Is photomorphogenic shade avoidance adaptive? Perspectives from population biology

Authors

  • J. SCHMITT

    Corresponding author
    1. Department of Ecology and Evolutionary Biology, Box G-W, Brown University, Providence, RI02912, USA
      Johanna Schmitt, Department of Ecology and Evolutionary Biology, Box G-W, Brown University, Providence, RI 02912, USA.
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Johanna Schmitt, Department of Ecology and Evolutionary Biology, Box G-W, Brown University, Providence, RI 02912, USA.

ABSTRACT

Photomorphogenic shade avoidance responses provide an ideal model system for integrating genetic, physiological and population biology approaches to the study of adaptive plasticity. The adaptive plasticity hypothesis predicts that shade avoidance phenotypes induced by low ratios of red to far-red light (R:FR) will have high relative fitness in dense stands, but will suffer a fitness disadvantage at low density. Experiments with transgenic and mutant plants in which photomorphogenic genes are disabled, as well as phenotype manipulation by means of altered R:FR, strongly support the shade avoidance hypothesis. The observation of photomorphogenic ecotypes in different selective environments also suggests that the shade avoidance response has undergone adaptive evolution. Quantitative genetic variation in R:FR sensitivity has been detected in wild populations, indicating that the evolutionary potential exists for response to natural selection. However, evolutionary response may be constrained by genetic correlations among developmentally linked traits. Therefore it cannot be assumed that an observed suite of photomorphogenic responses represents an adaptive optimum for every trait.

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