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Symbiont Shuffling in Corals: Is it Rare or Widespread?
Reference
Silverstein, R.N., Correa, A.M.S. and Baker, A.C. 2012. Specificity is rarely absolute in coral-algal symbiosis: implications for coral response to climate change. Proceedings of the Royal Society B 279: 2609-2618.

Background
The authors write that many reef-building corals "have been shown to respond to environmental change by shifting the composition of their algal symbiont (genus Symbiodinium) communities," and they say that "these shifts have been proposed as a potential mechanism by which corals might survive climate stressors, such as increased temperatures." Unfortunately, they note that "conventional molecular methods suggest this adaptive capacity may not be widespread because few (~25%) coral species have been found to associate with multiple Symbiodinium clades." But they hasten to add that "these methods can fail to detect low abundance symbionts (typically less than 10-20% of the total algal symbiont community)."

What was done
To determine whether additional Symbiodinium clades might be present but undetected in various corals using conventional discovery and identification techniques, Silverstein et al. say they "applied a high-resolution, real-time PCR [polymerase chain reaction] assay to survey Symbiodinium (in clades A-D) from 39 species of phylogenetically and geographically diverse scleractinian corals," which survey, according to their report, "included 26 coral species thought to be restricted to hosting a single Symbiodinium clade," which latter corals they refer to as symbiotic specialists.

What was learned
The three U.S. scientists say they "detected at least two Symbiodinium clades (C and D) in at least one sample of all 39 coral species tested," while "all four Symbiodinium clades were detected in over half (54%) of the 26 symbiotic specialist coral species." And they report that, "on average, 68% of all sampled colonies within a given coral species hosted two or more symbiont clades."

What it means
In light of their several discoveries, Silverstein et al. conclude that "the ability to associate with multiple symbiont clades is common in scleractinian (stony) corals," and that in regard to coral-algal symbiosis, "specificity is rarely absolute." And on this basis they express their opinion that "the potential for reef corals to adapt or acclimatize to environmental change via symbiont community shifts may therefore be more phylogenetically widespread than has previously been assumed."

Reviewed 21 November 2012