doi: 10.1038/srep08562.
Symbiodinium thermophilum sp. nov., a thermotolerant symbiotic alga prevalent in corals of the world's hottest sea, the Persian/Arabian Gulf
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- PMID: 25720577
- PMCID: PMC4342558
- DOI: 10.1038/srep08562
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Symbiodinium thermophilum sp. nov., a thermotolerant symbiotic alga prevalent in corals of the world's hottest sea, the Persian/Arabian Gulf
B C C Hume et al.
Sci Rep.
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Abstract
Coral reefs are in rapid decline on a global scale due to human activities and a changing climate. Shallow water reefs depend on the obligatory symbiosis between the habitat forming coral host and its algal symbiont from the genus Symbiodinium (zooxanthellae). This association is highly sensitive to thermal perturbations and temperatures as little as 1°C above the average summer maxima can cause the breakdown of this symbiosis, termed coral bleaching. Predicting the capacity of corals to survive the expected increase in seawater temperatures depends strongly on our understanding of the thermal tolerance of the symbiotic algae. Here we use molecular phylogenetic analysis of four genetic markers to describe Symbiodinium thermophilum, sp. nov. from the Persian/Arabian Gulf, a thermally tolerant coral symbiont. Phylogenetic inference using the non-coding region of the chloroplast psbA gene resolves S. thermophilum as a monophyletic lineage with large genetic distances from any other ITS2 C3 type found outside the Gulf. Through the characterisation of Symbiodinium associations of 6 species (5 genera) of Gulf corals, we demonstrate that S. thermophilum is the prevalent symbiont all year round in the world's hottest sea, the southern Persian/Arabian Gulf.
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(A-E) represent previous sampling locations from Baker et al. 2004 (A&B), Mostafavi et al. 2007 (C&D), Shahhosseiny et al. 2011 (E) and Hume et al. 2013 (F). 1–3 represent sampling locations from this study: Dalma (1), Saadiyat (2) and Umm Al Quwain (3). Major cities are marked with a ⋆. Both the main and insert map were created from a mosaic of LandSat 8 OLI/TIRS "Natural Colour" images acquired through the USGS's EarthExplorer (http://earthexplorer.usgs.gov/ ). Images were collated in GNU Image Manipulation Program (GIMP) 2.6.11 (www.gimp.org ). Land-Sea boundaries were identified and land and sea masses were coloured to contrast, also in GIMP. Latitude and Longitude markers were added manually along with sampling locations, map scale, and major city locations.
Top) Classification of predominant Symbiodinium type associated with 6 species of southern Gulf (Saadiyat) corals at each of 8 seasonal time points. Sampling date is denoted by position along the x axis of the plot below. * denotes the time point at which coral bleaching was visually observed on the reef during sample collection. Each pie chart represents the number of times a given symbiont (for example C3), or mix of symbionts (for example a mix of C3 and A1) was detected in a coral colony (symbiont mixes identified by the vertical division of a slice; the proportion of each symbiont making up a mix was not quantified). Novel ITS2 variant C3v1 is denoted by a 1 within a C3 section of chart. Further details of coral phylotyping can be found in Supplementary Table S1. Bottom) Plot of remotely sensed sea surface temperatures (SSTs) for waters in close proximity to the sampling sites of Baker et al. 2004 (Jana island; 27.3N 49.9E;–), Mostafavi et al. 2006 (Larak island; 26.8N 56.4E;---) and this study (Saadiyat; 24.7N 54.4E;–). SST data were obtained from the GHRSST Level 4 K10_SST Global 1 meter Sea Surface Temperature Analysis dataset (http://www.nodc.noaa.gov/SatelliteData/ghrsst/accessdata.html ).
(a) High resolution phylogeny of Gulf and non-Gulf ITS2 type C3 and closely related ITS2 type variants as estimated through Bayesian Inference of the chloroplast psbAncr. Sequences are annotated according to their ITS2 type. Gulf ITS2 type C3 sequences are annotated S. thermophilum as described in this report. Support for nodes is assessed using posterior probabilities (PP) presented on the tree as follows: 0.75-1.00, no annotation; 0.5-0.75, marked by (▴). No nodes had a support of less than 0.5. The tree is rooted according to an ITS2 type C3 sequence collected at the Great Barrier Reef (accession JQ043643). The tree showing the full details of node support and sample accession numbers is shown in Supplementary Fig. S2. Full details of the sequences used in the phylogenetic estimation are available in Supplementary Tables S3 and S4. (b) Maximum parsimony ITS2 haplotype network of the ITS2 types included in the phylogenetic analysis. (c) Within and between-group mean pairwise genetic differences with error bars (standard deviation). (d) Magnified region of the psbAncr tree including S. thermophilum samples annotated with host and location sampling information.
Support of nodes was assessed using posterior probabilities (PP). PPs above 0.75 are not displayed. Both trees are drawn to the same scale and analysed sequences are annotated according to their ITS2 type. See Supplementary Table S5 for a list of sequences used in both inferences.
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