Significant population methylation divergence and local environmental influence in an invasive ascidian Ciona intestinalis at fine geographical scales

Biological invasion provides a promising system for studying rapid environmental accommodation and adaptation in the wild. Mounting evidence indicates that epigenetic modifications such as DNA methylation play crucial roles in rapid local accommodation and adaptation. Thus, we hypothesize that different local environments can trigger methylation divergence among marine invasive populations at fine geographical scales. In this study, we examined population methylation patterns in the invasive ascidian, Ciona intestinalis, along the Atlantic coast of Nova Scotia, Canada, where significant temperature differences exist at defined locations along the coast. Using the methylation-sensitive amplification polymorphism (MSAP) technique, we observed a high level of intra- and inter-population diversity, as well as significant population methylation differentiation. We identified a correlation between local environments and methylation patterns, and further consistently recovered 14 temperature-related subepiloci by using multiple analyses. All these results demonstrate a substantial role of temperature in shaping population methylation patterns and an epigenetic response to environmental changes during range expansions. The complex fine-scale methylation structures among populations of C. intestinalis observed in this study suggest that multiple biotic and abiotic factors, as well as their interactions, should be further investigated to reveal epigenetic mechanisms of local accommodation and adaptation during biological invasions in marine ecosystems.