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The Effects of Population Density and Knock-Downs of Lipid Metabolism Genes on the Expression of Cuticular Hydrocarbons in Droso

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The Effects of Population Density and Knock-Downs of Lipid Metabolism Genes on the Expression of Cuticular Hydrocarbons in Droso The effects of population density and knock-downs of lipid metabolism genes on the expression of cuticular hydrocarbons in Drosophila melanogaster By Adrienne Chu A thesis submitted in conformity with the requirements for the degree of Master of Science Graduate Department of Ecology and Evolutionary Biology University of Toronto © Copyright by Adrienne Chu 2009 The effects of population density and knock-downs lipid metabolism genes on the expression of cuticular hydrocarbons in Drosophila melanogaster 2009 Adrienne Chu Graduate Department of Ecology and Evolutionary Biology University of Toronto Abstract In Drosophila melanogaster, chemical cues in the form of cuticular hydrocarbons play an important role in reproductive behavior. The social and genetic processes that regulate their expression, however, are poorly understood. The social environment has been shown to influence hydrocarbon display. In this study, the effect of population density on the expression of hydrocarbons was evaluated. I demonstrate that the production of certain hydrocarbons depends on the population density in which the animal is reared. Individual hydrocarbons fluctuate in quantity independently from one another but the peaks during a light-dark cycle are static depending mostly on chain length. The regulation of fly hydrocarbons which are density-dependent is shown to be sexually dimorphic. The RNAi knockdown of various putative lipid metabolism genes was also used to study hydrocarbon expression. This study reveals that lipid metabolism genes which are not obvious mediators of HC synthesis influence cuticular hydrocarbon profiles. ii Acknowledgments I would like to gratefully acknowledge all those who helped me with this project as it would not have been possible without them. I would like to thank Joel Levine, Richard Dunbar-Yaffe, and Clement Kent for help with preparation of this manuscript. Throughout my project, Joshua Krupp, Jean-Christophe Billeter, Tony So, Amanda Formosa, and Jade Atallah have been helpful with the gas chromatography work and various other aspects of biology. I thank Dr. Barry Dickson for his gracious provision of RNAi lines. The entire Levine and Sokolowski lab were also extremely helpful throughout my project and defense. Finally, I thank Joel Levine and Marla Sokolowski for their supervision and guidance. iii Table of contents Abstract........................................................................................................................... ii Acknowledgments..................................................................................................... iii Table of contents ........................................................................................................iv Introduction .................................................................................................................. 1 Hydrocarbons (HCs).................................................................................................... 1 Courtship in Drosophila melanogaster...................................................................... 2 Hydrocarbon affects during courtship ......................................................................................... 3 Behaviors shaped by gene and environment ......................................................... 4 Genetic control of CH profiles ....................................................................................................... 5 Environmental influences in hydrocarbon profiles................................................................... 6 Summary ......................................................................................................................... 7 Chapter 1 ........................................................................................................................ 9 Introduction .................................................................................................................. 9 Density influences courtship and mating behaviors......................................... 10 Genetic and behavioral changes due to environment...................................... 12 Genes and density influences behaviors ................................................................ 13 Summary ....................................................................................................................... 14 Material and Methods............................................................................................. 14 Rearing conditions............................................................................................................ 14 Extraction of cuticular hydrocarbons....................................................................... 15 GC Chromatography ........................................................................................................ 16 Statistical analysis ............................................................................................................ 16 Results............................................................................................................................ 17 Hydrocarbon expression changes with density ................................................... 17 Female hydrocarbons have diurnal variations..................................................... 25 Desat1 mutants males and females differ in density regulation ................ 29 Discussion..................................................................................................................... 29 Chapter Two ................................................................................................................ 35 Introduction ................................................................................................................ 35 Genetic Screens.................................................................................................................. 35 The mechanism of RNA interference (RNAi).......................................................... 36 Creating RNAi screening in Drosophila ................................................................... 38 iv Hydrocarbon synthesis ........................................................................................... 38 RNAi screening........................................................................................................... 40 Summary............................................................................................................................... 41 Material and Methods............................................................................................. 41 Rearing conditions............................................................................................................ 41 Extraction of cuticular hydrocarbons....................................................................... 42 GC Chromatography ........................................................................................................ 43 Courtship Experiment ..................................................................................................... 43 Statistical analysis ............................................................................................................ 44 Results............................................................................................................................ 44 Hydrocarbon profile of male and female RNAi lines......................................... 44 Courtship of RNAi lines .................................................................................................. 49 Discussion..................................................................................................................... 49 General Discussion ................................................................................................... 54 Appendix A .................................................................................................................. 58 Appendix B................................................................................................................... 63 References.................................................................................................................... 76 v 1 Introduction Endogenous chemical signals contribute to reproduction, survival and group activities in insects and other animals. I am interested in the social and genetic processes that regulate these chemical signals in Drosophila melanogaster. These chemical displays are not simply determined by gene expression or driven by environmental conditions but instead they define a response to gene-environment interactions and contribute to the social experience of each fly. My thesis consists of two studies that addressed the regulation of hydrocarbons in the fruit fly. The first study emphasized effects of environmental conditions. In particular, I evaluated the effects of density on the expression of chemical signals. In addition, I examined how group density interacted with light-dark cycles to control hydrocarbon levels on the cuticle of females. In the second study I evaluated cuticular hydrocarbon expression in courtship mutants. These mutants were identified by the Dickson laboratory in an RNA interference screen for genetic loci that affected courtship. It is important to appreciate the past and recent research into hydrocarbons as it pertains directly to the work presented here. In addition, a cursory understanding of courtship behavior of D. melanogaster is needed.
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