Biological Sciences, School of


First Advisor

Lawrence Harshman

Second Advisor

Paul Black

Date of this Version



L. Ko., L.G. Harshaman., P.N. Black., Investigation of Lipid Profile Patterns Along Latitude in an Eastern Australian Cline and After Stress Selection in the Laboratory, and Experiments on Stress Tolerance with RNAi Knockdown of Lipid Biosynthesis Genes. University of Nebraska-Lincon, Dec. 2016


A DISSERATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Biological Sciences (Genetics, Cellular, and Molecular Biology), Under the Supervision of Professors Lawrence Harshman and Paul Black, Lincoln, Nebraska: December, 2016

Copyright 2016 Li Ko


Homeoviscous adaptation in membranes and changes in energy storage lipids such as triacylglycerols (TAGs) are the two main themes of adaptation to environmental conditions. Basal patterns of lipid compositional profile of Drosophila melanogaster along a latitudinal gradient in the eastern coast of Australia indicate variations of lipidome associated with climatic patterns. Lipidome data were collected for eight locations along the eastern Australian cline for both sexes in D. melanogaster and D. simulans. To further investigate the relationship between lipidome patterns and environmental factors, we utilized laboratory selection studies using stress conditions including high temperature tolerance, desiccation survival, and chill-coma recovery. Furthermore, to gain insights into possible underlying mechanisms between lipid biosynthesis and stress tolerance, knockdowns using RNA interference (RNAi) for various lipid biosynthesis enzymes were investigated. Observations in geographic patterns in the eastern Australian cline include a higher degree of acclimation in membrane lipids in phosphatidylcholine and phosphatidylethanolamine (PE/PC) ratio for higher latitude populations. There are increases of abundance for polyunsaturated and monounsaturated phospholipids as latitude increased Additionally, D. melanogaster populations originated from the only urban population consist of higher abundances for most lipid classes when compared to all other locations along the latitude. In selection studies, PE/PC ratio did not have any noticeable variations under any of the stress selections. There is an increase of diacylglycerols (DAGs) in heat tolerance selected lines, this finding is consistent with the previous study of physiological response to heat stress. Furthermore, there is the unexpected finding of few responses to selection for chill-coma recovery in the laboratory. For RNAi knocked down studies, there is the surprising finding of chill-coma recovery patterns differ significantly between two isoforms of stearoyl-CoA desaturases knockdowns. Moreover, there are decreases in heat tolerance when TAG synthesis was disrupted. The cline study generates patterns of variation in lipids that suggests adaptation in wild populations. Insight into the evolution of lipid composition was obtained from stress-based laboratory selection experiments. Disruptions of lipid biosynthesis pathways provided insight into the relationship between lipids and stress tolerance.

Advisors: Lawrence Harshman, Paul Black

Included in

Biology Commons