The relationship between environmental stress and variance

Here we investigate increased variance about mean enzyme activity levels as an alternative biomarker of environmentally induced stress using the rice weevil, Sitophilus oryzae, and the common house mosquito, Culex pipiens. Wh en reared on a. toxic food (yellow split-pea), S. oryzae show very little c hange in mean activity in two detoxifying enzyme systems compared with enzy me activity on a relatively nontoxic food (wheat). When transferred between food types, again there was very little effect on mean enzyme activity, bu t the variance about mean activity increased significantly, especially when the animals were transferred to the more toxic food. Increased variance wa s also shown to persist following long-term genetic selection by the toxica nt. In a pesticide-resistant strain of C. pipiens, a shift in the mean este rase activity was associated with high levels of variance. Furthermore, var iance about the mean was not related to the number of alleles influencing t he detoxifying enzyme system. These results are discussed in relation to th e potential value of the use of variance about the mean as a biomarker alte rnative or complementary to mean enzyme activity.