Re: What is phenotypic plasticity, and how might it complicate taxonomy?

Hello Ed,

Phenotypic plasticity is when an organism activates different phenotypes in response to its environment. It is believed that phenotypic plasticity evolved to allow organisms a greater chance of survival in their ever-changing surroundings. This phenomenon can be seen throughout the natural world and is especially prevalent in symbiotic relationships. An example of phenotypic plasticity can be found in the northwestern Atlantic snail, Littorina obtusata, which develops a thicker shell upon exposure to predacious crabs (1). This affords the snail greater protection and therefore a greater chance of survival. These traits may revert back to the original phenotypes when the "inducer" is absent. Occurrence of phenotypic plasticity may cause some organisms to look different from each other even though they are genetically identical.

This brings us to the second part of your question: How might it complicate taxonomy? There are also many examples of organisms that scientists thought to be separate species, only later to find out that they were the same creature expressing different phenotypes. This occurs when one classifies using morphological phylogeny instead of molecular phylogeny, which is based on the DNA sequence of the 16S ribosomal subunit. As mentioned before these organisms are genetically identical so utilizing molecular phylogeny is one way of avoiding confusion.

One of the novel difficulties encountered when confronting phenotypic plasticity is that of biodiversity conservation (2). An organism that has used phenotypic plasticity to adapt to a unique environment may not be genetically different than its cousin in the next pond over, BUT it has the potential to evolve into a different species. In other words, you may protect a particular species, but that doesn't guarantee that future species will be protected. So one is faced with the question of whether one should protect a genetically distinct organism and/or protect a unique environment where expression of an alternate phenotype may lead to the emergence of a new type of beast altogether. Thanks for the great question.

derrick

P.S. I highly recommend reading the third reference. It is a great review of phenotypic plasticity and goes into much greater detail. It also has some great pics!

1. G.C. Trussell, L.D. Smith, Proc. Ntl. Acad. Sci. 97, 2123 (2000)
2. K.A. Young, Conservation Biology 15, 784 (2001)
3. A.A. Agrawal, Science. 294, 321 (2001)