Genetic evidence of dispersal limitation and local adaptation in Samoan reef corals: report on ongoing research
Palumbi S and Oliver T. 2006. Genetic evidence of dispersal limitation and local adaptation in Samoan reef corals: report on ongoing research. Stanford University. Stanford, CA
This research project has used genetic sampling to document the genetic diversity of corals and their dinoflagellate symbionts (Symbiodinium sp.) in three locations in American Samoa. The major goals were to assess these species’ scale of dispersal and quantify American Samoa’s level of genetic diversity relative to other sampled sites in the Pacific. In August of 2004 samples of two species of staghorn corals, Acropora hyacinthus and Acropora cytherea, were collected at three sites in American Samoa. In two of these sites, samples were taken in two distinct habitats: the warmer, less exposed back reef, and the cooler, more exposed fore reef. Analysis of the resulting sequences shows four major findings: 1) genetic distinction between the two morphologically distinct species of coral is low, indicating some level of introgression; 2) Analysis of F-statistics shows strongly that the coral populations from each sampled location are genetically distinct, implying that coral dispersal between localities occurs only rarely, whereas locations in close proximity (back reef vs fore reef) show no genetic distinction for the corals; 3) Symbiodinium sp. shows little evidence of isolation between islands or separate locations within islands, but it shows genetic distinction across habitat boundaries at a single site. This suggests that local selection is playing a larger role in determining Symbiodinium genotype at the local level. This is further supported by evidence of positive selection in the cytochrome b phylogeny, in which Symbiodinium carrying a positively selected type of cytochrome b occur only in warm back reef environments at two sites. 4) Contrary to hypotheses that geographic patterns in genetic diversity should mirror species richness patterns, Symbiodinium genetic diversity housed in sampled Acropora species from American Samoa dwarfs that of Palmyra Atoll and the Philippines.