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AbstractWe tested the impact of temperature and symbiont state on calcification in corals, using the facultatively symbiotic coral Astrangia poculata as a model system. Symbiotic and aposymbiotic colonies of A. poculata were reared in 15, 20, and 27 °C conditions. We used scanning electron microscopy to quantify how these physiological and environmental conditions impact skeletal structure. Buoyant weight data over time revealed that temperature significantly affects calcification rates. Scanning electron microscopy of A. poculata skeletons showed that aposymbiotic colonies appear to have a lower density of calcium carbonate in actively growing septal spines. We describe a novel approach to analyze the roughness and texture of scanning electron microscopy images. Quantitative analysis of the roughness of septal spines revealed that aposymbiotic colonies have a rougher surface than symbiotic colonies in tropical conditions (27 °C). This trend reversed at 15 °C, a temperature at which the symbionts of A. poculata may exhibit parasitic properties. Analysis of surface texture patterns showed that temperature impacts the spatial variance of crystals on the spine surface. Few published studies have examined the skeleton of A. poculata by using scanning electron microscopy. Our approach provides a way to study detailed changes in skeletal microstructure in response to environmental parameters and can serve as a proxy for more expensive and time-consuming analyses. Utilizing a facultatively symbiotic coral that is native to both temperate and tropical regions provides new insights into the impact of both symbiosis and temperature on calcification in corals.

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Anthropogenic activities and climate change have resulted in an increase of hypoxic conditions in nearshore ecosystems worldwide. Depending on the persistence of a hypoxic event, the survival of aquatic animals can be compromised. Temperate fish exposed to hypoxia display a reduction in the probability of eliciting startle responses thought to be important for escape from predation. Here we examine the effect of hypoxia on the probability of eliciting fast-startle responses (fast-starts) of a tropical fish, the white grunt (Haemulon plumieri), and whether hypoxia has a prolonged impact on behavior once the fish are returned to normoxic conditions. White grunts collected from the San Juan Bay Estuary in Puerto Rico were exposed to an oxygen concentration of 2.5 mg L-1 (40% dissolved oxygen). We found a significant reduction in auditory-evoked fast-starts that lasted for at least 24 hours after fish were returned to normoxic conditions. Accessibility to the neuronal networks that underlie startle responses was an important motivator for this study. Mauthner cells are identifiable neurons found in most fish and amphibians, and these cells are known to initiate fast-starts in teleost fishes. The assumption that most of the short-latency responses in this study are Mauthner cell initiated provided the impetus to characterize the white grunt Mauthner cell. The identification of the cell provides a first step in understanding how low oxygen levels may impact a single cell and its circuit and the behavior it initiates.

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BACKGROUND: The roles of gorgonian sclerites as structural components and predator deterrents have been widely studied. Yet their role as barriers against microbes has only recently been investigated, and even less is known about the diversity and roles of the chemical compounds associated with sclerites. METHODS: Here, we examine the semi-volatile organic compound fraction (SVOCs) associated with sclerites from healthy and diseased Gorgonia ventalina sea fan corals to understand their possible role as a stress response or in defense of infection. We also measured the oxidative potential of compounds from diseased and healthy G. ventalina colonies. RESULTS: The results showed that sclerites harbor a great diversity of SVOCs. Overall, 70 compounds were identified, the majority of which are novel with unknown biological roles. The majority of SVOCs identified exhibit multiple immune-related roles including antimicrobial and radical scavenging functions. The free radical activity assays further confirmed the anti-oxidative potential of some these compounds. The anti-oxidative activity was, nonetheless, similar across sclerites regardless of the health condition of the colony, although sclerites from diseased sea fans display slightly higher anti-oxidative activity than the healthy ones. DISCUSSION: Sclerites harbor great SVOCs diversity, the majority of which are novel to sea fans or any other corals. Yet the scientific literature consulted showed that the roles of compounds found in sclerites vary from antioxidant to antimicrobial compounds. However, this study fell short in determine the origin of the SVOCs identified, undermining our capacity to determine the biological roles of the SVOCs on sclerites and sea fans.

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BACKGROUND: Porites astreoides is a ubiquitous species of coral on modern Caribbean reefs that is resistant to increasing temperatures, overfishing, and other anthropogenic impacts that have threatened most other coral species. We assembled and annotated a transcriptome from this coral using Illumina sequences from three different developmental stages collected over several years: free-swimming larvae, newly settled larvae, and adults (>10 cm in diameter). This resource will aid understanding of coral calcification, larval settlement, and host-symbiont interactions. FINDINGS: A de novo transcriptome for the P. astreoides holobiont (coral plus algal symbiont) was assembled using 594 Mbp of raw Illumina sequencing data generated from five age-specific cDNA libraries. The new transcriptome consists of 867 255 transcript elements with an average length of 685 bases. The isolated P. astreoides assembly consists of 129 718 transcript elements with an average length of 811 bases, and the isolated Symbiodinium sp. assembly had 186 177 transcript elements with an average length of 1105 bases. CONCLUSIONS: This contribution to coral transcriptome data provides a valuable resource for researchers studying the ontogeny of gene expression patterns within both the coral and its dinoflagellate symbiont.

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ADAR editing enzymes are found in all multicellular animals and are conserved in sequence and protein organization. The number of ADAR genes differs between animals, ranging from three in mammals to one in Drosophila. ADAR is also alternatively spliced to generate isoforms that can differ significantly in enzymatic activity. Therefore, to study the enzyme in vitro, it is essential to have an easy and reliable method of expressing and purifying recombinant ADAR protein. To add to the complexity of RNA editing, the number of transcripts that are edited by ADARs differs in different organisms. In humans there is extensive editing of Alu sequences, whereas in invertebrates transcripts expressed in the central nervous system are edited and this editing increases during development. It is possible to quantify site-specific RNA editing by sequencing of clones derived from RT-PCR products. However, for routine assaying of an edited position within a particular transcript, this is both expensive and time consuming. Therefore, a nonradioactive method based on poison primer extension assay is an ideal alternative.

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Recent data suggest that small differences in editing efficiency can have significant functional consequences. Here we present a fluorescent poisoned primer extension assay that is capable of distinguishing editing efficiency differences as low as 5%. For a poison-primer extension assay to be accurate, the extension product must stop at the intended base. Sometimes, however, it runs beyond. We tested the effect of specific enzyme-terminator combinations on the amount of run through. In the worst cases it accounted for 70% of the total signal, and in the best cases <5%. In addition, the specific base can affect run through, with G producing the least. The accuracy of the assay was demonstrated on templates derived from mixed plasmids and then verified on two biological substrates. Using either a K(+) channel mRNA that contains a site for adenosine deamination or an ndhB mRNA that contains a site for cytidine deamination, the editing efficiency predicted by the assay closely matched that predicted by bulk sequencing of individual cDNA clones. This assay should prove useful for analyzing small changes in editing efficiency or for quantifying single nucleotide polymorphisms.

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