Morphological developmental stability in plants: Patterns and causes

Minor bilateral or radial asymmetry of leaves or flowers, the frequency of phenodeviants, intraindividual variation in repeated characters, and fracta l dimensions of morphology are considered to represent measures of developm ental instability since deviations from regularity of the phenotype constit ute a measure of the inability to maintain developmental precision during o ntogeny. First, we review patterns of fluctuating asymmetry in plants and s how that levels of asymmetry are considerably greater than in animals. Whil e petal asymmetry tends to decrease with petal size within species, leaf as ymmetry tends to increase with leaf size. Intraspecific correlations of pet al asymmetry and leaf asymmetry are weakly positive. Second, a meta-analysi s of the effects of environmental factors hypothesized to increase asymmetr y in leaves and flowers, such as radiation, ultraviolet light, excess artif icial fertilizer, pollutants, extreme saline conditions, herbivory, and com petition, showed intermediate (i.e., explaining 10% of the variance) to lar ge (i.e., explaining 25% of the variance) effects. Third, a meta-analysis o f the effects of genetic factors hypothesized to contribute to increased as ymmetry in plants, such as homozygosity, hybridization, mutation, and quant itative genetic differences among individuals, showed variable but usually significant effects, although the number of studies generally was small. Co ntrolled experimental studies of environmental and genetic effects on devel opmental instability of plants may increase our understanding of the mechan isms causing developmental instability.