Author: ["E. J. Howells","V. H. Beltran","N. W. Larsen","L. K. Bay","B. L. Willis","M. J. H. van Oppen"]
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Abstract
An analysis shows that the coral endosymbiont Symbiodinium—a dinoflagellate genus underpinning the ecological and evolutionary success of reef corals—can adapt to local thermal regimes, thereby shaping the fitness of coral hosts. This may explain why many corals show fidelity for single Symbiodinium types over wide thermal ranges. Coral thermal tolerance is strongly influenced by the identity of obligate photosymbionts, which encompass numerous types belonging to the dinoflagellate genus Symbiodinium1. Physiological advantages achieved by partnering with functionally diverse symbionts2,3,4 have been assumed to be available only to corals that can form associations with multiple Symbiodinium types. Functional variation among populations of the same type of Symbiodinium has been overlooked, despite local adaptation being feasible because of large population sizes5,6, genetic isolation7,8 and short asexual generation times9. Here we demonstrate divergent thermal tolerance in a generalist Symbiodinium type from two different thermal environments. Symbiodinium from the warmer reef maintained greater photo-chemical performance and survivorship when exposed to an elevated temperature of 32 °C, both in symbiosis and in culture. Juvenile corals associated with Symbiodinium from the warmer reef grew rapidly when exposed to 32 °C, yet underwent bleaching and tissue death when associated with Symbiodinium from the cooler reef. These results demonstrate that Symbiodinium types can adapt to local differences in thermal climate and that this adaptation shapes the fitness of coral hosts. If Symbiodinium populations are able to further adapt to increases in temperature at the pace at which ocean climates warm, they may assist corals to increase their thermal tolerance and persist into the future.Cite this article
Howells, E., Beltran, V., Larsen, N. et al. Coral thermal tolerance shaped by local adaptation of photosymbionts. Nature Clim Change 2, 116–120 (2012). https://doi.org/10.1038/nclimate1330 