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Variation in the transcriptional response of threatened coral larvae to elevated temperatures

ABSTRACT: Coral populations have declined worldwide largely due to increased sea surface temperatures. Recovery of coral populations depends in part upon larval recruitment. Many corals reproduce during the warmest time of year when further increases in temperature can lead to low fertilization rates of eggs and high larval mortality. Microarray experiments were designed to capture and assess variability in the thermal stress responses of Acropora palmata larvae from Puerto Rico. Transcription profiles showed a striking acceleration of normal developmental gene expression patterns with increased temperature. The transcriptional response to heat suggested rapid depletion of larval energy stores via peroxisomal lipid oxidation and included key enzymes that indicated the activation of the glyoxylate cycle. High temperature also resulted in expression differences in key developmental signalling genes including the conserved WNT pathway that is critical for pattern formation and tissue differentiation in developing embryos. Expression of these and other important developmental and thermal stress genes such as ferritin, heat shock proteins, cytoskeletal components, cell adhesion and autophagy proteins also varied among larvae derived from different parent colonies. Disruption of normal developmental and metabolic processes will have negative impacts on larval survival and dispersal as temperatures rise. However, it appears that variation in larval response to high temperature remains despite the dramatic population declines. Further research is needed to determine whether this variation is heritable or attributable to maternal effects.

ORGANISM(S): Acropora palmata

PROVIDER: GSE36983 | GEO | 2012/12/13

SECONDARY ACCESSION(S): PRJNA157441

REPOSITORIES: GEO

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Project description:Coral populations have declined worldwide largely due to increased sea surface temperatures. Recovery of coral populations depends in part upon larval recruitment. Many corals reproduce during the warmest time of year when further increases in temperature can lead to low fertilization rates of eggs and high larval mortality. Microarray experiments were designed to capture and assess variability in the thermal stress responses of Acropora palmata larvae from Puerto Rico. Transcription profiles showed a striking acceleration of normal developmental gene expression patterns with increased temperature. The transcriptional response to heat suggested rapid depletion of larval energy stores via peroxisomal lipid oxidation and included key enzymes that indicated the activation of the glyoxylate cycle. High temperature also resulted in expression differences in key developmental signalling genes including the conserved WNT pathway that is critical for pattern formation and tissue differentiation in developing embryos. Expression of these and other important developmental and thermal stress genes such as ferritin, heat shock proteins, cytoskeletal components, cell adhesion and autophagy proteins also varied among larvae derived from different parent colonies. Disruption of normal developmental and metabolic processes will have negative impacts on larval survival and dispersal as temperatures rise. However, it appears that variation in larval response to high temperature remains despite the dramatic population declines. Further research is needed to determine whether this variation is heritable or attributable to maternal effects. Hybridization followed a dual channel loop design using two biological replicates (dye-swapped) from each treatment that maximized power to detect differential expression in contrasts between temperatures and batches (within time-points) as well as the amount of data obtained from each slide (Simon and Dobbin 2003). A total of 18 arrays on two 12 plex slides were used (Table S1). Additional samples from other sub-batches (b3/b4) were included in the microarray experiment but are not used in this analysis. Each array measures the expression level of 135,185 genes from the elkhorn coral (Acropora palmata) transcriptome (Polato et al. 2011). Two 60-mer probes were designed for each contig (n = 85,260), and a single probe was designed for each singleton sequence (n = 45,390). Two additional probes each were developed for sequences associated with annotation information relating to calcium metabolism and stress response (n = 4,798). Replicate probes for individual sequences from the assembled transcriptome were not identical; rather they represented multiple different 60-mer sequences from the original template.

Project description:Projected elevation of seawater temperatures poses a threat to the reproductive success of Caribbean reef-building corals that have planktonic development during the warmest months of the year. This study examined the transcriptomic changes that occurred during embryonic and larval development of the elkhorn coral, Acropora palmata, at a non-stressful temperature (28Â°C) and further assessed the effects of two elevated temperatures (30Â°C and 31.5Â°C) on these expression patterns. Using cDNA microarrays, we compared expression levels of 2,051 genes from early embryos and larvae at multiple developmental stages (including pre-blastula, blastula, gastrula, and planula stages) at each of the three temperatures. At 12 hours post-fertilization in 28Â°C treatments, genes involved in cell replication/cell division and transcription were up-regulated in A. palmata embryos, followed by a reduction in expression of these genes during later growth stages. From 24.5 to 131 hours post-fertilization at 28Â°C, A. palmata altered its transcriptome by up-regulating genes involved in protein synthesis and metabolism. Temperatures of 30Â°C and 31.5Â°C caused major changes to the A. palmata embryonic transcriptomes, particularly in the samples from 24.5 hpf post-fertilization, characterized by down-regulation of numerous genes involved in cell replication/cell division, metabolism, cytoskeleton, and transcription, while heat shock genes were up-regulated compared to 28Â°C treatments. These results suggest that increased temperature may cause a breakdown in proper gene expression during development in A. palmata by down-regulation of genes involved in essential cellular processes, which may lead to the abnormal development and reduced survivorship documented in other studies. Our experimental setup followed a reference design where all samples were hybridized against the same pool made up of equal amounts of RNA from all samples in the experiment. Biological duplicate samples were used for each temperature at each developmental time period. Common reference samples were labeled with Cy3 dye, while temperature samples were labeled with Cy5 dye. Microarrays for A. palmata contained 2,051 coding sequences, of which 54.3% had functional annotations as determined by homology to known genes.

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:We combined heritability analysis of larval development rate with a global expression analysis of this phenotype to investigate genotype by environment interactions across three ecologically relevant temperatures in the Glanville fritillary butterfly (Melitaea cinxia). We focused upon the development of final instar caterpillars which is greatly affected by temperature, and during this stage the caterpillars build up most of the resources for adult life. Second generation, lab reared larvae, initially collected from the Åland metapopulation, were reared in standard lab condition until 6th larval instar. At the beginning of the final (7th) instar stage the larvae were separated into of three temperature conditions: Cold treatment (temperature profile: 8°C 18:00-9:59, 14°C 10:00-11:59, 20°C 12:00-15:59 and 14°C 16:00-17:59) Standard treatment (temperature profile: 15°C 17:00-6:59, 18°C 7:00-8:59, 22°C 9:00-10:59 and 26°C 11:00-16:59) Hot treatment (temperature profile: 8°C 20:00-7:59, 15°C 8:00-9:59, 35°C 10:00-17:59 and 15°C 18:00-19:59) The temperature profiles mimic the diurnal thermal variation of the natural habitat (Åland islands) of samples. Cold treatment mimics a cool and cloudy summer, Standard represents an average temperature profile in the Åland islands and Hot treatment mimics an exceptionally hot and sunny summer, with cold night-time temperatures. The experiment contained several larval families (full-sib) of which three were selected for gene expression analysis. Samples were snap-frozen in liquid nitrogen during mid-development (after 6, 5 and 4 days, for Cold, Standard and Hot respectively). Additional larvae from the same treatments were assayed for survival and growth. Gene expression was analyzed using a mixed model approach to identify genes with potential heritable expression variation (variation among families), genes with plastic expression responses (treatment induced changes) and genes with treatment dependent expression that varies among families (family by treatment interactions).

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Variation in the transcriptional response of threatened coral larvae to elevated temperatures

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