Background
The authors write that "genetic data are rapidly advancing our understanding of various biological systems including the ecology and evolution of coral-algal symbioses," noting that "each improvement in genetic resolution provides new insights necessary for deducing ecological and evolutionary processes underpinning cnidarian-dinoflagellate symbioses."

What was done
By applying microsatellite markers developed for both host and symbiont, Pettay et al. studied the intra-colony diversity, prevalence and stability of Symbiodinium glynni (type D1) multilocus genotypes that were associated with dense populations of Pocillopora corals at two sites in the Gulf of California, analyzing samples from multiple locations within individual colonies and resampling some of them approximately one year later and again at the end of the study.

What was learned
The four researchers - all from the Biology Department of Pennsylvania State University (USA) - discovered populations of S. glynni comprised of numerous clonal lineages, a large proportion of which genotypes were found in only one colony during one sampling time. Others, however, were common to many colonies, were widely distributed (up to 10 km), and were found to persist in the community for at least three years, all of which observations indicate, as they describe it, that "individual genotypes of host and symbiont switch through time, providing a mechanism for colonies to acquire physiological variants adapted to local environmental conditions."

What it means
According to the Penn State research team, the abundance of sexually recombinant genotypes of S. glynni that they identified, combined with the greater flexibility they found them to possess, could well provide "adaptive mechanisms" for these symbioses that would allow them to "evolve rapidly" in response to "changes in environmental conditions," thereby enabling "particular symbiont genotypes to spread through a host population."

Clearly, we are only just beginning to appreciate the many different ways in which earth's coral-algal symbioses are capable of coping with significant changes in the planet's climate. They are true survivors.