Geometric morphometrics and leaf phenotypic plasticity: Assessing fluctuating asymmetry and allometry in European white oaks (Quercus)

Abstract

Because plants are unable to move away from unfavourable habitats and environmental perturbations, leaf phenotypic plasticity facilitates light absorption and gas exchange. Oaks (Quercus spp.) are particularly known for their adaptability and plastic phenotypes, and leaf allometry and developmental instability may represent important mechanisms for their adaptation to environments and evolution. Because of its important role in the adaptation of plant populations to different environments, allometry can be involved in diversifying selection. Developmental instability is related to environmental perturbations and stresses by producing random deviations in structures characterized by bilateral symmetry, such as oak leaves. In addition, developmental instability can also arise from genetic bottlenecks or as a result of hybridization. The splitting of symmetric and asymmetric components of variation and their separate analysis allows the variability in leaf shape traits to be summarized, reducing the variation produced by developmental instability. The geometric morphometric approach is a useful method for the study of leaf asymmetry and allometric patterns. This method provides an important tool for the visualization of shape attributes that characterize species with highly variable leaf phenotypic patterns. In this study, leaf shape and size variability of three white oak species was investigated by means of a two-dimensional landmark-based method providing improved knowledge of variance partitioning, species discrimination, fluctuating asymmetry and allometric patterns of variation resulting from the different analyses.