EVOLUTION OF DEVELOPMENT AND GENE EXPRESSION IN DROSOPHILA

Abstract

Evolutionary developmental biology (evo-devo) is the study of trait evolution through variation in development. As early as the modern synthesis, it was recognized that to an understanding of the function of genes during development was critical to understanding evolution as a whole. To that end, modern evo-devo leverages advances in next-generation sequencing to study both the molecular changes that produce interspecific differences in development, as well as the molecular changes associated with evolution in life-history. In this thesis, I use lab-adapted populations selected for early (Fast) and late-life (Slow) fertility to better understand how life-history selection has led to changes in development and gene expression. These replicated selection lines provide a microevolutionary lens of development time and associated changes in gene expression, both at the transcriptome and the individual gene level. I found development time to be highly diverged between Fast and Slow selection treatments, though the differences are not proportionate throughout ontogeny. Furthermore, development was highly convergent, with replicate Fast/Slow lines exhibiting highly similar development time. Preliminary transcriptome analysis through RNA-seq suggests the difference in development could be at least partially due to differential ecdysone regulation. Overall, differences in the developmental transcriptome between Fast and Slow were driven by trans-regulatory divergence – a result consistent with strong selection on a microevolutionary timescale. Lastly, I found no clear evidence that Fast and Slow flies differ greatly in their molecular response to stress, suggesting the heat-shock stress response does not trade-off with divergent life-history in this system. In this thesis, I have shown that the developmental transcriptome can change dramatically on a microevolutionary time-scale. Furthermore, I showed some evidence that developmental evolution can be highly convergent at the phenotypic and global transcriptome level. However, this is not necessarily the case when looking at specific pathways. Overall, my research adds to the growing body of literature on gene expression evolution and provides a foundation for further research into the molecular dynamics of evo-devo changes on microevolutionary time-scales.