Determining the Role of Epigenetics in the Variations of Thermal Tolerance and Plasticity Between Populations of Tigriopus californicus

Changing ocean conditions such as increased temperature and pCO2will have major consequences on marine ecosystems. These conditions can act as a driving selective pressure and negatively affect the fitness of marine organisms. Phenotypic plasticity, the capacity of a single genotype to exhibit variable phenotypes across different environments, can drive acclimatory response to such pressures. Plasticity can vary between different species and populations.However, how these differences evolve is still poorly understood. Plasticity is partially attributed toepigenetic processes such as DNA methylation, a cellular-level process that regulates the quantity and variability of a gene’s expression. Thus, epigenetic pathways may have diverged among populations with differences in plasticity. The intertidal copepod Tigriopus californicusdisplays varying levels of (i) thermal tolerance and (ii) plasticity in thermal tolerance between populations, with both tolerance and plasticity increasing as latitude decreases. We exposed two populations of T. californicus collected from different latitudes to acute heat stress and measured their subsequent thermal tolerance, respiration rate, and froze replicates for downstream for measuring DNA methyltransferase activity to determine the correlation between epigenetic activity and changes in plasticity. We found that populations from Pt. Dume (southern) and Santa Cruz (northern) showed significant differences in both body size and thermal tolerance, (2) neither population displayed changes in thermal tolerance after heat stress and (3) respiration rates varied as a function sex, temperature, and population. Analysis of methyltransferase activity within this experiment may provide a better understanding of the role of epigenetics in adaptational plasticit