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

Understanding constraints to phenotypic plasticity is key given its role on the response of organisms to environmental change. It has been suggested that phenotypic integration, the structure of trait covariation, could limit trait plasticity. However, the relationship between plasticity and integration is far from resolved. Using a database of functional plasticity to drought of a Mediterranean shrub that included 20 ecophysiological traits, we assessed environmentally-induced changes in phenotypic integration and whether integration constrained the expression of plasticity, accounting for thewithin-environment phenotypic variation of traits. Furthermore, we provide the first test of the association between differential trait plasticity and trait integration across an optimumand a stressful environment. Phenotypic plasticity was positively associated with phenotypic integration in both environments, but this relationship was lost when phenotypic variation was considered. The similarityin the plastic response of two traits predicted their integration across environments, with integrated traits having more similar plasticity. Such variation in the plasticity of traits partly explained 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.
This work was funded by grants GYPSEVOL (CGL2016-75566-P), Remedinal (TE-CM: S2018/EMT-4338), Phenotypes (PGC2018-099115-B-I00) and the Ramon y Cajal Programme of the Spanish Ministry of Economy and Competitiveness.