Project description:Coral reefs are declining globally. Temperature anomalies disrupt coral-algal symbioses at the molecular level, causing bleaching and mortality events. In terrestrial mutualisms, diversity in pairings of host and symbiont individuals (genotypes) results in ecologically and evolutionarily relevant stress response differences. The extent to which such intraspecific diversity provides functional variation in coral-algal systems is unknown. Here we assessed functional diversity among unique pairings of coral and algal individuals (holobionts). We targeted six genetically distinct Acropora palmata coral colonies that all associated with a single, clonal Symbiodinium ‘fitti’ strain in a natural common garden. No other species of algae or other strains of S. ‘fitti’ could be detected in host tissues. When colony branches were experimentally exposed to cold stress, host genotype influenced the photochemical efficiency of the symbiont strain, buffering the stress response to varying degrees. Gene expression differences among host individuals with buffered vs. non-buffered symbiont responses included biochemical pathways that mediate iron availability and oxygen stress signaling—critical components of molecular interactions with photosynthetic symbionts. Spawning patterns among hosts reflected symbiont performance differences under stress. These data are some of the first to indicate that genetic interactions below the species level affect coral holobiont performance. Intraspecific diversity serves as an important but overlooked source of physiological variation in this system, contributing raw material available to natural selection. Note: in the final publication, only ambient and cold treatments are discussed, but there was an additional hot treatment for each genotype at 34C. Most colonies expired after 6 hours, so PAM data could not be collected. The microarray data from 3.5 hours are included here.
Project description:Publication Abstract: As climate changes, sea surface temperature anomalies that negatively impact coral reef organisms continue to increase in frequency and intensity. Yet, despite widespread coral mortality, genetic diversity remains high even in those coral species listed as threatened. While this is good news in many ways it presents a challenge for the development of biomarkers that can identify resilient or vulnerable genotypes. Taking advantage of three coral restoration nurseries in Florida that serve as long-term common garden experiments, we exposed over thirty genetically distinct Acropora cervicornis colonies to hot and cold temperature shocks seasonally and measured pooled gene expression responses using RNAseq. Targeting a subset of twenty genes, we designed a high-throughput qPCR array to quantify expression in all individuals separately under each treatment with the goal of identifying predictive and/or diagnostic thermal stress biomarkers. We observed extensive transcriptional variation in the population, suggesting abundant raw material is available for adaptation via natural selection. However, this high variation made it difficult to correlate gene expression changes with colony performance metrics such as growth, mortality, and bleaching susceptibility. Nevertheless, we identified several promising diagnostic biomarkers for acute thermal stress that may improve coral restoration and climate change mitigation efforts in the future.
Project description:Florida’s coral reefs are currently experiencing a multi-year disease-related mortality event, that has resulted in massive die-offs in multiple coral species. Approximately 21 species of coral, including both Endangered Species Act-listed and the primary reef-building species, have displayed tissue loss lesions which often result in whole colony mortality [Stony Coral Tissue Loss Disease (SCTLD)]. Determining the causative agent(s) of coral disease relies on a multidisciplinary approach since the causation may be a combination of abiotic, microbial or viral agents. Metaproteomics was used to survey changes in the molecular landscape in the coral holobiont with the goal of providing useful information not only in diagnosis, but for prediction and prognosis. Specifically, in the case of SCTLD, defining molecular changes in the coral holobiont will help define disease progression and aid in identifying the causative agent by clearly defining traits of disease progression shared across affected species. Using samples from nine coral species (46 samples total; those appearing healthy, n = 23, and diseased, n = 23), analysis of the coral and its associated microbiome were performed using bottom-up proteomics. Ongoing analysis (including improving coral holobiont genome-based search space) will demonstrate the utility of this approach and help define improved future experiments.
Project description:Short title: Coral Meta-Transcriptomics Reveal Pollutant Stress Background: Corals represent symbiotic meta-organisms that require harmonization among the coral animal, photosynthetic zooxanthellae and associated microbes to survive environmental stresses. We investigated integrated-responses among coral and zooxanthellae in the scleractinian coral Acropora formosa in response to an emerging marine pollutant, the munitions constituent, 1,3,5-trinitro-1,3,5 triazine (RDX; 5 day exposures to 0 (control), 0.5, 0.9, 1.8, 3.7, and 7.2 mg/L, measured in seawater). Results: RDX accumulated readily in coral soft tissues with bioconcentration factors ranging from 1.1 to 1.5). Next-generation sequencing of a normalized meta-transcriptomic library developed for the eukaryotic components of the A. formosa coral holobiont was leveraged to conduct microarray-based global transcript expression analysis of integrated coral / zooxanthellae responses to the RDX exposure. Total differentially expressed transcripts (DET) increased with increasing RDX exposure concentrations as did the proportion of zooxanthellae DET relative to the coral animal. Transcriptional responses in the coral demonstrated higher sensitivity to RDX compared to zooxanthellae where increased expression of gene transcripts coding xenobiotic detoxification mechanisms (ie. cytochrome P450 and UDP glucuronosyltransferase 2) were initiated at the lowest exposure concentration. Increased expression of these detoxification mechanisms was sustained at higher RDX concentrations as well as production of a physical barrier to exposure through a 40% increase in mucocyte density at the maximum RDX exposure. At and above the 1.8 mg/L exposure concentration, DET coding for genes involved in central energy metabolism, including photosynthesis, glycolysis and electron-transport functions, were decreased in zooxanthellae although preliminary data indicated that zooxanthellae densities were not affected. In contrast, significantly increased transcript expression for genes involved in cellular energy production including glycolysis and electron-transport pathways was observed in the coral animal. Conclusions: Transcriptional network analysis for central energy metabolism demonstrated highly correlated responses to RDX among the coral animal and zooxanthellae indicative of potential compensatory responses to lost photosynthetic potential within the holobiont. These observations underscore the potential for complex integrated responses to RDX exposure among species comprising the coral holobiont and highlight the need to understand holobiont-species interactions to accurately assess pollutant impacts.