I'm trying to understand better these two concepts, but I cannot see a clear difference yet.

Reaction norm: "set of phenotypes that can be produced by an individual genotype when exposed to different environmental conditions"

Phenotypic plasticity: "ability of individual genotypes to produce different phenotypes when exposed to different environmental conditions"

Are phenotypic plasticity changes temporary changes in genes; are they an extension of the reaction norm?

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    $\begingroup$ You should cite the sources from which you are quoting these definitions. $\endgroup$ – WYSIWYG May 10 '19 at 8:31

I think it's a little simpler than what you describe- phenotypic plasticity is the abstract property of phenotypes differing with respect to environment, whereas a reaction norm is a particular environmental response.

So you might make an argument like this:

"Daphnia show extensive phenotypic plasticity in their morphology. For example, see the attached figure showing head morphology norms of reaction (y axis) of two Daphnia strains with respect to food richness (x axis)."

enter image description here

This is figure 9 from Woltereck's original publication on reaction norms. It shows that as you grow Daphnia with denser cultures of algae (their food), more individuals in the population show a distinctive head morphology. It shows further that the shape of the curve is similar between two Daphnia strains (solid and dotted lines). Each curve is what Woltereck called a norm of reaction.

Hope that helps.


Phenotypic plasticity, as you define in your question, is an ability or a property of the organism (a given genotype) to manifest different phenotypes in different environments (Pigliucci et al., 2006).

Reaction norm is an analysis of the pattern of phenotypes exhibited in different environments. In other words it is an analysis of the phenotypic plasticity.

  • $\begingroup$ I'd pick on this a little. A norm of reaction (at least as originally defined by Woltereck 1909) is the pattern. It is the specific biological phenomenon expressed as differences in phenotype with respect to some environmental variable. $\endgroup$ – Maximilian Press May 10 '19 at 10:24
  • $\begingroup$ @MaximilianPress usually people represent these patterns as graphs/curves etc and that's what I meant by analysis. Some sources just defined it as a "curve". So I just used the term "analysis" because it appears like a post experiment analysis. $\endgroup$ – WYSIWYG May 10 '19 at 10:38
  • $\begingroup$ I agree that the representation is normally in the form of some quantitative visualization - but I think it's important to separate the phenomenon (a particular phenotypic response) from the analysis or visualization of the phenomenon (e.g. an ANOVA plot). See also my answer. $\endgroup$ – Maximilian Press May 10 '19 at 10:43

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