Developmental stability and pollination

A number of different: insect species (ranging from Diptera, Lepidoptera an d Coleoptera to Hymenoptera) have been shown to discriminate between small degrees of asymmetry when visiting flowers or flower-like models. Such pref erences for symmetry may have an innate basis. Small degrees of bilateral o r radial asymmetry of flowers are considered to represent a measure of deve lopmental instability, since deviations from perfect symmetry reflect the i nability to maintain developmental precision during ontogeny. Environmental factors causing increased asymmetry in leaves and flowers include radioact ive radiation, ultraviolet radiation, excess artificial fertilizer, various pollutants, extreme saline conditions, herbivory and competition. Genetic factors that contribute to increased asymmetry in plants include homozygosi ty, hybridization, mutation and quantitative genetic differences among indi viduals. Insect preferences for symmetric flowers increase reproductive suc cess of both pollen donors and recipients by affecting seed set and embryo abortion. The ability of insects to discriminate between flowers of superio r and inferior quality is hypothesized to depend on the level of developmen tal instability of the perceptive apparatus of insects. Hence, asymmetry of insects may have consequences for plant reproductive success and mating pa tterns.