Phenotypic integration and plastic correlations in Phlox drummondii (Polemoniaceae)

Clones from two populations of Phlox drummondii were grown in three different nutrient environments to determine the extent to which the overall level and pattern of correlation among traits within an environment changes across environments. With one exception, the level of phenotypic correlation in both populations was the same across environments. Plants from Lexington, Texas exhibited a significantly lower level of phenotypic correlation when grown at a high nutrient concentration. The two populations did not differ from one another in their levels of phenotypic correlation when compared within environments. The pattern of correlation was homogenous both within populations across environments and among populations within environments. Tests of a priori hypotheses regarding the associations among functionally or developmentally related traits suggest that the correlations among traits are higher in traits that share a common function or developmental origin. We also compared the level and pattern of plasticity correlations among populations for three different components of the plastic response. We found that the level and pattern of plastic correlation for the average, linear, and nonlinear components of the plastic response did not differ among the two populations. With only one exception, the relationships among the plastic responses of different traits fit our model of functional and developmental integration. The results from our analyses of phenotypic and plastic correlations support the hypothesis that plastic correlations determine the extent to which phenotypic correlations are environment-dependent.