Anthropogenic stress and natural selection: variability in radish biomass accumulation increases with increasing SO2 dose

Abstract

Although there is a strong relationship between genetically based variability of a given character and the potential for natural selection to act on that character, most studies of the effects of environmental factors on plants examine the mean responses of plants in a population and not the variability among plants in the population. Yet variability in the response among individuals to an environmental stress could foretell changes in a population that might not be evident from examination of mean responses. Here we report an analysis of data from several experiments on radish plants showing a significant relationship between the coefficient of variation for biomass production by radish plants and the concentration of SO2 at which these plants were fumigated. Increased variability as a result of SO2 exposure may have been due to genotypic differences in SO2 resistance among plants, suggesting a route by which the rapid selection of SO2 resistant plant populations may occur in habitats characterized by severe SO2 stress. Increased variability may have also been due to the effect of SO2 on processes controlling phenotypic plasticity of radish growth. Since SO2 affected variability without necessarily affecting mean plant growth, these results also show that examination of variability in the responses of plants to stresses may be equally or more biologically meaningful than sole examination of mean responses. Furthermore, these results show that care must be taken when constructing parametrically derived dose–response models for predicting the effect of SO2 on plants. If it is common for SO2 to increase the amount of variation in plant populations, then parametric statistical functions would be an inappropriate tool for predicting the effect of SO2 on plants.