Abstract
The application of genomics technology in ecological contexts allows for examination of how rapid environmental change may shape standing molecular level variation and organismal response. We previously demonstrated an effect of oil pollution on gene expression patterns and genetic variation, but not methylation variation, in oil-exposed populations of the foundation salt marsh grass, Spartina alterniflora. Here, we used a reduced representation bisulfite sequencing approach, epigenotyping by sequencing (epiGBS), to examine relationships among DNA sequence, DNA methylation, gene expression, and exposure to oil pollution. With the increased resolution of epiGBS, we document genetic and methylation differentiation between oil-exposed and unexposed populations, and a correlation of genome-wide methylation patterns and gene expression, independent of population genetic structure. Overall, these findings demonstrate that variation in DNA methylation is abundant, responsive, and correlated to gene expression in natural populations, and may represent an important component of the response to environmental stress.