Moderate reductions in dissolved oxygen may compromise performance in an ecologically-important estuarine invertebrate

Oxidative stress-mediated deleterious effects of hypoxia in the brackish water flea Diaphanosoma celebensis

In this study, we investigated the acute toxicity, in vivo effects, oxidative stress, and gene expression changes caused by hypoxia on the brackish water flea Diaphanosoma celebensis. The no-observed-effect concentration (NOEC) of 48 h of hypoxia exposure was found to be 2 mg/L O2. Chronic exposure to NOEC caused a significant decline in lifespan but had no effect on total fecundity. The induction of reactive oxygen species increased in a time-dependent manner over 48 h, whereas the content of antioxidant enzymes (superoxide dismutase and catalase) decreased. The transcription and translation levels were modulated by hypoxia exposure. In particular, a significant increase in hemoglobin level was followed by up-regulation of hypoxia-inducible factor 1α gene expression and activation of the mitogen-activated protein kinase pathway. In conclusion, our findings provide a better understanding of the molecular mechanism of the adverse effects of hypoxia in brackish water zooplankton.

Acclimation to warming but not hypoxia alters thermal tolerance and metabolic sensitivity in an estuarine crustacean

Coastal species are challenged by multiple anthropogenic stressors. Plasticity may buffer the effects of environmental change, but investigation has largely been restricted to single-stressor performance. Multistressor studies have often been short-term and relatively less is known about the consequences of plasticity under one stressor for performance under another. Here, we aimed to test for the effects of thermal or hypoxic acclimation on thermal tolerance in the amphipod Gammarus chevreuxi. Animals were chronically exposed to raised temperature or hypoxia prior to determination of upper thermal limits and routine metabolic rate (RMR). Warm acclimation increased all metrics of thermal tolerance, but hypoxic acclimation had no effect. Different responses to the two stressors was also observed for the thermal sensitivity of RMR. Consequently, this species possesses the ability to increase thermal tolerance via plasticity in response to chronic warming but increasing duration of hypoxic episodes will not confer cross-tolerance to a warming environment.

The embryonic thermal environment has positive but weak effects on thermal tolerance later in life in the aquatic invertebrate Gammarus chevreuxi

Recent evidence suggests that the adult phenotype is influenced by temperatures experienced in early life. However, our understanding of the extent to which the embryonic environment can modulate thermal tolerance later in life is limited, owing to the paucity of studies with appropriate experimental designs to test for this form of developmental plasticity. We investigated whether the thermal environment experienced during embryonic development affects thermal limits in later life. Embryos of the estuarine amphipod Gammarus chevreuxi were incubated until hatching to 15 °C, 20 °C and 25 °C, then reared under a common temperature. Using thermal ramping assays, we determined upper thermal limits in juveniles, four weeks post-hatch. Individuals exposed to higher temperatures during embryonic development displayed greater thermal tolerance as juveniles (acclimation response ratio ≈ 0.10-0.25 for upper lethal temperature). However, we suggest that the degree of developmental plasticity observed is limited, and will provide little benefit under future climate change scenarios.

Time-Course and Tissue-Specific Molecular Responses to Acute Thermal Stress in Japanese Mantis Shrimp Oratosquilla oratoria

Current understanding of adaptability to high temperatures is increasingly important as extreme weather events that can trigger immediate physiological stress in organisms have occurred more frequently. Here, we tracked transcriptomic responses of gills, hepatopancreas, and muscle to acute thermal exposure at 30 °C for 0.5, 6, and 12 h in an economically important crustacean, Oratosquilla oratoria, to gain a preliminary understanding of the tissue-specific and dynamic physiological regulation process under acute heat stress. The unique physiological responses of muscle, hepatopancreas, and gills to acute thermal stress were associated with protein degradation, lipid transport, and energy metabolism in O. oratoria, respectively. Functional enrichment analysis of differentially expressed transcripts and heat-responsive gene clusters revealed a biphasic protective responsiveness of O. oratoria developed from the early responses of signal transduction, immunity, and cytoskeleton reorganization to the responses dominated by protein turnover and energy metabolism at the mid-late stages under acute heat stress. Noteworthy, trend analysis revealed a consistently upregulated expression pattern of high molecular weight heat shock protein (HSP) family members (HSP60, HSP70, and HSP90) during the entire thermal exposure process, highlighting their importance for maintaining heat resistance in O. oratoria. Documenting the whole process of transcriptional responses at fine temporal resolution will contribute to a far-reaching comprehension of plastic responses to acute heat stress in crustaceans, which is critical in the context of a changing climate.

Phenomics enables measurement of complex responses of developing animals to global environmental drivers

Phenomics offers technological advances for high-dimensional phenotyping, facilitating rapid, high-throughput assessment of physiological performance and has proven invaluable in global research challenges including drug discovery and food security. However, this rapidly growing discipline has remained largely inaccessible to the increasingly urgent challenge of assessing organismal functional sensitivity to global change drivers. Here, we investigate the response of an ecologically important marine invertebrate to multiple environmental drivers using Energy Proxy Traits (EPTs), a new approach for measuring complex phenotypes captured on video as a spectrum of energy levels across different temporal frequencies in fluctuating pixel values. We imaged three developmental stages of the common prawn Palaemon serratus at different salinities and temperatures, and measured EPTs and heart rate, a major proxy of physiological performance in ectotherms present across stages. Significant interactions were detected between temperature, developmental stage and salinity in frequency-specific energy levels. Despite cardiac activity being a significant contributor to the EPT spectra, treatment interactions were different from those observed on EPTs, highlighting additional phenotypic drivers of EPTs. Elevated temperature resulted in a shift of the EPT spectra towards higher frequency signals, indicating a reallocation of resources within the phenome. Using a non-linear dimensionality reduction, we interrogated the responses of EPT spectra in high-dimensional space. We discovered complex developmental-stage specific sensitivities, highlighting both the complexity of phenotypic responses, and the limits of using univariate approaches with pre-selected traits to assess responses to multiple global environmental drivers. EPTs are a high-dimensional, transferrable method of phenotyping, and are therefore highly relevant to addressing the current limitations of traditional methods of phenotyping applied to assessing biological sensitivity to drivers of global change. We predict that EPTs will become an important tool for indiscriminate phenotyping, transferrable between species, developmental stages and experimental designs.

Regulation of gene expression during ontogeny of physiological function in the brackishwater amphipod Gammarus chevreuxi

Embryonic development is a complex process involving the co-ordinated onset and integration of multiple morphological features and physiological functions. While the molecular basis of morphological development in embryos is relatively well known for traditional model species, the molecular underpinning of the development of physiological functions is not. Here, we used global gene expression profiling to investigate the transcriptional changes associated with the development of morphological and physiological function in the amphipod crustacean Gammarus chevreuxi. We compared the transcriptomes at three timepoints during the latter half of development, characterised by different stages of the development of heart form and function: 10 days post fertilisation (dpf, Early: no heart structure visible), 15 dpf (Middle: heart present but not fully functional), and 18 dpf (Late: regular heartbeat). Gene expression profiles differed markedly between developmental stages, likely representing a change in the activity of different processes throughout the latter period of G. chevreuxi embryonic development. Differentially expressed genes belonged to one of three distinct clusters based on their expression patterns across development. One of these clusters, which included key genes relating to cardiac contractile machinery and calcium handling, displayed a pattern of sequential up-regulation throughout the developmental period studied. Further analyses of these transcripts could reveal genes that may influence the onset of a regular heartbeat. We also identified morphological and physiological processes that may occur alongside heart development, such as development of digestive caeca and the cuticle. Elucidating the mechanisms underpinning morphological and physiological development of non-model organisms will support improved understanding of conserved mechanisms, addressing the current phylogenetic gap between relatively well known model species.

Consequences of thermal plasticity for hypoxic performance in coastal amphipods

Physiological plasticity may confer an ability to deal with the effect of rapid climate change on aquatic ectotherms. However, plasticity induced by one stressor may only be adaptive in situ if it generates cross-tolerance to other stressors. Understanding the consequences of thermal acclimation on hypoxia thresholds is vital to understanding future climate-driven hypoxia. We tested if thermal acclimation benefits hypoxic performance in four closely-related amphipod species. The effects of thermal acclimation (7 days at 10 or 20 °C) on routine metabolic rate (RMR) and critical oxygen tensions (P_crit) were determined at a standardised test temperature (20 °C). Gammarus chevreuxi and Echinogammarus marinus displayed increased P_crit with acute warming but warm acclimation negated this increase. P_crit of Gammarus duebeni was thermally insensitive. Gammarus zaddachi displayed increased P_crit upon acute warming but little change via acclimation. Cross-tolerance between thermal plasticity and hypoxia may improve performance for some, but not all, species under future environmental change.

A Review on Machine Learning, Artificial Intelligence, and Smart Technology in Water Treatment and Monitoring

Artificial-intelligence methods and machine-learning models have demonstrated their ability to optimize, model, and automate critical water- and wastewater-treatment applications, natural-systems monitoring and management, and water-based agriculture such as hydroponics and aquaponics. In addition to providing computer-assisted aid to complex issues surrounding water chemistry and physical/biological processes, artificial intelligence and machine-learning (AI/ML) applications are anticipated to further optimize water-based applications and decrease capital expenses. This review offers a cross-section of peer reviewed, critical water-based applications that have been coupled with AI or ML, including chlorination, adsorption, membrane filtration, water-quality-index monitoring, water-quality-parameter modeling, river-level monitoring, and aquaponics/hydroponics automation/monitoring. Although success in control, optimization, and modeling has been achieved with the AI methods, ML models, and smart technologies (including the Internet of Things (IoT), sensors, and systems based on these technologies) that are reviewed herein, key challenges and limitations were common and pervasive throughout. Poor data management, low explainability, poor model reproducibility and standardization, as well as a lack of academic transparency are all important hurdles to overcome in order to successfully implement these intelligent applications. Recommendations to aid explainability, data management, reproducibility, and model causality are offered in order to overcome these hurdles and continue the successful implementation of these powerful tools.

Large within, and between, species differences in marine cellular responses: Unpredictability in a changing environment

Predicting the impacts of altered environments on future biodiversity requires a detailed understanding of organism responses to change. To date, studies evaluating mechanisms underlying marine organism stress responses have largely concentrated on oxygen limitation and the use of heat shock proteins as biomarkers. However, whether these biomarkers represent responses that are consistent across species and different environmental stressors remains open to question. Here we show that responses to four different thermal stresses (three rates of thermal ramping (1 °C h^-1, 1 °C day^-1 or 1 °C 3 day^-1) and a three-month acclimation to warming of 2 °C) applied to three species of Antarctic marine invertebrate produced highly individual responses in gene expression profiles, both within and between species. Mapping the gene expression profiles from each treatment for each of the three species, identified considerable difference in numbers of differentially regulated transcripts ranging from 10 to 3011. When these data were correlated across the different temperature treatments, there was no evidence for a common response with only 0-2 transcripts shared between all four treatments within any one species. There were also no shared differentially expressed genes across species, even at the same thermal ramping rates. The classical cellular stress response (CSR) i.e. up-regulation of heat shock proteins, was only strongly present in two species at the fastest ramping rate of 1 °C h^-1, albeit with different sets of stress genes expressed in each species. These data demonstrate the wide variability in response to warming at the molecular level in marine species. Therefore, identification of biodiversity stress responses engendered by changing conditions will require evaluation at the species level using targeted key members of the ecosystem, strongly correlated to the local biotic and abiotic factors.

Transcriptional frontloading contributes to cross-tolerance between stressors

The adaptive value of phenotypic plasticity for performance under single stressors is well documented. However, plasticity may only truly be adaptive in the natural multifactorial environment if it confers resilience to stressors of a different nature, a phenomenon known as cross-tolerance. An understanding of the mechanistic basis of cross-tolerance is essential to aid prediction of species resilience to future environmental change. Here, we identified mechanisms underpinning cross-tolerance between two stressors predicted to increasingly challenge aquatic ecosystems under climate change, chronic warming and hypoxia, in an ecologically-important aquatic invertebrate. Warm acclimation improved hypoxic performance through an adaptive hypometabolic strategy and changes in the expression of hundreds of genes that are important in the response to hypoxia. These 'frontloaded' genes showed a reduced reaction to hypoxia in the warm acclimated compared to the cold acclimated group. Frontloaded genes included stress indicators, immune response and protein synthesis genes that are protective at the cellular level. We conclude that increased constitutive gene expression as a result of warm acclimation reduced the requirement for inducible stress responses to hypoxia. We propose that transcriptional frontloading contributes to cross-tolerance between stressors and may promote fitness of organisms in environments increasingly challenged by multiple anthropogenic threats.