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Symbiodinium Diversity in Soritid Foraminfera
Reference
Pochon, X., Garcia-Cuetos, L., Baker, A.C., Castella, E. and Pawlowski, J. 2007. One-year survey of a single Micronesian reef reveals extraordinarily rich diversity of Symbiodinium types in soritid foraminifera. Coral Reefs 26: 867-882.

Background
The authors note that "recent molecular studies of symbiotic dinoflagellates (genus Symbiodinium) from a wide array of invertebrate hosts have revealed exceptional fine-scale symbiont diversity whose distribution among hosts, regions and environments exhibits significant biogeographic, ecological and evolutionary patterns," and we note that this reservoir of symbiont diversity can be drawn upon by the phenomenon of symbiont shuffling to help the vast array of invertebrate hosts, including corals, to rapidly adjust to changing environmental circumstances, such as those that may accompany any future global warming.

What was done
In a further assessment of the size of the symbiont diversity reservoir, which Pochon et al. describe as "the most targeted and exhaustive sampling effort ever undertaken for any group of Symbiodinium-bearing hosts," the five researchers collected more than 1,000 soritid specimens over a depth of 40 meters on a single reef at "Gun Beach" on the island of Guam, Micronesia, throughout the course of an entire year, which they then studied by means of molecular techniques to identify unique internal transcribed spacer-2 (ITS-2) types of ribosomal DNA (rDNA).

What was learned
Pochon et al. identified 61 unique symbiont types in only three soritid host genera, making the Guam Symbiodinium assemblage the most diverse derived to date from a single reef. In addition, they report that "the majority of mixed genotypes observed during this survey were usually harbored by the smallest hosts."

What it means
The Swiss and U.S. researchers note that symbiont diversity has been suggested to provide "considerable physiological flexibility for the host in question, allowing it to respond to changes in environmental conditions," and because greater Symbiodinium diversity was typically observed in the smallest hosts in their study, they speculate that "juvenile foraminifera may be better able to switch or shuffle heterogeneous symbiont communities than adults," so that as juveniles grow, "their symbiont communities become 'optimized' for the prevailing environmental conditions," suggesting that this phenomenon "may be a key element in the continued evolutionary success of these protests in coral reef ecosystems worldwide."

Reviewed 23 April 2008