The transcriptional regulation of plastic responses to stress in Drosophila melanogaster

2017-04-05T00:38:04Z (GMT) by Allannah Clemson
Climate change is enhancing the fluctuations in weather conditions including increasing temperature and precipitation variability. This imposes a great deal of stress on terrestrial arthropods such as <i>Drosophila</i>, which rely on the environment to maintain homeostasis. To counteract these deleterious effects, phenotypic plasticity can enable species to maintain their optimal fitness and allow them to persist in an otherwise harmful environment. While some work has focused on understanding the extent to which species can use phenotypic plasticity to mediate climatic change, little progress has been made on elucidating the molecular mechanisms facilitating this adaptive strategy. Therefore, this thesis aims to address this deficit and attempts to link plastic responses at the transcript level to plastic responses at the quantitative trait level.<br><br>    My goal was first to understand the extent to which two populations of <i>D. melanogaster</i> from ends of the east Australian latitudinal cline could elicit plastic responses when exposed to different developmental temperatures and humidity conditions. In total, I measured six quantitative traits; fecundity, body size, viability, heat and cold tolerance were examined on flies developed at six different temperatures (18<sup>o</sup>C – 30<sup>o</sup>C), and desiccation resistance on flies exposed to different stress pre-treatments. All six quantitative traits were plastic, and all, except viability, differed between the two populations. However, only two (fecundity and desiccation resistance) showed evidence for geographic variation in plasticity.<br> <br>    I then examined a subset of candidate genes for thermal tolerance and desiccation resistance to characterise their expression profiles and determine the extent to which they mirrored the phenotypic results. Despite the expression patterns of many of the 23 thermal candidate genes and one of the 12 desiccation resistance candidate genes differing between the populations, I did not find evidence for genetic variation maintaining expression plasticity. However, given the complex physiological architecture of desiccation resistance and, to a lesser extent, heat tolerance, my results provide the first insights into the molecular basis of desiccation plasticity, and make a significant contribution to understanding the molecular mechanisms underpinning environmental adaptation.