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      Signaling cascades and the importance of moonlight in coral broadcast mass spawning

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          Abstract

          Many reef-building corals participate in a mass-spawning event that occurs yearly on the Great Barrier Reef. This coral reproductive event is one of earth's most prominent examples of synchronised behavior, and coral reproductive success is vital to the persistence of coral reef ecosystems. Although several environmental cues have been implicated in the timing of mass spawning, the specific sensory cues that function together with endogenous clock mechanisms to ensure accurate timing of gamete release are largely unknown. Here, we show that moonlight is an important external stimulus for mass spawning synchrony and describe the potential mechanisms underlying the ability of corals to detect environmental triggers for the signaling cascades that ultimately result in gamete release. Our study increases the understanding of reproductive chronobiology in corals and strongly supports the hypothesis that coral gamete release is achieved by a complex array of potential neurohormones and light-sensing molecules.

          DOI: http://dx.doi.org/10.7554/eLife.09991.001

          eLife digest

          Sexual reproduction in corals is possibly the most important process for replenishing degraded coral reefs. Most corals are “broadcast spawners” that reproduce by releasing their egg cells and sperm cells into the sea water surface. To maximize their chances of reproductive success, most coral in the Great Barrier Reef – over 130 species – spawn on the same night, during a time window that is approximately 30-60 minutes long. This is the largest-scale mass spawning event of coral in the world, and is triggered by changes in sea water temperature, tides, sunrise and sunset and by the intensity of the moonlight.

          How corals tune their spawning behavior with the phases of the moonlight was an unanswered question for decades. Now, Kaniewska, Alon et al. have exposed the coral Acropora millepora – which makes up part of the Great Barrier Reef – to different light treatments and sampled the corals before, during and after their spawning periods. This revealed that light causes changes to gene expression and signaling processes inside cells. These changes are specifically related to the release of egg and sperm cells, and occur only on the night of spawning.

          Furthermore, by exposing corals to light conditions that mimic artificial urban “light pollution”, Kaniewska, Alon et al. caused a mismatch in certain cellular signaling processes that prevented the corals from spawning. Reducing the exposure of corals to artificial lighting could therefore help to protect and regenerate coral reefs.

          Future work will involve comparing these results with information about a coral species from another part of the world to investigate whether there is a universal mechanism used by corals to control when they spawn.

          DOI: http://dx.doi.org/10.7554/eLife.09991.002

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          Most cited references 27

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          Mass spawning in tropical reef corals.

          Synchronous multispecific spawning by a total of 32 coral species occurred a few nights after late spring full moons in 1981 and 1982 at three locations on the Great Barrier Reef, Australia. The data invalidate the generalization that most corals have internally fertilized, brooded planula larvae. In every species observed, gametes were released; external fertilization and development then followed. The developmental rates of externally fertilized eggs and longevities of planulae indicate that planulae may be dispersed between reefs.
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            Whole transcriptome analysis of the coral Acropora millepora reveals complex responses to CO₂-driven acidification during the initiation of calcification.

             A. Moya,  L Huisman,  E E Ball (2012)
            The impact of ocean acidification (OA) on coral calcification, a subject of intense current interest, is poorly understood in part because of the presence of symbionts in adult corals. Early life history stages of Acropora spp. provide an opportunity to study the effects of elevated CO(2) on coral calcification without the complication of symbiont metabolism. Therefore, we used the Illumina RNAseq approach to study the effects of acute exposure to elevated CO(2) on gene expression in primary polyps of Acropora millepora, using as reference a novel comprehensive transcriptome assembly developed for this study. Gene ontology analysis of this whole transcriptome data set indicated that CO(2) -driven acidification strongly suppressed metabolism but enhanced extracellular organic matrix synthesis, whereas targeted analyses revealed complex effects on genes implicated in calcification. Unexpectedly, expression of most ion transport proteins was unaffected, while many membrane-associated or secreted carbonic anhydrases were expressed at lower levels. The most dramatic effect of CO(2) -driven acidification, however, was on genes encoding candidate and known components of the skeletal organic matrix that controls CaCO(3) deposition. The skeletal organic matrix effects included elevated expression of adult-type galaxins and some secreted acidic proteins, but down-regulation of other galaxins, secreted acidic proteins, SCRiPs and other coral-specific genes, suggesting specialized roles for the members of these protein families and complex impacts of OA on mineral deposition. This study is the first exhaustive exploration of the transcriptomic response of a scleractinian coral to acidification and provides an unbiased perspective on its effects during the early stages of calcification. © 2012 Blackwell Publishing Ltd.
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                Author and article information

                Contributors
                Role: Reviewing editor
                Journal
                eLife
                Elife
                eLife
                eLife
                eLife
                eLife Sciences Publications, Ltd
                2050-084X
                15 December 2015
                2015
                : 4
                Affiliations
                [1 ]Australian Institute of Marine Science , Queensland, Australia
                [2 ]deptSchool of Biological Sciences , The University of Queensland , St Lucia, Australia
                [3 ]deptGeorge S Wise Faculty of Life Sciences, Department of Neurobiology , Tel Aviv University , Tel Aviv, Israel
                [4 ]deptMina and Everard Goodman Faculty of Life Sciences , Bar-Ilan University , Ramat Gan, Israel
                [5 ]deptGlobal Change Institute and ARC Centre of Excellence for Coral Reef Studies , The University of Queensland , St Lucia, Australia
                University Medical Center Groningen , Netherlands
                University Medical Center Groningen , Netherlands
                Author notes
                [‡]

                Media LabMassachusetts Institute of TechnologyCambridgeUnited States.

                [†]

                These authors contributed equally to this work.

                Article
                09991
                10.7554/eLife.09991
                4721961
                26668113
                © 2015, Kaniewska et al

                This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited.

                Product
                Funding
                Funded by: FundRef http://dx.doi.org/10.13039/501100000923, Australian Research Council;
                Award Recipient :
                The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
                Categories
                Ecology
                Short Report
                Custom metadata
                2.5
                Artificial light causes changes to gene expression and cellular signaling cascades that coordinate mass spawning events for a species of coral from the Great Barrier Reef.

                Life sciences

                coral, cnidarians, mass spawning, reproduction, signalling cascade, other, moon light

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