THE EFFECTS OF NOVEL AND STRESSFUL ENVIRONMENTS ON TRAIT DISTRIBUTION

1. Ecotoxicology seeks to blend the disciplines of toxicology and ecol ogy 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 asses s this risk with little or no consideration of the importance of the v ariation about the mean. 2. Several populations of the Rice Weevil, Si tophilus oryzae, were examined that had been bred on toxic (Yellow Spl it-pea) or non-toxic (Wheat) foodstuffs, or transferred between the tw o. The goal was to establish the effect of stress on the levels of act ivity of two detoxification enzyme systems, esterases and glutathione- S-transferases, and the variation about the mean enzyme activity.3. po pulations kept on their original foodstuffs showed similar levels of e nzyme activity irrespective of whether they bred on toxic or non-toxic foods. When transferred to a novel food stuff there was a small incre ase 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 foodstu ff showed similar levels of variation about the mean, but the variatio n 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 foll owing transfer was largely due to a small number of individuals showin g particularly high levels of enzyme activity. The consequence of the generation of this type of distribution in response to an environmenta l stress is discussed.