Posts Tagged 'physiology'

Investigating the response of sea urchin early developmental stages to multiple stressors related to climate change

Within climate change biology, the red sea urchin Mesocentrotus franciscanus has
remained relatively overlooked despite its sizeable ecological and economic importance, particularly within the context of multi-stressor effects. I assembled and described a developmental transcriptome for M. franciscanus, providing a useful molecular resource with which to study this organism. I then examined both the physiological and molecular mechanisms that underlie the response of early developmental stage (EDS) M. franciscanus to different combinations of pH levels and temperatures that represented ecologically
relevant present and future ocean conditions. Elevated pCO2 levels decreased embryo body size, but at the prism embryo stage, warmer temperatures helped to offset this via an increase in body size. Warmer temperatures also slightly increased the thermal tolerance of prism stage embryos. Neither pCO2 nor temperature stressors affected prism metabolic rate as measured by rate of oxygen consumption. Gene expression patterns differed by developmental stage and by temperature exposure. Elevated temperatures led to an upregulation of cellular stress response genes. Under colder temperatures, the embryos
exhibited an up-regulation of epigenetic genes related to histone modifications.
There was a comparatively minimal transcriptomic response to different pCO2 levels. Examining the physiological and molecular responses of EDS M. franciscanus to multiple stressors provided much needed information regarding a species of significant ecological and economic value by examining its capacity to respond to stressors related to climate change and ocean acidification under an ecologically relevant context.

I also investigated the role of transgenerational plasticity (TGP), in which the
environmental conditions experienced by parents affect progeny phenotypes. TGP may provide a valuable mechanism by which organisms can keep pace with relatively rapid environmental change. Adult S. purpuratus were conditioned to two divergent, but ecologically relevant pH levels and temperatures throughout gametogenesis. The adults were spawned and crossed, and their progeny were raised under different pH levels to determine if maternal conditioning impacted the response of the progeny to low pH stress. I investigated maternal provisioning, a mechanism of TGP, by measuring the size, total protein content, and total lipid content of the eggs that they produced. Acclimatization of the
adult urchins to simulated upwelling conditions (combined low pH, low temperature) appeared to increase maternal provisioning of lipids to the eggs but did not affect egg size or protein content. I also investigated the physiology and gene expression of progeny responding to low pH stress, which were affected more by maternal conditioning than by offspring pH treatment. Maternal conditioning to simulated upwelling resulted in larger offspring body sizes. Additionally, I found the progeny expressed differential regulatory
patterns of genes related to epigenetic modifications, ion transport, metabolic processes and ATP production. This work showed that adult exposure to upwelling conditions can improve the resilience of EDS progeny to low pH levels.

Continue reading ‘Investigating the response of sea urchin early developmental stages to multiple stressors related to climate change’

Impact of ocean acidification and warming on mitochondrial enzymes and membrane lipids in two Gadoid species

Mitochondrial respiration is a multi-step pathway that involves matrix and membrane-associated enzymes and plays a key role in acclimation to variable environmental conditions, but until now it has not been clear which of these steps would be most important in acclimation to changing temperatures and CO2 levels. Considering scenarios of ocean warming and acidification we assessed the role and limitation to phenotypic plasticity in the hearts of two Gadoid species adapted to different thermal ranges: the polar cod (Boreogadus saida), an Arctic stenotherm, and the Northeast Arctic population of Atlantic cod (NEAC, Gadus morhua), a cold eurytherm. We analysed the capacity of single enzymes involved in mitochondrial respiration [citrate synthase (CS), succinate dehydrogenase (SDH), cytochrome c oxidase (CCO)], the capacity of the electron transport system and the lipid class composition of the cellular membranes. Juveniles of the two species were held for four months at four temperatures (0, 3, 6, 8 °C for polar cod and 3, 8, 12, 16 °C for NEAC), at both ambient and elevated PCO2 (400 µatm and 1170 µatm, respectively). Polar cod showed no changes in mitochondrial enzyme capacities and in the relative lipid class composition in response to altered temperature or elevated PCO2. The lack of cardiac cellular plasticity together with evidence at the whole-animal level coming from other studies is indicative of little or no ability to overcome stenothermy, in particular during acclimation to 8 °C. In contrast, eurythermal NEAC exhibited modifications of membrane composition towards a more rigid structure and altered enzyme capacities to preserve functionality at higher temperatures. Furthermore, in NEAC, the capacities of SDH, CCO and CS were increased by high levels of CO2 if combined with high temperatures (12 and 16 °C), suggesting the compensation of an inhibitory effect. These results indicate that the cold eurythermal species (NEAC) is able to alter its mitochondrial function to a far greater extent than the Arctic stenotherm (polar cod), indicating greater resilience to variable environmental conditions. This difference in plasticity may underpin differences in the resilience to climate change and affect future species distributions and, eventually, survival.

Continue reading ‘Impact of ocean acidification and warming on mitochondrial enzymes and membrane lipids in two Gadoid species’

Reduced pH and elevated salinities affect the physiology of intertidal crab Minuca mordax (Crustacea, Decapoda)

Minuca mordax is a model for studies on ocean acidification and sea-level rise because lives in mangroves and riverbanks with low pH. We investigated the physiology of the crabs exposed to differents pH (6.5 and 5.8) and salinity (25, 30, 35, 40 45S). There was not mortality or alterations in the hypo-osmoregulation, suggesting that the factors did not affect salt absorption/secretion. Reduced pH changed metabolism, ammonia excretion, and hepatosomatic index in relation to the animals kept in control pH. At elevated salinities, metabolism increased when animals were kept in control pH, but it decreased when they were exposed to acidified pH. energy substrate, varied between proteins to a mixture of proteins and lipids. Important physiological parameters, related to the catabolism of amino acids and to the energy demand are changed and the consequences might include alterations in growth and reproduction due to the energy channeling to limiting processes of homeostasis.

Continue reading ‘Reduced pH and elevated salinities affect the physiology of intertidal crab Minuca mordax (Crustacea, Decapoda)’

Ocean acidification’s potential effects on keratin protein in cetacean baleen and other integumentary tissue

Marine uptake of atmospheric CO2 from increased anthropogenic carbon emissions is leading to ocean acidification, which poses a grave threat to marine life. The potential risk of acidified seawater to cetaceans (whales, dolphins, and porpoises) and other marine mammals has received little attention, but deserves close scrutiny due to their long lifespan. Cetaceans also lack the protective fur coat which protects typical mammals, and the feeding of mysticete whales depends on a filter made of a unique tissue: baleen. Like hair and other integumentary products, baleen is made of keratin, a fibrous structural protein. We submerged baleen and skin samples from bowhead whales (Balaena mysticetus) and North Atlantic right whales (Eubalaena glacialis) for 12 weeks in seawater of varying pH representing current and projected acidification. When tested for mechanical strength via loading in compression and tension, the acid-exposed specimens were slightly but not statistically different in weakness (as measured by deformation for a given stress or the force needed to fracture the sample). Other samples exposed to low pH were examined via nuclear magnetic resonance testing to search for the presence of amino acids expected if the keratin protein deteriorated due to acid exposure; even at extreme acidity these amino acids were not found, suggesting keratin is strongly resistant to acid-induced breakdown. Finally, whale skin samples exposed to acidified seawater and examined microscopically did not demonstrate notable changes in appearance, texture, or resistance to stretching. Ocean acidification can possibly harm keratin-based cetacean tissues, but no acidrelated effects were conclusively demonstrated by these tests.

Continue reading ‘Ocean acidification’s potential effects on keratin protein in cetacean baleen and other integumentary tissue’

Effects of pH on growth and biochemical responses in Agarophyton vermiculophyllum under different temperature conditions

The effects of pH (6.2, 7.2, 8.2, 9.2, and 10.2) under rising temperature (30 °C vs 20 °C) on Agarophyton vermiculophyllum growth and bio-physiology were investigated. Results showed that A. vermiculophyllum exhibited lower growth rates under elevated temperature in all pH values. Chlorophyll a, carotenoid, and phycocyanin levels were significantly enhanced by temperature elevation (p < 0.05). Enhanced H2O2 production either at lower or higher pH values correlated with lipid peroxidation (LPO) levels under elevated temperature, which suggested oxidative stress development. Oxidative damage was more severe at elevated pH values, which is confirmed by higher reactive oxygen species (ROS) levels. Compared with ambient pH 8.2 value, lower pH values under elevated temperature lead to increase activities of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST), indicating that these enzymes played an important role to combat stress. However, decreased glutathione reductase (GR) and glutathione peroxidase (GPx) activities indicate least contribution for ROS scavenging at lower pH values. On contrary, SOD and CAT declined at elevated pH values compared with ambient pH, suggesting least contribution for ROS removal. Moreover, enhanced GR and GPx activities at elevated pH and temperature are not enough to scavenge ROS production. These data are consistent with higher H2O2 and LPO levels, and lower GST activities. Collectively, our results indicated that either pH fluctuations or elevated temperature displayed a disadvantageous influence on growth and bio-physiology of A. vermiculophyllum. Therefore, rising temperature alleviates adverse effects of seawater acidification, but it aggravates the negative effects of seawater alkalization on growth and bio-physiology of A. vermiculophyllum.

Continue reading ‘Effects of pH on growth and biochemical responses in Agarophyton vermiculophyllum under different temperature conditions’

Molecular and physiological responses to long-term carbon dioxide exposure in Atlantic salmon (Salmo salar)

Highlights

• Atlantic salmon was exposed to six CO2 concentrations (5–40 mg/L) for 12 weeks followed by 6-weeks without exposure (<5 mg/L).

• Positive (pH, K+, HCO3− and PCO2) and negative (Na+, Cl−) linear relationships with CO2 exposure were observed as long as CO2 exposure persists, returning to normal levels when CO2 exposure is ended.

• Microarrays analysis of gill tissue detected 71 differentiated expressed genes that responded to CO2 and after termination of exposure 27 down-regulated genes showed compensatory up-regulation.

• The assumption that Atlantic salmon is unaffected by CO2 concentrations below the 15 mg/L threshold should be revised.

Abstract

Optimal water quality is vital for the growth of Atlantic salmon aquaculture production. Recent data showed that Atlantic salmon feed intake and growth reduce linearly with increasing water carbon dioxide (CO2) concentrations, suggesting that even relatively low concentrations may impact fish performance. This study evaluated the molecular and physiological responses of Atlantic salmon (Salmo salar) to long-term CO2 exposure. For this purpose, Atlantic salmon post-smolts (N = 900; 67 ± 8 g) were exposed to six CO2 treatments (5, 12, 19, 26, 33 and 40 mg/L) for 12-weeks (RAS phase) followed by non-CO2 exposure for a (<5 mg/L) period of 6-weeks (seawaterphase). Results from blood analysis of fish exposed to CO2 for 12 weeks showed that CO2 lead to significantly higher pH, K+, HCO3− and PCO2 and lower Na+ and Cl− plasma concentrations. Whereas, haematocrit, Ca+, Mg2+, urea and glucose concentrations were similar among all CO2 treatments. After 6 weeks in the seawater phase, all the parameters that were previously altered, became similar among all CO2 treatments. Gill microarray results analysis showed 88 differentially expressed genes, resulting from the CO2 exposure. At the end of the RAS phase (week 12), fish exposed to high CO2 (40 mg/L) in comparison to fish exposed to low CO2 (5 mg/L), showed 60 down-regulated genes, including genes encoding proteins involved in immune responses, differentiation, and maintenance of tissue structure. There was no evidence for stress and metabolic changes directed to neutralization of disturbance caused with high CO2. After 6 weeks in the seawater phase, a switch of expression from down regulated to up-regulated was observed. In conclusion, the present study brings new insights on the molecular and physiological responses of Atlantic salmon post-smolts to long-term CO2 exposure. Several osmoregulation and acid-base balance parameters as well as gill gene expression levels were altered for as long as CO2 exposure persisted. Moreover, most of these parameters were linearly related with the environmental CO2 concentrations (5–40 mg/L range). The data from this study adds to recent findings that CO2 concentrations below the 15 mg/L threshold still have an impact on Atlantic salmon. This finding may be relevant for a better dimensioning and management of production systems where CO2 may accumulate in the water such as in recirculating aquaculture systems (RAS).

Continue reading ‘Molecular and physiological responses to long-term carbon dioxide exposure in Atlantic salmon (Salmo salar)’

Combined effects of CO2-driven ocean acidification and Cd stress in the marine environment: enhanced tolerance of Phaeodactylum tricornutum to Cd exposure

Highlights

• Combined effects of OA and Cd exposure on Phaeodactylum tricornutum were analyzed.

• Either OA (1500 ppm) or Cd stress (1.2 mg/L) alone inhibited the growth of P. tricornutum.

• A significantly enhanced tolerance of P. tricornutum to Cd of 1.2 mg/L occurred under OA.

Abstract

Ocean acidification (OA) and heavy metals are common stress factors for marine ecosystems subject to anthropogenic impacts. OA coupled with the heavy metal is likely to affect marine species. This study investigated the single and combined effects of OA (1500 ppm) and cadmium (Cd; 0.4, 1.2 mg/L) on the marine diatom Phaeodactylum tricornutum under 7 d exposure. The results clearly indicated that either OA or Cd stress (1.2 mg/L) alone inhibited the growth of P. tricornutum. However, under the combined OA-Cd stress, the growth inhibition disappeared, and the intracellular oxidative damage was mitigated. These results indicated a significantly enhanced tolerance of P. tricornutum to Cd while under OA conditions, which could be beneficial to the survival of this diatom. This study will ultimately help us understand the responses of marine organisms to multiple stressors and have broad implications for the potential ecological risks of Cd under future OA conditions.

Continue reading ‘Combined effects of CO2-driven ocean acidification and Cd stress in the marine environment: enhanced tolerance of Phaeodactylum tricornutum to Cd exposure’


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