The environment, the phenotype, and
the genotype of an organism are closely related. They play off each other,
ultimately affecting the organism. Phenotypes are usually defined as the
appearance of a genetically controlled trait; however, this is not always the
case. The environment can influence the phenotype of an organism as well. The
word describing the environment’s impact on phenotype is phenotypic plasticity.
Phenotypes that are plastic have individuals with the same genotype but have
different phenotypes due to the variation in their environments. Phenotypic
plasticity is able to evolve and is adaptive. Environments frequently change.
The changes in environment can disrupt an organism’s ability to cope with the
environment and thus lower fitness. Phenotypic plasticity allows the balance
between an organism’s phenotype and the environment to be restored.
Grasshoppers and their mandibles provide a good example of phenotypic
plasticity. Most grasshoppers prefer leafy, lush food such as leaves. They have special mouthparts called mandibles
that move horizontally to crush the leaves between the two mandibles.
Phenotypic plasticity can be seen in grasshopper mandible size when their diet
changes. Drought or climate change is usually the reason for this. When the
food becomes more fibrous the mandibles become larger and more muscle
attachments appear. The change in environmental climate caused a shift in vegetation,
which caused the grasshopper mandible to change. Other examples of phenotypic
plasticity can be seen in the change in polar bear diet due to the increase in
global temperatures or in aphid colonies where females produce offspring best
suited for the environment the colony is facing. Phenotypic plasticity is not
the same as adaptations. Phenotypic plasticity is a direct and intentional
shift. Phenotypic plasticity allows organisms of the same genotype to vary in
their phenotypes.
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