Project description:Given the overwhelming evidence that symbiont genotypes differentially affect host processes such as growth, bleaching susceptibility, and nutrient acquisition, we set out to measure gene expression differences in fragments of Montastraea faveolata harboring two different clades of Symbiodinium. On the reefs near Puerto Morelos, MÃ©xico, colonies of M. faveolata are known to shift algal symbiont clade with depth, often associating with clade A at the top, clade B in the middle, and clade C near the bottom of the colony. By measuring photosynthetic efficiency and gene expression in control and heat-stressed fragments containing either clade B, clade C, or a mix of both, we found that: 1) the algal response to thermal stress is due to both host and algal factors; 2) fragments of M. faveolata express different genes in response to sub-bleaching thermal stress depending on algal genotype; 3) the overall effect of heat stress on coral gene expression is less significant than the effect of housing different zooxanthellae types. Overall, we present convincing evidence that different Symbiodinium clades may be functionally distinct, which in turn, greatly influences host gene expression. Six fragments (9.5 Â± 3.5cm2) from the top (2.7m), middle (3.7m), and bottom (5.2m) of one massive colony of Montastraea faveolata were collected with a hammer and chisel at âLa Bocanaâ reef near Puerto Morelos, Quintana Roo, Mexico on 31 July 2007. The fragments were divided evenly between two aquaria (50L) that received a constant flow of seawater (~0.64L/min). Each aquarium was fit with a water pump connected to a spray-bar to provide constant water movement and aeration. Both aquaria were placed in a common pond with flowing water to buffer diurnal temperature fluctuations, and both aquaria were exposed to shaded ambient light. All coral fragments were mounted on plasticene and kept at a depth of ~7cm. From 10 to 19 August 2007 (acclimation #1), both aquaria received an average water temperature of 27.9 Â± 0.6oC (as recorded by HOBO Light/Temperature Data Loggers by Onset Corp.). Effective quantum yield (ÎF/Fmâ) measurements were taken at noon, and maximum quantum yield (Fv/Fm) measurements were taken at dusk for all 18 coral fragments using a DIVING-PAM (Walz) beginning on 11 August. Photosynthetically active radiation (PAR) was measured at noon and averaged 318 Â± 129 umol/m2/sec. From 20 to 21 August 2007, all coral fragments were brought inside during the passage of Hurricane Dean. On 22 August, the experiment was reconstituted, and a second acclimation period began on 23 August and lasted until 1 September. During this time, both aquaria received water at an average temperature of 28.5 Â± 0.8oC, and PAR at an average of 371 Â± 169 umol/m2/sec. On the night of 1 September, one 200-Watt aquarium heater was turned on in the treatment aquarium, and a second heater was turned on 3 days later. During the thermal stress experiment, the control aquarium received an average water temperature of 28.8 Â± 1.2oC; the heated aquarium, 31.5 Â± 1.1oC. PAR present during the thermal stress experiment averaged 420 Â± 152 uE. On the night of 7 September, all fragments were frozen in liquid nitrogen. Eighteen total microarray hybridizations were performed. A reference RNA sample was created by pooling RNA from all 18 prepâs. All control and heat-stressed samples were competitively hybridized against the reference RNA to the M. faveolata microarray (1,310 features).

Project description:A mutualistic relationship between reef-building corals and endosymbiotic algae (Symbiodinium spp.) forms the basis for the existence of coral reefs. Genotyping tools for Symbiodinium spp. have added a new level of complexity to studies concerning cnidarian growth, nutrient acquisition, and stress. For example, the response of the coral holobiont to thermal stress is connected to the host-Symbiodinium genotypic combination, as different partnerships can have different bleaching susceptibilities. If, and to what extent, differences in algal symbiont clade contents can exert effects on the coral host transcriptome is currently unknown. In this study, we monitored algal physiological parameters and profiled the coral host transcriptional responses in acclimated, thermally stressed, and recovered coral fragments using a custom cDNA gene expression microarray. Combining these analyses with results from algal and host genotyping revealed a striking symbiont effect on both the acclimated coral host transcriptome and the magnitude of the thermal stress response. This is the first study that links coral host transcriptomic patterns to the clade content of their algal symbiont community. Our data provide a critical step to elucidating the molecular basis of the apparent variability seen among different coral-algal partnerships. Sample Collection and Tank Experiment. On July 31 2007, six replicate fragments (9.5 Â± 3.5cm2) were collected using hammer and chisel from the upper sun-exposed surface of five different, healthy-looking Montastraea faveolata colonies near Puerto Morelos, Quintana Roo, MÃ©xico (20o52â28.77âN and 86o51â04.53âW). The fragments were transported to the institute within 1 h and divided evenly between two 50 L aquaria (i.e., 3 fragments from each colony were placed into each tank) that received a constant flow of seawater (0.6 L/min). Each aquarium was fit with a water pump connected to a spray-bar to provide constant water movement and aeration. Both aquaria were placed in a common pond with flowing water to buffer diurnal temperature fluctuations, and both aquaria were acclimated to the same shaded ambient light condition. All coral fragments were mounted on plasticene and kept at a depth of 7 cm. From 10 to 19 August 2007, both aquaria received an average water temperature of 27.9 Â± 0.6oC (as recorded by HOBO Light/Temperature Data Loggers, Onset Corp.). Beginning on 11 August, dark-adapted maximum quantum yields for charge separation (Fv/Fm) were measured at dusk for all coral fragments using a DIVING-Pulse Amplitude Modulated (PAM) fluorometer (Walz, Germany). Photosynthetically active radiation (PAR) was measured at noon and averaged 318 Â± 129 Âµmol m-2 s-1. From 20 to 21 August 2007, all coral fragments were brought inside during the passage of Hurricane Dean. On 22 August, the experiment was reconstituted, and acclimation continued on 23 August and lasted until 1 September. During this time, both aquaria received a mean water temperature of 28.5 Â± 0.8oC, and mean PAR of 371 Â± 169 Âµmol m-2 s-1. On the night of 1 September, control time point samples from five different colonies were collected from each tank (Figure 1), before one 200-Watt aquarium heater was turned on in the treatment aquarium. A second heater was turned on 3 days later. During the thermal stress experiment, the control aquarium received mean water temperature of 28.8 Â± 1.2oC; the heated aquarium, 31.5 Â± 1.1oC. During the thermal stress experiment, tanks received mean PAR of 420 Â± 152 Âµmol m-2 s-1. On 11 September, and 19 October, one sample each from five different colonies was collected from each tank for the bleaching and recovery time point, respectively. Microarray Gene Expression Analysis of Coral Host Gene Expression. For the biologically replicated time series experiment, a pool of RNA from all control tank fragments was used as a reference RNA sample, against which each sample from the treatment tank was competitively hybridized. All control and heat-stressed samples were competitively hybridized against the reference RNA. Dye swaps were not performed, as any dye bias present is equal in all comparisons to the reference. Note: Samples VALUEs used for statistical analysis of differential expression. GSE15253_shini_cbr_matrix2_norm.txt used for hierarchical clustering.

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:BACKGROUND:Although the term holobiont has been popularized in corals with the advent of the hologenome theory of evolution, the underlying concepts are still a matter of debate. Indeed, the relative contribution of host and environment and especially thermal regime in shaping the microbial communities should be examined carefully to evaluate the potential role of symbionts for holobiont adaptation in the context of global changes. We used the sessile, long-lived, symbiotic and environmentally sensitive reef-building coral Pocillopora damicornis to address these issues. RESULTS:We sampled Pocillopora damicornis colonies corresponding to two different mitochondrial lineages in different geographic areas displaying different thermal regimes: Djibouti, French Polynesia, New Caledonia, and Taiwan. The community composition of bacteria and the algal endosymbiont Symbiodinium were characterized using high-throughput sequencing of 16S rRNA gene and internal transcribed spacer, ITS2, respectively. Bacterial microbiota was very diverse with high prevalence of Endozoicomonas, Arcobacter, and Acinetobacter in all samples. While Symbiodinium sub-clade C1 was dominant in Taiwan and New Caledonia, D1 was dominant in Djibouti and French Polynesia. Moreover, we also identified a high background diversity (i.e., with proportions <?1%) of A1, C3, C15, and G Symbiodinum sub-clades. Using redundancy analyses, we found that the effect of geography was very low for both communities and that host genotypes and temperatures differently influenced Symbiodinium and bacterial microbiota. Indeed, while the constraint of host haplotype was higher than temperatures on bacterial composition, we showed for the first time a strong relationship between the composition of Symbiodinium communities and minimal sea surface temperatures. CONCLUSION:Because Symbiodinium assemblages are more constrained by the thermal regime than bacterial communities, we propose that their contribution to adaptive capacities of the holobiont to temperature changes might be higher than the influence of bacterial microbiota. Moreover, the link between Symbiodinium community composition and minimal temperatures suggests low relative fitness of clade D at lower temperatures. This observation is particularly relevant in the context of climate change, since corals will face increasing temperatures as well as much frequent abnormal cold episodes in some areas of the world.

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Symbiodinium clade content drives host transcriptome more than thermal stress in the coral Montastraea faveolata

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