Separating Developmental and Environmental Effects on Fluctuating Asymmetry in Lythrum salicaria and Penthorum sedoides

Environmental stress can disrupt developmental processes on biological, physiological, and chemical levels and thereby affect the symmetry of a trait. For this reason, fluctuating asymmetry is often proposed as a measure of stress encountered by an individual. One problem is that asymmetry may have multiple causes, including developmental noise and genetic background, and genetic differences may interact with any physiological stress imposed by the environment. The main objective of this research was to determine whether developmental noise and genetic stress can be separated from environmental effects on leaf asymmetry. The experiments were conducted on two wetland plants, Lythrum salicaria (purple loosestrife) and Penthorum sedoides (ditch stonecrop). Replicates of different genotypes were measured when young and after they matured, with the latter group grown under two nutrient treatments. The largest and healthiest leaf of each plant was measured for length, width, and differences in width between the left and right sides (measuring from the central vein at the widest point). Nutrient enrichment increased leaf asymmetry, while age reduced asymmetry in L. salicaria. However, leaf asymmetry changed only as a consequence of development in P. sedoides and decreased. Genotype did not affect asymmetry in either species.