The effects of novel and stressful environments on trait distribution

1. Ecotoxicology seeks to blend the disciplines of toxicology and ecology to provide a means of assessing the risk that natural populations of organisms are exposed to when confronted by an environmental stress, such as a pollutant. The LC₅₀ of a compound is usually used to assess this risk with little or no consideration of the importance of the variation about the mean.
2. Several populations of the Rice Weevil, Sitophilus oryzae , were examined that had been bred on toxic (Yellow Split-pea) or non-toxic (Wheat) foodstuffs, or transferred between the two. The goal was to establish the effect of stress on the levels of activity of two detoxification enzyme systems, esterases and glutathione- S -transferases, and the variation about the mean enzyme activity.
3. Populations kept on their original foodstuffs showed similar levels of enzyme activity irrespective of whether they bred on toxic or non-toxic foods. When transferred to a novel food stuff there was a small increase in enzyme activity, perhaps reflecting induction, but transfer to a more toxic food did not produce a greater increase in activity than transfer to a non-toxic food.
4. Populations on their original foodstuff showed similar levels of variation about the mean, but the variation about the mean increased considerably following transfer to a novel food. There was some evidence that this increase was greater when the transfer was to the more toxic food.
5. The increase in variation following transfer was largely due to a small number of individuals showing particularly high levels of enzyme activity. The consequence of the generation of this type of distribution in response to an environmental stress is discussed.