Reaction norm

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As a norm of reaction is known in the genetics , the variation of the phenotype resulting from the same genotype at different environmental factors can develop. The term was introduced in 1909 by Richard Woltereck ; Modification width is also used synonymously .

If one exposes hereditary creatures to different environments, they will develop different manifestations in many characteristics. Conversely, if genetically different creatures of the same species are exposed to the same environment, they develop different manifestations solely because of the different alleles. In real populations in real habitats, there is therefore a phenotypic variability that can be traced back to both the genetic variability between individuals and the variability of the individually experienced environmental parameters. The phenotypic change that is caused not by different genes but by different environmental influences is called modification .

Response norm and evolutionary success

Since the reaction to environmental conditions is genetically designed, the selection also has an effect on the reaction norm. In an environment with greater variability, another response norm promises greater fitness than a narrower one. Conversely, for a mutation with an extended response norm in environments in which the factors change only little, no increased reproduction rate is to be expected. In a stable ecological niche, the specialized initial population is therefore little changed.


Many plants are able to develop different leaf shapes: harder, smaller sun leaves and thinner, shadow leaves . Many animals can develop summer fur or winter fur depending on the season . This gives them an evolutionary advantage over plants and animals, which cannot adapt their phenotype so well to external conditions.

Ecological response norm

The reaction norm of all individuals in a population can be integrated into the reaction norm of the population in an ecosystem . This means that at different locations the individuals belonging to a certain population can have different characteristics, even though they all belong to the same species . Under certain circumstances, the variations in the phenotype are so broad that based on their appearance alone, the same species is not initially suspected.

The reaction norm determines which habitats a species can colonize and what its ecological niche there is like.

See also

Individual evidence

  1. Woltereck R. (1909): Further experimental investigations on species changes, especially on the nature of quantitative species differences in Daphnids. Negotiations of the German Zoological Society, 1909: 110-172.
  2. ^ Stearns SC, JC Koella (1986): The Evolution of Phenotypic Plasticity in Life-History Traits: Predictions of Reaction Norms for Age and Size at Maturity. Evolution, Vol. 40, No. 5., pp. 893-913. ( PDF  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice .; 5.6 MB)@1@ 2Template: Dead Link /  
  3. Ernst Mayr: That is evolution. Wilhelm Goldmann Verlag, Munich 2005, ISBN 9783442153497 , p. 118.
  4. Gabriel W., M. Lynch (1992): The selective advantage of reaction norms for environmental tolerance. Journal of Evolutionary Biology 5: 41-59. ( PDF ; 1.0 MB).
  5. Douglas J. Futuyma: Evolutionsbiologie , Birkhäuser, Basel 1990, pp. 60f.