EXAMPLE: CLAUSEN, KECK and HIESEY EXPERIMENT
Clausen, Keck and Hiesey (1940) examined the contribution of genetic and environmental differences to variation in growth form of the herb Potentilla glandulosa. Plants sampled at various points along an east-west transect in California exhibit great variation in growth form:
Clausen, Keck and Hiesey performed a common garden experiment
to determine the degree to which genetic and environmental differences contributed
to this observed phenotypic variation. Experimental gardens were established
at sites designated Stanford, Mather and Timberline, which differed in elevation.
Plants from four different areas (designated four different subspecies) were
grown in each of these gardens. Typical growth forms of the plants
from each of these areas in each of the gardens is portrayed schematically
below:
Effects of environment on the phenotype (holding genetic composition
constant) are reflected by comparisons across a row in this figure.
Such effects are substantial, indicating that growth form in this species
is phenotypically plastic, i.e. is influenced by the environment
in which a plant grows. Effects of differences in genetic composition
are reflected by comparisons down a column in the figure. It is clear
that in a common garden, groups from different areas exhibit very different
growth forms. Because environment was held constant by growing the
plants in the same garden, the observed differences must be due to underlying
genetic differences among the plants from the different areas.
Reference
Clausen, J., D. D. Keck, and W. Hiesey. 1940.
Experimental studies on the nature of species. I. Effects of varied environments
on western North American plants. Carnegie Inst. Wash. Publ. 520.
Figures taken from O. T. Solbrig and D. J. Solbrig. 1979. An
Introduction to Population Biology and Evolution.
Addison Wesley, Reading, MA.
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