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First published online May 26, 2006
Journal of Experimental Biology 209, 2362-2367 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02070
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Phenotypic plasticity and evolution by genetic assimilation

Massimo Pigliucci1,*, Courtney J. Murren2 and Carl D. Schlichting3

1 Department of Ecology and Evolution, SUNY-Stony Brook, 650 Life Science Building, Stony Brook NY 11794, USA
2 Department of Biology, College of Charleston, Charleston, SC 29424, USA
3 Department of Ecology Evolutionary Biology, University of Connecticut, Storrs, CT 06269, USA


Figure 1
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  		Fig. 1. An example of genotypic reaction norms illustrating the concept of phenotypic plasticity. In the simple case of two environments, the lines represent the norms of reaction of each genotype, while the slope is a measure of the degree and pattern (positive or negative) of phenotypic plasticity. So, for example, genotypes 1 and 3 are both plastic, but display opposite patterns in response to the same environments; genotype 2, on the other hand, shows little plasticity for this trait in this environmental set.

 

Figure 2
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  		Fig. 2. The concept of genetic assimilation, seen in the modern light of reaction norms and phenotypic plasticity. The population is initially occupying one environment (A), although there is an unexpressed capacity for plasticity, should the environment change. If the environment does change (B), the pre-existing reaction norm allows the population to persist, producing a novel phenotype with no initial genetic change. Finally, if natural selection keeps operating only in the new environment (C), the novel phenotype may become genetically fixed (assimilated), and the original reaction norm may lose plasticity, for example because of drift or costs associated with maintaining plasticity when it is not favored by natural selection (because the old environment is no longer experienced).

 

Figure 3
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  		Fig. 3. The hierarchical/conceptual relationships among phenotypic plasticity, natural selection, and genetic assimilation or phenotypic accommodation. Plasticity is a developmental process on which the evolutionary mechanism of selection may operate, yielding the evolutionary outcome (under certain conditions) of assimilation/accommodation. Seen this way, there is no possibility of confusing plasticity as ontologically equivalent to natural selection, and therefore somehow a threat to the Modern Synthesis.

 




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