Fluctuating Asymmetry of Leaves in Digitalis thapsi under Field and Common Garden Conditions

The degree of developmental instability has been hypothesized to reflect the level of environmental and genetic stress. However, levels of fluctuating asymmetry or other indicators of developmental instability are rarely measured in the same populations under field and common garden conditions, making it difficult to determine whether differences in asymmetry derived from field measurements are simply phenotypic or genetic in origin. We studied fluctuating asymmetry of leaves in three populations of Digitalis thapsi L. that differed dramatically in mean seed production under field conditions and when reared in a common garden. While absolute asymmetry decreased with leaf position, there was no position effect on relative asymmetry after adjustment for leaf width. Absolute and relative asymmetry did not differ between seedlings and mature plants in the greenhouse. There was no significant difference in absolute or relative asymmetry of leaves between plants grown in the greenhouse and in the field, although there was a significant population 3 rearing environment interaction. The number of leaves and the maximum length and width of leaves of mature plants reared in the common garden differed among populations. Fluctuating asymmetry in leaves was not significantly correlated with any measure of vegetative growth or reproduction. These findings indicate that the effects of environmental conditions and selection may override the effects of inherent differences. Thus, conclusions about levels of developmental instability in different populations based on field studies may differ considerably from conclusions based on results from common garden experiments.