Posts Tagged 'molecular biology'

Effects of multiple climate change stressors on gene expression in blue rockfish (Sebastes mystinus)

Highlights

  • Marine fishes will be exposed to multiple stressors under climate change.
  • Hypoxia and high pCO2 are both expected to cause shifts in energy metabolism.
  • No signs of energetic shifts were observed at transcriptomic or enzymatic levels.
  • Multiple stressor transcriptomes are not predictable based on responses to single stressors.
  • Blue rockfish may be relatively tolerant to intensified upwelling conditions.

Abstract

Global climate change is predicted to increase the co-occurrence of high pCO2 and hypoxia in upwelling zones worldwide. Yet, few studies have examined the effects of these stressors on economically and ecologically important fishes. Here, we investigated short-term responses of juvenile blue rockfish (Sebastes mystinus) to independent and combined high pCO2 and hypoxia at the molecular level, using changes in gene expression and metabolic enzymatic activity to investigate potential shifts in energy metabolism. Fish were experimentally exposed to conditions associated with intensified upwelling under climate change: high pCO2 (1200 μatm, pH~7.6), hypoxia (4.0 mg O2/L), and a combined high pCO2/hypoxia treatment for 12 h, 24 h or two weeks. Muscle transcriptome profiles varied significantly among the three treatments, with limited overlap among genes responsive to both the single and combined stressors. Under elevated pCO2, blue rockfish increased expression of genes encoding proteins involved in the electron transport chain and muscle contraction. Under hypoxia, blue rockfish up-regulated genes involved in oxygen and ion transport and down-regulated transcriptional machinery. Under combined high pCO2 and hypoxia, blue rockfish induced a unique set of ionoregulatory and hypoxia-responsive genes not expressed under the single stressors. Thus, high pCO2 and hypoxia exposure appears to induce a non-additive transcriptomic response that cannot be predicted from single stressor exposures alone, further highlighting the need for multiple stressor studies at the molecular level. Overall, lack of a major shift in cellular energetics indicates that blue rockfish may be relatively resistant to intensified upwelling conditions in the short term.

Continue reading ‘Effects of multiple climate change stressors on gene expression in blue rockfish (Sebastes mystinus)’

Changes in the metabolic potential of the sponge microbiome under ocean acidification

Anthropogenic CO2 emissions are causing ocean acidification, which can affect the physiology of marine organisms. Here we assess the possible effects of ocean acidification on the metabolic potential of sponge symbionts, inferred by metagenomic analyses of the microbiomes of two sponge species sampled at a shallow volcanic CO2 seep and a nearby control reef. When comparing microbial functions between the seep and control sites, the microbiome of the sponge Stylissa flabelliformis (which is more abundant at the control site) exhibits at the seep reduced potential for uptake of exogenous carbohydrates and amino acids, and for degradation of host-derived creatine, creatinine and taurine. The microbiome of Coelocarteria singaporensis (which is more abundant at the seep) exhibits reduced potential for carbohydrate import at the seep, but greater capacity for archaeal carbon fixation via the 3-hydroxypropionate/4-hydroxybutyrate pathway, as well as archaeal and bacterial urea production and ammonia assimilation from arginine and creatine catabolism. Together these metabolic features might contribute to enhanced tolerance of the sponge symbionts, and possibly their host, to ocean acidification.

Continue reading ‘Changes in the metabolic potential of the sponge microbiome under ocean acidification’

Little evidence of adaptation potential to ocean acidification in sea urchins living in “future ocean” conditions at a CO2 vent

Ocean acidification (OA) can be detrimental to calcifying marine organisms, with stunting of invertebrate larval development one of the most consistent responses. Effects are usually measured by short‐term, within‐generation exposure, an approach that does not consider the potential for adaptation. We examined the genetic response to OA of larvae of the tropical sea urchin Echinometra sp. C. raised on coral reefs that were either influenced by CO2 vents (pH ~ 7.9, future OA condition) or nonvent control reefs (pH 8.2). We assembled a high quality de novo transcriptome of Echinometra embryos (8 hr) and pluteus larvae (48 hr) and identified 68,056 SNPs. We tested for outlier SNPs and functional enrichment in embryos and larvae raised from adults from the control or vent sites. Generally, highest FST values in embryos were observed between sites (intrinsic adaptation, most representative of the gene pool in the spawned populations). This comparison also had the highest number of outlier loci (40). In the other comparisons, classical adaptation (comparing larvae with adults from the control transplanted to either the control or vent conditions) and reverse adaptation (larvae from the vent site returned to the vent or explanted at the control), we only observed modest numbers of outlier SNPs (6–19) and only enrichment in two functional pathways. Most of the outliers detected were silent substitutions without adaptive potential. We conclude that there is little evidence of realized adaptation potential during early development, while some potential (albeit relatively low) exists in the intrinsic gene pool after more than one generation of exposure.

Continue reading ‘Little evidence of adaptation potential to ocean acidification in sea urchins living in “future ocean” conditions at a CO2 vent’

Mangrove lagoons of the Great Barrier Reef support coral populations persisting under extreme environmental conditions

Global degradation of coral reefs has increased the urgency of identifying stress-tolerant coral populations, to enhance understanding of the biology driving stress tolerance, as well as identifying stocks of stress-hardened populations to aid reef rehabilitation. Surprisingly, scientists are continually discovering that naturally extreme environments house established coral populations adapted to grow within extreme abiotic conditions comparable to seawater conditions predicted over the coming century. Such environments include inshore mangrove lagoons that carry previously unrecognised ecosystem service value for corals, spanning from refuge to stress preconditioning. However, the existence of such hot-spots of resilience on the Great Barrier Reef (GBR) remains entirely unknown. Here we describe, for the first time, 2 extreme GBR mangrove lagoons (Woody Isles and Howick Island), exposing taxonomically diverse coral communities (34 species, 7 growth morphologies) to regular extreme low pH (<7.6), low oxygen (7°C) conditions. Coral cover was typically low (0.5 m diameter), with net photosynthesis and calcification rates of 2 dominant coral species (Acropora millepora, Porites lutea) reduced (20-30%), and respiration enhanced (11-35%), in the mangrove lagoon relative to adjacent reefs. Further analysis revealed that physiological plasticity (photosynthetic ‘strategy’) and flexibility of Symbiodiniaceae taxa associations appear crucial in supporting coral capacity to thrive from reef to lagoon. Prevalence of corals within these extreme conditions on the GBR (and elsewhere) increasingly challenge our understanding of coral resilience to stressors, and highlight the need to study unfavourable coral environments to better resolve mechanisms of stress tolerance.

Continue reading ‘Mangrove lagoons of the Great Barrier Reef support coral populations persisting under extreme environmental conditions’

Factors regulating nitrification in the Arctic Ocean: potential impact of sea ice reduction and ocean acidification

Nitrification is susceptible to changes in light and pH and, thus, could be influenced by recent sea ice reductions and acidification in the Arctic Ocean. We investigated the sensitivity of nitrification to light, pH, and substrate availability in a natural nitrifier community of the Arctic Ocean. Nitrification was active near the bottom of the shelf region (250 m). In pH control experiments, nitrification rates significantly declined when the pH was manipulated to be 0.22 lower than the controls. However, nitrification was relatively insensitive to changes in pH compared to changes in light. Light control experiments showed that nitrification was inhibited by a light intensity above 0.11 mol photons m−2 day−1, which was presumably the light threshold. A light intensity greater than the light threshold extended to the shelf bottom and upper halocline layer, limiting nitrification in these waters. Satellite data analyses indicated that the area where light levels inhibit nitrification has increased throughout the Arctic Ocean due to the recent sea ice reduction, which may lead to a declining trend in nitrification. Our results suggest that stronger light levels in the future Arctic Ocean could further suppress nitrification and alter the composition of inorganic nitrogen, with implications for the structure of ecosystems.

Continue reading ‘Factors regulating nitrification in the Arctic Ocean: potential impact of sea ice reduction and ocean acidification’

The inhibition of ocean acidification on the formation of oyster calcified shell by regulating the expression of Cgchs1 and Cgchit4

The biosynthesis of a calcified shell is critical for the development of oyster larvae. This process can be severely inhibited by CO2-induced ocean acidification, causing mass mortality of oyster larvae. However, the underlying molecular mechanism of such process has not been well explored until now. In the present study, a homolog of chitin synthase (named as Cgchs1) and a homolog of chitinase (named as Cgchit4) were identified from the Pacific oyster Crassostrea gigas. The cDNA sequences of Cgchs1 and Cgchit4 were of 813 bp and 2118 bp, encoding a putative polypeptide of 271 amino acids and 706 amino acids, respectively. There were a Chitin_synth_2 domain and a Glyco_18 domain in the inferred amino acid sequences of Cgchs1 and Cgchit4, respectively. Both Cgchs1 and Cgchit4 shared high sequence identity with their homologs in vertebrates. In addition, when oyster larvae were exposed to acidification treatment (pH 7.4), their shell biosynthesis process was seriously restrained. The expression level of Cgchs1 mRNA was significantly suppressed while that of Cgchit4 was dramatically activated upon acidification treatment. Cgchs1 and Cgchit4 are critical enzymes for chitin metabolism, and such changes in their mRNA expression could result in the decrease of chitin content in oyster larvae’s shells, which might lead to the failure of shell formation. Therefore, results in the present study suggested that acidified seawater might inhibit the formation of oyster calcified shell by suppressing the biosynthesis of chitin.

Continue reading ‘The inhibition of ocean acidification on the formation of oyster calcified shell by regulating the expression of Cgchs1 and Cgchit4’

Hsp70 knockdown reduced the tolerance of Litopenaeus vannamei post larvae to low pH and salinity

Highlights

• Injection of the white-leg shrimp with Hsp70 dsRNA eliminated Hsp70 mRNA and protein in post-larvae but had no apparent effect on survival.

• However, the survival of post larvae lacking Hsp70, as compared to those containing the heat shock protein, was reduced more than two-fold 48 h after exposure to low salinity and pH, strongly indicating that Hsp70 is required for protection against these abiotic stressors.

• This is the first time to our knowledge that RNAi has been used to demonstrate a role for Hsp70 in protecting P. vannamei post larvae against salinity and pH stress, an effect undoubtedly due to the importance Hsp70 assumes in maintaining protein homeostasis within cells.

Abstract

To better understand stress tolerance of the White leg shrimp, Litopenaeus vannamei, RNA interference (RNAi) was used to assess the role of the molecular chaperone, Hsp70 in protecting post larvae against low pH and salinity. As revealed by SDS-polyacrylamide gel electrophoresis and immunoprobing of western blots, injection of L. vannamei post larvae with Hsp70 and Hsc70 dsRNA reduced Hsp70 but had no apparent effect on survival. However, the survival of post larvae lacking Hsp70, as compared to those containing the heat shock protein, was reduced more than two-fold 48 h after exposure to low salinity and pH, strongly indicating that Hsp70 is required for protection against these abiotic stressors. This is the first time to our knowledge that RNAi has been used to demonstrate a role for Hsp70 in protecting L. vannamei post larvae against salinity and pH stress, an effect undoubtedly due to the importance Hsp70 assumes in maintaining protein homeostasis within cells. Information generated in this work provides further understanding of Hsp70 function in the stress response of Penaeid shrimp and will assist in the development of strategies to mitigate abiotic stresses experienced by aquatic invertebrates during aquaculture.

Continue reading ‘Hsp70 knockdown reduced the tolerance of Litopenaeus vannamei post larvae to low pH and salinity’


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Ocean acidification in the IPCC AR5 WG II

OUP book