Changes in DNA methylation in response to heat stress and symbiotic conditions in coral primary polyps

Abstract

The symbiotic relationship between scleractinian corals and dinoflagellates is a cornerstone of coral reef ecosystems. Various mechanisms underlying the adaptability of corals to environmental changes have been studied, but the effects of epigenetic mechanisms (i.e. DNA methylation, DNAm) on heat stress and the symbiotic conditions of corals remain unclear. Moreover, the DNAm patterns relevant to the primary polyp life stage of corals are not known. Hence, we conducted an aquarium factorial experiment to evaluate the effects of symbiotic conditions and temperatures on global DNAm rates in primary Acropora digitifera polyps. The tested conditions included symbiotic (infected with Symbiodinium ITS2 type A3) and aposymbiotic (without Symbiodinium) groups, at either heated (32°C) or ambient (27°C) temperatures. The results indicated that the presence of Symbiodinium within primary A. digitifera polyps significantly decreased basal DNAm rates of the coral holobiont. In addition, the presence of Symbiodinium in the early primary polyp stage increased DNAm in the coral holobiont when exposed to heat stress. These results suggest that the symbiotic relationship between host corals and Symbiodinium is one of the major factors related to global DNAm rate changes in primary A. digitifera polyps.