Reaction Norms of Arabidopsis. IV. Relationships between plasticity and fitness
Massimo Pigliucci* and Carl D. Schlichting
Department of Ecology and Evolutionary Biology, University
of Connecticut, Storrs CT 06269
*Author for correspondence.
Current address: Department
of Botany, University of Tennessee, Knoxville, TN 37996-1100.
Email: pigliucci@utk.edu.
HomePage:http://suncirf.bio.utk.edu/botany/pgl/mphome.htm
Abstract
The study of the association between fitness and reaction
norms is of primary importance given the hypothesized
role for phenotypic plasticity in shaping evolutionary
patterns: in microevolution, as one mechanism for maintaining
genetic variation, and in macroevolution, as a means
of generating phenotypic novelties. In a glasshouse
experiment, we investigated variation in reaction norms
to nutrient availability in populations of Arabidopsis
thaliana, and the relationship between this variation
and reproductive fitness. We found evidence for across-treatment
directional selection on the means for leaf number,
flowering time, plant height, branching, and growth
rate; across-treatment stabilizing selection was detected
for growth rate; and across-treatment disruptive selection
was significant for leaf number. We also uncovered
selection on the plasticity of some traits: directional
for the plasticity of branching, and stabilizing for
the plasticity of both branching and growth rate. When
the two environments were considered separately, directional
selection for height was detected under low nutrients;
under high nutrients, we found evidence for directional
selection on leaf number and height, and for disruptive
selection on flowering time. The genetic correlation
between a trait's expression in one environment and
its expression in the alternate environment was positive
and highly significant only for flowering time and
growth rate. A principal components analysis revealed
possible constraints on future selection responses,
due to correlations among character means and among
character plasticities.