Phenotypic integration does not constrain phenotypic plasticity:differential plasticity of traits is associated to their integrationacross environments

Abstract

Understanding constraints to phenotypic plasticity is key given its role on the response oforganisms to environmental change. It has been suggested that phenotypic integration, thestructure of trait covariation, could limit trait plasticity. However, the relationship betweenplasticity and integration is far from resolved. Using a database of functional plasticity to drought of a Mediterranean shrub that included20 ecophysiological traits, we assessed environmentally-induced changes in phenotypic inte-gration and whether integration constrained the expression of plasticity, accounting for thewithin-environment phenotypic variation of traits. Furthermore, we provide the first test ofthe association between differential trait plasticity and trait integration across an optimumand a stressful environment. Phenotypic plasticity was positively associated with phenotypic integration in both environ-ments, but this relationship was lost when phenotypic variation was considered. The similarityin the plastic response of two traits predicted their integration across environments, with inte-grated traits having more similar plasticity. Such variation in the plasticity of traits partlyexplained the lower phenotypic integration found in the stressful environment. We found no evidence that integration may constitute an internal constraint to plasticity.Rather, we present the first empirical demonstration that differences in plastic responses mayinvolve a major reorganization of the relationships among traits, and challenge the notion thatstress generally induces a tighter phenotype.