Ontogenetic changes in the phenotypic integration and modularity of leaf functional traits

1. Changes in resource availability, functional demands, hormonal regulation and developmental constraints can promote differences in the expression of leaf traits during plant development and foster changes in the targets of natural selection. As a consequence, the pattern and magnitude of covariation among traits, and therefore their phenotypic integration and modularity are equally expected to change throughout ontogeny. However, these changes have not been described yet. 2. We measured leaf economic, defensive and morphological traits in plants of Turnera velutina and estimated the magnitude and pattern of foliar integration and modularity for juvenile and reproductive individuals. In addition, we assessed the relationship between plant biomass and foliar integration within and among ontogenetic stages. 3. Both the pattern and magnitude of foliar integration changed across plant ontogeny. Foliar integration was lower in juvenile than in reproductive plants, and the pattern of phenotypic integration and modularity was different between ontogenetic stages, whereas leaves from juvenile plants showed two functional modules related to plant defence and leaf economy, traits from reproductive plants had greater interconnectivity and hence lower modularity. 4. The relationship between plant biomass and foliar integration was negative within each ontogenetic stage but positive between ontogenetic stages, suggesting that processes intrinsic to plant development influenced the magnitude of foliar integration to a greater extent than plant size. 5. Our findings indicate that plants can change the patterns of covariation among leaf traits during their development. However, a lower foliar integration in juvenile plants could allow for greater lability to explore a multi- trait phenotypic space, canalisation of leaf attributes along ontogeny should promote greater phenotypic integration, constraining the number of multi- trait combinations that plants can express. Hence, we suggest that ontogenetic changes in foliar integration allow plants to deal with changing selective dynamics and physiological priorities along their development. A is available for this article.