This was a test question, and I'm not too sure about the answer.

Which statement about phenotypic plasticity is false?

a. Because the plasticity of a phenotypic trait may be costly to maintain, it will not be favoured in stable environments.

b. A trait that is an adaptation will not vary with environmental conditions within one generation.

c. Phenotypic plasticity can itself be an adaptation to varying environmental conditions.

d. Variation in phenotype among populations of a given species across different environments is only caused by phenotypic plasticity.

If you could explain the answer to me, that would be great.

  • $\begingroup$ When you say phenotypic plasticity, do you mean developmental phenotypic plasticity? Do you exclude phenotypic flexibility (lifetime REVERSIBLE and adaptive change in phenotype in response to environment)? $\endgroup$
    – Remi.b
    Nov 6 '13 at 20:02
  • $\begingroup$ What did you answer and why? $\endgroup$ Nov 7 '13 at 9:17
  • $\begingroup$ what level was this question set at? (what is the group being examined.. undergrads, post grads, high school??). I think B would be false if it read "A trait that is plastic will not vary with environmental conditions within one generation." $\endgroup$
    – rg255
    Nov 7 '13 at 9:27
  • 1
    $\begingroup$ Horrible phrasing of options. $\endgroup$ Nov 7 '13 at 10:51
  • 1
    $\begingroup$ If you can change teachers, do. That is a horribly worded question and very unclear. You can make arguments that everything is false depending on how you interpret the terms used. IN any case, D is 100% false with all interpretations so if the "teacher" only wants one answer, choose that. $\endgroup$
    – terdon
    Nov 7 '13 at 14:18

I'll try to answer but I'll encounter some difficulties: first because I don't know what you mean by "plasticity". Does it mean non-reversible developmental plasticity or reversible flexibity. Then, because, I don't really like the word adaptation! Anyway'll try...

a: Plasticity is some kind of mechanism allowing organisms to adapt to various environment. If the environment is stable and under the assumption the plasticity is associated with a intrinsic (physiological for example) cost, then a population would tend to evolve so that they always display the most optimal phenotype. I would argue that this is under the assumption that we gave enough time for the right mutations happen and under the assumptions that such mutation might exist!

b I don't really understand this statement. Does it mean that between two generations (which mean in one generation time) an adaptation cannot vary.…in what terms? in frequency? Through time any trait vary because of selection, environment, genetic drift and mutations. And to what environment is the trait under consideration adapted for? Can we accept that the environment is changing from one generation to the other in this question? What does this question has to do with plasticity? I guess that when one says that a trait is an adaptation it means (among other things) that the population has no more variance for this trait. Therefore, only mutations would bring variations if there were no environmental change making the trait not adaptive anymore.

c: Well, yes. Plasticity is an adaptation to fluctuating environment. It allows to display a rather optimal phenotype in multiple different environments.

Answer d is wrong for sure. There is variation within a population due to genetic variance and non-adaptive environmental variance (and their interactions). Variance due to plasticity is just some kind of subset of the variance du to the genetic-environnment interaction

Hope this helps a bit!

  • 3
    $\begingroup$ Agree with you there @Remi.b - A (with caveats) and C are true, D is definitely false (Phenotype = Genotype + Environment + GE... Plasticity is just one component of GE) and B doesn't make much sense (especially given the question is about plasticity). $\endgroup$
    – rg255
    Nov 7 '13 at 9:17

I think the answer should be (d) as variation in phenotype among populations of species living in different environments are not caused only by phenotypic plasticity, they may also be caused by genetic differences which arose due to different selective pressures.


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