| Summary: | Dissertation In this thesis, I investigate the influence of three different factors (environment, chromatin regulation, and genome structure) on gene expression in the evolution and development of the sea urchin species Heliocidaris erythrogramma and Heliocidaris tuberculata. This species pair share a recent common ancestor but exhibit different life history modes, and thus are an excellent model for studying how evolution acts over (relatively) short time scales to influence phenotype. In Chapter 1, I provide an overview of the research that has been conducted on this species pair over the past several decades. I also survey the literature on gene expression in the context of evolution and development, and discuss the various mechanisms that influence gene expression. In Chapter 2, I evaluate how gene expression in H. erythrogramma is affected by exposure to low-pH seawater, in an effort to quantify how this species may be affected by ocean acidification (OA) caused by anthropogenic climate change. It has been previously shown that OA from seawater uptake of rising carbon dioxide emissions impairs development in marine invertebrates, particularly in calcifying species. Plasticity in gene expression is thought to mediate many of these physiological effects, but how these responses change across life history stages remains unclear. The abbreviated lecithotrophic development of the sea urchin Heliocidaris erythrogramma provides a valuable opportunity to analyze gene expression responses across a wide range of life history stages, including the benthic, post-metamorphic juvenile. I measured the transcriptional response to OA in H. erythrogramma at three stages of the life cycle (embryo, larva, and juvenile) in a controlled breeding design. The results reveal a broad range of strikingly stage-specific impacts of OA on transcription, including changes in the number and identity of affected genes; the magnitude, sign, and variance of their expression response; and the developmental trajectory of expression. The ...
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