Membrane lipid metabolism, heat shock response and energy costs mediate the interaction between acclimatization and heat-hardening response in the razor clam Sinonovacula constricta

Diurnal temperature variation exacerbates the effects of phenanthrene on Trochus pyramis Born in a warmer ocean

Under global change scenarios, rising seawater temperature could affect the toxicity of chemical pollutants on marine organisms. Tropical species inhabiting coastal areas are especially vulnerable to diurnal temperature variation (DTV), yet the impacts of DTV on pollutant toxicity remains obscured. This study evaluated how a 4℃ DTV affects the toxicity of phenanthrene (PHE) on the physiological traits of Trochus pyramis, a key herbivorous gastropod in coral reef ecosystems, under both control (28°C) and elevated temperature (31°C) conditions. T. pyramis were exposed to PHE (1 and 10 μg/L) across different temperature scenarios for 14 days. Subsequently, PHE bioaccumulation, heat tolerance, antioxidant responses, and energy budgets of T. pyramis were assessed. The results showed that PHE had minimal effect on T. pyramis under DTV at 28°C, likely due to enhanced antioxidant responses and adaptive energy supply strategies induced by DTV. Conversely, DTV exacerbated the deleterious effect of PHE at 31°C, particularly under exposure to high-concentration PHE (10 μg/L), leading to reduced heat tolerance, suppressed antioxidant responses, and disturbed energy metabolism. These results underscore the necessity of incorporating DTV into PHE risk assessments for coral reef ecosystems in the context of global warming.

Integrated transcriptomic and metabolomic analysis reveals the causes of mass mortality in juvenile pearl oysters (Pinctada maxima)

Pinctada maxima is a pearl oyster species producing large, high-quality marine pearls. However, juvenile mortality (shell length < 5 cm) in this species adversely affects commercial pearl production. Understanding the molecular mechanism and genes related to mass mortality will help mitigate this problem. Therefore, the present study investigated the transcriptomic and metabolic differences between pearl oysters during high mortality (HM) and after this period (PD) to shed light on the causes of juvenile mass mortality. Initial analysis of biochemical parameters revealed that protease, α-amylase, and catalase activities in the hepatopancreatic tissues of pearl oysters at the HM stage were significantly lower than at the PD stage. Conversely, glutathione and lysozyme contents, and superoxide dismutase, acid phosphatase, alkaline phosphatase activities were notably higher at the HM stage than at the PD stage. Metabolomic analysis identified 98 metabolites in the adductor muscle significantly different between the two stages, which enriched glycerophospholipid metabolism, glutathione metabolism, arachidonic acid metabolism, oxidative phosphorylation, and neuroactive ligand-receptor interaction pathways. Transcriptome analysis identified 677 differentially expressed genes in the adductor muscle between these stages, which enriched neuroactive ligand-receptor interaction, glutathione metabolism, and ECM-receptor interaction pathways. Finally, an integrated analysis of the metabolome and transcriptome suggested that pearl oysters at the HM stage experience oxidative stress, activate immune-related genes, and exacerbate the low energy status. These findings on the causes of mass mortality lay a theoretical foundation for improving the survival rate of juveniles and advancing the industrialization of P. maxima.

Oxidative Damage and Antioxidants as Markers for the Selection of Emersion Hardening Treatments in GreenshellTM Mussel Juveniles (Perna canaliculus)

Transport out of the water is one of the most challenging events for juvenile Perna canaliculus and can be a highly inefficient process, with many juveniles subsequently being lost following extended periods of emersion. Hardening techniques offer a possible method for reducing transport-related stress. In this study, different hardening treatments (short, long and intermittent sub-lethal emersion) were used to prepare ~1.2 mm P.canaliculus for transport (20 h) and subsequent reoxygenation stress during re-immersion (i.e., recovery). The oxidative stress responses, resettlement behaviour, respiration rates and survival of the mussels after transport and during recovery were all assessed. Short emersion (1 h) as a hardening treatment prior to transport did not cause major stress to the mussels, which maintained respiration at control levels, showed significantly stimulated antioxidant defences during recovery, showed greater resettlement behaviour and remained viable after 24 h of recovery. In comparison, the long and intermittent emersion treatments negatively impacted oxidative stress responses and affected the viability of the mussels after 24 h of recovery. This study showed that exposing juvenile P.canaliculus to a mild stress prior to transport may stimulate protective mechanisms, therefore eliciting a hardening response, but care must be taken to avoid overstressing the mussels. Improving the management of stress during the transport of juvenile mussels may be key to minimising mussel losses and increasing harvest production, and biomarkers associated with oxidative stress/antioxidant metabolism could be valuable tools to ensure emersion hardening does not overstress the mussels and reduce survival.

Hiding from heat: The transcriptomic response of two clam species is modulated by behaviour and habitat

Rising occurrence of extreme warming events are profoundly impacting ecosystems, altering their functioning and services with significant socio-economic consequences. Particularly susceptible to heatwaves are intertidal shellfish beds, located in estuarine areas already stressed by factors such as rainfall events, red tides, eutrophication, and pollution. In Galicia, Northwestern Spain, these beds support vital shellfisheries, featuring the native clam Ruditapes decussatus and the non-indigenous R. philippinarum. Over recent decades, these populations have experienced notable abundance shifts due to various anthropogenic impacts, including climate change. In this habitat, patches of the seagrass Zostera noltei that coexist with bare sand can act as thermal refuges for benthic organisms such as clams. To assess the impact of heatwaves on these ecosystems, a mesocosm experiment was conducted. Juveniles of both clam species in two habitat types-bare sand and sand with Z. noltei-were exposed to simulated atmospheric heatwaves during diurnal low tide for four consecutive days. Subsequent transcriptomic analysis revealed that high temperatures had a more pronounced impact on the transcriptome of R. philippinarum compared to R. decussatus. The habitat type played a crucial role in mitigating heat stress in R. philippinarum, with the presence of Z. noltei notably ameliorating the transcriptomic response. These findings have direct applications in shellfishery management, emphasizing the importance of preserving undisturbed patches of Z. noltei as thermal refuges, contributing to the mitigation of heatwave effects on shellfish populations.

Rapid heat hardening in embryos of the lizard Anolis sagrei

Adaptive thermal tolerance plasticity can dampen the negative effects of warming. However, our knowledge of tolerance plasticity is lacking for embryonic stages that are relatively immobile and may benefit the most from an adaptive plastic response. We tested for heat hardening capacity (a rapid increase in thermal tolerance that manifests in minutes to hours) in embryos of the lizard Anolis sagrei. We compared the survival of a lethal temperature exposure between embryos that either did (hardened) or did not (not hardened) receive a high but non-lethal temperature pre-treatment. We also measured heart rates (HRs) at common garden temperatures before and after heat exposures to assess metabolic consequences. 'Hardened' embryos had significantly greater survival after lethal heat exposure relative to 'not hardened' embryos. That said, heat pre-treatment led to a subsequent increase in embryo HR that did not occur in embryos that did not receive pre-treatment, indicative of an energetic cost of mounting the heat hardening response. Our results are not only consistent with adaptive thermal tolerance plasticity in these embryos (greater heat survival after heat exposure), but also highlight associated costs. Thermal tolerance plasticity may be an important mechanism by which embryos respond to warming that warrants greater consideration.

Heat-shock responses: systemic and essential ways of malaria parasite survival

Fever is a part of the human innate immune response that contributes to limiting microbial growth and development in many infectious diseases. For the parasite Plasmodium falciparum, survival of febrile temperatures is crucial for its successful propagation in human populations as well as a fundamental aspect of malaria pathogenesis. This review discusses recent insights into the biological complexity of the malaria parasite's heat-shock response, which involves many cellular compartments and essential metabolic processes to alleviate oxidative stress and accumulation of damaged and unfolded proteins. We highlight the overlap between heat-shock and artemisinin resistance responses, while also explaining how the malaria parasite adapts its fever response to fight artemisinin treatment. Additionally, we discuss how this systemic and essential fight for survival can also contribute to parasite transmission to mosquitoes.

Loss of mitochondrial performance at high temperatures is correlated with upper thermal tolerance among populations of an intertidal copepod

Environmental temperatures have pervasive effects on the performance and tolerance of ectothermic organisms, and thermal tolerance limits likely play key roles underlying biogeographic ranges and responses to environmental change. Mitochondria are central to metabolic processes in eukaryotic cells, and these metabolic functions are thermally sensitive; however, potential relationships between mitochondrial function, thermal tolerance limits and local thermal adaptation in general remain unresolved. Loss of ATP synthesis capacity at high temperatures has recently been suggested as a mechanistic link between mitochondrial function and upper thermal tolerance limits. Here we use a common-garden experiment with seven locally adapted populations of intertidal copepods (Tigriopus californicus), spanning approximately 21.5° latitude, to assess genetically based variation in the thermal performance curves of maximal ATP synthesis rates in isolated mitochondria. These thermal performance curves displayed substantial variation among populations with higher ATP synthesis rates at lower temperatures (20-25 °C) in northern populations than in southern populations. In contrast, mitochondria from southern populations maintained ATP synthesis rates at higher temperatures than the temperatures that caused loss of ATP synthesis capacity in mitochondria from northern populations. Additionally, there was a tight correlation between the thermal limits of ATP synthesis and previously determined variation in upper thermal tolerance limits among populations. This suggests that mitochondria may play an important role in latitudinal thermal adaptation in T. californicus, and supports the hypothesis that loss of mitochondrial performance at high temperatures is linked to whole-organism thermal tolerance limits in this ectotherm.

Metabolomic analysis provides new insights into the heat-hardening response of Manila clam (Ruditapes philippinarum) to high temperature stress

The temperature has always been a key environmental factor in Manila clam (Ruditapes philippinarum) culture. In this study, the Manila clam was treated to different temperature pre-heat (28 °C, 30 °C) and gained heat tolerance after recover of 12 h, and a survival rate (14.7 %-49.1 %) advantage after high temperature challenge (30 and 32 °C). To further investigate the physiological and metabolism changes in Manila clam that had experienced a heat stress, non-targeted metabolomics (LC-MS/MS) was used to analyze the metabolic responses of gills in three group Manila clams during the heat challenge. Metabolic profiles revealed that high temperature caused changes in fatty acid composition, energy metabolism, antioxidant metabolites, hydroxyl compounds, and amino acids in heat-hardened clams compared to non-hardened clams. We found a number of significantly enriched pathways, including cAMP signaling pathway, serotonergic synapse, and biosynthesis of unsaturated fatty acids in heat-hardened Manila clam compared with non-hardened and untreated Manila clam. After a brief high temperature treatment, the physiological maintenance ability of Manila clam was improved. Combined with metabolomics analysis, heat hardening treatment may improve the energy metabolism and antioxidant ability of Manila clam. These results provide new insights into the cellular and metabolic responses of Manila clams following high temperature stress.