Genetic variations within Symbiodinium clade C among zooxanthellate corals (Scleractinia) in the temperate zone of Japan

Abstract

In a recent study most of the temperate-living corals were found to harbor stress-sensitive Symbiodinium clade C, which is common in the tropical zone. In this study, we investigated the genetic variations within Symbiodinium clade C among corals living in temperate waters of Japan (17 genera; 26 species) using rDNA internal transcribed spacers (ITSs) to clarify the genetic differences between climatic zones. We also focused on two widespread coral species, Acropora hyacinthus and Pocillopora damicornis, to compare the genetic differences of Symbiodinium clade C between subtropical and temperate regions. We found multiple haplotypes of Symbiodinium ITSs in clade C, which formed nine subclades. Our data indicate that five genera (Acropora, Cyphastrea, Stylocoeniella, Porites, Pocillopora) contained host-specific Symbiodinium, while members of the family Faviidae and others contained several Symbiodinium ITS haplotypes from two or three subclades. A comparative analysis using Acropora and Pocillopora also revealed that the temperate zone coral population formed a single subclade of Symbiodinium clade C that was genetically isolated from those of subtropical populations. In summary, the majority of corals living in temperate waters of Japan, such as faviid corals, have several ITS haplotypes which possibly are utilized as an opportunistic survival strategy under severe environmental conditions, whereas Acropora and Pocillopora at the very least harbor temperate zone-specific Symbiodinium.