Project description:The potential to adapt to a changing climate depends in part upon the standing genetic variation present in wild populations. In corals, the dispersive larval phase is particularly vulnerable to the effects of environmental stress. Larval survival and response to stress during dispersal and settlement will play a key role in the persistence of coral populations. To test the hypothesis that larval transcription profiles reflect population specific responses to thermal stress, symbiont-free gametes of the scleractinian coral Montastraea faveolata were collected from Florida and Mexico and raised under normal and elevated temperatures. These populations have been shown to exchange larvae frequently enough to prevent significant differentiation of neutral loci. Differences among thousands of genes were simultaneously characterized using microarrays, allowing investigation of gene expression patterns among wild populations under stressful environmental conditions. Results show site-specific signatures of gene expression in larvae of a reef-building coral from different parts of its range (despite low genetic divergence), and reveal both local and general components of stress response during later stages of larval development. These results provide evidence of site-specific variation in the face of gene flow, which may represent functional genetic variation in different subpopulations, and support the idea that coral host genomes may indeed house the adaptive potential needed to deal with changing environmental conditions. The experimental setup followed a reference design, i.e. all samples were hybridized against the same pool made up of equal amounts of RNA from all samples collected in Mexico. For samples from Mexico we used three technical replicates for each treatment temperature, for samples from Florida three biological replicates were used for each treatment temperature, except for the high temperature samples at day two where only two replicates were available due to high larval mortality at that temperature. Common reference samples were labeled with Cy3, temperature treatment samples with Cy5. Microarrays for M. faveolata contained 1,314 coding sequences, of which 43% had functional annotations as determined by homology to known genes.

Project description:Projected elevation of seawater temperatures poses a threat to the reproductive success of Caribbean reef-building corals that have planktonic development during the warmest months of the year. This study examined the transcriptomic changes that occurred during embryonic and larval development of the elkhorn coral, Acropora palmata, at a non-stressful temperature (28Â°C) and further assessed the effects of two elevated temperatures (30Â°C and 31.5Â°C) on these expression patterns. Using cDNA microarrays, we compared expression levels of 2,051 genes from early embryos and larvae at multiple developmental stages (including pre-blastula, blastula, gastrula, and planula stages) at each of the three temperatures. At 12 hours post-fertilization in 28Â°C treatments, genes involved in cell replication/cell division and transcription were up-regulated in A. palmata embryos, followed by a reduction in expression of these genes during later growth stages. From 24.5 to 131 hours post-fertilization at 28Â°C, A. palmata altered its transcriptome by up-regulating genes involved in protein synthesis and metabolism. Temperatures of 30Â°C and 31.5Â°C caused major changes to the A. palmata embryonic transcriptomes, particularly in the samples from 24.5 hpf post-fertilization, characterized by down-regulation of numerous genes involved in cell replication/cell division, metabolism, cytoskeleton, and transcription, while heat shock genes were up-regulated compared to 28Â°C treatments. These results suggest that increased temperature may cause a breakdown in proper gene expression during development in A. palmata by down-regulation of genes involved in essential cellular processes, which may lead to the abnormal development and reduced survivorship documented in other studies. Our experimental setup followed a reference design where all samples were hybridized against the same pool made up of equal amounts of RNA from all samples in the experiment. Biological duplicate samples were used for each temperature at each developmental time period. Common reference samples were labeled with Cy3 dye, while temperature samples were labeled with Cy5 dye. Microarrays for A. palmata contained 2,051 coding sequences, of which 54.3% had functional annotations as determined by homology to known genes.

Project description:Mesophotic coral reefs have been proposed as refugia for corals, providing shelter and larval propagules for shallow-water reefs that are disproportionately challenged by global climate change and local anthropogenic stressors. Yet, knowledge of the capacity of coral larvae to adjust to different depth environments is still limited. In this study, planulae of the reef-building coral Stylophora pistillata from 5-8 and 40-44 m depth in the Gulf of Aqaba were tested in a long-term in situ translocation experiment for their ability to settle and acclimate to reciprocal depth conditions. We assessed survival rates, photochemical, physiological and morphological characteristics, as well as gene expression variations in juveniles grown at different depths, comparing them to non-translocated adults, juveniles and planulae. We found high mortality rates among mesophotic-origin planulae, irrespective of translocation depth. Gene expression patterns suggested that deep planulae lacked settlement competency and experienced increased developmental stress upon release. Symbiont photochemical acclimation to depth occurred rapidly within 8 days, with symbiont populations showing changes in photochemical traits but no symbiont species shuffling between deep and shallow juveniles. In contrast, coral host physiological and morphological acclimation were less evident. We observed minimal overlap in gene expression patterns between different life stages and depths, indicating that gene expression significantly depends on life stage. The study also identified a set of DEGs associated with initial stress responses following translocation, lingering stress response, and environmental effects of depth. In conclusion, though our data reveal rapid symbiont acclimation, host acclimation to match deep coral phenotypes was incomplete within 60 days for planulae translocated to different depths. These results have implications for understanding the ecological significance of mesophotic reefs as potential larval sources in the face of environmental stressors.

Project description:In this study, we examined the very early transcriptional response of aposymbiotic coral larval host (still not engaged in symbiosis) to hyperthermal stress. This experimental setting provided a scenario and opportunity to study the direct effect of environmental stressors on the host cell per se. Using a cDNA microarray constructed for Acropora millepora and Q-RT-PCR assays, we identified a number of genes that were significantly up- and down-regulated with increase of seawater temperature. Down-regulation of several key component of DNA/RNA metabolism was detected implying inhibition of this cellular metabolic process, however the down-regulation of overall protein synthesis was not simple and random, which suggest that the response to stress is a more complicated adjustment to the metabolic needs of the cell. We identified four significant outcomes during the very early hours of the transcriptional response to hyperthermal stress in coral larvae. First, molecular chaperones responded to hyperthermal stress by increasing their expression as expected, but the response was immediate and extremely rapid during the first 3 hours of heat exposure. Secondly, elevated temperature triggers down-regulation of a fluorescent protein homolog, DsRed-type FP, suggesting that this gene might be used as a potential molecular marker for monitoring hyperthermal stress in nature. Thirdly, the downregulation of a coral mannose-binding lectin under hyperthermal stress might compromise the coral immune defense and bring about susceptibility to pathogenic diseases. And lastly, an absence in the response of oxidative stress genes in aposymbiotic coral larvae during the early hours to hyperthermal stress suggest that the up-regulation of cnidarian host oxidative stress genes reported during thermal stress in algal/host symbiosis might be triggered directly by ROS generated by photosynthetic-dysfunctionally algal endosymbionts that diffuse into host cells, as very little ROS seems to be produced by the host cells from thermal-associated host cellular damage.

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Embryonic development of reef-building coral Dipsastraea veroni

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