The proteomic response of the mussel congeners Mytilus galloprovincialis and M. trossulus to acute heat stress: implications for thermal tolerance limits and metabolic costs of thermal stress

High water temperature raised the requirements of methionine for spotted seabass (Lateolabrax maculatus)

This study evaluated the effects of dietary methionine level and rearing water temperature on growth, antioxidant capacity, methionine metabolism, and hepatocyte autophagy in spotted seabass (Lateolabrax maculatus). A factorial design was used with six methionine levels [0.64, 0.85, 1.11, 1.33, 1.58, and 1.76%] and two temperatures [moderate temperature (MT): 27 ℃, and high temperature (HT): 33 ℃]. The results revealed the significant effects of both dietary methionine level and water temperature on weight gain (WG) and feed efficiency (FE), and their interaction effect was found on WG (P < 0.05). In both water temperatures tested, fish WG increased with increasing methionine level up to 1.11% and decreased thereafter. The groups of fish reared at MT exhibited dramatically higher WG and FE than those kept at HT while an opposite trend was observed for feed intake. Liver antioxidant indices including reduced glutathione and malondialdehyde (MDA) concentrations, and catalase and superoxide dismutase (SOD) activities remarkably increased in the HT group compared to the MT group. Moreover, the lowest MDA concentration and the highest SOD activity were recorded at methionine levels between 1.11% and 0.85%, respectively, regardless of water temperatures. Expression of methionine metabolism-related key enzyme genes (mat2b, cbs, ms, and bhmt) in the liver was increased at moderate methionine levels, and higher expression levels were detected at MT compared to HT with the exception of ms gene relative expression. Relative expression of hepatocyte autophagy-related genes (pink1, atg5, mul1, foxo3) and hsp70 was upregulated by increasing methionine level up to a certain level and decreased thereafter and increasing water temperature led to significantly enhanced expression of hsp70. In summary, HT induced heat stress and reduced fish growth, and an appropriate dietary methionine level improved the antioxidant capacity and stress resistance of fish. A second-order polynomial regression analysis based on the WG suggested that the optimal dietary methionine level for maximum growth of spotted seabass is 1.22% of the diet at 27 ℃ and 1.26% of the diet at 33 ℃, then 1.37 g and 1.68 g dietary methionine intake is required for 100 g weight gain at 27 ℃ or 33 ℃, respectively.

Acclimation of intertidally reproducing sea-snails protects embryos from lethal effects of transient hyperthermia

Embryos of Ilyanassa obsoleta (from Massachusetts and Florida) and Phrontis vibex (from Florida) were exposed to temperatures from 33 to 37°C. In both species, very young embryos are especially sensitive to thermal stress. Brief early heat shock did not disturb spiral cleavage geometry but led to variable, typically severe defects in larval morphogenesis and tissue differentiation. In Ilyanassa but not P. vibex, early heat shock resulted in immediate slowing or arrest of interphase progression during early cleavage. This reversible arrest was correlated with improved prognosis for larval development and (in Massachusetts snails, at least) depended on parental acclimation to warm temperature (~25.5°C). Embryos from Massachusetts snails housed at lower temperature (16°C) exhibited cytokinesis failure when briefly incubated at 33°C during early cleavage, and tissue differentiation failure during incubation at 33°C begun at later stages. This preliminary study reveals a case in which stress-conditioned parents may endow embryos with protection against potentially lethal thermal stress during the most vulnerable stages of life.

Uncovering the roles of sirtuin activity and food availability during the onset of the heat shock response in the California mussel (Mytilus californianus): Implications for antioxidative stress responses

Sirtuins are a class of NAD+-dependent deacylases, with known regulatory roles in energy metabolism and cellular stress responses in vertebrates. Previous work using marine mussels have suggested a similar role in invertebrates, providing a potential mechanism linking food availability and thermal sensitivity in Mytilids. Sirtuin inhibitors affect mussels' recovery from environmental stressors, including acute heat shock and well-fed mussels exposed to sirtuin inhibitors and/or acute heat shock respond differently than poorly fed mussels, at the protein and whole-organism levels. While this implies a relationship between sirtuins, food availability, and temperature, the direct effects of sirtuin inhibitors (nicotinamide and suramin) on sirtuin activity or their putative effectors have not been explicitly tested. In this study, adult Mytilus californianus were acclimated to a low or high food availability and exposed to one of the following treatments: control, acute heat shock, sirtuin inhibitors, or acute heat shock and sirtuin inhibitors. Mussels increased sirtuin activity during early recovery (5 h) from sirtuin inhibition and acute heat shock, but only if acclimated to a high food availability. Redox balance was also impacted in mussels acclimated to high food availability and exposed to sirtuin inhibitors, signifying interactions between ration, acute heat shock, and sirtuin inhibitors. Additionally, we found a correlation between sirtuin and superoxide dismutase activities, suggesting a potential regulatory role of oxidative stress by sirtuins. Following prolonged recovery (17 h), we found increased sirtuin activity in mussels acclimated to low food availability, indicating that endogenous sirtuin activity may be related to food availability in mussels.

The mechanisms involved in byssogenesis in Pteria penguin under different temperatures

Byssus is important for marine bivalves to adhere robustly to diverse substrates and resist environmental impacts. The winged pearl oyster, Pteria penguin, can reattach or not reattach to the same environment, which leaves the development and survival of the oyster population at risk. In this study, diverse methods were employed to evaluate the byssus quality and explore the mechanism of byssus secretion at different temperatures. The results demonstrated that oysters maintained their byssus properties at different temperatures through polyphenol oxidase (PPO) and reactive oxygen species (ROS) variation. They were both higher at 27 °C than at 21 °C. Furthermore, PPO activities of WB27 (31.78 U/g ± 1.50 U/g) were significantly higher than NB27, WB21, and NB21. Sectional observation revealed three types of vesicles, from which a novel vesicle might participate in byssogenesis as a putative metal storage particle. Moreover, cytoskeletal proteins may cooperate with cilia to transport byssal proteins, which then facilitate byssus formation under the regulation of upstream signals. Transcriptome analysis demonstrated that protein quality control, ubiquitin-mediated proteolysis, and cytoskeletal reorganization-related genes contributed to adaptation to temperature changes and byssus fabrication, and protection-related genes play a critical role in byssogenesis, byssus toughness, and durability. These results were utilized to create a byssogenesis mechanism model, to reveal the foot gland and vesicle types of P. penguin and provide new insights into adaptation to temperature changes and byssus fabrication in sessile bivalves.

Population Genetic Divergence among Worldwide Gene Pools of the Mediterranean Mussel Mytilus galloprovincialis

The Mediterranean mussel Mytilus galloprovincialis is distributed in both hemispheres either natively or introduced. The updated population genetic distribution of this species provides a useful knowledge against which future distribution shifts could be assessed. This study, performed with seven microsatellite markers and three reference species (M. edulis, M. chilensis and M. trossulus), aimed to determine the scenario of genetic divergence between 15 samples of M. galloprovincialis from 10 localities in Europe, Africa, Asia, Australia, North America and South America. In agreement with previous data, M. trossulus was the most divergent taxon of the genus, but M. chilensis appeared as an intermediate taxon between M. edulis and M. galloprovincialis, though closer to this latter. M. galloprovincialis from the Atlantic Northeast appears as the most likely source of worldwide exotic settlements instead of the previously thought Mediterranean population. The successful worldwide establishment of M. galloprovincialis suggests it is a flexible evolutionary species (FES), i.e., a species or population whose genetic background allows it to rapidly adapt to changing environments. This natural endowed plastic adaptation makes it a candidate resilient species amidst the ongoing climatic change.

Multi-omics reveals largely distinct transcript- and protein-level responses to the environment in an intertidal mussel

Organismal responses to stressful environments are influenced by numerous transcript- and protein-level mechanisms, and the relationships between expression changes at these levels are not always straightforward. Here, we used paired transcriptomic and proteomic datasets from two previous studies from gill of the California mussel, Mytilus californianus, to explore how simultaneous transcript and protein abundance patterns may diverge under different environmental scenarios. Field-acclimatized mussels were sampled from two disparate intertidal sites; individuals from one site were subjected to three further treatments (common garden, low-intertidal or high-intertidal outplant) that vary in temperature and feeding time. Assessing 1519 genes shared between the two datasets revealed that both transcript and protein expression patterns differentiated the treatments at a global level, despite numerous underlying discrepancies. There were far more instances of differential expression between treatments in transcript only (1451) or protein only (226) than of the two levels shifting expression concordantly (68 instances). Upregulated expression of cilium-associated transcripts (likely related to feeding) was associated with relatively benign field treatments. In the most stressful treatment, transcripts, but not proteins, for several molecular chaperones (including heat shock proteins and endoplasmic reticulum chaperones) were more abundant, consistent with a threshold model for induction of translation of constitutively available mRNAs. Overall, these results suggest that the relative importance of transcript- and protein-level regulation (translation and/or turnover) differs among cellular functions and across specific microhabitats or environmental contexts. Furthermore, the degree of concordance between transcript and protein expression can vary across benign versus acutely stressful environmental conditions.

Oxytetracycline-induced inflammatory process without oxidative stress in blue mussels Mytilus trossulus

Potentially harmful compounds including pharmaceuticals are commonly found in marine waters and sediments. Amongst those, antibiotics and their metabolites are detected worldwide in various abiotic (at concentrations as high as µg/L) and biotic matrices at ng/gram of tissue, posing a risk to non-target species exposed to them such as blue mussels. Amongst those, oxytetracycline (OTC) belongs to the most detected antibiotics in the marine environment. In this work, we concentrated on studying the potential induction of oxidative stress, activation of cellular detoxification processes (including Phase I and Phase II xenobiotic biotransformation enzymes) and multixenobiotic resistance pumps (Phase III) as well as changes in the aromatisation efficiency in Mytilus trossulus exposed to 100 μg/L OTC. Our results show that 100 µg/L OTC concentration did not provoke cellular oxidative stress and did not affect the expression of genes involved in detoxification processes in our model. Moreover, no effect of OTC on aromatisation efficiency was found. Instead, phenoloxidase activity measured in haemolymph was significantly higher in OTC exposed mussels than in those from the control (30.95 ± 3.33 U/L and 17.95 ± 2.75 U/L, respectively). OTC exposed mussels were also characterised by a tissue-dependant activation of major vault protein (MVP) gene expression (1.5 times higher in gills and 2.4 times higher in the digestive system) and a decreased expression of the nuclear factor kappa B-a (NF-κB) gene (3.4 times lower in the digestive system) when compared to those from the control. Additionally, an elevated number of regressive changes and inflammatory responses in tissues such as gills, digestive system and mantle (gonads) was observed underlining the worsening of bivalves' general health. Therefore, instead of a free-radical effect of OTC, we for the first time describe the occurrence of typical changes resulting from antibiotic therapy in non-target organisms like M. trossulus exposed to antibiotics such as OTC.

Cardiac performance and heart gene network provide dynamic responses of bay scallop Argopecten irradians irradians exposure to marine heatwaves

The increased frequency of marine heat waves (MHWs) caused by global climate change is predicted to threaten the survival of economic bivalves, therefore having severely adverse effects on local ecological communities and aquaculture production. However, the study of scallops facing MHWs is still scarce, particularly in the scallop Argopecten irradians irradians, which has a significant share of "blue foods" in northern China. In the present study, bay scallop heart was selected to detect its cardiac performance, oxidative impairment and dynamic molecular responses, accompanied by assessing survival variations of individuals in the simulated scenario of MWHs (32 °C) with different time points (0 h, 6 h, 12 h, 24 h, 3 d, 6 d and 10 d). Notably, cardiac indices heart rate (HR), heart amplitude (HA), rate-amplitude product (RAP) and antioxidant enzyme activities superoxide dismutase (SOD) and catalase (CAT) all peaked at 24 h but sharply dropped on 3 d, coinciding with mortality. Transcriptome analysis revealed that the heart actively defended against heat stress at the acute stage (<24 h) via energy supply, misfolded proteins correction and enhanced signal transduction, whereas regulation of the defense response and apoptotic process combined with twice transcription initiation were the dominant responses at the chronic stage (3-10 d). In particular, HSP70 (heat shock protein 70), HSP90 and CALR (calreticulin) in the endoplasmic reticulum were identified as the hub genes (top 5 %) in the HR-associated module via WGCNA (weighted gene co-expression network analysis) trait-module analysis, followed by characterization of their family members and diverse expression patterns under heat exposure. Furthermore, RNAi-mediated knockdown of CALR expression (after 24 h) significantly weakened the thermotolerance of scallops, as evidenced by a drop of 1.31 °C in ABT (Arrhenius break temperature) between the siRNA-injected group and the control group. Our findings elucidated the dynamic molecular responses at the transcriptome level and verified the cardiac functions of CALR in bay scallops confronted with stimulated MHWs.

Liquid chromatography-mass spectrometry based metabolomics investigation of different tissues of Mytilus galloprovincialis

The Mediterranean mussel (Mytilus galloprovincialis) is widely used in monitoring programs and in ecotoxicological studies to examine the biological effects of physicochemical parameter changes and the impact of chemical pollutants. Metabolomics has recently demonstrated high potential to gain further insight into the molecular effects of chemical exposure and the success of its application is dependent on the extent of prior metabolomics knowledge available on the target organism. Therefore, the purpose of this study was the investigation of the metabolites of five different functional tissues of male and female Mediterranean mussels (digestive gland, foot, gill and gonad tissues and in the remaining soft tissues) accessible to the analysis using the most common sample preparation recommended for tissue analysis (i.e. Bligh & Dyer). Metabolic fingerprints were acquired via liquid chromatography high-resolution mass spectrometry and the identification was based on an internal database developed in the laboratory. It led to the identification of 110 metabolites, among which amino acids, carboxylic acids, purine and pyrimidine metabolites were often the most abundant. The metabolic contents of the five tissues quantitatively and qualitatively differed, with a clear distinction between male and female contents observed in the gonads and digestive glands. These results underline the importance of selecting the most suitable tissue and sex to study the impact of contamination on metabolism and the need for further research to deeper characterize the metabolome of this organism.

Cataglyphis desert ants use distinct behavioral and physiological adaptations to cope with extreme thermal conditions

Some ant species live in hot and arid environments, such as deserts and savannas. Worker polymorphism-variation in worker size and/or morphology within colonies-is adaptive in such ecosystems because it enhances resistance to heat stress and increases the efficiency of resource exploitation. However, species with small, monomorphic workers are also frequently found in these environments. How species with distinct worker size and degrees of polymorphism deal with such stressful environments remains poorly studied. We investigated the behavioral, physiological, and molecular adaptations that may enhance heat and desiccation tolerance in two sympatric species of Cataglyphis desert ants that differ dramatically in worker size and polymorphism: C. viatica is polymorphic, while C. cubica is small and monomorphic. We found that worker size, water content, water loss, and protein regulation play a key role in thermal resistance. (i) Large C. viatica workers better tolerated heat and desiccation stress than did small C. viatica or C. cubica workers. The former had greater water content and lost proportionally less water to evaporation under thermal stress. (ii) Despite their similar size distribution, workers of C. cubica are more heat tolerant than small C. viatica. This higher degree of tolerance likely stemmed from C. cubica workers having greater relative water content. (iii) Under thermal stress, small C. viatica workers metabolized larger quantities of fat and differentially expressed proteins involved in cellular homeostasis. In contrast, C. cubica downregulated the expression of numerous proteins involved in mitochondrial respiration likely reducing ROS accumulation. (iv) Consistent with these results, large C. viatica workers remained active throughout the day; C. cubica workers displayed a bimodal activity pattern, and small C. viatica remained poorly active outside the nest. Our study shows that ecologically similar ant species with different degrees of worker size polymorphism evolved distinct strategies for coping with extreme heat conditions.

Effects of elevated temperature on 8-OHdG expression in the American oyster (Crassostrea virginica): Induction of oxidative stress biomarkers, cellular apoptosis, DNA damage and γH2AX signaling pathways

Global temperature is increasing due to anthropogenic activities and the effects of elevated temperature on DNA lesions are not well documented in marine organisms. The American oyster (Crassostrea virginica, an edible and commercially important marine mollusk) is an ideal shellfish species to study oxidative DNA lesions during heat stress. In this study, we examined the effects of elevated temperatures (24, 28, and 32 °C for one-week exposure) on heat shock protein-70 (HSP70, a biomarker of heat stress), 8‑hydroxy-2'-deoxyguanosine (8-OHdG, a biomarker of pro-mutagenic DNA lesion), double-stranded DNA (dsDNA), γ-histone family member X (γH2AX, a molecular biomarker of DNA damage), caspase-3 (CAS-3, a key enzyme of apoptotic pathway) and Bcl-2-associated X (BAX, an apoptosis regulator) protein and/or mRNA expressions in the gills of American oysters. Immunohistochemical and qRT-PCR results showed that HSP70, 8-OHdG, dsDNA, and γH2AX expressions in gills were significantly increased at high temperatures (28 and 32 °C) compared with control (24°C). In situ TUNEL analysis showed that the apoptotic cells in gill tissues were increased in heat-exposed oysters. Interestingly, the enhanced apoptotic cells were associated with increased CAS-3 and BAX mRNA and/or protein expressions, along with 8-OHdG levels in gills after heat exposure. Moreover, the extrapallial (EP) fluid (i.e., extracellular body fluid) protein concentrations were lower; however, the EP glucose levels were higher in heat-exposed oysters. Taken together, these results suggest that heat shock-driven oxidative stress alters extracellular body fluid conditions and induces cellular apoptosis and DNA damage, which may lead to increased 8-OHdG levels in cells/tissues in oysters.

Metabolic remodeling caused by heat hardening in the Mediterranean mussel Mytilus galloprovincialis

Organisms can modify and increase their thermal tolerance faster and more efficiently after a brief exposure to sublethal thermal stress. This response is called 'heat hardening' as it leads to the generation of phenotypes with increased heat tolerance. The aim of this study was to investigate the impact of heat hardening on the metabolomic profile of Mytilus galloprovincialis in order to identify the associated adjustments of biochemical pathways that might benefit the mussels' thermal tolerance. Thus, mussels were exposed sequentially to two different phases (heat hardening and acclimation phases). To gain further insight into the possible mechanisms underlying the metabolic response of the heat-hardened M. galloprovincialis, metabolomics analysis was complemented by the estimation of mRNA expression of phosphoenolpyruvate carboxykinase (PEPCK), pyruvate kinase (PK) and alternative oxidase (AOX) implicated in the metabolic pathways of gluconeogenesis, glycolysis and redox homeostasis, respectively. Heat-hardened mussels showed evidence of higher activity of the tricarboxylic acid (TCA) cycle and diversification of upregulated metabolic pathways, possibly as a mechanism to increase ATP production and extend survival under heat stress. Moreover, formate and taurine accumulation provide an antioxidant and cytoprotective role in mussels during hypoxia and thermal stress. Overall, the metabolic responses in non-heat-hardened and heat-hardened mussels underline the upper thermal limits of M. galloprovincialis, set at 26°C, and are in accordance with the OCLTT concept. The ability of heat-hardened mussels to undergo a rapid gain and slow loss of heat tolerance may be an advantageous strategy for coping with intermittent and often extreme temperatures.

Effects of seawater temperature and acute Vibriosp. challenge on the haemolymph immune and metabolic responses of adult mussels (Perna canaliculus)

The New Zealand Greenshell™ mussel (Perna canaliculus) is an endemic bivalve species with cultural importance, that is harvested recreationally and commercially. However, production is currently hampered by increasing incidences of summer mortality in farmed and wild populations. While the causative factors for these mortality events are still unknown, it is believed that increasing seawater temperatures and pathogen loads are potentially at play. To improve our understanding of these processes, challenge experiments were conducted to investigate the combined effects of increased seawater temperature and Vibrio infection on the immune and metabolic responses of adult mussels. Biomarkers that measure the physiological response of mussels to multiple-stressors can be utilised to study resilience in a changing environment, and support efforts to strengthen biosecurity management. Mussels acclimated to two temperatures (16 °C and 24 °C) were injected with either autoclaved, filtered seawater (control) or Vibriosp. DO1 (infected). Then, haemolymph was sampled 24 h post-injection and analysed to quantify haemocyte immune responses (via flow-cytometry), antioxidant capacity (measured electrochemically) and metabolic responses (via gas chromatography-mass spectrometry) to bacterial infection. Both seawater temperature and injection type significantly influenced the immune and metabolite status of mussels. A lack of interaction effects between temperature and injection type indicated that the effects of Vibrio sp. 24 h post-infection were similar between seawater temperatures. Infected mussels had a higher proportion of dead haemocytes and lower overall haemocyte counts than uninfected controls. The proportion of haemocytes showing evidence of apoptosis was higher in mussels held at 24 °C compared with those held at 16 °C. The proportion of haemocytes producing reactive oxygen species did not differ between temperatures or injection treatments. Mussels held at 24 °C exhibited elevated levels of metabolites linked to the glycolysis pathway to support energy production. The saccharopin-lysine pathway metabolites were also increased in these mussels, indicating the role of lysine metabolism. A decrease in metabolic activity (decreases in BCAAs, GABA, urea cycle metabolites, oxidative stress metabolites) was largely seen in mussels injected with Vibrio sp. Itaconate increased as seen in previous studies, suggesting that antimicrobial activity may have been activated in infected mussels. This study highlights the complex nature of immune and metabolic responses in mussels exposed to multiple stressors and gives an insight into Vibrio sp. infection mechanisms at different seawater temperatures.

Divergent Effects of Ocean Warming On Byssal Attachment in Two Congener Mussel Species

Organisms rely on the integrity of the structural materials they produce to maintain a broad range of processes, such as acquiring food, resisting predators or withstanding extreme environmental forces. The production and maintenance of these biomaterials, which are often modulated by environmental conditions, can therefore have important consequences for fitness in changing climates. One well-known example of such a biomaterial is mussel byssus, an array of collagen-like fibers (byssal threads) that tethers a bivalve mollusk securely to benthic marine substrates. Byssus strength directly influences mortality from dislodgement, predation or competition and depends on the quantity and quality of byssal threads produced. We compared the temperature sensitivity of byssal attachment strength of two mussel species common to the west coast of North America, Mytilus trossulus and M. galloprovincialis, when exposed to seawater temperatures ranging from 10 to 24˚C in the laboratory. We found the two species attached equally strong in seawater ≤ 18˚C, but higher temperatures caused byssal thread production rate and quality (break force and extensibility) to be greatly reduced in M. trossulus and increased in M. galloprovincialis, leading to a 2 to 10-fold difference in overall byssus strength between the two species. Using this threshold value (18˚C), we mapped habitat for each species along the west coast of North America based on annual patterns in sea surface temperature. Estimated ranges are consistent with the current distribution of the two species and suggest a potential mechanism by which ocean warming could facilitate the northern expansion of M. galloprovincialis and displacement of native M. trossulus populations.

Physiological and comparative proteomic analyzes reveal immune defense response of the king scallop Pecten maximus in presence of paralytic shellfish toxin (PST) from Alexandrium minutum

The king scallop, Pecten maximus is a highly valuable seafood in Europe. Over the last few years, its culture has been threatened by toxic microalgae during harmful algal blooms, inducing public health concerns. Indeed, phycotoxins accumulated in bivalves can be harmful for human, especially paralytic shellfish toxins (PST) synthesized by the microalgae Alexandrium minutum. Deleterious effects of these toxic algae on bivalves have also been reported. However, its impact on bivalves such as king scallop is far from being completely understood. This study combined ecophysiological and proteomic analyzes to investigate the early response of juvenile king scallops to a short term exposure to PST producing A. minutum. Our data showed that all along the 2-days exposure to A. minutum, king scallops exhibited transient lower filtration and respiration rates and accumulated PST. Significant inter-individual variability of toxin accumulation potential was observed among individuals. Furthermore, we found that ingestion of toxic algae, correlated to toxin accumulation was driven by two factors: 1/ the time it takes king scallop to recover from filtration inhibition and starts to filtrate again, 2/ the filtration level to which king scallop starts again to filtrate after inhibition. Furthermore, at the end of the 2-day exposure to A. minutum, proteomic analyzes revealed an increase of the killer cell lectin-like receptor B1, involved in adaptative immune response. Proteins involved in detoxification and in metabolism were found in lower amount in A. minutum exposed king scallops. Proteomic data also showed differential accumulation in several structure proteins such as β-actin, paramyosin and filamin A, suggesting a remodeling of the mantle tissue when king scallops are subjected to an A. minutum exposure.

Interactive effects of multiple stressors on the physiological performance of the invasive mussel Mytilus galloprovincialis

The invasive mussel Mytilus galloprovincialis is a heat-tolerant species relative to its competative congener M. trossulus, that dominates warm seawater environments but it is unknown how multiple stressors (MS) may affect its physiology. Our study determined the effects of MS on the metabolic rate (MR), superoxide dismutase (SOD) antioxidant enzyme activity, and clearance rate (CR) of M. galloprovincialis. Mussels were exposed for 7 d to hyposalinity (20, 28, 34 ppt) then to heat shock (17, 20, 25 °C) after which MR and SOD activity were determined. CR was quantified following a 30 min MS exposure. We found a significant influence of MS on MR, SOD, and CR. We identified synergistic effects on MR under the most extreme treatment. SOD activity was the greatest under 20 °C exposure while CR declined under heat shock. Thus, our study suggests that mussels experiencing MS may become energy limited as MR increases and feeding rates decrease.

Acclimation Effects of Natural Daily Temperature Variation on Longevity, Fecundity, and Thermal Tolerance of the Diamondback Moth (Plutella xylostella)

Simple Summary

Diurnal, monthly, or seasonal temperatures can fluctuate substantially. Daily temperature amplitudes (DTAs) can significantly impact the traits of insects but there is limited evidence from the natural environment. Therefore, we studied the acclimation effects of DTA on the longevity, total fecundity, early fecundity, and thermal tolerance of adult diamondback moths (Plutella xylostella) under environmental conditions. The longevity, total fecundity, early fecundity, and heat thermal tolerance of adults significantly changed under different DTAs. These findings highlight the effects of DTA on the acclimation response in the P.xylostella phenotype, and DTA should be incorporated into prediction models for assessing insect populations and the effects of climate change.

Abstract

Daily temperature amplitudes (DTAs) significantly affect the ecological and physiological traits of insects. Most studies in this field are based on laboratory experiments, while there is limited research on the effects of changes in DTA on insect phenotypic plasticity under natural conditions. Therefore, we studied the acclimation effects of DTA on the longevity, total fecundity, early fecundity, and the thermal tolerance of adult diamondback moths (Plutella xylostella L.) under naturally occurring environmental conditions. As DTAs increased, male longevity and total fecundity decreased, and early fecundity increased. An increase in DTA was significantly associated with the increased heat coma temperature (CT_max) of both males and females, but had no significant effect on their cold coma temperature (CT_min). Our findings highlight the effects of DTA on the acclimation response of P. xylostella and emphasize the importance of considering DTA in predicting models for assessing insect populations and the effects of climate change.

Transcriptomic response of the intertidal limpet Patella vulgata to temperature extremes

Global warming is challenging wild species in land and water. In the intertidal zone, species are already living at their thermal limits, being vulnerable even to small increases in maximum habitat temperatures. Knowledge of the mechanisms by which many intertidal zone species cope with elevated temperatures is limited. We analysed the molecular thermal stress response of the limpet Patella vulgata under slight and frequent (one-day), and extreme and rare (three-day) warming events. Using RNA-seq to assess differential gene expression among treatments, differing molecular responses were obtained in the two treatments, with more changes in gene expression after the three-day event; with one-third of the differentially expressed transcripts being down-regulated. However, across treatments we observed shifts in gene expression for common aspects of the heat stress response including intra-cellular communication, protein chaperoning, proteolysis and cell cycle arrest. Of the 71,675 transcripts obtained, only 259 were differentially expressed after both heating events. From these, 218 defined the core group (i.e. genes induced by thermal stress with similar expression patterns irrespective of the magnitude of the warming event). The core group was composed of already well-studied genes in heat stress responses in intertidal organisms (e.g. heat shock proteins), but also genes from less explored metabolic pathways, e.g. the ubiquitin system, which were also fundamental regardless of the magnitude of the imposed warming. Moreover, we have also identified 41 signaling genes (i.e. a set of genes responding to both events and with expression patterns specific to the intensity of thermal stress), principally including genes involved in the maintenance of extracellular structure that have previously not been identified as part of the response to thermal stress in intertidal zone organisms. These signaling genes will be useful heat stress molecular biomarkers for monitoring heat stress in natural populations.

Identification and characterization of the novel genes encoding glutathione S-transferases in Mytilus galloprovincialis

The superfamily of glutathione S-transferases (GST) plays an essential role in the xenobiotic metabolism, binding compounds to the glutathione, and is like a cell protector during the influence of various negative external factors. Nevertheless, there are very few works devoted to the investigation of these genes in marine invertebrates. Up to this time, only three classes of cytosolic GSTs for one of the leading commercial molluscs Mytilus galloprovincialis were described. We sequenced the whole transcriptome from the gill tissues and, using bioinformatic analysis, detected ten classes of glutathione S-transferases, which are expressed in the mussel M. galloprovincialis. For the first time, two subfamilies were described: mitochondrial GST (kappa class) and microsomal (MAPEG), as well as five classes of the family of cytosolic GSTs (mu, omega, rho, tau, theta). Omega and sigma GST classes might be rapidly regulated genes due to the lack of introns and this assumption was confirmed by the investigation of short-term hypoxia on M. galloprovincialis. Seven new classes of GST revealed a greater gene variety of this detoxifying enzyme in mussels than expected. The obtained nucleotide sequences are necessary for future investigations of GSTs expression in response to various external factors (pollution, oxygen starvation, infection, etc.).

An integrated, multi-level analysis of thermal effects on intertidal molluscs for understanding species distribution patterns

Elucidating the physiological mechanisms that underlie thermal stress and discovering how species differ in capacities for phenotypic acclimatization and evolutionary adaptation to this stress is critical for understanding current latitudinal and vertical distribution patterns of species and for predicting their future state in a warming world. Such mechanistic analyses require careful choice of study systems (species and temperature-sensitive traits) and design of laboratory experiments that reflect the complexities of in situ conditions. Here, we critically review a wide range of studies of intertidal molluscs that provide mechanistic accounts of thermal effects across all levels of biological organization - behavioural, organismal, organ level, cellular, molecular, and genomic - and show how temperature-sensitive traits govern distribution patterns and capacities for coping with thermal stress. Comparisons of congeners from different thermal habitats are especially effective means for identifying adaptive variation. We employ these mechanistic analyses to illustrate how species differ in the severity of threats posed by rising temperature. Counterintuitively, we show that some of the most heat-tolerant species may be most threatened by increases in temperatures because of their small thermal safety margins and minimal abilities to acclimatize to higher temperatures. We discuss recent molecular biological and genomic studies that provide critical foundations for understanding the types of evolutionary changes in protein structure, RNA secondary structure, genome content, and gene expression capacities that underlie adaptation to temperature. Duplication of stress-related genes, as found in heat-tolerant molluscs, may provide enhanced capacity for coping with higher temperatures. We propose that the anatomical, behavioural, physiological, and genomic diversity found among intertidal molluscs, which commonly are of critical importance and high abundance in these ecosystems, makes this group of animals a highly appropriate study system for addressing questions about the mechanistic determinants of current and future distribution patterns of intertidal organisms.

Heat hardening enhances mitochondrial potential for respiration and oxidative defence capacity in the mantle of thermally stressed Mytilus galloprovincialis

Ectotherms are exposed to a range of environmental temperatures and may face extremes beyond their upper thermal limits. Such temperature extremes can stimulate aerobic metabolism toward its maximum, a decline in aerobic substrate oxidation, and a parallel increase of anaerobic metabolism, combined with ROS generation and oxidative stress. Under these stressful conditions, marine organisms recruit several defensive strategies for their maintenance and survival. However, thermal tolerance of ectothermic organisms may be increased after a brief exposure to sub-lethal temperatures, a process known as "hardening". In our study, we examined the ability of M. galloprovincialis to increase its thermal tolerance under the effect of elevated temperatures (24, 26 and 28 °C) through the "hardening" process. Our results demonstrate that this process can increase the heat tolerance and antioxidant defense of heat hardened mussels through more efficient ETS activity when exposed to temperatures beyond 24 °C, compared to non-hardened individuals. Enhanced cell protection is reflected in better adaptive strategies of heat hardened mussels, and thus decreased mortality. Although hardening seems a promising process for the maintenance of aquacultured populations under increased seasonal temperatures, further investigation of the molecular and cellular mechanisms regulating mussels' heat resistance is required.

Circadian and circatidal rhythms of protein abundance in the California mussel (Mytilus californianus)

Coastal habitats fluctuate with the 12.4 h tidal and 24 h light/dark cycle to predictably alter conditions such as air exposure, temperature, and food availability. Intertidal sessile bivalves exhibit behavioral and physiological adjustments to minimize the challenges of this environment. We investigated a high-resolution time course of the changes in protein abundance in the gill tissue of the intertidal mussel Mytilus californianus in a simulated tidal environment of 12:12 h light:dark cycles and a matching 6:6 h high:low tide cycle within each 12 h period. Approximately 38% of detected proteins showed significant rhythms in their abundances, with diversity in the phases of rhythmic isoforms. The circadian rhythm was dominant in protein abundance changes, particularly with oxidative metabolism. A tidal cycle elicited changes within functional groups, including in cytoskeletal proteins, chaperones, and oxidative stress proteins. In addition to protein abundance changes, we found the possibility for post-translational modifications driving rhythms, including methylation, mitochondrial peptide processing (proteolysis), and acylation. Dynamic changes in the proteome across functional categories demonstrate the importance of the tidal environment in entraining cellular processes, confirming that differential expression studies should not assume a static baseline of cellular conditions in intertidal organisms.

Within- and Trans-Generational Life History Responses to Diurnal Temperature Amplitudes of the Pupal Stage in the Diamondback Moth

Diurnal temperature fluctuations in nature can have a significant effect on many ectodermic traits. However, studies on the effects of diurnal temperature fluctuations on organisms, especially the effects on specific life stages, are still limited. We examined the immediate effects of the same average temperature (25°C) and different temperature amplitudes (±4, ±6, ±8, ±10, ±12°C) on the development and survival of Plutella xylostella (Lepidoptera: Plutellidae). We also assessed carry-over effects on adult longevity, reproduction, development, and survival of offspring across generations. The effect of moderate temperature amplitudes was similar to that of constant temperature. Wide temperature amplitudes inhibited the development of pupae, reduced total reproduction, lowered intrinsic rates of population growth, and slowed the development and survival of eggs on the first day, but the proportion of females ovipositing on the first three days increased. Insects coped with the adverse effects of wide temperature amplitudes by laying eggs as soon as possible. Our results confirmed that a logistic model based on daily average temperature cannot predict development rates under wide temperature amplitudes. These findings highlight the effect of environmental temperature fluctuations at the pupal stage on the development and oviposition patterns of P. xylostella and should be fully considered when predicting field occurrence.

Signals of Positive Selection in Sea Slug Transcriptomes

AbstractUnderstanding how species may respond to climate change is of paramount importance. Species that occupy highly heterogenous environments, such as intertidal zone estuarine habitats, provide an ideal test case for examining phenotypic and genomic adaptations to different environmental conditions, which may influence their response to rapidly shifting climatic conditions. The California coast is projected to experience changes in both temperature and salinity, which currently vary seasonally and latitudinally. Using comparative transcriptomics, I documented patterns of positive selection between the northern-dwelling planktotrophic sacoglossan sea slug Alderia modesta, which is remarkably tolerant of low temperatures and low salinities, and its southern congener Alderia willowi, which exhibits a striking flexibility for larval type in response to seasonally shifting changes in temperature and salinity. Out of over 4000 1-to-1 orthologous genes, I found a signal of positive selection between A. willowi and A. modesta for genes involved in cell membrane and cell transport, particularly ion homeostasis (aquaporin), cell-cell signal transduction, and phosphorylation (reduced nicotinamide adenine dinucleotide [NADH] dehydrogenase). Positive selection for ion homeostasis in A. modesta has implications for its ability to tolerate the lower salinity of its northern range, and in A. willowi substitutions in NADH may assist in the high temperature tolerance of its southern California habitats. Identifying these candidate genes enables future studies of their functionalization as we seek to understand the relationship between phenotype and genotype in species whose phenotypes are influenced by environmental conditions.

Identification, Characterization, and Expression Analysis Reveal Diverse Regulated Roles of Three MAPK Genes in Chlamys farreri Under Heat Stress

Mitogen-activated protein kinase (MAPK) cascades are fundamental signal transduction modules in all eukaryotic organisms, participating growth and development, as well as stress response. In the present study, three MAPK genes were successfully identified from the genome of Chlamys farreri, respectively, named CfERK1/2, CfJNK, and Cfp38, and only one copy of ERK, JNK, and p38 were detected. Domain analysis indicated that CfMAPKs possessed the typical domains, including S_TKc, Pkinase, and PKc_like domain. Phylogenetic analysis showed that three CfMAPKs of MAPK subfamilies exists in the common ancestor of vertebrates and invertebrates. All CfMAPKs specifically expressed during larval development and in adult tissues, and the expression level of CfERK1/2 and Cfp38 was apparently higher than that of CfJNK. Under heat stress, the expression of CfERK1/2 and Cfp38 were significantly downregulated and then upregulated in four tissues, while the expression of CfJNK increased in all tissues; these different expression patterns suggested a different molecular mechanism of CfMAPKs for bivalves to adapt to temperature changes. The diversity of CfMAPKs and their specific expression patterns provide valuable information for better understanding of the functions of MAPK cascades in bivalves.

Molecular response of a sub-antarctic population of the blue mussel (Mytilus edulis platensis) to a moderate thermal stress

The Kerguelen Islands (49°26'S, 69°50'E) represent a unique environment due to their geographical isolation, which protects them from anthropogenic pollution. The ability of the endemic mussel, part of the Mytilus complex, to cope with moderate heat stress was explored using omic tools. Transcripts involved in six major metabolic functions were selected and the qRT-PCR data indicated mainly changes in aerobic and anaerobic energy metabolism and stress response. Proteomic comparisons revealed a typical stress response pattern with cytoskeleton modifications and elements suggesting increased energy metabolism. Results also suggest conservation of protein homeostasis by the long-lasting presence of HSP while a general decrease in transcription is observed. The overall findings are consistent with an adaptive response to moderate stresses in mussels in good physiological condition, i.e. living in a low-impact site, and with the literature concerning this model species. Therefore, local blue mussels could be advantageously integrated into biomonitoring strategies, especially in the context of Global Change.

Modulation of physiological oxidative stress and antioxidant status by abiotic factors especially salinity in aquatic organisms

Exposure to a variety of environmental factors such as temperature, pH, oxygen and salinity may influence the oxidative status in aquatic organisms. The present review article focuses on the modulation of oxidative stress with reference to the generation of reactive oxygen species (ROS) in aquatic animals from different phyla. The focus of the review article is to explore the plausible mechanisms of physiological changes occurring in aquatic animals due to altered salinity in terms of oxidative stress. Apart from the seasonal variations in salinity, global warming and anthropogenic activities have also been found to influence oxidative health status of aquatic organisms. These effects are discussed with an objective to develop precautionary measures to protect the diversity of aquatic species with sustainable conservation. Comparative analyses among different aquatic species suggest that salinity alone or in combination with other abiotic factors are intricately associated with modulation in oxidative stress in a species-specific manner in aquatic animals. Osmoregulation under salinity stress in relation to energy demand and supply are also discussed. The literature survey of >50 years (1960-2020) indicates that oxidative stress status and comparative analysis of redox modulation have evolved from the analysis of various biotic and/or abiotic factors to the study of cellular signalling pathways in these aquatic organisms.

Bioenergetics in environmental adaptation and stress tolerance of aquatic ectotherms: linking physiology and ecology in a multi-stressor landscape

Energy metabolism (encompassing energy assimilation, conversion and utilization) plays a central role in all life processes and serves as a link between the organismal physiology, behavior and ecology. Metabolic rates define the physiological and life-history performance of an organism, have direct implications for Darwinian fitness, and affect ecologically relevant traits such as the trophic relationships, productivity and ecosystem engineering functions. Natural environmental variability and anthropogenic changes expose aquatic ectotherms to multiple stressors that can strongly affect their energy metabolism and thereby modify the energy fluxes within an organism and in the ecosystem. This Review focuses on the role of bioenergetic disturbances and metabolic adjustments in responses to multiple stressors (especially the general cellular stress response), provides examples of the effects of multiple stressors on energy intake, assimilation, conversion and expenditure, and discusses the conceptual and quantitative approaches to identify and mechanistically explain the energy trade-offs in multiple stressor scenarios, and link the cellular and organismal bioenergetics with fitness, productivity and/or ecological functions of aquatic ectotherms.

Transcriptomic analyses provide insights into the adaptive responses to heat stress in the ark shells, Scapharca subcrenata

The ark shell, Scapharca subcrenata, is susceptible to high temperature which may lead to mass mortality in hot summers. Herein, we conducted the transcriptomic analyses of haemocytes in ark shells under thermal stress, to reveal the underlying molecular mechanisms of heat resistance in these animals. The results showed that a total of 7773, 11,500 and 13,046 unigenes were expressed differentially at 12, 24 and 48 h post thermal stress, respectively. The expression levels of key DEGs as revealed by RNA-seq were confirmed by quantitative real-time PCR. GO and KEGG enrichment analyses showed that the DEGs were mainly associated with apoptosis, NF-kappa B signaling pathway, TNF signaling pathway and RIG-I-like receptor signaling pathway. Among the DEGs, 40 were candidate heat stress response-related genes and 169 were identified to be involved in antioxidant defense, cell detoxification, protein metabolism and endoplasmic reticulum stress responses. It seemed that ark shells may adapt to short term thermal stress through regulation of protein metabolism, DNA replication and anti-apoptotic system. However, if the stress sustains, it may cause irreparable injury gradually in the animals due to oxygen limitation and metabolic dysregulation. Noteworthily, the expression of DEGs involved in protein biosynthesis and proteolysis was significantly elevated in ark shells under heat stress. These findings may provide preliminary insights into the molecular response of ark shells to acute thermal stress and lay the groundwork for marker-assisted selection of heat-resistant strains in S. subcrenata.

Natural distribution of pure and hybrid Mytilus sp. along the south Mediterranean and North-east Atlantic coasts and sensitivity of D-larvae stages to temperature increases and metal pollution

The distribution of the Mediterranean mussel Mytilus galloprovincialis extends more and more northwards in the Atlantic. Crossings are frequently observed with the blue mussel Mytilus edulis along the French and English coasts. The aim of this study is firstlyto identify the co-presence of M. galloprovincialis, M. edulis, and their hybrids in different sites of the Mediterranean and Atlantic coasts, and to provide insights for the thermal tolerance and toxicant susceptibility of Mytilus edulis, Mytilus galloprovincialis and their hybrids. Mussels were collected from the shore at 20 sampling sitesin Europe and Tunisia and identified using Me 15/16 primers targeting the adhesive protein gene sequence. Samples were screened for the presence of Mytilus edulis, Mytilus galloprovincialis, and hybrids alleles using PCR. To get more information on hybrids sensitivities to temperature and metals, freshly fertilized eggs of the two species and their hybrids were reared at four temperatures 18, 20, 22, and 24 °C and exposed to concentrations of Cu, Ag, and a mixture of both metals. Arrests of development and malformations were recorded after 48 h of exposure. The genotypic identification of the two species on 20 sites of the Mediterranean and Atlantic coasts carried out during this study confirms the presence of pure and hybrid species of mussel. Our results highlighted that hybrid larvae from a female of M. galloprovincialis are significantly more tolerant to temperature increases than pure larvae of M. galloprovincialis and pure and hybrid larvae of M. edulis. No significant interspecies-differences of sensitivity were noted for metal exposure alone. However, a co-exposure of larvae to both metal and high temperature highlighted the higher tolerance of hybrid larvae from a female of M. galloprovincialis to both stresses. The overall results could allow the prediction of the future evolution of mussel populations facing environmental changes.

Dynamic regulation of coral energy metabolism throughout the diel cycle

Coral reefs are naturally exposed to daily and seasonal variations in environmental oxygen levels, which can be exacerbated in intensity and duration by anthropogenic activities. However, coral’s diel oxygen dynamics and fermentative pathways remain poorly understood. Here, continuous oxygen microelectrode recordings in the coral diffusive boundary layer revealed hyperoxia during daytime and hypoxia at nighttime resulting from net photosynthesis and net respiration, respectively. The activities of the metabolic enzymes citrate synthase (CS), malate dehydrogenase, and strombine dehydrogenase remained constant throughout the day/night cycle, suggesting that energy metabolism was regulated through adjustments in metabolite fluxes and not through changes in enzyme abundance. Liquid chromatography-mass spectrometry analyses identified strombine as coral’s main fermentative end product. Strombine levels peaked as oxygen became depleted at dusk, indicating increased fermentation rates at the onset of nightly hypoxia, and again at dawn as photosynthesis restored oxygen and photosynthate supply. When these peaks were excluded from the analyses, average strombine levels during the day were nearly double those at night, indicating sifnificant fermentation rates even during aerobic conditions. These results highlight the dynamic changes in oxygen levels in the coral diffusive boundary layer, and the importance of fermentative metabolism for coral biology.

The effects of cold stress on Mytilus species in the natural environment

Environmental stressors induce changes in marine mussels from molecular (e.g., neurotransmitter and chaperone concentration, and expression of immune- and heat-shock protein-related genes) to physiological (e.g., filtration and heart rates, the number of circulating hemocytes) levels. Temperature directly affects the biogeographic distribution of mussels. Chaperones might form an essential part of endogenous protective mechanisms for the adaptation of these animals to low temperatures in nature. Here, we review the available studies dealing with cold stress responses of Mytilidae family members in their natural environment.

A year in the salt marsh: Seasonal changes in gill protein expression in the temperate intertidal mussel Geukensia demissa

Organisms living in temperate and polar regions experience extensive seasonal changes in the physical and biotic environment, including temperature, insolation, and food availability, among other factors. Sessile intertidal organisms respond to such seasonal fluctuations largely through physiological and biochemical means, because their behavioral responses are severely limited. In this study, we used a proteomic approach to examine changes in seasonal protein expression of gill from the intertidal mussel Geukensia demissa, a keystone species of the western Atlantic salt marsh, over the course of one year. Gill tissue of mussels collected in summer had the greatest number of proteins significantly increased in abundance (37 of 592 spots detected on two-dimensional polyacrylamide gels), although autumn mussels revealed a comparable proportion of up-regulated proteins (31 spots). In contrast, the number of proteins changing in abundance in winter and spring mussels were substantially smaller (15 and 9, respectively). Identification of these proteins revealed both expected and unanticipated changes to the proteome. Maintenance of gill cilia dominates in the summer when filter-feeding is most active, as evidenced by cytoskeletal proteins such as tektin-4 and tubulin isoforms; a signal of protection from heat stress is also present in summer (e.g., heat shock cognate 70). In autumn oxidative stress protection (peroxiredoxin-5 and manganese-containing superoxide dismutase) and aerobic ATP synthetic capacity (ATP synthase subunits a and delta) appear to increase. In winter a signal of cold-induced oxidative stress is apparent (Mn-SOD and NADP-dependent isocitrate dehydrogenase), perhaps in association with heavy metal toxicity and exposure to pathogens. Gill tissue from spring shows relatively little environmental acclimatization, other than a possible increase in protein synthesis capacity.

An integrated omics approach to investigate summer mortality of New Zealand Greenshell™ mussels

BACKGROUND

Green-lipped mussels, commercially known as Greenshell™ mussels (Perna canaliculus Gmelin 1791), contribute > $300 million to New Zealand's aquaculture exports. However, mortalities during summer months and potential pathogenic outbreaks threaten the industry. Thermal stress mechanisms and immunological responses to pathogen infections need to be understood to develop health assessment strategies and early warning systems.

METHODS

P. canaliculus were collected during a mortality event at a commercial aquaculture farm in Firth of Thames, New Zealand. Gill tissues from six healthy and six unhealthy mussels were excised and processed for metabolomic (GC-MS) and label-free proteomic (LC-MS) profiling. Univariate analyses were conducted separately on each data layer, with data being integrated via sparse multiple discriminative canonical correlation analysis. Pathway enrichment analysis was used to probe coordinated changes in functionally related metabolite sets.

RESULTS

Findings revealed disruptions of the tricarboxylic acid (TCA) cycle and fatty acid metabolism in unhealthy mussels. Metabolomics analyses also indicated oxidative stress in unhealthy mussels. Proteomics analyses identified under-expression of proteins associated with cytoskeleton structure and regulation of cilia/flagellum in gill tissues of unhealthy mussels. Integrated omics revealed a positive correlation between Annexin A4 and CCDC 150 and saturated fatty acids, as well as a negative correlation between 2-aminoadipic acid and multiple cytoskeletal proteins.

CONCLUSIONS

Our study demonstrates the ability of using integrative omics to reveal metabolic perturbations and protein structural changes in the gill tissues of stressed P. canaliculus and provides new insight into metabolite and protein interactions associated with incidences of summer mortality in this species.

Correlation between intermediary metabolism, Hsp gene expression, and oxidative stress-related proteins in long-term thermal-stressed Mytilus galloprovincialis

Long-term exposure of Mytilus galloprovincialis to temperatures beyond 26°C triggers mussel mortality. The present study aimed to integratively illustrate the correlation between intermediary metabolism, hsp gene expression, and oxidative stress-related proteins in long-term thermally stressed Mytilus galloprovincialis and whether they are affected by thermal stress magnitude and duration. We accordingly evaluated the gene expression profiles, in the posterior adductor muscle (PAM) and the mantle, concerning heat shock protein 70 and 90 ( hsp70 and hsp90), and the antioxidant defense indicators Mn-SOD, Cu/Zn-SOD, catalase, glutathione S-transferase, and the metallothioneins mt-10 and mt-20. Moreover, we determined antioxidant enzyme activities, oxidative stress through lipid peroxidation, and activities of intermediary metabolism enzymes. The pattern of changes in relative mRNA expression levels indicate that mussels are able to sense thermal stress even when exposed to 22°C and before mussel mortality is initiated. Data indicate a close correlation between the magnitude and duration of thermal stress with lipid peroxidation levels and changes in the activity of antioxidant enzymes and the enzymes of intermediary metabolism. The gene expression and increase in the activities of antioxidant enzymes support a scenario, according to which exposure to 24°C might trigger reactive oxygen species (ROS) production, which is closely correlated with anaerobic metabolism under hypometabolic conditions. Increase and maintenance of oxidative stress in conjunction with energy balance disturbance seem to trigger mussel mortality after long-term exposure at temperatures beyond 26°C. Eventually, in the context of preparation for oxidative stress, certain hypotheses and models are suggested, integrating the several steps of cellular stress response.

Trans-Atlantic Distribution and Introgression as Inferred from Single Nucleotide Polymorphism: Mussels Mytilus and Environmental Factors

Large-scale climate changes influence the geographic distribution of biodiversity. Many taxa have been reported to extend or reduce their geographic range, move poleward or displace other species. However, for closely related species that can hybridize in the natural environment, displacement is not the only effect of changes of environmental variables. Another option is subtler, hidden expansion, which can be found using genetic methods only. The marine blue mussels Mytilus are known to change their geographic distribution despite being sessile animals. In addition to natural dissemination at larval phase—enhanced by intentional or accidental introductions and rafting—they can spread through hybridization and introgression with local congeners, which can create mixed populations sustaining in environmental conditions that are marginal for pure taxa. The Mytilus species have a wide distribution in coastal regions of the Northern and Southern Hemisphere. In this study, we investigated the inter-regional genetic differentiation of the Mytilus species complex at 53 locations in the North Atlantic and adjacent Arctic waters and linked this genetic variability to key local environmental drivers. Of seventy-nine candidate single nucleotide polymorphisms (SNPs), all samples were successfully genotyped with a subset of 54 SNPs. There was a clear interregional separation of Mytilus species. However, all three Mytilus species hybridized in the contact area and created hybrid zones with mixed populations. Boosted regression trees (BRT) models showed that inter-regional variability was important in many allele models but did not prevail over variability in local environmental factors. Local environmental variables described over 40% of variability in about 30% of the allele frequencies of Mytilus spp. For the 30% of alleles, variability in their frequencies was only weakly coupled with local environmental conditions. For most studied alleles the linkages between environmental drivers and the genetic variability of Mytilus spp. were random in respect to “coding” and “non-coding” regions. An analysis of the subset of data involving functional genes only showed that two SNPs at Hsp70 and ATPase genes correlated with environmental variables. Total predictive ability of the highest performing models (r² between 0.550 and 0.801) were for alleles that discriminated most effectively M. trossulus from M. edulis and M. galloprovincialis, whereas the best performing allele model (BM101A) did the best at discriminating M. galloprovincialis from M. edulis and M. trossulus. Among the local environmental variables, salinity, water temperature, ice cover and chlorophyll a concentration were by far the greatest predictors, but their predictive performance varied among different allele models. In most cases changes in the allele frequencies along these environmental gradients were abrupt and occurred at a very narrow range of environmental variables. In general, regions of change in allele frequencies for M. trossulus occurred at 8–11 psu, 0–10 °C, 60%–70% of ice cover and 0–2 mg m⁻³ of chlorophyll a, M. edulis at 8–11 and 30–35 psu, 10–14 °C and 60%–70% of ice cover and for M. galloprovincialis at 30–35 psu, 14–20 °C.

Living on the Edge: Physiological and Kinetic Trade-Offs Shape Thermal Tolerance in Intertidal Crabs From Tropical to Sub-Antarctic South America

Temperature is an important abiotic factor that drives the evolution of ectotherms owing to its pervasive effects at all levels of organization. Although a species' thermal tolerance is environmentally driven within a spatial cline, it may be constrained over time due to differential phylogenetic inheritance. At the limits of thermal tolerance, hemolymph oxygen is reduced and lactate formation is increased due to mismatch between oxygen supply and demand; imbalance between enzyme flexibility/stability also impairs the ability to generate energy. Here, we characterized the effects of lower (LL₅₀) and upper (UL₅₀) critical thermal limits on selected descriptors of aerobic and anaerobic metabolism in 12 intertidal crab species distributed from northern Brazil (≈7.8°S) to southern Patagonia (≈53.2°S), considering their phylogeny. We tested for (i) functional trade-offs regarding aerobic and anaerobic metabolism and LDH kinetics in shaping thermal tolerance; (ii) influence of shared ancestry and thermal province on metabolic evolution; and (iii) presence of evolutionary convergences and adaptive peaks in the crab phylogeny. The tropical and subtropical species showed similar systemic and kinetic responses, both differing from the sub-Antarctic crabs. The lower UL₅₀'s of the sub-Antarctic crabs may reflect mismatch between the evolution of aerobic and anaerobic metabolism since these crabs exhibit lower oxygen consumption but higher lactate formation than tropical and subtropical species also at their respective UL₅₀'s. LDH activity increased with temperature increase, while K_m ^Pyr remained fairly constant; catalytic coefficient correlated negatively with thermal niche. Thermal tolerance may rely on a putative evolutionary trade-off between aerobic and anaerobic metabolism regarding energy supply, while temperature compensation of kinetic performance is driven by thermal habitat as revealed by the LDH affinity/efficiency equilibrium. The overall physiological evolution revealed two homoplastic adaptive peaks in the sub-Antarctic crabs with a further shift in the tropical/subtropical clade. The physiological traits at UL₅₀ have evolved in a phylogenetic manner while all others were more plastic. Thus, shared inheritance and thermal environment have driven the crabs' thermal tolerance and metabolic evolution, revealing physiological transformations that have arisen in both colder and warmer climes, especially at higher levels of biological organization and phylogenetic diversity.

Temperature affects susceptibility of intertidal limpets to bird predation

High temperatures resulting in physiological stress and the reduced ability to resist predation can have life-or-death consequences for an organism. We investigated the effects of temperature on the susceptibility to predation for an ectothermic intertidal mollusc (the owl limpet, Lottia gigantea) and its predator (the black oystercatcher, Haematopus bachmani). The ability of L. gigantea to resist bird predation during low tide is determined by the tenacity of attachment to the rock. We developed a transducer to measure the force of predatory attacks on limpets by a captive black oystercatcher, and tested the hypothesis that exposure to warm temperatures during low tide emersion would affect the limpet's ability to resist dislodgement in trials with a morphometrically accurate beak mimic and a live bird. In beak mimic trials, four times as many limpets exposed to warm low tides were removed, as compared with limpets exposed to cool low tides or in 'no low tide' submerged conditions. Minimum time before limpet removal in captive bird trials was more than six times longer for limpets in cool low tide or no low tide treatments compared with limpets in the warm low tide treatment. We measured shear forces up to 36.63 N during predatory strikes. These direct measurements of the forces exerted by a living oystercatcher provide context for interactions with multiple prey species. Our data suggest that naturally occurring variation in body temperatures among individual prey items in the field could be an important driver of predator-prey interactions and subsequently community patterns.

Acetylome Analysis Reveals Population Differentiation of the Pacific Oyster Crassostrea gigas in Response to Heat Stress

Lysine acetylation of proteins is a highly conserved post-translational modification that plays an important regulatory role in almost every aspect of metabolic processes in both terrestrial and aquatic species. Pacific oyster, Crassostrea gigas, a model marine species, is distributed worldwide and is economically and ecologically important. However, little is known about the role of acetylation in the adaptive response of oyster to heterogeneous intertidal environments. Here, we conducted the first-ever lysine acetylome analysis in two genetically and physiologically differentiated oyster populations, using a highly sensitive immune-affinity purification and high-resolution mass spectrometry. Overall, we identified 1054 lysine acetylation sites in 664 proteins, which account for 2.37% of the oyster proteome analysed in the current study. The modified proteins are involved in a wide range of biological processes and are localised in multiple cellular compartments. Motif analysis revealed that hydrophilic and polar amino acids histidine, lysine and arginine were the most enriched residues in the positions + 1 and + 2 of the acetylated sites. Further, the two oyster populations exhibited divergent acetylomic regulations of several biological pathways, particularly energy metabolism and glycine and serine amino acid metabolism, in response to thermal stress and differentiated acetylation patters of candidate heat-responsive proteins, e.g. molecular chaperone and myosin. These observations suggest that lysine acetylation plays a critical role in different thermal responses of these two oyster populations. These findings provide an important resource for in-depth exploration of the physiological role of lysine acetylation in adaptive evolution of marine invertebrates.

Molecular mechanisms underlying the effects of temperature increase on Mytilus sp. and their hybrids at early larval stages

The present work aims to investigate the effects of water temperature increase on Mytilus galloprovincilis and Mytilus edulis pure larvae (PG, PE) and their hybrids (HFG, HFE). D-larvae were maintained at 18 °C or exposed to a higher temperature of 22 °C for 48 h. Initially, Embryotoxicity test was evaluated. Second, a transcriptomic analysis using a recently developed microarray platform was applied to determine the main biological processes involved in early life stages responses to temperature increase. Finally, an immunofluorescence investigation was performed to bridge the gap between transcriptomic regulation and the real changes at cellular/tissue levels. Embryotoxicity test revealed a higher sensitivity of M. edulis (PE) D-larvae as well as hybrids from females M. edulis (HFE) to temperature increase, with the highest rate of larval malformations. Transcriptomic results indicated a lack of an adequate heat shock protein (Hsp) response in PE and HFE larvae (the high expression was observed in PG larvae); the differential expression of gene involved in translation, energy metabolism and oxidative stress response may contribute to explain the observed complex alterations in the studied conditions. As revealed by immunohistochemistry, cytoskeleton proteins changes associated with a drastic decrease of Histidine-Rich Glycoprotein (HRG) may elucidate the larval abnormalities in shell development observed for PE and HFE larvae. Overall, the results indicate that each type of pure larva (PG and PE) and their respective female hybrid (HFG and HFE) react similarly to the temperature increase. Our data should be carefully considered in view of the water temperature increase in marine ecosystems and especially for the mussel's species in confluence zones.

High-throughput quantification of protein structural change reveals potential mechanisms of temperature adaptation in Mytilus mussels

Background

Temperature exerts a strong influence on protein evolution: species living in thermally distinct environments often exhibit adaptive differences in protein structure and function. However, previous research on protein temperature adaptation has focused on small numbers of proteins and on proteins adapted to extreme temperatures. Consequently, less is known about the types and quantity of evolutionary change that occurs to proteins when organisms adapt to small shifts in environmental temperature. In this study, these uncertainties were addressed by developing software that enabled comparison of structural changes associated with temperature adaptation (hydrogen bonding, salt bridge formation, and amino acid use) among large numbers of proteins from warm- and cold-adapted species of marine mussels, Mytilus galloprovincialis and Mytilus trossulus, respectively.

Results

Small differences in habitat temperature that characterize the evolutionary history of Mytilus mussels were sufficient to cause protein structural changes consistent with temperature adaptation. Hydrogen bonds and salt bridges that increase stability and protect against heat-induced denaturation were more abundant in proteins from warm-adapted M. galloprovincialis compared with proteins from cold-adapted M. trossulus. These structural changes were related to deviations in the use of polar and charged amino acids that facilitate formation of hydrogen bonds and salt bridges within proteins, respectively. Enzymes, in particular those within antioxidant and cell death pathways, were over-represented among proteins with the most hydrogen bonds and salt bridges in warm-adapted M. galloprovincialis. Unlike extremophile proteins, temperature adaptation in Mytilus proteins did not involve substantial changes in the number of hydrophobic or large volume amino acids, nor in the content of glycine or proline.

Conclusions

Small shifts in organism temperature tolerance, such as that needed to cope with climate warming, may result from structural and functional changes to a small percentage of the proteome. Proteins in which function is dependent on large conformational change, notably enzymes, may be particularly sensitive to temperature perturbation and represent foci for natural selection. Protein temperature adaptation can occur through different types and frequencies of structural change, and adaptive mechanisms used to cope with small shifts in habitat temperature appear different from mechanisms used to retain protein function at temperature extremes.

Seasonal proteome variation in intertidal shrimps under a natural setting: Connecting molecular networks with environmental fluctuations

The ability of intertidal organisms to maintain their performance via molecular and physiological adjustments under low tide, seasonal fluctuations and extreme events ultimately determines population viability. Analyzing this capacity in the wild is extremely relevant since intertidal communities are under increased climate variability owing to global changes. We addressed the seasonal proteome signatures of a key intertidal species, the shrimp Palaemon elegans, in a natural setting. Shrimps were collected during spring and summer seasons at low tides and were euthanized in situ. Environmental variability was also assessed using hand-held devices and data loggers. Muscle samples were taken for 2D gel electrophoresis and protein identification through mass spectrometry. Proteome data revealed that 55 proteins (10.6% of the proteome) significantly changed between spring and summer collected shrimps, 24 of which were identified. These proteins were mostly involved in cytoskeleton remodelling, energy metabolism and transcription regulation. Overall, shrimps modulate gene expression leading to metabolic and structural adjustments related to seasonal differences in the wild (i.e. abiotic variation and possibly intrinsic cycles of reproduction and growth). This potentially promotes performance and fitness as suggested by the higher condition index in summer-collected shrimps. However, inter-individual variation (% coefficient of variation) in protein levels was quite low (min-max ranges were 0.6-8.3% in spring and 1.2-4.8% in summer), possibly suggesting reduced genetic diversity or physiological canalization. Protein plasticity is relevant to cope with present and upcoming environmental variation related to anthropogenic forcing (e.g. global change, pollution) but low inter-individual variation may limit evolutionary potential of shrimp populations.

Physiological responses to heat stress in an invasive mussel Mytilus galloprovincialis depend on tidal habitat

Mussels are ecologically important organisms that can survive in subtidal and intertidal zones where they experience thermal stress. We know little about how mussels from different tidal habitats respond to thermal stress. We used the mussel Mytilus galloprovincialis from separate subtidal and intertidal populations to test whether heart rate and indicators of potential aerobic (citrate synthase activity) and anaerobic (cytosolic malate dehydrogenase activity) metabolic capacity are affected by increased temperatures while exposed to air or submerged in water. Subtidal mussels were affected by warming when submerged in water (decreased heart rate) but showed no effect in air. In contrast, intertidal mussels were affected by exposure to air (increased anaerobic capacity) but not by warming. Overall, physiological responses of mussels to thermal stress were dependent on their tidal habitat. These results highlight the importance of considering the natural habitat of mussels when assessing their responses to environmental challenges.

RNAi based transcriptome suggests genes potentially regulated by HSF1 in the Pacific oyster Crassostrea gigas under thermal stress

Background

The Pacific oyster Crassostrea gigas is an important fishery resource that is sensitive to temperature fluctuations. Thus, it has evolved a protection mechanism against heat stress by increasing the expression of the gene coding for heat shock protein (HSP) 70 under elevated temperatures. In other animals, heat shock response is a transcriptional response driven by the heat shock transcription factor 1 (HSF1) and thermal stress can trigger HSP70 expression to protect the organism via HSF1. However, the regulatory relationship between HSF1 and HSP remains unclear in Pacific oyster. Therefore, in the present study, we examined the transcriptomic response of several to thermal stress following HSF1 interference.

Results

We identified 150 genes responsive to heat shock including seven HSP genes, six of which belonging to the group of 17 HSP genes enriched in response to heat shock, according to weighted gene co-expression network analysis (WGCNA). The other gene was enriched in the module correlated with HSF1 interference. In addition, we found 48 and 47 genes that were upregulated and downregulated by HSF1 in response to heat shock, respectively. In the upregulated genes, we identified one HSP70 potentially regulated by HSF1 in response to heat shock. Furthermore, based on differentially expressed genes and WGCNA analyses, we found that the hypoxia signaling pathway was enriched under heat shock conditions. Five genes were then selected to detect dynamic changes through time. The results suggested that gene expression was correlated with HSF1 expression. The regulation of HSP70 by HSF1 was preliminarily confirmed by binding site predictions and by a dual luciferase assay.

Conclusions

Our results revealed that the expression of HSP70 and HSP20 was initially triggered after 2 h of heat shock, and one of the HSP70 genes was potentially regulated by HSF1. From these results, it is evident that not all heat-inducible genes were triggered simultaneously in response to heat shock stress. Overall, the results revealed a possible HSF1–HSP regulatory relationship in Pacific oyster, providing valuable information on the mechanisms of thermal tolerance in this commercially important oyster.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-6003-8) contains supplementary material, which is available to authorized users.