Abstract
Catastrophic events offer unique opportunities to study rapid population response to stress in natural settings. In concert with genetic variation, epigenetic mechanisms may allow populations to persist through severe environmental challenges. In 2010, the Deepwater Horizon oil spill devastated large portions of the coastline along the Gulf of Mexico. However, the foundational salt marsh grass, Spartina alterniflora, showed high resilience to this strong environmental disturbance. Following the spill, we simultaneously examined the genetic and epigenetic structure of recovering populations of S. alterniflora to oil exposure. We quantified genetic and DNA methylation variation using amplified fragment length polymorphism and methylation sensitive fragment length polymorphism (MS‐AFLP) to test the hypothesis that response to oil exposure in S. alterniflora resulted in genetically and epigenetically based population differentiation. We found high genetic and epigenetic variation within and among sites and found significant genetic differentiation between contaminated and uncontaminated sites, which may reflect nonrandom mortality in response to oil exposure. Additionally, despite a lack of genomewide patterns in DNA methylation between contaminated and uncontaminated sites, we found five MS‐AFLP loci (12% of polymorphic MS‐AFLP loci) that were correlated with oil exposure. Overall, our findings support genetically based differentiation correlated with exposure to the oil spill in this system, but also suggest a potential role for epigenetic mechanisms in population differentiation.
Highlights
Ecological theory predicts that adaptation to local conditions can result when populations harbor heritable phenotypic variation for traits that increase tolerance to local conditions
We simultaneously examined genetic and epigenetic patterns in populations of S. alterniflora along the Gulf Coast that were exposed to heavy oiling following the Deepwater Horizon (DWH) oil spill (“heavy” sensu Lin et al, 2016; Nixon et al, 2016)
Redundancy analysis shows that overall patterns of methylation were not significantly correlated with oil exposure when controlling for the effects of genetic variation, which suggests that patterns of DNA methylation are explained almost entirely by genetic effects
Summary
Variation in DNA methylation is correlated with habitat type in mangroves (Lira-Medeiros et al, 2010) and knotweed (Richards et al, 2012), herbivory in viola (Herrera & Bazaga, 2010), and climate in natural accessions of Arabidopsis thaliana (Keller et al, 2016) This association between DNA methylation and plant ecology may reflect the modulation of gene expression (Bewick et al, 2016; Zilberman, Gehring, Tran, Ballinger, & Henikoff, 2007) or recombination rates (Mirouze et al, 2012), the release of transposable elements (Dowen et al, 2012), or other regulatory processes in response to environmental conditions in addition to covariance with genetic structure. We anticipated a concurrent but stronger epigenetic signature of oil exposure, given its reflection of gene expression and physiological response to environmental stimuli (Dowen et al, 2012; Verhoeven, Jansen, et al, 2010; Verhoeven, Van Dijk, et al 2010; Xie et al, 2015)
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