Stability of symbiont genotypes in Indo-Pacific corals: Do they 'switch'?

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A single clone or strain of symbiont often dominates a coral colony. However it is unknown whether genotypes are transient or if they persist over seasons or even years. To test the stability of Symbiodinium within host colonies, we tagged and re-sampled individual corals over 36 months. We use multi-locus genotyping to identify individual symbiont strains and screen for changes in dominant genotype over time.

Mixed genotype associations can occur within a host colony. Therefore, we perform randomized spatial sampling of colonies at a single time point to estimate the frequency of recovering more than one strain of symbiont simultaneously.

We leverage these spatial and temporal sampling efforts to ask the question:

Are the observed changes in symbiont genotype due to a switch or do they reflect recovery of alternate individuals in a mixed association?

Ecological specialization and species diversification of coral symbionts (Symbiodinium)

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Lewis, Allison M., Andie Chan, Todd C. LaJeunesse. "Ecological Specialization and Species Diversification in Shallow Water Coral Endosymbionts in the Western Atlantic" in prep.

Thornhill, Daniel J., Allison M. Lewis, Drew C. Wham, Todd C. Lajeunesse. "Host-Specialist Lineages Dominate the Adaptive Radiation of Reef Coral Endosymbionts." Evolution 68.2 (2014): 352-367. 

Calcification rates of corals with different species of symbiont: a temperature stress experiment

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The coral-Symbiodinium mutualism facilitates sustained rates of calcification required for coral growth, reproduction, and ultimately the construction of the reef ecosystem. However, this partnership is sensitive to environmental stressors; small increases in temperature above normal seasonal means can initiate the breakdown of the association. This is often detrimental to coral health and can lead to colony death. However, temperature stress has variable effects on corals and some individuals do better than others. Much of the variation in host tolerance has been attributed to the association with different symbiont species. 

We compare the performance of corals with alternative Symbiodinium pairings under experimental thermal stress. By exposing coral fragments to increased water temperatures we can measure changes in rates of calcification along with other physiological traits. In addition, we perform reciprocal transplants across reefs with distinct thermal environments. This work allows us to evaluate effects of long-term changes in the external environment on the symbiotic partnership and colony growth.  This research is based out of the Palau International Coral Reef Center.