Corals may be adapted to smaller ecological niches

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Populations of a single species of coral on a reef are more highly structured than previously supposed, according to research published in a recent issue of the journal PLoS ONE.

This implies that coral are adapted to smaller ecological niches and that the genetic diversity of the same species of coral within a reef is far greater than previously thought. 

Pim Bongaerts and colleagues studied the genetic structure of the Bird's nest coral (Seriatopora hystrix) across a single reef, and were surprised to find that the coral, which is extremely abundant, actually consists of various genetically unique strains that are each associated with a particular depth range on a coral reef.

The authors sampled coral from three adjacent reef habitats (at depths of 2, 6 and 27 metres) at three locations on the Great Barrier Reef.  The populations were assessed for genetic structure using a combination of mitochondrial (putative control region) and nuclear (three microsatellites) markers for the coral host, and the ITS2 region of the ribosomal DNA for the algal symbionts (Symbiodinium). 

The authors found strong genetic partitioning between the three different habitat types and a strong coupling of host and symbiont genotypes.  In contrast, they found no genetic differentiation among the same habitat types at different locations.

This structuring at particular reef environments rather than geographic location is consistent with divergence occurring through ecologically based selection.  Ecologically-driven speciation is a well-known process in rainforests, but this study provides compelling evidence that this phenomenon may also be an important driver for diversification in reef-building corals.

The genetic isolation of the coral living in different habitats within the same reef also has implications for reef conservation, as the findings of this study dispel the notion that corals from greater depths can be used to regenerate coral from shallower areas damaged by pollution, bleaching or other climate events.

For more information, see the paper: Bongaerts, P, C Riginos, T Ridgway, EM Sampayo, MJH van Oppen, N Englebert, F Vermeulen and O Hoegh-Guldberg (2010) Genetic divergence across habitats in the widespread coral Seriatopora hystrix and its associated Symbiodinium. PLoS ONE 5, e10871, doi:10.1371/journal.pone.0010871