PHENOTYPIC PLASTICITY OF ANNUAL PHLOX: TESTS OF SOME HYPOTHESES

Phenotypic plasticity is an important means by which individual plants respond to environmental heterogeneity. Relative plasticities were compared for three species of annual Phlox grown in a set of six environmental treatments. Two measures of plasticity were computed for 18 characters per species: the Coefficient of Variation to measure amounts of plasticity and a new measure, the correlation of responses between species, which compares patterns of plasticity. Three hypotheses concerning the species’ amounts and patterns of plasticity were examined. The heterozygosity hypothesis states that levels of heterozygosity and amounts of plasticity should be inversely related. The relatedness hypothesis states that more distantly related species should have less similar patterns and amounts of plasticity. The ecological hypothesis states that species from similar habitats should have more similar amounts and patterns of plasticity than species which evolved under differing conditions. The results suggest that heterozygosity, relatedness, and ecology may all affect patterns and amounts of plasticity, and that no single hypothesis is sufficient to explain the observed results. Some data from previous studies are examined in relation to the proposed hypotheses.