DNA Methylation Associated Gene Expression and Calcification Responses to Ocean Acidification in the Eastern Oyster (Crassostrea virginica)

Examination of the molecular mechanisms that regulate trait plasticity in response to environmental stress is fundamental for understanding how species respond to dynamic environments and future global change. Early evidence suggests that DNA methylation acts as an important mediator of phenotypic response to ocean acidification (OA) in marine calcifying species, but these investigations are generally restricted to a few coral species. Furthermore, few studies have evaluated the stability of environmentally induced DNA methylation through time or explicitly studied DNA methylation in the tissues directly involved in calcification. Here, we examined the role of DNA methylation in mediating oyster calcification response to OA over a 3-month period. Oysters were reared under ambient (550 uatm) or elevated (2850 uatm) pCO₂ treatments, and were sampled at 9 and 80 days. Mantle tissue, which is directly involved in oyster calcification, was collected at each timepoint and treatment along with several calcification related traits, including calcification rate and extra-pallial fluid pH. We examine the genome-wide association between environmentally induced DNA methylation and differential gene expression in response to OA, and evaluate the stability of these changes through time. Moreover, we determine whether changes in gene expression correlate with phenotypic response, offering insight into DNA methylation as a mediator of the Eastern oyster calcification response to OA.