Molecular basis of alcohol adaptation in Drosophilia melanogaster

Anderson, Steven
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The experiments presented in this dissertation are concerned with the study of the evolutionary process of adaptation, concentrating on alcohol adaptation in Drosophila melanogaster as a model system;In Drosophila melanogaster, the ability to exploit alcohol environments is directly related to the biochemical properties of the protein products of the alcohol dehydrogenase locus. The ability to tolerate alcohol correlates well with the enzymatic proprty of V(,max) or the level of ADH cross reacting material (CRM), thereby, organisms that possess high levels of ADH activity or ADH CRM, i.e., Adh('F) homozygotes, are better able to tolerate alcohol stress conditions. Conversely, the ability to utilize alcohol under nonstress conditions correlates well with the property of K(,m) for alcohol, thereby, organisms processing enzyme with a greater affinity for alcohol substrate, i.e., Adh('S) homozygotes, utilize such substrates as well if not better than those possessing enzyme with lesser affinity. Thus, these results demonstrate that fitness relationships between Adh('F) and Adh('S) homozygotes are not constant over all levels of environmental alcohol and suggest that selection and in particular a form of balancing selection is responsible for the maintenance of the Adh polymorphism. In addition, the organism's ability to adapt to secondary alcohol environments has been shown to involve dramatic alterations in the in vivo properties of the ADH protein enabling the organism to limit the production of toxic ketones and, therefore, enhancing its ability to inhabit such environments;In order to understand the regulation of the expression of the Adh gene, ADH activity and ADH CRM levels were examined in adults, throughout the developmental program and as influenced by trans-acting regulatory genes. In all cases, ADH activity levels are generally regulated by quantitative differences or changes in the number of ADH molecules produced rather than by qualitative effects. The proposed mechanism of regulation of these quantitative effects involves the process of ADH turnover, which has been demonstrated in this study to be responsible for CRM level differences in adults via differences in the rate of ADH synthesis;The results presented in this dissertation, therefore, provide not only for an increased understanding of alcohol adaptation in Drosophila melanogaster but also of the process of adaptation in general.