\u3ci\u3eDrosophila melanogaster\u3c/i\u3e Starvation Resistance: A Quantitative Genetic and Physiological Investigation in Relationship to Life History Traits

Starvation resistance is an important trait for insect survival. The studies presented in this dissertation investigated starvation resistance using Drosophila melanogaster in terms of genetic correlations, physiological mechanisms and evolutionary trajectory. Whether increase of starvation resistance can also extend lifespan is a controversial issue in D. melanogaster. Quantitative trait locus (QTL) mapping can provide good evidence concerning this controversial problem. A QTL analysis was conducted to test the correlation between starvation resistance and longevity using a set of recombination inbred lines (RILs) from a natural population of D. melanogaster. We found the QTL effects were consistent for sexes and environments. Importantly, one QTL region was associated with increased starvation resistance and increased longevity. This QTL region provides support for the hypothesis that starvation resistance and longevity may have a common genetic basis as a result of coupled evolution of the two traits. The same RILs derived from a natural population were used to investigate natural genetic variation for lipid abundance and starvation resistance. QTLs for lipid proportion (lipid abundance normalized by weight or protein abundance) were present on all chromosomes; a lipid proportion QTL on the third chromosome correlated with a QTL for starvation resistance observed in a previous study using the same set of RILs, suggesting it might underlie both traits. The laboratory selection lines are usually beneficial for us to compare against the physiological changes under starvation. We have been doing laboratory selection on starvation resistance for over 20 generations. Selected flies in our laboratory had similar traits that other papers had reported: lower early fecundity, higher lipid contents, and heavier mass, compared to control populations. Besides, we found our starvation-selected lines had longer lifespan, which not all laboratory starvation selection discovered. The idea that starvation resistant flies can use energy efficiently under stressful situation was also tested. The results showed that starvation resistant flies can maintain stable energy under stressful situations through physiological adjustment. Differential lipid (triglycerides and phospholipids) abundances were measured in starvation selected lines and control lines to examine the Y model, indicating differential allocation of limited internal resources. We identified the physiological and genetically causes of life-history variation and trade-off in starvation resistance and cost of reproduction in D. melanogaster by differential lipid allocation. Advisor: Lawrence G. Harshma