Coral “Bleaching”︁ as a Generalized Stress Response to Environmental Disturbance

Baker, Andrew C.; Cunning, Ross

doi:10.1002/9781118828502.ch30

Cited by 20 publications

(15 citation statements)

References 119 publications

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“…In particular, none of these genes had annotations relating directly to oxidative-stress response, a surprising result given the common expectation that symbiotic anemones would have higher levels of ROS due to their increased production by heatstressed algal chloroplasts (25,34,55,56). To explore this issue further, we asked if any of 99 Aiptasia genes with putative roles in the oxidative-stress response (the 97 genes manually curated in ref.…”

Section: Resultsmentioning

confidence: 99%

“…These results were initially surprising, given the prominence of models in which photosynthetically produced ROS play a central role in triggering bleaching (25,34,55,56). However, examination of the literature revealed that previous gene-expression studies have also found either the up-regulation of only one or a few oxidative-stress-response genes during heat exposure, and generally with only modest levels of up-regulation (14,19,26,(29)(30)(31)(32)(33) or no such up-regulation at all (18,(35)(36)(37).…”

Section: In Coralsmentioning

confidence: 96%

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Insights into coral bleaching under heat stress from analysis of gene expression in a sea anemone model system

Cleves

Krediet

Lehnert

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Loss of endosymbiotic algae (“bleaching”) under heat stress has become a major problem for reef-building corals worldwide. To identify genes that might be involved in triggering or executing bleaching, or in protecting corals from it, we used RNAseq to analyze gene-expression changes during heat stress in a coral relative, the sea anemone Aiptasia. We identified >500 genes that showed rapid and extensive up-regulation upon temperature increase. These genes fell into two clusters. In both clusters, most genes showed similar expression patterns in symbiotic and aposymbiotic anemones, suggesting that this early stress response is largely independent of the symbiosis. Cluster I was highly enriched for genes involved in innate immunity and apoptosis, and most transcript levels returned to baseline many hours before bleaching was first detected, raising doubts about their possible roles in this process. Cluster II was highly enriched for genes involved in protein folding, and most transcript levels returned more slowly to baseline, so that roles in either promoting or preventing bleaching seem plausible. Many of the genes in clusters I and II appear to be targets of the transcription factors NFκB and HSF1, respectively. We also examined the behavior of 337 genes whose much higher levels of expression in symbiotic than aposymbiotic anemones in the absence of stress suggest that they are important for the symbiosis. Unexpectedly, in many cases, these expression levels declined precipitously long before bleaching itself was evident, suggesting that loss of expression of symbiosis-supporting genes may be involved in triggering bleaching.

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Section: Resultsmentioning

confidence: 99%

Section: In Coralsmentioning

confidence: 96%

Insights into coral bleaching under heat stress from analysis of gene expression in a sea anemone model system

Cleves

Krediet

Lehnert

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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“…Further, similar viruses were detected from all experimental fragments of two different acroporid species (based on TEM). Relative to experimental corals, conspecific acroporids that remained on the reef flat during the study period experienced additional episodes of aerial exposure and coincident intense rainfall (on March 21st–22nd), which likely triggered the observed massive bleaching (e.g., Baker and Cunning, 2015 ). Thus, we hypothesize that our experimental corals and many Heron Island reef flat acroporids had high viral loads simultaneously.…”

Section: Discussionmentioning

confidence: 99%

Viral Outbreak in Corals Associated with an In Situ Bleaching Event: Atypical Herpes-Like Viruses and a New Megavirus Infecting Symbiodinium

et al. 2016

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Previous studies of coral viruses have employed either microscopy or metagenomics, but few have attempted to comprehensively link the presence of a virus-like particle (VLP) to a genomic sequence. We conducted transmission electron microscopy imaging and virome analysis in tandem to characterize the most conspicuous viral types found within the dominant Pacific reef-building coral genus Acropora. Collections for this study inadvertently captured what we interpret as a natural outbreak of viral infection driven by aerial exposure of the reef flat coincident with heavy rainfall and concomitant mass bleaching. All experimental corals in this study had high titers of viral particles. Three of the dominant VLPs identified were observed in all tissue layers and budding out from the epidermis, including viruses that were ∼70, ∼120, and ∼150 nm in diameter; these VLPs all contained electron dense cores. These morphological traits are reminiscent of retroviruses, herpesviruses, and nucleocytoplasmic large DNA viruses (NCLDVs), respectively. Some 300–500 nm megavirus-like VLPs also were observed within and associated with dinoflagellate algal endosymbiont (Symbiodinium) cells. Abundant sequence similarities to a gammaretrovirus, herpesviruses, and members of the NCLDVs, based on a virome generated from five Acropora aspera colonies, corroborated these morphology-based identifications. Additionally sequence similarities to two diagnostic genes, a MutS and (based on re-annotation of sequences from another study) a DNA polymerase B gene, most closely resembled Pyramimonas orientalis virus, demonstrating the association of a cosmopolitan megavirus with Symbiodinium. We also identified several other virus-like particles in host tissues, along with sequences phylogenetically similar to circoviruses, phages, and filamentous viruses. This study suggests that viral outbreaks may be a common but previously undocumented component of natural bleaching events, particularly following repeated episodes of multiple environmental stressors.

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“…The heterogeneous structures of coral calcium carbonate exoskeletons create habitat complexity on which entire reef ecosystems depend (Fisher et al, 2015). However, due to global warming, increasing light intensities and warming water temperatures are inducing the collapse of this mutualistic relationship in a process known as coral bleaching (Glynn, 1996; Baker & Cunning, 2015). In recent decades, repeated coral bleaching and subsequent coral mortality have led to a serious global decline in living coral coverage (Pandolfi et al, 2003; Bruno & Selig, 2007; Hughes et al, 2018a; Hughes et al, 2018b).…”

Section: Introductionmentioning

confidence: 99%

Genome‐wide SNP genotyping reveals hidden population structure of an acroporid species at a subtropical coral island: Implications for coral restoration

Zayasu

Takeuchi

Nagata³

et al. 2021

Aquatic Conservation

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It is essential to consider genetic composition for both conventional coral restoration management and for initiating new interventions to counter the significant global decline in living corals. Population genetic structure at a fine spatial scale should be carefully evaluated before implementing strategies to achieve self‐sustaining ecosystems via coral restoration. This study investigated the population genetic structure of two acroporid species at Kume Island, Okinawa, Japan. There were 140 colonies of Acropora digitifera collected from seven study sites, and 81 colonies of Acropora tenuis from six sites. In total, 384 single nucleotide polymorphism (SNP) loci for A. digitifera and 470 SNPs for A. tenuis were obtained using a comparatively economical technique, Multiplexed ISSR Genotyping by sequencing. Observed heterozygosity was significantly lower than expected heterozygosity at all SNP sites in both acroporid species, suggesting deficient genetic diversity possibly caused by past massive coral bleaching. Even though both species are broadcast spawners, the population structure was different in the two species. No detectable structure was evident in A. digitifera, but two distinct clades were found in A. tenuis. The genetic homogeneity of A. digitifera at Kume Island suggests that this species could be used as a focal species for active restoration in terms of genetic differentiation at this island. By contrast, A. tenuis unexpectedly included two distinct clades with little or no admixture within a small study area, possibly representing two reproductively isolated cryptic species. Thus, when using A. tenuis, it would be prudent to avoid disturbing the genetic composition of wild populations until this question is answered.

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Coral “Bleaching”︁ as a Generalized Stress Response to Environmental Disturbance

Cited by 20 publications

References 119 publications

Insights into coral bleaching under heat stress from analysis of gene expression in a sea anemone model system

Insights into coral bleaching under heat stress from analysis of gene expression in a sea anemone model system

Viral Outbreak in Corals Associated with an In Situ Bleaching Event: Atypical Herpes-Like Viruses and a New Megavirus Infecting Symbiodinium

Genome‐wide SNP genotyping reveals hidden population structure of an acroporid species at a subtropical coral island: Implications for coral restoration

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