some important practical applications. To reduce its effects, researchers have been studying plasticity.

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.

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!

Environmental factors such as nutrition can also influence human phenotypic expression.

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!

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.

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).