Elevated CO2 decreases leaf fluctuating asymmetry and herbivory by leaf miners on two oak species

Fluctuating asymmetry (FA) represents small, random variation from symmetry in otherwise bilaterally symmetrical characters. Significant increases in FA have been found for several species of plants and animals in response to various stresses, including environmental and genetic factors. In this study, we investigated the effects of elevated CO2 on leaf symmetry of two oak species, Quercus geminata and Q. myrtifolia, and the responses of three species of leaf miners and one gall-making species to random variation in leaf morphology. Leaf FA decreased with an increase in CO2 concentration. There were fewer asymmetric leaves and lower levels of asymmetry on leaf width and leaf area on elevated CO2 compared with ambient CO2. Leaf miners responded to leaf asymmetry, attacking asymmetric leaves more frequently than expected by chance alone. Differences in secondary chemistry and nitrogen (N) content between symmetric and asymmetric leaves may be responsible for these results due to lower levels of tannins and higher levels of N found on asymmetric leaves of Q. myrtifolia and Q. geminata.