Exploring Plasticity-Associated Traits Across an Intertidal Gradient: Variation in Adult DNA Methylation and Maternal Effects in California Mussels (Mytilus californianus)

Understanding (i) epigenetic mechanisms, (ii) transgenerational plasticity (TGP), and (iii) their intersection is important in determining how organisms will respond to rapid environmental change. Epigenetic modifications of DNA, such as DNA methylation, are thought to be processes that could drive rapid changes in organismal tolerance. In addition, maternal effects can transduce tolerances to progeny. The rocky intertidal zone is an ideal place to test these hypotheses due to the steep environmental stress gradients over small spatial scales. Specifically, natural variation in temperature experienced by sessile California mussels (Mytilus californianus) along the intertidal zone make them ideal candidates for determining how environmental conditions influence DNA methylation signatures. In this study, we assessed differences in levels of total DNA methylation in gill tissue from adult M. californianus inhabiting high and low zones of the rocky intertidal zone. Mean levels of DNA methylation did not differ between mussels from the high versus the low intertidal zone (p=0.224). However, mussels from the high zone had significantly higher variation in methylation levels (p<0.05). Here, dynamics in epigenetic signatures correlated with the greater and more variable temperatures conditions experienced by mussels in the high intertidal zone. In addition, in a similar experiment, we examined if long-term thermal conditioning of adults influenced progeny by comparing differences in maternal provisioning from high and low mussels. Egg size was significantly larger for mussels from the high intertidal zone as compared to the low (p<0.05). We plan to extend these preliminary findings with measurements of methylation to better determine the role of epigenetics mechanisms in TGP. Findings from this research will provide a better understanding of the role of DNA methylation in the thermal plasticity of California mussels, and more broadly, the role of epigenetics in natural populations.