Patterns of whole genome DNA methylation in Symbiodiniaceae are shaped by phylogenetic
and ecological diversity

Coral photosymbionts in the dinoflagellate family Symbiodiniaceae display extensive molecular,
ecological, and physiological diversity. Epigenetic factors such as DNA methylation are variable among symbiont species; this variation may influence coral colony health. However, it is
unknown whether methylation patterns among Symbiodiniaceae are driven by evolutionary
history and/or ecological factors. Here, we quantified whole genome DNA methylation among
phylogenetically diverse Symbiodiniaceae using an ELISA-like assay. To explore the influence of
evolutionary history, we reared cultures of 26 species under identical conditions and estimated
phylogenetic signal (the extent to which related species exhibit similar methylation due to
shared evolutionary history) using multiple indices. To explore the influence of ecological state, we will introduce three cultured species to symbiont-free sea anemone polyps and compare their methylation levels within and without a host. Overall, methylation levels were high among
Symbiodiniaceae (1-29.3%) compared to other algae and displayed moderate to strong
phylogenetic signal. Additionally, we predict algal methylation will be elevated when cells are
engaged in symbiosis with a host compared to the free-living state. We anticipate our results
will indicate that Symbiodiniaceae whole genome DNA methylation patterns are both
phylogenetically and ecologically determined.