The Proposed Anti-herbivory Roles of White Leaf Variegation

Abstract

It has been suggested that white variegation, the outcome of various developmental, genetic, and physiological processes, may defend leaves and other plant organs from herbivory by several proposed mechanisms: camouflage, aposematism (including Mullerian and Batesian mimicry), mimicry of insect damage and fungal attacks, dazzle effects that make it hard for large herbivores to decide where to bite the leaves and for insects to land on them, and by visual repellence of insects from landing as well as by unknown mechanisms. Very few cases of these suggested leaf defenses by variegation have been examined in depth. Some such studied cases were indeed found to actually operate as defense from herbivory either in nature or in experiments, suggesting the potential defensive function of others. However, the specific operating defensive mechanism by white variegation was not always identified or even proposed, even when variegation was found to be associated with reduced herbivory. Studying white variegation has a significant advantage over studying other types of plant defensive coloration because even bi-chromatic vision is sufficient to see these patterns. Moreover, white variegation is probably visible under most types of natural light conditions, including strong moonlight. While in this essay I wish to stimulate an effort for a broader and deeper understanding of the defensive roles of white variegation, the possible simultaneous physiological roles of white leaf variegation that will not be reviewed here should not be ignored.