SANTOS, SR; GUTIERREZ-RODRIGUEZ, C; LASKER, HR; COFFROTH, MA*; University of Arizona, Tucson; University at Buffalo, NY; University at Buffalo, NY; University at Buffalo, NY: Microsatellites detect high levels of genetic variation and population structure in dinoflagellates symbiotic with the Caribbean gorgonian Pseudopterogorgia elisabethae

Invertebrate-Symbiodinium associations are a common occurrence in marine environments. While a number of studies have documented the diversity within this genus of symbiotic dinoflagellates, little is known about their population structure. In this study, we elucidate the population structure of Symbiodinium hosted by the Caribbean gorgonian Pseudopterogorgia elisabethae using microsatellite markers. P. elisabethae colonies were sampled from 12 populations across the Bahamas and their algal symbionts genotyped at 2 polymorphic microsatellite loci. We identified 23 unique genotypes belonging to Symbiodinium clade B associated with P. elisabethae. Most P. elisabethae colonies harbored only a single algal genotype, but in rare instances, colonies simultaneously harbored multiple algal genotypes. At most sites, the majority of gorgonian colonies harbored the same algal genotype and this genotype was either unique for that P. elisabethae population or found infrequently in other populations. This distribution of algal genotypes resulted in statistically significant population differentiation in 62 of 66 pairwise comparisons. Although clonal propagation may maintain these distinct Symbiodinium populations, tests of linkage disequilibrium suggest that the Symbiodinium populations associated with P. elisabethae also undergo recombination. Although Symbiodinium populations have been thought to be cosmopolitan, our data demonstrate that Symbiodinium genotypes are not as widespread as previously thought.