Characterizing the genetic and morphological responses to a changing environment in Strongylocentrotus purpuratus

Abstract

Anthropogenic climate change has increased the frequency and intensity of marine heatwaves which may broadly impact the health of marine invertebrates. Rising ocean temperatures lead to increases in disease prevalence in marine organisms. Thus, it is critical to understand how marine heatwaves impact the host immune response. Epigenetic modifications such as DNA methylation are a way in which organisms are able to respond to these fluctuations in environmental conditions. However, to understand how organisms utilize these epigenetic modifications in response to environmental stress, we first must identify if and how these patterns change across early life stages under ambient conditions. In Chapter 1, I assessed the role of environmental temperature on the development of larval immune cells in the purple sea urchin (Strongylocentrotus purpuratus). I found that larvae raised in elevated temperatures have more pigment cells and are slightly larger compared to those raised at ambient temperature. Further, significant variation is observed in larval phenotypes among unique genetic crosses, highlighting the importance of genotype in structuring how the immune system develops in the context of the environment. Overall, these results suggest that developmental temperature plays a role in shaping the development of the larval immune system and may adversely affect survival long-term. In Chapter 2, I identified how DNA methylation patterns vary throughout various stages of Strongylocentrotus purpuratus development, and whether genotype influences these methylation patterns, or if they are stage specific. I found both significant differences between DNA methylation patterns between developmental stage and genotype, indicating an interactive relationship between the two. Additionally, I identified differentially methylated CpG sites (DMCpG), with most sites occurring in the intergenic regions of the genome. Additionally, gene-specific DMCpGs were identified, with genes associated with molecular functions, such as genes associated with protein binding and the structural constituent of chromatin, significantly enriched. These results provide novel insights into the variation in DNA methylation profiles between genotypes and developmental stage of an important marine invertebrate. Overall, my thesis provides fundamental, however critical, insights into developmental variability and responses of Strongylocentrotus purpuratus larvae and illuminates the variation in DNA methylation patterns across critical developmental stages. Together, these results show the interplay of genotype and developmental condition on the success of Strongylocentrotus purpuratus.