Arrhenius Break Research Articles

AMPK-mediated regulation of cardiac energy metabolism: Implications for thermotolerance in Argopecten irradians irradians

AMPK is a key regulator of metabolism in eukaryotes across various pathways related to energy regulation. Although extensive investigations of AMPK have been conducted in mammals and some model organisms, research on AMPK in scallops is comparatively limited. In this study, three AMPK family genes (AiAMPKα, AiAMPKβ and AiAMPKγ) in scallop Argopecten irradians irradians were identified through genome scanning. Structure prediction and phylogenetic analyses of AiAMPKs were performed to determine their structural features and evolutionary relationships. Spatiotemporal expression patterns of AiAMPKs at different developmental stages and in healthy adult tissues were analyzed to elucidate the function of AiAMPKs in bay scallops’ growth and development. The spatiotemporally specific expression of AiAMPKs implied their important roles in growth and development of bay scallops. Heat stress experiment was performed to determine the regulations of AiAMPKs in four kinds of thermosensitive tissues. Expression profiles revealed distinct molecular mechanisms of AiAMPKs in different tissues in response to heat stress: significant down-regulations in mobile hemocytes, but dominant up-regulations occurring in stationary gills, mantles and hearts. Functional verification including knock-down of AiAMPKα and inhibition of AiAMPK was separately conducted in the thermotolerant tissue heart at the post-transcription and translation levels. The thermotolerant index Arrhenius break temperature (ABT) showed a significant decrease and the rate-amplitude product (RAP) peaked earlier in the individuals after RNAi targeting AiAMPKα, displaying an earlier transition to anaerobic metabolism under heat stress, indicating an impairing ability of aerobic metabolism. After AiAMPK inhibition, widespread down-regulations of genes in key energy metabolism pathways, RNA polymerase II-mediated transcription, and aminoacyl-tRNA synthesis pathways were obviously observed, revealing the post-translational inhibition of AiAMPK hindered cardiac energy metabolism, basal transcription and translation. Overall, our findings provide evidences for exploring the molecular mechanisms of energy regulation in thermotolerant traits in bay scallops under ongoing global warming.

Transcriptomic analysis reveals PC4's participation in thermotolerance of scallop Argopecten irradians irradians by regulating myocardial bioelectric activity

Rising ocean temperatures due to global warming pose a significant threat to the bay scallop aquaculture industry. Understanding the mechanisms of thermotolerance in bay scallops is crucial for developing thermotolerant breeds. Our prior research identified Arg0230340.1, part of the positive cofactor 4 (PC4) family, as a key gene associated with the thermotolerance index Arrhenius break temperature (ABT) in bay scallops. Further validation through RNA interference (RNAi) reinforced PC4's role in thermotolerance, offering a solid basis for investigating thermal response mechanisms in these scallops. In this study, we performed a comparative transcriptomic analysis on the temperature-sensitive hearts of bay scallops after siRNA-mediated RNAi targeting Arg0230340.1, to delve into the detailed molecular mechanism of PC4's participation in thermotolerance regulation. The analysis revealed that silencing Arg0230340.1 significantly reduced the expression of mitochondrial tRNA and rRNA, potentially affecting mitochondrial function and the heart's blood supply capacity. Conversely, the up-regulation of genes involved in energy metabolism, RNA polymerase II (RNAPII)-mediated basal transcription, and aminoacyl-tRNA synthesis pathways points to an intrinsic protective response, providing energy and substrates for damage repair and maintenance of essential functions under stress. GO and KEGG enrichment analyses indicated that the up-regulated genes were primarily associated with energy metabolism and spliceosome pathways, likely contributing to myocardial remodeling post-Arg0230340.1 knockdown. Down-regulated genes were enriched in ion channel pathways, particularly those for Na+, K+, and Ca2+ channels, whose dysfunction could disrupt normal myocardial bioelectric activity. The impaired cardiac performance resulting from RNAi targeting Arg0230340.1 reduced the cardiac workload in scallop hearts, thus affecting myocardial oxygen consumption and thermotolerance. We propose a hypothetical mechanism where PC4 down-regulation impairs cardiac bioelectric activity, leading to decreased thermotolerance in bay scallops, providing theoretical guidance for breeding thermotolerant scallop varieties and developing strategies for sustainable aquaculture in the face of long-term environmental changes.

In Hot Water: Current Thermal Threshold Methods Unlikely to Predict Invasive Species Shifts in NW Atlantic.

As global temperatures continue to rise, accurate predicted species distribution models will be important for forecasting the movement of range-shifting species. These predictions rely on measurements of organismal thermal tolerance, which can be measured using classical threshold concepts such as Arrhenius break temperatures and critical thermal temperatures, or through ecologically relevant measurements such as the temperature at which reproduction and growth occur. Many species, including invasive species, exhibit thermal plasticity, so these thresholds may change based on ambient temperature, life stage, and measurement techniques. Here, we review thermal thresholds for 15 invertebrate species invasive to the Gulf of Maine. The high degree of variability within a species and between applied conceptual frameworks suggests that modeling the future distribution of these species in all ecosystems, but especially in the rapidly warming northwest Atlantic and Gulf of Maine, will be challenging. While each of these measurement techniques is valid, we suggest contextualization and integration of threshold measurements for accurate modeling.

Changes in water temperature: The effect of triploid performance in Pacific abalone (Haliotis discus hannai)

The triploid Pacific abalone (Haliotis discus hannai) has significant economic value and promising application prospects. However, the optimal cultural conditions that maximize the advantages of triploidy in the abalone have yet to be determined. This study examined the properties of triploid Pacific abalone after 3 months of culture under three constant temperatures (18 °C, 22 °C, and 26 °C) to fill up this information gap. The results showed that the survival rate of triploids in the 26 °C group was significantly higher than that of diploids (P < 0.05), while the survival rate of triploids in the other two groups was similar to that of diploids (P > 0.05). Except for the shell width of the 22 °C group and the shell length of the 26 °C group, triploid Pacific abalone exhibited significantly superior growth traits compared to diploids at all temperatures (P < 0.05). The most notable improvement was observed in the foot muscle weight trait, where there were triploid advantage rates of 81.44% (18 °C), 76.21% (22 °C), and 54.96% (26 °C). The specific growth rate and the ratio of shell length and body weight indicated that triploids grew the fastest in the 22 °C group. Furthermore, the thermal resistance of diploids and triploids was evaluated through the Arrhenius break temperature (ABT) of cardiac performance. The results demonstrated that the ABT of triploids was significantly higher than that of diploids (P < 0.05, ABT2N = 30.81 ± 0.43 °C, ABT3N = 31.38 ± 0.72 °C). Both diploid and triploid foot adhesion forces were measured, and the results showed that triploid foot adhesion force was stronger than that of diploids (P < 0.05). Additionally, there was a significant positive correlation between foot adhesion force and meat yield traits (foot muscle weight, fullness index (FI) and foot muscle-soft tissue index (FMSI)) (P < 0.05). In summary, this study confirmed the triploid advantage in meat yield of Pacific abalone and identified a temperature range that maximizes their growth rate. Moreover, triploids exhibited improved thermal resistance and adhesion capacity compared to diploids, with an increase in meat yield. The results of this study could serve as a reference for identifying a culture model suitable for triploid Pacific abalone and thus could promote the development of the triploid aquaculture industry.

Surviving hot summer: Roles of phenotypic plasticity of intertidal mobile species considering microhabitat environmental heterogeneity

For species inhabiting warming and variable thermal environment, coordinated changes in heat tolerance to temperature fluctuations, which largely depend on phenotypic plasticity, are pivotal in buffering high temperatures. Determining the roles of phenotypic plasticity in wild populations and common garden experiments help us understand how organisms survive hot summer and the warming world. We thus monitored the operative temperature of the intertidal limpets Cellana toreuma in both emergent rock and tidal pool microhabitats from June to October 2021, determined the variations of upper thermal limits of short-term acclimated and long-term acclimated limpets from different microhabitats (emergent rock and tidal pool), and further calculated the relationship between the upper thermal limits and acclimation capacity. Our results indicated that living on the emergent rock, limpets encountered more extreme events in summer. For the short-term acclimated samples, limpets on the emergent rock exhibited obvious variations of sublethal thermal limit (i.e., Arrhenius Break Point of cardiac performance, ABT) during summer months, however, this variation of ABT was absent in the limpets in the tidal pool. After the laboratory long-term acclimation, the ABTs and FLTs (Flat Line Temperature of cardiac performance, as an indicator of lethal temperature) of limpets both on the rock and in the tidal pool increased significantly in October, implying the potential existence of selection during the hot summer. Our results further showed that environmental temperature was an important driver of phenotypic plasticity. This study highlighted the changes in the thermal tolerance of intertidal limpets during summer in different microhabitats.

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.

Non-Arrhenius behavior: Influence of antioxidants on lifetime predictions for materials used in the cable and wire industries

Thermo-oxidation (70–160 °C) of peroxide cross-linked polyethylene (XLPE) formulations stabilised with different antioxidants were studied. In order to separately study the influence of three commonly used antioxidants, three formulations were prepared with only one antioxidant each (0.3% w/w): a sterically hindered phenolic antioxidant (Irganox 1010), an organosulfur antioxidant (Hostanox SE4) and an oligomeric, sterically hindered amine light stabiliser (HALS 94). The materials were characterised by infrared spectroscopy measurements and tensile testing. Results proved that the addition of antioxidants causes in each case an Arrhenius break, occurring at a different temperature depending on the nature of the added antioxidant. Interestingly, the study of the thermo-oxidation (50–105 °C) of a certified antioxidant-free polyethylene (non-cross-linked) revealed no Arrhenius deviation. In a previous paper, we reported an Arrhenius deviation at low temperature (50 °C) for two cross-linked PE and EPR, containing residual process antioxidants. These results strengthen our hypothesis that several Arrhenius deviations could be explained by the presence of antioxidants (residual process antioxidants or formulation antioxidants), which “activity” is extremely dependent on the temperature.

Three-way cross hybrid abalone exhibit heterosis in growth performance, thermal tolerance, and hypoxia tolerance

Abalone is an economically important aquaculture resource worldwide, with high commercial value. Abalone productivity, stress resistance, and profitability have been improved by interspecific and intraspecific hybridization. In this study, a systematic comparative assessment of heterosis for survival, growth, thermal tolerance, and hypoxia tolerance in Haliotis gigantea (SS), H. discus hannai (DD), H. discus hannai♀ × H. fulgens♂ (DF), and three-way cross hybrids SS♀ × DF♂ and DF♀ × SS♂ was conducted. Two three-way cross hybrids, SS × DF and DF × SS, showed positive mid-parent heterosis in the growth rates of shell length and total wet weight in different months. The proportion of large individuals with higher total wet weight or shell length in DF × SS and SS × DF was higher than in other abalone species. The thermal and hypoxia tolerance of these abalone were assessed using Arrhenius break temperatures (ABT) and the breakpoint of dissolved oxygen (BPDO) of cardiac performance, respectively. The mid-parental heterosis values of ABT in SS × DF and DF × SS were 2.29% and 1.38%, respectively, while the BPDO values in SS × DF and DF × SS were − 11.48% and − 11.96%, respectively, confirming heterosis for thermal and hypoxia tolerance in these three-way cross hybrids. Overall, this is the first three-way interspecific cross of abalone, and the improvement of commercial traits can be achieved through a combination of selection and further hybridization among purebred and hybrid abalone.

Study of hybrid and backcross abalone populations uncovers trait separation and their thermal resistance capacity

Hybridization and backcrossing are classical breeding methods that can effectively improve the genetic characteristics of organisms through heterosis. The hybrid abalone (Haliotis discus hannai ♀ × H. fulgens ♂, DF) and backcrosses are cultured on a large scale due to their high survival rates under heat stress in summer. The thermal resistance of purebreds, hybrid F1 and backcross populations were evaluated through Arrhenius break temperature (ABT) of cardiac performance in this study. The results showed that the hybrid F1 had the best thermal resistance, and the ABT gradually decreased with the increase in recurring number. In addition, a growth experiment of DD × DF (H. discus hannai ♀ × DF ♂) populations showed that DD × DF-Y (presence of black spots in the visceral mass of DD × DF) grew faster than DD × DF-N (absence of spots in the visceral mass of DD × DF) (p < 0.05), but the ABT of DD × DF-Y was lower than that of DD × DF-N (p < 0.05). The results suggest that the presence or absence of black spots in the visceral mass could be used as a breeding trait for the thermal resistance and growth of backcross abalone. This study provides basic data for further study of the response of abalone to heat stress for the healthy and sustainable development of the abalone industry.

Transcriptome analysis reveals the molecular mechanisms of heterosis on thermal resistance in hybrid abalone

BackgroundHeterosis has been exploited for decades in different animals and crops due to it resulting in dramatic increases in yield and adaptability. Hybridization is a classical breeding method that can effectively improve the genetic characteristics of organisms through heterosis. Abalone has become an increasingly economically important aquaculture resource with high commercial value. However, due to changing climate, abalone is now facing serious threats of high temperature in summer. Interspecific hybrid abalone (Haliotis gigantea ♀ × H. discus hannai ♂, SD) has been cultured at large scale in southern China and has been shown high survival rates under heat stress in summer. Therefore, SD has become a good model material for heterosis research, but the molecular basis of heterosis remains elusive.ResultsHeterosis in thermal tolerance of SD was verified through Arrhenius break temperatures (ABT) of cardiac performance in this study. Then RNA-Sequencing was conducted to obtain gene expression patterns and alternative splicing events at control temperature (20 °C) and heat stress temperature (30 °C). A total of 356 (317 genes), 476 (435genes), and 876 (726 genes) significantly diverged alternative splicing events were identified in H. discus hannai (DD), H. gigantea (SS), and SD in response to heat stress, respectively. In the heat stress groups, 93.37% (20,512 of 21,969) of the expressed genes showed non-additive expression patterns, and over-dominance expression patterns of genes account for the highest proportion (40.15%). KEGG pathway enrichment analysis showed that the overlapping genes among common DEGs and NAGs were significantly enriched in protein processing in the endoplasmic reticulum, mitophagy, and NF-κB signaling pathway. In addition, we found that among these overlap genes, 39 genes had undergone alternative splicing events in SD. These pathways and genes may play an important role in the thermal resistance of hybrid abalone.ConclusionMore alternative splicing events and non-additive expressed genes were detected in hybrid under heat stress and this may contribute to its thermal heterosis. These results might provide clues as to how hybrid abalone has a better physiological regulation ability than its parents under heat stress, to increase our understanding of heterosis in abalone.

Computational analysis of protein conformational heterogeneity

In this paper, we applied the molecular dynamics (MD) simulations and used thermolysin as the system to study the overall protein dynamics and side chain dihedral angles across the Arrhenius break. Simulations were performed at a high temperature of 36 °C which is above the previously observed Arrhenius break, and the lower temperature of 20 °C which is below the Arrhenius break. We observed different protein dynamics and conformational heterogeneity of side chain dihedral angles of thermolysin at the two temperatures. Our results indicated that certain regions of thermolysin have a higher level of fluctuation at lower temperature. A temperature dependent dihedral angles were also observed at the two temperatures. The changes observed in the protein indicated key areas of temperature sensitivity within the protein. Communicated by Ramaswamy H. Sarma

Genome-Wide Association Study Reveals PC4 as the Candidate Gene for Thermal Tolerance in Bay Scallop (Argopecten irradians irradians).

The increasing sea temperature caused by global warming has resulted in severe mortalities in maricultural scallops. Therefore, improving thermal tolerance has become an active research area in the scallop farming industry. Bay scallop (Argopecten irradians irradians) was introduced into China in 1982 and has developed into a vast aquaculture industry in northern China. To date, genetic studies on thermal tolerance in bay scallops are limited, and no systematic screening of thermal tolerance-related loci or genes has been conducted in this species. In the present study, we conducted a genome-wide association study (GWAS) for thermal tolerance using the Arrhenius break temperature (ABT) indicators of 435 bay scallops and 38,011 single nucleotide polymorphism (SNP) markers. The GWAS identified 1,906 significant thermal tolerance-associated SNPs located in 16 chromosomes of bay scallop. Gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses showed that 638 genes were enriched in 42 GO terms, while 549 annotated genes were enriched in aggregation pathways. Additionally, the SNP (15-5091-20379557-1) with the lowest P value was located in the transcriptional coactivator p15 (PC4) gene, which is involved in regulating DNA damage repair and stabilizing genome functions. Further analysis in another population identified two new thermal tolerance-associated SNPs in the first coding sequence of PC4 in bay scallops (AiPC4). Moreover, AiPC4 expression levels were significantly correlated (r = 0.675–0.962; P < 0.05) with the ABT values of the examined bay scallops. Our data suggest that AiPC4 might be a positive regulator of thermal tolerance and a potential candidate gene for molecular breeding in bay scallop aiming at thermal tolerance improvement.

Seasonal variation of the thermal tolerance indicator ABT and the development of a rapid detection method in scallop Chlamys farreri

Zhikong scallop (Chlamys farreri Jones et Preston 1904) is one of the most economically important shellfish in the aquaculture industry of China. Improving thermal tolerance of the scallop by breeding has become a critical task for the sustainable farming industry. The detection of the majority of the current indicators of the thermal tolerance of the scallop is generally short-term, low-throughput and laborious/time-consuming. In the present study, we first monitored variations in Arrhenius break temperature (ABT) with annually natural seawater temperature changes and found that ABT showed seasonal characteristics. Then, correlation analysis between ABT and survival rate in both scallop sexes was conducted, revealing that the correlation coefficient between |Δ ABT| and |Δ survival rate| of Zhikong scallops was relatively high and significant (r = 0.863, P = 0.050). Notably, a tremendous decrease in ABT and natural survival rate, and significant differences between scallop sexes were simultaneously observed in October. Further verification of reproductive cycle of Zhikong scallops with seasonal changes demonstrated that ABT could be applied for detecting seasonal and sexual differences of thermal tolerance in Zhikong scallops. Finally, correlation coefficients (r = −0.710, P = 0.001) between heart rate (HR) variations and the ultimate ABT values were further evaluated, representing the first report of the feasibility of HR at 11 °C to be an indirect indicator for thermal tolerance detection in Zhikong scallops (ABT = -0.427*HR11 °C + 33.159, R2 = 0.5028). Our results emphasize the importance of ABT in detecting seasonal and sexual differences of thermal tolerance in scallops and provide a valuable indicator detection method for developing breeding strategies for Zhikong scallops.

The synergistic effects of elevated temperature and CO2-induced ocean acidification reduce cardiac performance and increase disease susceptibility in subadult, female American lobsters Homarus americanus H. Milne Edwards, 1837 (Decapoda: Astacidea: Nephropidae) from the Gulf of Maine

Abstract Increased greenhouse gas emissions have caused rapid ocean warming (OW) and reduced ocean pH via acidification (OA). Both OW and OA will likely impact marine crustaceans, but they are often examined in isolation. We conducted an environmental-stressor experiment to understand how exposure to current summer conditions (16 °C, pH 8.0), OW only (20 °C, pH 8.0), OA only (16 °C, pH 7.6), or both acidification and warming, OAW (20 °C, pH 7.6), differentially influence thermal physiology and immune response of female subadults of the American lobster, Homarus americanus H. Milne Edwards, 1837. Following a 42 d exposure, cardiac performance was assessed during an acute thermal stress, and lobsters were subjected to a subsequent 21 d pathogen challenge with the bacterium Aerococcus viridans var. homari, the causative agent of gaffkemia. Lobsters under OAW had significantly lower (P ≤ 0.02) Arrhenius break temperatures (ABT), an indicator of thermal limits of capacity, compared to lobsters exposed to all other treatments, suggesting these stressors act synergistically to reduce physiological performance. Individuals from the OW and OAW treatments also had significantly lower (P ≤ 0.035) total hemocyte counts (THCs), an indicator of immune response, and showed a reduced median time to death (by up to 5 d sooner) post A. viridans injection compared to lobsters exposed to current summer conditions. Moreover, nearly twice as many lobsters exposed to OAW lost at least one claw during the pathogen challenge compared to all other treatment groups, potentially increasing the risk of mortality due to secondary infection. Together, these results suggest that OAW will impact the physiology and immune response of subadult H. americanus, potentially influencing successful recruitment to the fishery.

Temperature-dependent activity of kinesins is regulable

Cytoskeletal transport in cells is driven by enzymes whose activity shows sensitive, typically Arrhenius, dependence on temperature. Often, the duration and outcome of cargo transport is determined by the relative success of kinesin vs. dynein motors, which can simultaneously bind to individual cargos and move in opposite direction on microtubules. The question of how kinesin and dynein activity remain coupled over the large temperature ranges experienced by some cells is one of clear biological relevance. We report a break in the Arrhenius behavior of both kinesin-1 and kinesin-3 enzymatic activity at 4.7 °C and 10.5 °C, respectively. Further, we report that this transition temperature significantly changes as a function of chemical background: addition of 200 mM TMAO increases transition temperatures by ∼6 °C in all cases. Our results show that Arrhenius trend breaks are common to all cytoskeletal motors and open a broad question of how such activity transitions are regulated in vivo. Statement of significanceMany cytoskeletal motors studied to date follow Arrhenius kinetics, at least from room temperature up to mammalian body temperature. However the thermal dynamic range is typically finite, and breaks in Arrhenius trends are commonly observed at biologically relevant temperatures. Here we report that the thermal dynamic range of kinesins is also limited and moreover that the location of the Arrhenius break for kinesins can shift significantly based on chemical backgrounds. This implies that the balance of multiple motor cargo transport along the cytoskeleton is far more tunable as a function of temperature than previously appreciated.

Impedance Pneumography for Minimally Invasive Measurement of Heart Rate in Late Stage Invertebrates

Temperatures in oceans are increasing rapidly as a consequence of widespread changes in world climates. As organismal physiology is heavily influenced by environmental temperature, this has the potential to alter thermal physiological performance in a variety of marine organisms. Using the American lobster (Homarus americanus) as a model organism, this protocol describes the use of impedance pneumography to understand how cardiac performance in late stage invertebrates changes under acute thermal stress. The protocol presents a minimally invasive technique that allows for real-time collection of heart rate during a temperature ramping experiment. Data are easily manipulated to generate an Arrhenius plot that is used to calculate Arrhenius break temperature (ABT), the temperature at which heart rate begins to decline with increasing temperatures. This technique can be used in a variety of late stage invertebrates (i.e., crabs, mussels, or shrimps). Although the protocol focuses solely on the impact of temperature on cardiac performance, it can be modified to understand the potential for additional stressors (e.g., hypoxia or hypercapnia) to interact with temperature to influence physiological performance. Thus, the method has potential for wide-ranging applications to further understand how marine invertebrates respond to acute changes in the environment.

The use of internal heart rate loggers in determining cardiac breakpoints of fish.

As marine environments are influenced by global warming there is a need to thoroughly understand the relationship between physiological limits and temperature in fish. One quick screening method of a physiological thermal tipping point is the temperature at which maximum heart rate (ƒHmax) can no longer scale predictably with warming and is referred to as the Arrhenius break temperature (TAB). The use of this method has been successful for freshwater fish by using external electrodes to detect an electrocardiogram (ECG), however, the properties of this equipment pose challenges in salt water when evaluating marine fish. To overcome these challenges, this study aimed to explore the potential use of implantable heart rate loggers to quantify the TAB of Chrysoblephus laticeps, a marine Sparid, following the ECG method protocols where ƒHmax is monitored over an acute warming event and the TAB is subsequently identified using a piece-wise linear regression model. Of the nine experimental fish, only five (56%) returned accurate ƒHmax data. The TAB of successful trials was identified each time and ranged from 18.09 to 20.10 °C. This study therefore provides evidence that implantable heart rate loggers can estimate TAB of fish which can be applied to many marine species.

Thermal performance of the European flat oyster, Ostrea edulis (Linnaeus, 1758)—explaining ecological findings under climate change

Climate change challenges marine organisms by constraining their temperature-dependent scope for performance, fitness, and survival. According to the concept of Oxygen and Capacity Limited Thermal Tolerance (OCLTT), the overall thermal performance curve relates to an organism’s aerobic power budget, its overall aerobic scope for growth, exercise, reproduction, and other performances. We hypothesize that physiological principles shaping tolerance in extant ecosystems have also been operative during climatic changes in the distant past. To compare response patterns in extant fauna and their palaeo-relatives, we started here by studying the metabolic background of performance in the European flat oyster Ostrea edulis at organismic and cellular levels, focusing on the acute thermal window and the metabolic changes towards upper lethal temperatures. We investigated the response of the oysters (pre-acclimated at 12 °C) to a short-term warming protocol (by 2 °C every 48 h) from 14 to 36 °C which we identified as the lethal temperature. At the organismic level, heart and filtration rates were recorded. Gill metabolites were studied by 1H NMR spectroscopy to address thermal responses at the cellular level. Feeding activity by O. edulis (assessed by the filtration rates) was highest between 18 and 24 °C when overall energy expenditure (indicated by heart rate as a proxy for routine metabolic rate) was moderate. We conclude that this range reflects the thermal optimum of this species. Beyond 26 °C, the gill tissue of O. edulis became partly anaerobic, and cardiac dysfunction (arrhythmia) developed at 28 °C followed by an Arrhenius break point (30 °C). This mirrors performance constraints and indicates a wide temperature range of passive tolerance which may be a long-standing characteristic of ostreids supporting survival in extreme environments as well as during past and present climate oscillations.

The physiology of Venezillo arizonicus: water balance and the cuticular water barrier

This study investigated the water balance physiology of Venezillo arizonicus, a land isopod endemic to the Southwest Desert Ecoregion of North America. Evaporative water losses were measured in two ways: gravimetric in dry air, and by perfusing animals with dry air in a respirometry chamber and monitoring downstream relative humidity (RH). The respective mean loss flux estimates were 0.140 and 0.177 μg h−1 cm−2 Pa−1, lower than other N. American Oniscidea described to date (≥0.491 μg h−1 cm−2 Pa−1). Humidity monitoring revealed intermittent sharp peaks in RH, attributed to the release of maxillary urine. Whole-animal flux increased as a function of temperature, with a critical temperature (Tc) between 38 and 42 °C identifiable by a clear Arrhenius break point. Hexane-rinsed whole animals yielded straight-chain, saturated hydrocarbons (C21–C33). The surface density of extracted alkanes (0.64 µg cm−2) was somewhat higher than previously determined values for mesic species, although modest compared to insects and arachnids. Dehydrated animals exposed to high RH (>88%) demonstrated active water vapor absorption (WVA) like other Crinocheta, with an extrapolated uptake threshold of approximately 85% RH (Aw = 0.85), the lowest value reported for Oniscidea. The maximum uptake flux increased linearly as a function of ambient RH. Mass-specific uptake in 100% RH was 49% d−1, similar to values determined previously for Armadillidium vulgare and Porcellio scaber. The low WVA threshold of V. arizonicus, and the species’ low permeability, are consistent with its known range in the arid desert southwest and the desiccation stress of its typical aeolian sand and seasonal wash habitats.

Ocean acidification alters thermal cardiac performance, hemocyte abundance, and hemolymph chemistry in subadult American lobsters Homarus americanus H. Milne Edwards, 1837 (Decapoda: Malcostraca: Nephropidae)

ABSTRACTIncreased anthropogenic input of carbon dioxide into the atmosphere has caused widespread patterns of ocean acidification (OA) and increased the frequency of extreme warming events. We explored the sublethal effects of OA on the hemolymph chemistry and physiological response to acute thermal stress in the American lobster (Homarus americanus H. Milne Edwards, 1837). We exposed subadult lobsters to current or predicted end-century pH conditions (8.0 and 7.6, respectively) for 60 days. Following exposure, we assessed hemolymph L-lactate and calcium concentrations (as indicators of oxygen carrying capacity), ecdysterone concentrations, total protein content, and total hemocyte counts (THCs) as an indicator of immune response. We also assessed cardiac performance in the context of an acute warming event using impedance pneumography. Calcium, total protein, and ecdysterone concentrations were not significantly altered (P ≥ 0.10) by OA exposure. Control lobsters, however, had significantly higher levels of L-lactate concentrations compared to acidified lobsters, suggesting reduced oxygen carrying capacity under OA. THCs were also 61% higher in control versus acidified lobsters, suggesting immunosuppression under chronic OA. Lobsters exposed to acidified conditions exhibited reduced cardiac performance under acute warming as indicated by significantly lower (P = 0.040) Arrhenius Break Temperatures compared to control lobsters. These results suggest that although some physiological endpoints of American lobster are not impacted by OA, the stress of OA will likely be compounded by acute heat shock and may present additional physiological challenges for this species in the face of future change.