Patterns of coral–dinoflagellate associations in Acropora: significance of local availability and physiology of Symbiodiniumstrains and host–symbiont selectivity

Like other reef-building corals, members of the genus Acroporaform obligate endosymbioses with dinoflagellates (zooxanthellae) belonging to the genus Symbiodinium. Both Symbiodiniumand its hosts are diverse assemblages, and the relationships between host and algal genotypes are unclear. In this study, we determined phylogenetic relationships between Symbiodiniumisolates from a wide range of Acroporaspecies and plotted the algal genotypes onto a molecular phylogeny of 28 Acroporaspecies, using the same samples for the host and symbiont genotyping. In addition, we performed a preliminary survey of zooxanthella distribution in Acroporaspecies from the central Great Barrier Reef. Three of the four known major zooxanthellae clades were represented in the 168 samples examined, and within the major clade C, three distinct subclades were identified. No evidence was found for coevolution, but several clear patterns of specificity were identified. Moreover, composition of the zooxanthella pool varied among locales and in one host species we found light–related patterns of zooxanthella distribution