UBC Theses and Dissertations
Environmental epigenomics in stickleback : plasticity of DNA methylation and gene expression patterns across time scales Metzger, David Calin Hartley
Epigenetic mechanisms such as DNA methylation have been proposed as an important source of variation that can influence phenotypic plasticity and adaptive evolutionary processes, yet little is known about the role of DNA methylation in an ecological or evolutionary context in vertebrates. In this thesis I examine the effects of the environment and sex on DNA methylation and gene expression patterns in the threespine stickleback fish (Gasterosteus aculeatus), an ecological and evolutionary model system that has been used to study mechanisms involved in the evolution of adaptive phenotypes in novel environments. The dynamic regulation of DNA methylation and gene expression patterns during early developmental periods plays an important role in cell differentiation and establishing adult phenotypes. Here I demonstrate that adult DNA methylation and gene expression patterns are modified in response to the temperature and salinity experienced during development. Similarly, maternal stress can have long-term effects on neurodevelopment and the behavior of offspring that can influence offspring performance and population evolutionary trajectories. I demonstrate that the effects of maternal stress on the brain transcriptome differ between adult male and female stickleback offspring. These sex-specific effects of maternal stress suggest that male and female offspring may respond differently to maternal stress exposure, which could have important implications when assessing the long-term ecological and evolutionary impacts of stress across generations. DNA methylation has also been proposed to play a key role in regulating sexually dimorphic phenotypes and in the evolution of sex determination mechanisms. I compare genome-wide DNA methylation patterns between male and female stickleback and identify apparent differential methylation on the stickleback sex chromosome that correspond to the regions of genetic divergence between the X and Y chromosome. These data provide evidence of a potential role of DNA methylation in the evolution of sex chromosomes in vertebrates. Taken together, these data demonstrate that there is a complex relationship between genetic, epigenetic, and transcriptomic processes that are dynamically regulated during development and in response to environmental cues, and that epigenetic processes may be involved in regulating evolutionary processes.
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