Coral reefs are one of the most diverse and complex ecosystems in the world, sheltering thousands of reef fishes, protecting coastal environments and providing a source of income for local communities. However, these reefs are globally threatened by increasing sea surface temperatures due to global warming. Thermal acclimation has been considered a potential response to help corals withstand high temperatures. Although substantial effort is being made to understand physiological mechanisms of coral stress tolerance and acclimation, virtually nothing is currently known about the mechanisms that might enable their adaptation to the changing climate. One method of understanding these mechanisms may lie in genetic maps and association studies. An association study examines many common genetic variants in different individuals to see if any variant, a single nucleotide polymorphism, (SNP) is associated with a trait. Having a genetic linkage map to complement association studies is an important tool to identify the location of genes that cause variation. Recent genetic maps developed across multiple organisms have provided insights into genome organization, evolution and function. The knowledge gained from these comparative analyses provides hope for coral reef studies. A linkage map and appropriate acclimation data would enable identification of a particular trait loci associated with these and other adaptation-relevant physiological traits. The proposed work hypothesizes that acclimation can be associated with particular traits along a linkage map in the species Orbicella faveolata. Performing a phenotypic and genotypic comparison will allow identification of particular loci that are associated with an increased acclimatize response.
This summer I will be traveling to Bocas del Toro, Panama to work at the Smithsonian Tropical Research Institute and Institute for Tropical Ecology and Conservation. A total of 100 Orbicella faveolata genotypes will be collected off the coast of Bocas del Toro. Corals will be maintained for 4 weeks in control (25C) and elevated acclimation (29C) temperatures. Next, the temperature in the acclimation tank will be gradually increased (acute heat stress to bleaching temperature of 32Â°C). Corals will be monitored to evaluate bleaching response, and the effects of acclimation will be scored as the number of degree heating weeks (DHW) required to induce bleaching. Bleaching responses will be further quantified using qPCR to analyze symbiont cell densities, and spectrophotometric measurements of chlorophyll content to quantify photosynthetic capacities. DNA will be extracted from both control and acclimated treatment corals for genotyping. SNP genotyping will follow the 2b-RAD (Restriction Site-Associated DNA) protocol. Examining SNPs one by one, each locus will be inspected to determine if the bleaching response depends on genotype at that particular locus. Associations between genotype and phenotype will be tested using linear mixed models analysis of variance.