Published papers

Corals are under siege by both local and global threats, creating a worldwide reef crisis. Cryopreservation is an important intervention measure and a vital component of the modern coral conservation toolkit, but preservation techniques are currently limited to sensitive reproductive materials that can only be obtained a few nights per year during spawning. Here, we report the successful cryopreservation and revival of cm-scale coral fragments via mL-scale isochoric vitrification. We demonstrate coral viability at 24 h post-thaw using a calibrated oxygen-uptake respirometry technique, and further show that the method can be applied in a passive, electronics-free configuration. Finally, we detail a complete prototype coral cryopreservation pipeline, which provides a platform for essential next steps in modulating post-thaw stress and initiating long-term growth. These findings pave the way towards an approach that can be rapidly deployed around the world to secure the biological genetic diversity of our vanishing coral reefs.

Ultraviolet (UV) filters are compounds utilized in many manufacturing processes and personal care products such as sunscreen to protect against UV-radiation. These highly lipophilic compounds are emerging contaminants of concern in aquatic environments due to their previously observed potential to bioaccumulate and exert toxic effects in marine ecosystems. Currently, research into the toxic effects of UV filter contamination of freshwater ecosystems is lacking, thus the present study sought to model the effects of acute and chronic developmental exposures to UV filters avobenzone, oxybenzone and octocrylene as well as a mixture of these substances in the freshwater invertebrate, Daphnia magna, at environmentally realistic concentrations. Median 48-hour effect and lethal concentrations were determined to be in the low mg/L range, with the exception of octocrylene causing 50% immobilization near environmental concentrations. 48-hour acute developmental exposures proved to behaviourally impair daphnid phototactic response; however, recovery was observed following a 19-day post-exposure period. Although no physiological disruptions were detected in acutely exposed daphnids, delayed mortality was observed up to seven days post-exposure at 200 μg/L of avobenzone and octocrylene. 21-day chronic exposure to 7.5 μg/L octocrylene yielded complete mortality within 7 days, while sublethal chronic exposure to avobenzone increased Daphnia reproductive output and decreased metabolic rate. 2 μg/L oxybenzone induced a 25% increase in metabolic rate of adult daphnids, and otherwise caused no toxic effects at this dose. These data indicate that UV filters can exert toxic effects in freshwater invertebrates, therefore further study is required. It is clear that the most well-studied UV filter, oxybenzone, may not be the most toxic to Daphnia, as both avobenzone and octocrylene induced behavioural and physiological disruption at environmentally realistic concentrations.

Aging is accompanied by profound changes in energy metabolism, yet the underlying drivers and modulators of these shifts remain incompletely understood. Here, we investigated how life‐history evolution shapes metabolic aging and pharmacological responsiveness by leveraging Drosophila melanogaster lines divergently selected for reproductive timing. We measured organismal oxygen consumption rate and performed untargeted metabolomics in young and old flies of both sexes from long‐lived “O” lines (selected for female late‐life reproduction) and unselected “B” control lines. Males and females from the O lines maintained stable metabolic rates and largely preserved metabolite profiles with age, whereas B line flies showed age‐related increases in oxygen consumption, citrate accumulation, and elevated levels of medium‐ and long‐chain fatty acids, hallmarks of mitochondrial inefficiency and impaired lipid oxidation. Aged B flies also displayed elevated S‐adenosylmethionine, reduced sarcosine, and diminished heme levels, indicating dysregulation of one‐carbon metabolism and impaired heme biosynthesis. Furthermore, Vitamin B6 metabolites, pyridoxamine, pyridoxal, and 4‐pyridoxate, increased with aging only in B line females. Motivated by evidence implicating the renin‐angiotensin system in metabolic aging, we treated flies with the angiotensin‐converting enzyme (ACE) inhibitor lisinopril. Lisinopril prevented the age‐related rise in metabolic rate in B line females, aligning their metabolic phenotype with that of O line flies. This suggests that ACE inhibition may buffer against age‐associated increases in metabolic rate and contribute to enhanced metabolic stability. Our results show that selection for delayed reproduction and increased lifespan modifies age‐related metabolic trajectories and modulates physiological responses to pharmacological intervention.

Evidence suggests that angiotensin-converting enzyme inhibitors (ACEIs) may increase metabolic rate by promoting thermogenesis, potentially through enhanced fat oxidation and improved insulin. More research is, however, needed to understand this intricate process. In this study, we used 22 lines from the Drosophila Genetic Reference Panel to assess the metabolic rate of virgin female and male flies that were either fed a standard medium or received lisinopril for one week or five weeks. We demonstrated that lisinopril affects the whole-body metabolic rate in Drosophila melanogaster in a genotype-dependent manner. However, the effects of genotypes are highly context-dependent, being influenced by sex and age. Our findings also suggest that lisinopril may increase the Drosophila metabolic rate via the accumulation of a bradykinin-like peptide, which, in turn, enhances cold tolerance by upregulating Ucp4b and Ucp4c genes. Finally, we showed that knocking down Ance, the ortholog of mammalian ACE in Malpighian/renal tubules and the nervous system, leads to opposite changes in metabolic rate, and that the effect of lisinopril depends on Ance in these systems, but in a sex- and age-specific manner. In conclusion, our results regarding D. melanogaster support existing evidence of a connection between ACEI drugs and metabolic rate while offering new insights into this relationship.

Aquatic organisms are exposed to low concentrations of neuro-active chemicals, many of them acting also as neuroendocrine disruptors that can be hazardous during earlier embryonic stages. The present study aims to assess how exposure early in live to environmental low concentrations of two selective serotonin reuptake inhibitors (SSRIs), fluoxetine and sertraline, and tributyltin (TBT) affected cognitive, metabolic and cardiac responses in the model aquatic crustacean Daphnia magna. To that end, newly brooded females were exposed for an entire reproductive cycle (3-4 days) and the response of collected juveniles in the first, second and third consecutive broods, which were exposed, respectively, as embryos, provisioned and un-provisioned egg stages, was monitored. Pre-exposure to the selected SSRIs during embryonic and egg developmental stages altered the swimming behaviour of D. magna juveniles to light in a similar way reported elsewhere by serotonergic compounds while TBT altered cognition disrupting multiple neurological signalling routes. The studied compounds also altered body size, the amount of storage lipids in lipid droplets, heart rate, oxygen consumption rates and the transcription of related serotonergic, dopaminergic and lipid metabolic genes in new-born individuals, mostly pre-exposed during their embryonic and provisioning egg stages. The obtained cognitive, cardiac and metabolic defects in juveniles developed from exposed sensitive pre-natal stages align with the "Developmental Origins of Health and Disease (DoHAD)" paradigm.

Being composed of small cells may carry energetic costs related to maintaining ionic gradients across cell membranes as well as benefits related to diffusive oxygen uptake. Here, we test the hypothesis that these costs and benefits of cell size in ectotherms are temperature dependent. To study the consequences of cell size for whole-organism metabolic rate, we compared diploid and triploid zebrafish larvae differing in cell size. A fully factorial design was applied combining three different rearing and test temperatures that allowed us to distinguish acute from acclimated thermal effects. Individual oxygen consumption rates of diploid and triploid larvae across declining levels of oxygen availability were measured. We found that both acute and acclimated thermal effects affected the metabolic response. In comparison with triploids, diploids responded more strongly to acute temperatures, especially when reared at the highest temperature. These observations support the hypothesis that animals composed of smaller cells (i.e. diploids) are less vulnerable to oxygen limitation in warm aquatic habitats. Furthermore, we found slightly improved hypoxia tolerance in diploids. By contrast, warm-reared triploids had higher metabolic rates when they were tested at acute cold temperature, suggesting that being composed of larger cells may provide metabolic advantages in the cold. We offer two mechanisms as a potential explanation of this result, related to homeoviscous adaptation of membrane function and the mitigation of developmental noise. Our results suggest that being composed of larger cells provides metabolic advantages in cold water, while being composed of smaller cells provides metabolic advantages in warm water.

Aging is accompanied by increased susceptibility to infections including with viral pathogens resulting in higher morbidity and mortality among the elderly. Significant changes in host metabolism can take place following virus infection. Efficient immune responses are energetically costly, and viruses divert host molecular resources to promote their own replication. Virus-induced metabolic reprogramming could impact infection outcomes, however, how this is affected by aging and impacts organismal survival remains poorly understood. RNA virus infection of Drosophila melanogaster with Flock House virus (FHV) is an effective model to study antiviral responses with age, where older flies die faster than younger flies due to impaired disease tolerance. Using this aged host-virus model, we conducted longitudinal, single-fly respirometry studies to determine if metabolism impacts infection outcomes. Analysis using linear mixed models on Oxygen Consumption Rate (OCR) following the first 72-hours post-infection showed that FHV modulates respiration, but age has no significant effect on OCR. However, the longitudinal assessment revealed that OCR in young flies progressively and significantly decreases, while OCR in aged flies remains constant throughout the three days of the experiment. Furthermore, we found that the OCR signature at 24-hours varied in response to both experimental treatment and survival status. FHV-injected flies that died prior to 48- or 72-hours measurements had a lower OCR compared to survivors at 48-hours. Our findings suggest the hostâs metabolic profile could influence the outcome of viral infections.

The hydrophobic surface of plastics adsorbs hydrophobic persistent organic pollutants (POP) such as Perfluorooctanoic acid (PFOA). The potential for hydrophobic nanoparticles such as titanium dioxide (TiO 2 ) to associate with PFOA and alter accumulation rates has not been investigated. Nanoparticles form ecocorona by adsorption of multiple constituents in water, but few studies have examined if this results in differences in the rate of PFOA accumulation in freshwater animals. We demonstrate the PFOA associates with the hydrophobic surfaces of nano-sized TiO 2 particles and this increases the rate of uptake of PFOA into Daphnia magna. Accumulation of PFOA in daphnia was measurement over multiple concentrations, flux times and particle sizes using a radiotracer-based method ( 14 C-labelled PFOA). Our results show that TiO 2 NPs have a high sorption capacity for PFOA and PFOA sorption decreased aggregation of TiO 2 as evidenced by a decrease in average hydrodynamic diameter, decreased zeta potential and increased polydispersity index. Uptake of PFOA at 10 μg/L was found to be 45 % higher in the presence of 500 μg/L of 5 nm TiO 2 compared to control PFOA alone uptake. Potentiation of PFOA uptake using 25 nm TiO 2 NPs was 25 % higher than control PFOA alone. PFOA alone (0.5 mg/L) reduced metabolic oxygen consumption (MO 2 ) in daphnia by 52 %, but exposure to (100 mg/L) 5 nm TiO 2 NPs sorbed with (0.5 mg/L) PFOA decreased metabolic oxygen consumption (MO 2 ) by ~88 %. These findings show that TiO 2 nanoparticles act as vectors for hydrophobic organic pollutant accumulation and significantly potentiate PFOA accumulation and toxicity in aquatic organisms.

Mitochondrial replacement therapy (MRT) presents a promising preventative measure to combat mitochondrial diseases. However, the long-term consequences of disrupting mitonuclear coevolution at both the molecular and organismal levels remain understudied. Data on sex-specific effects are also lacking despite predictions that males may be especially vulnerable to mitochondrial replacement. To address this, we used backcrossed lines of the copepod Tigriopus californicus to produce offspring with nuclear genotype contributions from two populations and a mitochondrial genotype from a third, separate, population. When compared to hybrid controls with mitochondrial genotypes that matched the maternal nuclear genotype but not the paternal, these “three-parent offspring” did not significantly differ in lifespan or routine metabolic rate. While these organismal-level traits showed no effect, molecular metrics of mitochondrial health revealed consequences of mitochondrial replacement. Oxidative DNA damage, measured by 8-hydroxy-2’-deoxyguanosine content, was higher in three-parent offspring, and mitochondrial DNA content was lower than in hybrid controls. While differences between sexes were present in some traits, sex did not interact with mitochondrial replacement for any of these metrics. Although these results could be due either to donor mitochondrial DNA matching neither of the nuclear parents, or to deficits in the donor mitochondrial DNA itself, they highlight the importance of considering molecular level consequences of mitochondrial replacement that may be masked at the organismal level when evaluating the health impacts of this treatment.

In recent decades, rising industrial demand for palladium (Pd), driven by its unique properties and affordability compared to other noble metals, has increased its environmental release into aquatic systems. This highlights the need to assess its effects on organisms, given the lack of standardized toxicity studies and regulations for this element. This study examines the acute and chronic impacts of Pd exposure on D. magna. Acute lethality was assessed over 48 h at measured Pd concentrations ranging from 2 to 110 μg/L, yielding an LC 50 of 52 ± 2 μg/L and an LC 10 of 33 ± 3 μg/L. The impact of natural organic matter from the Suwannee River on Pd lethality and bioaccumulation was also examined. No mortality occurred at DOC concentrations of 1, 2, 5, and 8 mg C/L, in contrast with the results obtained at 0.8 mg C/L, which resulted in an LC 50 of 74 ± 1 μg/L. Pd bioaccumulation decreased significantly with increasing DOC concentrations compared to controls. After 15 days of chronic exposure, offspring viability significantly declined, with an EC 50 of 1 ± 0.1 μg/L, alongside reductions in total broods per D. magna (EC 50: 7 ± 2 μg/L). Parental dry weight also decreased significantly, though the timing of the first brood and weight‐normalized oxygen consumption rates remained unaffected across treatments. Parental survival was notably affected, with an LC 50 value of 14 ± 2 μg/L. These results emphasize Pd's potential for both lethal and sublethal effects, highlighting the need for environmental standards to protect aquatic life. This study examines acute and chronic impacts of Pd exposure on Daphnia magna. Acute lethality yielded an LC 50 of 52 ± 2 μg/L and an LC 10 of 33 ± 3 μg/L. Pd toxicity and bioaccumulation decreased with increasing dissolved organic carbon concentrations. Chronic exposure led to a decline in offspring viability and total brood size. These results emphasize Pd's potential for lethal and sublethal effects, highlighting the need for environmental standards to protect aquatic life.

Potential ecotoxicity of the solar chlor-photo-Fenton (SCPF) process as a novel approach for wastewater reclamation has been investigated in relation to reuse for crop irrigation. Several secondary effluents from wastewater treatment plants across different geolocations were treated by applying the process with low reagent concentrations of 0.1 mM of ferric nitrilotriacetate (Fe 3+ -NTA), 0.73 mM of hydrogen peroxide, at different chlorine doses ranging from 0.13 to 0.40 mM. Chlorination, using comparable chlorine concentrations, and the solar photo-Fenton process were evaluated in parallel to compare with SCPF. A UVB-LED system was also used to perform the SCPF treatment, demonstrating its adaptability to both solar and artificial light-driven applications. Potential environmental toxicity was assessed using a battery of bioassays, including bacterial toxicity and genotoxicity, phytotoxicity in algae and plants, and toxicity toward mixed microbial communities (microrespirometry). Water treated with SCPF exhibited minimal bacterial and algal toxicity (<13 %), low phytotoxicity as assessed by plant germination (35 % at high chlorine concentration) and shoot/root elongation (22 % and -30 %), low toxicity toward mixed microbial communities (<30 %), and low apparent levels of genotoxicity. In comparison, chlorination yielded higher ecotoxic responses across the bioassays, suggesting that SCPF may mitigate these adverse effects. Although Fe 3+ -NTA dissolution showed toxicity its ecotoxic impact was markedly reduced at the operational concentration of 0.1 mM used in SCPF. These results indicate that chlor-photo-Fenton can produce treated water with low apparent ecotoxicity, supporting its potential as an environmentally friendly and scalable solution for wastewater treatment and reuse.

Copepods are the dominant crustacean group in groundwater, where they perform valuable ecosystem services related to carbon recycling. The life-history traits of stygobitic (groundwater-obligate dweller) copepods, however, have only been casually studied in the past. In addition, next to nothing is known about the responses of stygobitic copepods to climate change. In this study, we investigated the life-history traits and respiratory metabolism of a species of harpacticoid copepods, Moraria sp., endemic to the Corchia Cave in the Apuan Alps (Italy). We collected the specimens of Moraria sp. from the dripping waters of the cave and observed their development, survival, and reproduction rates in the laboratory for one year. We also evaluated the acclimation ability of adult females of Moraria sp. by measuring their oxygen consumption in a temperature range from 8 °C (average annual temperature of the dripping water in the Stalactites Gallery of the Corchia Cave) to 12.5 °C (maximum temperature of the dripping water of the cave expected according to climate change scenarios in 2100). Our results indicate that Moraria sp. Is a stenothermal species showing remarkable stygobitic traits (long life span, low metabolic rates). We noted that the metabolism of this species is significantly affected by small (+1.5 °C) thermal changes. Our results showed no metabolic compensation occurring in this species over two weeks of exposure to temperatures higher than 8 °C. The outcomes of this study suggest that Moraria sp. May not be able to tolerate thermal changes brought on by climate change.

The reproductive process in Octopus maya was analyzed to establish the amount of reactive oxygen species that the embryos inherit from females, during yolk synthesis. At the same time, respiratory metabolism, ROS production, and the expression of some genes of the antioxidant system were monitored to understand the ability of embryos to neutralize maternal ROS and those produced during development. The results indicate that carbonylated proteins and peroxidized lipids (LPO) were transferred from females to the embryos, presumably derived from the metabolic processes carried out during yolk synthesis in the ovary. Along with ROS, females also transferred to embryos glutathione (GSH), a key element of the antioxidant defense system, thus facilitating the neutralization of inherited ROS and those produced during development. Embryos are capable of neutralizing ROS thanks to the early expression of genes such as catalase (CAT) and superoxide dismutase (SOD), which give rise to the synthesis of enzymes when the circulatory system is activated. Also, it was observed that the levels of the routine metabolic rate of embryos are almost as high as those of the maximum activity metabolism, which leads, on the one hand, to the elevated production of ROS and suggests that, at this stage of the life cycle in octopuses, energy production is maximum and is physically limited by the biological properties inherent to the structure of embryonic life (oxygen transfer through the chorion, gill surface, pumping capacity, etc.). Due to its role in regulating vascularization, a high expression of HIf-1A during organogenesis suggests that circulatory system development has begun in this phase of embryo development. The results indicate that the routine metabolic rate and the ability of O. maya embryos to neutralize the ROS are probably the maximum possible. Under such circumstances, embryos cannot generate more energy to combat the free radicals produced by their metabolism, even when environmental factors such as high temperatures or contaminants could demand excess energy.

Understanding how macroalgal forests will respond to environmental change is critical for predicting future impacts on coastal ecosystems. Although measures of adult macroalgae physiological responses to environmental stress are advancing, measures of early life‐stage physiology are rare, in part due to the methodological difficulties associated with their small size. Here we tested a novel, high‐throughput method (rate of oxygen consumption and production; V̇O2 via a sensor dish reader microplate system to rapidly measure physiological rates of the early life stages of three habitat‐forming macroalgae, the kelp Ecklonia radiata and the fucoids Hormosira banksii and Phyllospora comosa. We measured the rate of O2 consumption (respiration) and O2 production (net primary production) to then calculate gross primary production (GPP) under temperatures representing their natural thermal range. The V̇O2 microplate system was suitable for rapidly measuring physiological rates over a temperature gradient to establish thermal performance curves for all species. The V̇O2 microplate system proved efficient for measures of early life stages of macroalgae ranging in size from approximately 50 μm up to 150 mm. This method has the potential for measuring responses of early life stages across a range of environmental factors, species, populations, and developmental stages, vastly increasing the speed, precision, and efficacy of macroalgal physiological measures under future ocean change scenarios.

This individual-based study reveals sex-specific differences in stress responses of the copepod Calanus finmarchicus to oxidative stress, with males showing higher sensitivity but no significant different metabolic strategies compared with females. It also identifies the antagonistic and synergistic effects of heat and paraquat-induced oxidative stress on antioxidant gene expression, and a potential maximum threshold for superoxide dismutase and catalase fold change in females.

Environments with fluctuating oxygen are intense challenges for organisms both on land and in the water. Aquatic organisms can be exposed to especially stressful bouts of hypoxia that come on rapidly and to extreme levels. The copepod Tigriopus californicus inhabits supralittoral rocky pools and appears tolerant of hypoxia levels considered lethal for other aquatic organisms despite lacking molecular components typically used by animals to detect and respond to low environmental oxygen. Here, we quantified the natural regime of dissolved oxygen (DO) pools inhabited by T. californicus via deployment of continuous oxygen sensors in copepod pools in Oregon, USA. Using wild-derived cultures from northern (Oregon) and southern (Californian) populations, we exposed copepods to hypoxia and anoxia and assayed loss of equilibrium (LOE) and survival. We also quantified respiratory regulation via critical oxygen tension, oxygen supply capacity, and regulation index. The pools underwent extreme daily cycles of DO, and near anoxia often persisted for up to 6 h. Respiratory statistics indicated individuals could regulate oxygen consumption even near anoxia, predicting a species with hypoxia tolerance ranking high among aquatic taxa. Copepods survived hypoxia below 0.3 mg O 2 l -1 for up to 72 h with some individuals not showing any LOE. Survival was high following even 6 and 15 h exposure to anoxia. We observed sex and population differences in lethality and LOE, with southern populations exhibiting higher resilience. Intraspecific variation in tolerance makes this system a candidate for future studies to investigate alternative molecular and physiological pathways of hypoxia response.

Washing of road tunnels is essential for removing accumulated pollutants such as tyre wear particles, brake dust, exhaust residues, and road debris to ensure visibility and safe driving. Tunnel washing generates large volumes of contaminated runoff known as untreated tunnel wash runoff (UTWR). Some countries filter UTWR through a sedimentation process before release to reduce contamination, generating what is known as treated tunnel wash runoff (TWR). This study investigates the potential environmental impact of diluted UTWR (25 %) and TWR (50 %) by evaluating their toxicity in fish and comparing the effect to tyre-particle leachate (TPL, 2 g/L). UTWR was collected during tunnel cleaning, and TWR was collected after 14 days of filtration through sand sediments, from the Bodø tunnel in Norway. Zebrafish larvae, used as a fish model, exposed to contaminated runoff exhibited increased mortality, impaired growth, developmental anomalies, altered swimming behaviour, and changes in gene expression. Both UTWR and TWR exposure induced significant toxicity in zebrafish larvae, though the toxicity caused by TWR was notably lower than that of UTWR. This study shows that current filtration methods of tunnel wash water reduce the levels of most pollutants, however, more research is needed on how tunnel wash-water runoff affect aquatic ecosystems.

Under global warming, understanding the evolutionary adaptation of ectotherms resting metabolic rate (RMR) is critical for predicting long‐term populations' response to temperature increases. While several studies have evaluated metabolic rate evolution under different thermal context, most focused on space‐for‐time substitutions rather than assessment of populations' adaptation over time. Here, applying the method of resurrection ecology, we used sediment cores as an archive of populations' evolution and hatched ephippia from different sediment layers to examine the metabolic evolution of modern vs. ancient Daphnia longispina populations. Focusing on an oligotrophic subalpine lake, for which temperature has been monitored for almost a century, we were able to link population response to historical thermal contexts. We demonstrate that modern (2021) clonal lines exhibit a 60% higher RMR than ancient ones (1997) when measured at 20°C. The higher RMR correlated with reduced juvenile growth rates at 20°C but increased survival rates at high temperatures, with a higher thermal limit 2°C higher in modern populations. These findings reflect a trade‐off favoring survival over growth under warming and likely result from increased oxygen uptake capacities, which provide an advantage at high temperatures but constrain individual energy budgets at non‐stressful temperatures. Overall, this study suggests that survival at extreme weather events, such as heatwaves, may play an important role in shaping the RMR adaptation of Daphnia and, more generally, zooplankton populations.

In marine benthic environments, oxygen availability is highly variable across temporal and spatial scales. Such variability generates heterogeneous microhabitats in which organisms experience marked changes from saturated (i.e. normoxic) to anoxic conditions. For sessile colonial species, fine spatial differences in oxygen availability can trigger intra-colony phenotypic differences, influencing the overall colony performance/fitness. Here, we assessed the extent to which intra-colony differences in oxygen regimens influence biological characteristics in adult and larval stages of the colonial bryozoan Bugula neritina. For this, we measured the critical sensitivity to low oxygen for upper and lower zones of adult colonies and their larvae. We also measured larval swimming–exploring behaviour and settlement under hypoxia and normoxia. Although the results show similar intra-colony tolerances in the adults, differences were found in their larvae. While the lower zones of the colonies showed higher tolerant larvae, the upper zones had larvae with higher sensitivity and a tendency to avoid low-oxygen microhabitats. These larvae settle more quickly and in greater numbers compared with their lower-zone counterparts. Our results suggest that intra-colony differences in sensitivity to low-oxygen conditions (particularly during larval stages) can be important regulators of ecological processes (e.g. recruitment) and the resilience of benthic colonial species in deoxygenated oceans.

The establishment of laboratory-based species has facilitated the standardization of biological research methods; however, the stable culturing conditions of laboratories are dissimilar to the dynamic conditions of natural environments, potentially influencing fundamentally different research outcomes between laboratory and wild populations. This study sought to compare the toxicity of ultraviolet filters (UVFs) avobenzone, octocrylene, and oxybenzone to laboratory and wild populations of Daphnia pulex, while also testing the effects of culturing both populations in either laboratory or lake water in 48 hr and 21 day toxicity tests. Both daphnid populations demonstrated poor performance when cultured in nonancestral waters for three generations (i.e., laboratory Daphnia in lake water or wild Daphnia in laboratory water), including 25% decreased reproduction in control treatments and ≥ 50% mortality to most UVF treatments. Toxicity varied in each population cultured in ancestral waters; laboratory D. pulex were more sensitive to 30.7 μg/L of avobenzone and 18.8 μg/L of oxybenzone (> 25% greater mortality, ≥ 20% decreased reproduction vs. wild daphnids), whereas wild D. pulex were more sensitive to 25.6 μg/L of octocrylene (30% decreased mortality, 44% decreased reproduction vs. laboratory daphnids). These results demonstrate that Daphnia populations can deviate after decades of isolation, highlighting the challenges of relating laboratory-generated data to field results. In addition, culture water greatly affected daphnid performance during experimentation, potentially leading to misinterpreted results when studying wild organisms. This research highlights the importance of understanding how laboratory and wild organisms can differ, so that research modeling environmental outcomes can be applied in an appropriate context.

Parental care can increase the fitness of parents through increased offspring survival but can also reduce reproductive output by limiting time and energy allocated to additional mating opportunities. The evolutionary origin of parental care is often associated with shifts in life‐history traits (e.g., high investment in few, large offspring, slow offspring growth), but little is known about whether the evolutionary loss of care is associated with reciprocal shifts in the same life‐history traits. Here, we capitalize on the divergence of parental care between ecotypes of three‐spined stickleback ( Gasterosteus aculeatus ) to test for associations between parental care and life‐history traits. While males from most stickleback populations provide care, an unusual “white” ecotype has recently lost paternal care. We found support for the hypothesis that the evolutionary loss of paternal care is associated with shifts in female life‐history traits; relative to females of the ecotype with paternal care, females of the white ecotype that lack paternal care produced clutches with a similar overall mass and a greater number of smaller eggs, despite their smaller body size, suggesting lower per‐offspring investment. We did not detect an ecotypic difference in embryonic development rate, metabolic rate, or offspring age at hatching, contrary to the ‘safe harbor hypothesis’. These results support the theory that behavioral traits such as parental care co‐evolve with other life‐history traits and highlight opportunities for future study of the underlying causal mechanisms.

Coastal seawater hypoxia is increasing in temperate estuaries under global climate change, yet it is unknown how low oxygen conditions affect most estuarine species. We found that hypoxia has increased since the 1990s in an estuary hosting the sea anemone Nematostella vectensis (Jacques Cousteau National Estuarine Research Reserve, New Jersey, USA). Adult N. vectensis bred from anemones collected in this estuary exposed to three consecutive nights of hypoxia (dissolved oxygen = 0.5–1.5 mg L −1 for ~12 h night −1 ) during gametogenesis displayed decreased aerobic respiration rates and biomass, indicating metabolic disruption. Physiological declines were correlated with changes in the expression of genes related to oxygen‐dependent metabolic processes, many of which are targets of hypoxia‐inducible factor 1α (HIF1α), demonstrating the activity of this transcription factor for the first time in this early‐diverging metazoan. The upregulation of genes involved in the unfolded protein response and endoplasmic reticulum and Golgi apparatus homeostasis suggested that misfolded proteins contributed to disrupted physiology. Notably, these responses were more pronounced in females, demonstrating sex‐specific sensitivity that was also observed in reproductive outcomes, with declines in female but not male fecundity following hypoxia exposure. However, sperm from exposed males had higher mitochondrial membrane potential, indicating altered spermatogenesis. Further, crosses performed with gametes from hypoxia‐exposed adults yielded strikingly low developmental success (~2%), yet larvae that did develop displayed similar respiration rates and accelerated settlement compared to controls. Overall, hypoxia depressed fitness in N. vectensis by over 95%, suggesting that even stress‐tolerant estuarine species may be threatened by coastal deoxygenation.

Genome size is an important correlate of many biological features including body size, metabolic rate, and developmental rate and can vary due to a variety of mechanisms, including incorporation of repetitive elements, duplication events, or reduction due to selective constraints. Our ability to understand the causes of genome size variation is hampered by limited sampling of many nonmodel taxa, including monogonont rotifers. Here, we used high-throughput Nanopore sequencing and flow cytometry to estimate genome sizes of nine species of monogonont rotifers representing seven families, including three representatives of Superorder Gnesiotrocha. We annotated the genomes and classified the repetitive elements. We also compared genome size with two biological features: body size and metabolic rate. Body sizes were obtained from the literature and our estimates. Oxygen consumption was used as a proxy for metabolic rate and was determined using a respirometer. We obtained similar genome size estimates from genome assemblies and flow cytometry, which were positively correlated with body size and size-specific respiration rate. Importantly, we determined that genome size variation is not due to increased numbers of repetitive elements or large regions of duplication. Instead, we observed higher numbers of predicted proteins as genome size increased, but currently many have no known function. Our results substantially expand the taxonomic scope of available genomes for Rotifera and provide opportunities for addressing genetic mechanisms underlying evolutionary and ecological processes in the phylum.

Agri-chemicals such as fungicides are applied in natural settings and hence are exposed to the environment's ultraviolet (UV) light. Recently, many fungicides in commerce are being modified as nano-enabled formulations to increase agricultural productivity and reduce potential off-target effects. The present study investigated the impacts of sunlight-grade UV emission on the effects of either conventional or nano-enabled azoxystrobin (Az or nAz, respectively), a commonly applied agricultural fungicide, on Daphnia magna. Daphnids were exposed to increasing concentrations of Az or nAz under either full-spectrum (Vis) or full-spectrum Vis + UV (Vis + UV) lighting regimes to evaluate LC 50 s. Az LC 50 was calculated at 268.8 and 234.2 μg/L in Vis or Vis + UV, respectively, while LC 50 for nAz was 485.6 and 431.0 μg/L under Vis or Vis + UV light, respectively. Daphnids were exposed to 10% LC 50 of either Az or nAz under Vis or Vis + UV lighting regime for 48 h or 21 d (acute and chronic, respectively). By 48 h, both Az and nAz reduced O 2 consumption and increased TBARS. Heart rate was increased in Az-exposed daphnids but not in nAz groups. Neither of the two chemicals impacted thoracic limb activity. In 21 d exposures, Az significantly reduced biomass production and fecundity, but nAz groups were not significantly different from controls. The results of the present study demonstrate that conventional Az is more toxic to D. magna at lethal and sub-lethal levels in acute and chronic exposures, and sunlight strength UV can potentiate both acute and chronic effects of Az and nAz on D. magna.

Ocean warming is increasing organismal oxygen demand, yet at the same time the ocean’s oxygen supply is decreasing. For a patch of habitat to remain viable, there must be a minimum level of environmental oxygen available for an organism to fuel its metabolic demand—quantified as its critical oxygen partial pressure ( p O 2crit ). The temperature-dependence of p O 2crit sets an absolute lower boundary on aerobically viable ocean space for a species, yet whether certain life stages or geographically distant populations differ in their temperature-dependent hypoxia tolerance remains largely unknown. To address these questions, we used the purple sea urchin Strongylocentrotus purpuratus as a model species and measured p O 2crit for 3 populations of adult urchins (Clallam Bay, WA [n = 39], Monterey Bay, CA [91], San Diego, CA [34]) spanning 5-22°C and for key embryonic and larval developmental phases (blastula [n = 11], gastrula [21], prism [31], early-pluteus [21], late-pluteus [14], settled [12]) at temperatures of 10-19°C. We found that temperature-dependent hypoxia tolerance is consistent among adult populations exposed to different temperature and oxygen regimes, despite variable basal oxygen demands, suggesting differential capacity to provision oxygen. Moreover, we did not detect evidence for a hypoxia tolerance bottleneck for any developmental phase. Earlier larval phases are associated with higher hypoxia tolerance and greater temperature sensitivity, while this pattern shifts towards lower hypoxia tolerance and reduced temperature sensitivity as larvae develop. Our results indicate that, at least for S. purpuratus, models quantifying aerobically viable habitat based on p O 2crit -temperature relationships from a single adult population will conservatively estimate viable habitat.

A multitude of anthropogenic stressors impact biological communities and ecosystem processes in urban streams. Prominent among them are salinization, increased temperature, and altered flow regimes, all of which can affect microbial decomposer communities and litter decomposition, a fundamental ecosystem process in streams. Impairments caused by these stressors individually or in combination and recovery of communities and ecosystem processes after release from these stressors are not well understood. To improve our understanding of multiple stressors impacts we performed an outdoor stream mesocosm experiment with 64 experimental units to assess the response of microbial litter decomposers and decomposition. The three stressors we applied in a full-factorial design were increased salinity (NaCl addition, 0.53 mS cm -1 above ambient), elevated temperature (3.5 °C above ambient), and reduced flow velocity (3.5 vs 14.2 cm s -1 ). After two weeks of stressor exposure (first sampling) and two subsequent weeks of recovery (second sampling), we determined leaf-associated microbial respiration, fungal biomass, and the sporulation activity and community composition of aquatic hyphomycetes in addition to decomposition rates of black alder (Alnus glutinosa) leaves confined in fine-mesh litter bags. Microbial colonization of the litter was accompanied by significant mass loss in all mesocosms. However, there was little indication that mass loss, microbial respiration, fungal biomass, sporulation rate or community composition of aquatic hyphomycetes was strongly affected by either single stressors or their interactions. Two exceptions were temperature effects on sporulation and decomposition rate. Similarly, no notable differences among mesocosms were observed after the recovery phase. These results suggest that microbial decomposers and leaf litter decomposition are either barely impaired by exposure to the tested stressors at the levels applied in our experiment, or that communities in restored urban streams are well adapted to cope with these stressor levels.

Coloniality may grant colony members an energetic advantage in the form of lower individual respiration rates as colony size increases. If this occurs it should be apparent as negative allometric scaling of respiration with colony size, and colonial organisms should have scaling factors <1. However, colonial members from phylum Rotifera have yet to be examined. To test if colonial rotifers possess allometric scaling relationships between respiration rate and colony size, we measured respiration rates for four solitary and three colonial rotifer species; from these respiration rates we estimated scaling factors. We found mixed evidence for allometric scaling of respiration rate in colonial rotifers. Both rotifers with allometric scaling of respiration rate, Conochilus hippocrepis and Lacinularia flosculosa, have extensive mucilaginous coverings. These coverings may represent an investment of colony members into a shared structure, lowering individual metabolic costs and thus respiratory needs. Additionally, we determined which traits are associated with allometric scaling of respiration. We compiled known scaling factors for animal phyla from a wide phylogenetic spectrum with colonial representatives and conducted a hierarchical mixed regression that included attributes of colonies. Allometric scaling was found for two of the three colonial species measured. Traits associated with allometric scaling in colonial animals included colony shape, the presence of shared extrazooidal structures, and planktonic lifestyle. There are many other colonial rotifers and animal taxa for which allometric scaling factors have yet to be estimated, knowing these may enlighten our understanding of the benefits of coloniality in animals.

Organic ultraviolet filters (UVFs) are known to contaminate many aquatic ecosystems, with much environmental contamination attributed to the use of UVF-containing skin care products such as sunscreens during aquatic recreation. Most studies addressing the impact of sunscreen contamination have focused on the effects of UVFs under the assumption that they are the primary contaminants of concern from sunscreen pollution; however, the extent to which the toxicity of UVFs is representative of the environmental impacts of the whole sunscreen mixture is unknown. To address this knowledge gap, this study compared the mixture toxicity of five off-the-shelf sunscreen spray products containing the UVFs avobenzone, homosalate, octisalate, octocrylene and oxybenzone to the toxicity of each UVF in isolation to the freshwater invertebrate Daphnia magna. It was found that sunscreen toxicity was not proportional to their total UVF content, as the sunscreen containing the fewest UVFs was approximately equivalent to the sunscreen with the most UVFs, causing ≥90 % mortality and inhibiting all daphnid reproduction over 21 d exposures. Sunscreen toxicity was typically lower than expected when compared to the toxicity of each individual UVF within the mixture, as some sunscreens causing ≤20 % mortality contained octocrylene and/or oxybenzone at concentrations exceeding those which caused 90 % mortality during exposure to the UVF alone. Despite sunscreens causing large impairments in reproduction, growth and metabolism, poor correlations existed between the severity of most sublethal endpoints with respect to the measured UVF content of each sunscreen. Overall, these results indicate that potential antagonistic relationships between sunscreen ingredients can greatly reduce the toxicity of UVFs, creating more uncertainty regarding the level of threat that UVFs pose to the environment as a result of sunscreen contamination.

Changes in the environment promote variations in fish physiological responses. Genetic variation also plays a role in physiological variation. To explore the role of genetics in physiological variation, we assessed variation of cardiac function (heart rate, stroke volume, and cardiac output), oxygen consumption, yolk conversion efficiency, and cost of development in embryonic and larval AB wild-type and NHGRI-1 zebrafish (low heterozygosity line backcrossed from AB wild-type) exposed to different temperature and oxygen regimes. Fish were exposed from fertilization to 7 days post-fertilization (dpf) to control conditions (28 °C, 21% O2) or to low temperature (23 °C, 21% O2), high temperature (33 °C, 21% O2), moderate hypoxia (28 °C, 13% O2), or severe hypoxia (28 °C, 10% O2). We hypothesized that (1) assessed physiological variables will respond similarly in both fish lines and (2) data variability in the low heterozygosity NHGRI-1 zebrafish will be lower than in AB zebrafish. Cardiac function decreased at lower temperature and in hypoxia in both AB and NHGRI-1 zebrafish. Oxygen consumption was increased by higher temperature and hypoxia in AB fish and by severe hypoxia in NHGRI-1 fish. Yolk conversion efficiency was decreased by lower temperature and hypoxia in AB fish and increased by higher temperature and decreased by hypoxia in NHGRI-1 fish. Cost of development was higher mainly in hypoxia-treated fish. Supporting our hypothesis that genetics contributes to physiological variation, NHGRI-1 zebrafish data showed significantly lower coefficients of variation in 84% of assessed endpoints. We conclude that (1) there is a strong genetic component to physiological variation in fishes and (2) low heterozygosity NHGRI-1 zebrafish are useful models for reducing the ‘noise’ from genetic backgrounds in physiological research in fish, which may aid interpretation of experimental results and facilitate reproducibility.

Understanding the fates of organisms and ecosystems under global change requires consideration of the organisms’ rapid adaptation potential. In the Arctic, the recent temperature increase strongly impacts freshwater ecosystems which are important sentinels for climate change. However, a mechanistic understanding on the adaptive capacity of their key zooplankton grazers, among them polyploid, obligate parthenogenetic Daphnia, is lacking. Theory suggests low adaptation potential of asexual animals, yet examples exist of asexuals persisting through marked environmental changes. Here, we studied asexual Daphnia pulicaria from a meromictic lake in South-West Greenland. Its oxycline hosts purple sulphur bacteria (PSB), a potential food source for Daphnia. We tested two key phenotypic traits: (1) thermal tolerance as a response to rapid regional warming and (2) hypoxia tolerance tied to grazing of PSB in the hypoxic/anoxic transition zone. We resurrected Daphnia from dormant eggs representing a historical subpopulation from 2011, sampled modern subpopulation representatives in 2022 and measured phenotypic variation of thermal (time to immobilization -Timm) and hypoxia tolerance (respiration rate and critical oxygen limit -Pcrit) in clonal lineages of both subpopulations. Whole genome sequencing of the tested clonal lineages identified three closely related genetic clusters, one with clones from both subpopulations and two unique to each subpopulation. We observed significantly lower Timm and Pcrit and a trend for higher respiration rates in the modern subpopulation, indicating a lower tolerance to both high temperature and hypoxia in comparison to the historical subpopulation. As these two traits share common physiological mechanisms, the observed phenotypic divergence might be driven by a relaxed selection pressure on hypoxia tolerance linked to variation in PSB abundance. Our results, while contrary to our expectation of higher thermal tolerance of the modern subpopulation, provide evidence for phenotypic change within a decade in this asexual Daphnia population.

As Arctic sea temperatures rise and sea ice declines, boreal species are becoming more abundant in these waters. Generally, both inter- and intra-species variations show larger body sizes at higher latitudes and in colder climates. Continued Arctic amplification may lead to shifts in the size and composition of marine plankton, with cascading effects throughout the ecosystem. This study examines the metabolic rates of three common zooplankton species, Calanus finmarchicus, C. glacialis, and Metridia longa, across different temperatures (0°C, 3°C, and 6°C) to understand these dynamics. Results showed a distinct decrease in aerobic scope with rising temperatures for all three copepod species, indicating potential fitness reductions in warmer waters. Larger copepods exhibited higher aerobic scopes than smaller ones at all temperatures; however, this advantage diminished at 6°C, suggesting that smaller body sizes may confer metabolic benefits at higher temperatures. Conversely, larger sizes are favored in colder waters. These findings help explain the increase of smaller boreal species in warming Arctic seas and why colder Arctic conditions favor larger individuals.

This study explores the metabolic response and carbon budget of two cyclopoid copepod species, Diacyclops belgicus Kiefer, 1936 (a stygobitic, groundwater-adapted species) and Diacyclops crassicaudis crassicaudis (Sars G.O., 1863) (a stygophilic, predominantly surface-associated species). We measured oxygen consumption rates (OCRs), carbon requirements (CRs), ingestion (I) rates, and egestion (E) rates at 14 °C and 17 °C, representing current and predicted future conditions in the collection habitats of the two species. Diacyclops belgicus displayed OCRs (28.15 and 18.32 µL O2/mg DW × h at 14 and 17 °C, respectively) and carbon budget (CR: 0.14 and 0.10 µg C/mg × d at 14 and 17 °C) lower than those of D. crassicaudis crassicaudis (OCR: 55.67 and 47.93 µL O2/mg DW × h at 14 and 17 °C; CR: 0.3 and 0.27 µg C/mg × d at 14 and 17 °C). However, D. belgicus exhibited metabolic rates and carbon requirements comparable to those of other epigean species, challenging the assumption that low metabolic rates are universal among stygobitic species. Temperature variations did not significantly affect the metabolic responses and carbon requirements of the two species, suggesting that they may cope with moderate temperature increases.

The primary function of spermatozoa is to fertilize the oocyte, which depends on their motility and is directly associated with their metabolic state. The oxygen consumption rate (OCR) of spermatozoa reflects the respiratory capacity of sperm mitochondria under various physiological conditions and is an essential marker of sperm quality. We determined the OCR of common carp (Cyprinus carpio) sperm using two respirometry methods: the conventionally used polarographic method with a Clark-type electrode and fluorometric assay with an Oxo Dish optochemical oxygen sensor. The latter was used for the first time to evaluate spermatozoa oxygen consumption in various metabolic states (under different treatments) at different dilution rates. These two methods were compared using Bland–Altman analysis, and the applicability of the optochemical oxygen sensor for evaluating carp sperm oxygen consumption was discussed. Sperm motility and progressive velocity parameters were also assessed to evaluate the effect of sperm respiration under different metabolic states and dilution rates and preincubation period on the physiological status of spermatozoa. The comparison of these respirometry methods clearly shows that while the polarographic method allows immediate measurement of oxygen levels after adding a sperm sample, the optochemical oxygen sensor has a priority in the amount of data obtained due to simultaneous measurements of several samples (e.g., different males, different fish species, repetitions of the same sample or various experimental conditions), even at a later time after adding sperm to the measuring chamber. However, the compared methods are complementary, and the proposed methodology can be applied to other fish species.

Nanoplastics (NPs) and persistent organic pollutants such as polychlorinated biphenyls (PCBs) are ubiquitous aquatic pollutants. The coexistence of these pollutants in the environment emphasises the need to study their combined toxicity. NPs can cross biological membranes and act as vectors for other pollutants, whereas PCBs are known for their ability to bioaccumulate and biomagnify. The present work aimed to study the combined toxicity of polystyrene NPs and PCB-153 using physiological (development, heart rate, respiration), behavioural (swimming behaviour) and molecular (transcriptome) endpoints in zebrafish larvae. The results show that exposure to NPs, PCB and their mixture significantly affected the development and respiration in zebrafish larvae. Larvae co-exposed to NPs and PCB exhibited significant hyperlocomotion, whereas no such effect was observed after exposure to NPs or PCB alone. The transcriptomic results revealed that NPs exposure significantly affected several pathways associated with DNA compaction and nucleosome assembly, whereas PCB exposure significantly affected critical neurogenic pathways. In contrast, co-exposure to NPs and PCB generated multi-faceted toxicity and suppressed neurobehavioural, immune-related and detoxification pathways. The study highlights the complex interplay between NPs and PCBs, and documents how the two toxicants in combination give a stronger effect than the single toxicants alone. Understanding the mixture toxicity of these two pollutants is important to assess the environmental risks and developing effective management strategies, ultimately safeguarding ecosystems and human health.

Attempting to differentiate phenotypic variation caused by environmentally-induced alterations in gene expression from that caused by actual allelic differences can be experimentally difficult. Environmental variables must be carefully controlled and then interindividual genetic differences ruled out as sources of phenotypic variation. We investigated phenotypic variability of cardiorespiratory physiology as well as biometric traits in the parthenogenetically-reproducing marbled crayfish Procambarus virginalis Lyko, 2017, all offspring being genetically identical clones. Populations of P. virginalis were reared from eggs tank-bred at four different temperatures (16, 19, 22 and 25 °C) or two different oxygen levels (9.5 and 20 kPa). Then, at Stage 3 and 4 juvenile stages, physiological (heart rate, oxygen consumption) and morphological (carapace length, body mass) variables were measured. Heart rate and oxygen consumption measured at 23 °C showed only small effects of rearing temperature in Stage 3 juveniles, with larger effects evident in older, Stage 4 juveniles. Additionally, coefficients of variation were calculated to compare our data to previously published data on P. virginalis as well as sexually-reproducing crayfish. Comparison revealed that carapace length, body mass and heart rate (but not oxygen consumption) indeed showed lower, yet notable coefficients of variation in clonal crayfish. Yet, despite being genetically identical, significant variation in their morphology and physiology in response to different rearing conditions nonetheless occurred in marbled crayfish. This suggests that epigenetically induced phenotypic variation might play a significant role in asexual but also sexually reproducing species.

Tacrolimus (FK506) is a common immunosuppressant that is used in organ transplantation. However, despite its importance in medical applications, it is prone to adverse side effects. While some studies have demonstrated its toxicities to humans and various animal models, very few studies have addressed this issue in aquatic organisms, especially zebrafish. Here, we assessed the adverse effects of acute and chronic exposure to tacrolimus in relatively low doses in zebrafish in both larval and adult stages, respectively. Based on the results, although tacrolimus did not cause any cardiotoxicity and respiratory toxicity toward zebrafish larvae, it affected their locomotor activity performance in light–dark locomotion tests. Meanwhile, tacrolimus was also found to slightly affect the behavior performance, shoaling formation, circadian rhythm locomotor activity, and color preference of adult zebrafish in a dose-dependent manner. In addition, alterations in the cognitive performance of the fish were also displayed by the treated fish, indicated by a loss of short-term memory. To help elucidate the toxicity mechanism of tacrolimus, molecular docking was conducted to calculate the strength of the binding interaction between tacrolimus to human FKBP12. The results showed a relatively normal binding affinity, indicating that this interaction might only partly contribute to the observed alterations. Nevertheless, the current research could help clinicians and researchers to further understand the toxicology of tacrolimus, especially to zebrafish, thus highlighting the importance of considering the toxicity of tacrolimus prior to its usage.

Metabolic rates are linked to key life-history traits that are thought to set the pace of life and affect fitness, yet the role that parents may have in shaping the metabolism of their offspring to enhance survival remains unclear. Here, we investigated the effect of temperature (24°C or 30°C) and feeding frequency experienced by parent zebrafish ( Danio rerio ) on offspring phenotypes and early survival at different developmental temperatures (24°C or 30°C). We found that embryo size was larger, but survival lower, in offspring from the parental low food treatment. Parents exposed to the warmer temperature and lower food treatment also produced offspring with lower standard metabolic rates—aligning with selection on embryo metabolic rates. Lower metabolic rates were correlated with reduced developmental and growth rates, suggesting selection for a slow pace of life. Our results show that intergenerational phenotypic plasticity on offspring size and metabolic rate can be adaptive when parent and offspring temperatures are matched: the direction of selection on embryo size and metabolism aligned with intergenerational plasticity towards lower metabolism at higher temperatures, particularly in offspring from low-condition parents. These findings provide evidence for adaptive parental effects, but only when parental and offspring environments match.

Across diverse taxa, sublethal exposure to abiotic stressors early in life can lead to benefits such as increased stress tolerance upon repeat exposure. This phenomenon, known as hormetic priming, is largely unexplored in early life stages of marine invertebrates, which are increasingly threatened by anthropogenic climate change. To investigate this phenomenon, larvae of the sea anemone and model marine invertebrate Nematostella vectensis were exposed to control (18 °C) or elevated (24 °C, 30 °C, 35 °C, or 39 °C) temperatures for 1 h at 3 days post-fertilization (DPF), followed by return to control temperatures (18 °C). The animals were then assessed for growth, development, metabolic rates, and heat tolerance at 4, 7, and 11 DPF. Priming at intermediately elevated temperatures (24 °C, 30 °C, or 35 °C) augmented growth and development compared to controls or priming at 39 °C. Indeed, priming at 39 °C hampered developmental progression, with around 40% of larvae still in the planula stage at 11 DPF, in contrast to 0% for all other groups. Total protein content, a proxy for biomass, and respiration rates were not significantly affected by priming, suggesting metabolic resilience. Heat tolerance was quantified with acute heat stress exposures, and was significantly higher for animals primed at intermediate temperatures (24 °C, 30 °C, or 35 °C) compared to controls or those primed at 39 °C at all time points. To investigate a possible molecular mechanism for the observed changes in heat tolerance, the expression of heat shock protein 70 (HSP70) was quantified at 11 DPF. Expression of HSP70 significantly increased with increasing priming temperature, with the presence of a doublet band for larvae primed at 39 °C, suggesting persistent negative effects of priming on protein homeostasis. Interestingly, primed larvae in a second cohort cultured to 6 weeks post-fertilization continued to display hormetic growth responses, whereas benefits for heat tolerance were lost; in contrast, negative effects of short-term exposure to extreme heat stress (39 °C) persisted. These results demonstrate that some dose-dependent effects of priming waned over time while others persisted, resulting in heterogeneity in organismal performance across ontogeny following priming. Overall, these findings suggest that heat priming may augment the climate resilience of marine invertebrate early life stages via the modulation of key developmental and physiological phenotypes, while also affirming the need to limit further anthropogenic ocean warming.

Spring conditions, especially in temperate regions, may fluctuate abruptly and drastically. Environmental variability can expose organisms to temperatures outside of their optimal thermal ranges. For ectotherms, sudden changes in temperature may cause short- and long-term physiological effects, including changes in respiration, morphology, and reproduction. Exposure to variable temperatures during active development, which is likely to occur for insects developing in spring, can cause detrimental effects. Using the alfalfa leafcutting bee, Megachile rotundata, we aimed to determine if oxygen consumption could be measured using a new system and to test the hypothesis that female and male M. rotundata have a thermal performance curve with a wide optimal range. Oxygen consumption of M. rotundata pupae was measured across a large range of temperatures (6–48°C) using an optical oxygen sensor in a closed respirometry system. Absolute and mass-specific metabolic rates were calculated and compared between bees that were extracted from their brood cells and those remaining in the brood cell to determine whether pupae could be accurately measured inside their brood cells. The metabolic response to temperature was non-linear, which is an assumption of a thermal performance curve; however, the predicted negative slope at higher temperatures was not observed. Despite sexual dimorphism in body mass, sex differences only occurred in mass-specific metabolic rates. Higher metabolic rates in males may be attributed to faster development times, which could explain why there were no differences in absolute metabolic rate measurements. Understanding the physiological and ecological effects of thermal environmental variability on M. rotundata will help to better predict their response to climate change.

Fenpropathrin, a pyrethroid insecticide, has been widely used for many years in agricultural fields. It works by disturbing the voltage-gated sodium channel, leading to paralysis and the death of the target animal. While past studies have focused on neurodegeneration following fenpropathrin poisoning in humans, relatively few pieces of research have examined its effect on other peripheral organs. This study successfully investigated the potential toxicity of fenpropathrin on the cardiovascular system using zebrafish as an animal model. Zebrafish larvae exposed to varying doses of fenpropathrin underwent an evaluation of cardiac physiology by measuring the heart rate, stroke volume, cardiac output, and shortening fraction. The blood flow velocity and the dorsal aorta diameter were also measured to assess the impact of fenpropathrin exposure on the vascular system. Furthermore, molecular docking was performed to evaluate the pesticide binding affinity to various proteins associated with the cardiovascular system, revealing the potential mechanism of the fenpropathrin cardiotoxic effect. The findings demonstrated a significant dose-dependent increase in the heart rate stroke volume, cardiac output, shortening fraction, and ejection fraction of zebrafish larvae after 24 h of acute treatment with fenpropathrin. Additionally, zebrafish treated at a concentration of 1 ppm exhibited significantly larger blood vessels in diameter and an increased blood flow velocity compared to the control group. According to molecular docking, fenpropathrin showed a high affinity for various voltage-gated sodium channels like scn1lab, cacna1sb, and clcn3. Finally, from the results, we found that fenpropathrin caused cardiomegaly, which may have been induced by the voltage-gated sodium channel disruption. This study highlights the significant disruption of fenpropathrin in the cardiovascular system and emphasizes the need for further research on the health implications of this pesticide.

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-quinone) is a degradation product of 6PPD, an antioxidant widely used in rubber tires. 6PPD-quinone enters aquatic ecosystems through urban stormwater runoff and has been identified as the chemical behind the urban runoff mortality syndrome in coho salmon. However, the available data suggest that the acute effects of 6PPD-quinone are restricted to a few salmonid species and that the environmental levels of this chemical should be safe for most fish. In this study, larvae of a "tolerant" fish species, Danio rerio, were exposed to three environmental concentrations of 6PPD-quinone for only 24 h, and the effects on exploratory behavior, escape response, nonassociative learning (habituation), neurotransmitter profile, wake/sleep cycle, circadian rhythm, heart rate and oxygen consumption rate were analyzed. Exposure to the two lowest concentrations of 6PPD-quinone resulted in altered exploratory behavior and habituation, an effect consistent with some of the observed changes in the neurotransmitter profile, including increased levels of acetylcholine, norepinephrine, epinephrine and serotonin. Moreover, exposure to the highest concentration tested altered the wake/sleep cycle and the expression of per1a, per3 and cry3a, circadian clock genes involved in the negative feedback loop. Finally, a positive chronotropic effect of 6PPD-quinone was observed in the hearts of the exposed fish. The results of this study emphasize the need for further studies analyzing the effects of 6PPD-quinone in "tolerant" fish species.

Unionid mussels are imperiled worldwide. Understanding the impacts of thermal and hypoxia stress on larval (glochidia) and adult physiology is critical for understanding the potential impacts of climate change. We tested whether brood viability (proportion of glochidia competent to attach to a host) was correlated with oxygen demand (MO 2 ), ability to regulate oxygen consumption (regulation index (RI)), and/or critical dissolved oxygen concentration (DO crit ). We then examined the effects of temperature on MO 2, RI, and DO crit. The results were coupled with a previous study to estimate the fraction of brooding female oxygen demand comprised of glochidial respiration. We found little evidence that respiratory patterns of glochidia changed with declining brood viability, but strong evidence for decreasing glochidial RI and increasing DO crit with increasing temperatures. Glochidial respiration temperature coefficient ( Q 10 ) values were approximately 2–3× those estimated for brooding females, indicating greater temperature sensitivity. The proportion of gravid female respiration comprised of glochidial respiration reached its maximum at temperatures (23–28 °C) coinciding with brood expulsion. These patterns suggest high temperatures may have deleterious effects on unionids by decreasing the hypoxia tolerance of glochidia, increasing the rate at which glochidia deplete energy reserves, and increasing the proportion of oxygen consumption by gravid females that is comprised of glochidial oxygen demand.

Mesophotic reefs have been proposed as climate change refugia but are not synonymous ecosystems with shallow reefs and remain exposed to anthropogenic impacts. Planulae from the reef-building coral Stylophora pistillata, Gulf of Aqaba, from 5- and 45-m depth were tested ex situ for capacity to settle, grow, and acclimate to reciprocal light conditions. Skeletons were scanned by phase contrast-enhanced micro-CT to study morphology. Deep planulae had reduced volume, smaller diameter on settlement, and greater algal symbiont density. Light conditions did not have significant impact on settlement or mortality rates. Photosynthetic acclimation of algal symbionts was evident within 21-35 days after settlement but growth rate and polyp development were slower for individuals translocated away from their parental origin compared to controls. Though our data reveal rapid symbiont acclimation, reduced growth rates and limited capacity for skeletal modification likely limit the potential for mesophotic larvae to settle on shallow reefs.

The moon jellyfish Aurelia coerulea is the most common blooming scyphozoan jellyfish in global coastal waters. A. coerulea polyps can rapidly increase their population through asexual reproduction, which is influenced directly by the ambient seawater temperature. However, the physiological responses of A. coerulea polyps to future elevated seasonal seawater temperature scenarios are largely unknown. In this study, we performed an experiment to test the hypothesis that the elevated seasonal seawater temperatures (current seawater temperatures + 3°C) will increase the asexual reproduction, feeding, and respiration rates of A. coerulea polyps. After 42 days of exposure, the asexual reproduction and feeding rates of the A. coerulea polyps increased under the elevated seawater temperatures predicted for all seasons. The highest asexual reproduction rates occurred in predicted average summer seawater temperatures. The respiration rates of A. coerulea polyps were suppressed significantly under winter temperature conditions, suggesting that more available energy was allocated to asexual reproduction than to metabolism after warming. Overall, this study suggests that A. coerulea polyp populations will benefit from the predicted higher seawater temperatures in all four seasons, thereby further increasing the potential and scale of A. coerulea blooms.

Oceanic absorption of atmospheric CO2 results in alterations of carbonate chemistry, a process coined ocean acidification (OA). The economically and ecologically important eastern oyster (Crassostrea virginica) is vulnerable to these changes because low pH hampers CaCO3 precipitation needed for shell formation. Organisms have a range of physiological mechanisms to cope with altered carbonate chemistry; however, these processes can be energetically expensive and necessitate energy reallocation. Here, the hypothesis that resilience to low pH is related to energy resources was tested. In laboratory experiments, oysters were reared or maintained at ambient (400 ppm) and elevated (1300 ppm) pCO2 levels during larval and adult stages, respectively, before the effect of acidification on metabolism was evaluated. Results showed that oysters exposed to elevated pCO2 had significantly greater respiration. Subsequent experiments evaluated if food abundance influences oyster response to elevated pCO2. Under high food and elevated pCO2 conditions, oysters had less mortality and grew larger, suggesting that food can offset adverse impacts of elevated pCO2, while low food exacerbates the negative effects. Results also demonstrated that OA induced an increase in oyster ability to select their food particles, likely representing an adaptive strategy to enhance energy gains. While oysters appeared to have mechanisms conferring resilience to elevated pCO2, these came at the cost of depleting energy stores, which can limit the available energy for other physiological processes. Taken together, these results show that resilience to OA is at least partially dependent on energy availability, and oysters can enhance their tolerance to adverse conditions under optimal feeding regimes.

Macroinvertebrates that rely on a supply of planktonic larvae for recruitment play a significant role in maintaining productivity in mangrove ecosystems. Thus, identifying the spatial distribution and physiological limitations of invertebrate larval communities within mangroves is important for targeted conservation efforts to maintain population persistence amid the threat of climate change. Here, the role of spatial, lunar, and environmental factors in structuring invertebrate larval communities in Ting Kok, the second largest mangrove forest in Hong Kong, was examined. Results indicate that, spatially, invertebrate larval communities were influenced by environmental filtering, habitat type, and the lunar tidal cycle. This indicates the fundamental role of habitat heterogeneity and connectivity for the transport, distribution, and development of crustacean larvae. Larvae of key sesarmids exhibited metabolic depression at water temperatures forecasted to be regularly experienced by the year 2050, according to current climate projections. The impacts of climate change, coupled with habitat destruction and degradation of hydrological connectivity, make larval communities increasingly vulnerable to mass-mortality and displacement. This places ecosystem productivity and functionality at risk through cascading negative effects of recruitment limitation. Further focus on this subject will help disentangle the effects of process rates and scales of transport that underlie community assemblages in mangrove systems. Furthermore, identifying physiological bottlenecks of key taxa and habitat provisioning that enhance larval survival will be helpful to prioritize strategies for conservation management in dynamic intertidal settings.

For marine animals with biphasic life stages, different environmental conditions are experienced during ontogeny so that physiological constraints on early stages could explain adult distributions and life history traits. The invasive and cool-temperate adapted Mytilus galloprovincialis intertidal mussel approaches the eastern limit of its biogeographic distribution on the south coast of South Africa, where it shares a habitat with the warm-temperate adapted and indigenous Perna perna mussel. As adults, the two species exhibit different metabolic regulation capacities in response to temperature. We compared the acute metabolic response to temperature between species during the post-settlement recruit stage. Aerobic respiration rates of recently settled recruits were measured monthly for 5 months for temperatures 5 °C above or below the ambient field seawater temperature at the time of collection. Unlike adults, the capacity for aerobic metabolic regulation in response to temperature differed little between species under the conditions tested, indicating a similar degree of phenotypic or developmental plasticity in response to the thermal environment. In addition, monthly variations in metabolic patterns indicate unexpectedly high plasticity in response to recent seasonal thermal history for both species.

Carryover effects of environmental stressors occur when experiences of the environment in earlier life stages or seasons influence the performance of individuals later in life. These can be especially critical for species that have diverse developmental transition periods in their life cycle, such as salmonid fish. Sublethal changes in metabolism, size, or growth experienced in early life stages may have a long‐lasting effect on the subsequent life performance of these species, but very few studies have formally tested these changes in relation to environmental stressors. Here, we investigated whether different types of fine sediment result in carryover effects that change the life performance of migratory brown trout. First, we manipulated the early habitat conditions of brown trout through the life stages from egg to fry by incubating them in varying substrate treatments (i.e., gravel without added sediment, gravel with added fine sand, and gravel with added organic matter). Exposure to fine sediment during early development had serious effects on the metabolism, size, escape responses, timing of emergence, and potential survival of early life stages. These carryover effects were persistent and remained present over the critical life shift from relying on parentally provided resources as immobile eggs to independent exogenous feeding as parr. Second, fish were relocated as parr to either their original or different treatment environments and their metabolism, size, and growth were reanalyzed. The effects of environmental stress were observed later in their life cycle when fry from the gravel treatment were relocated to sand or organic‐rich treatments. These were found to be significantly smaller in size and had a higher metabolic rate than fry maintained in their original treatment environment. Together, our study experimentally demonstrated that the carryover effects of environmental stressors experienced in early stages may influence the fitness outcomes of migratory fish later in life. We suggest that sublethal environmental stressors should be better considered in restoration schemes and management strategies to reverse the current trend of declining salmonid populations.

Metabolic rate has long been used in animal adaptation and performance studies, and individual oxygen consumption is used as proxy of metabolic rate. Stygofauna are organisms adapted to groundwater with presumably lower metabolic rates than their surface relatives. How stygofauna will cope with global temperature increase remains unpredictable. We studied the thermal acclimation and metabolic scaling with body mass of a stygobitic crustacean, Proasellus lusitanicus, in the climate change scenario. We measured oxygen consumption rates in a thermal ramp-up experiment over four assay temperatures and tested two hypotheses: (i) P. lusitanicus exhibits narrow thermal plasticity, inadequate for coping with a fast-increasing thermal regime; and (ii) oxygen consumption rates scale with the body mass by a factor close to 0.75, as commonly observed in other animals. Our results show that P. lusitanicus has low thermal plasticity in a fast-increasing thermal regime. Our data also suggest that oxygen consumption rates of this species do not follow mass-dependent scaling, potentially representing a new trait of metabolic optimization in groundwater habitats, which are often limited in food and oxygen. Species with limited dispersal capacities and rigid metabolic guilds face extinction risk due to climate change and omitting groundwater ecosystems from climate change agendas emphasizes the unprotected status of stygofauna.

The shared-pathway hypothesis offers a cellular explanation for the connection between ketocarotenoid pigmentation and individual quality. Under this hypothesis, ketocarotenoid metabolism shares cellular pathways with mitochondrial oxidative phosphorylation such that red carotenoid-based coloration is inextricably linked mitochondrial function. To test this hypothesis, we exposed Tigriopus californicus copepods to a mitochondrially targeted protonophore, 2,4-dinitrophenol (DNP), to induce proton leak in the inner mitochondrial membranes. We then measured whole-animal metabolic rate and ketocarotenoid accumulation. As observed in prior studies of vertebrates, we observed that DNP treatment of copepods significantly increased respiration and that DNP-treated copepods accumulated more ketocarotenoid than control animals. Moreover, we observed a relationship between ketocarotenoid concentration and metabolic rate, and this association was strongest in DNP-treated copepods. These data support the hypothesis that ketocarotenoid and mitochondrial metabolism are biochemically intertwined. Moreover, these results corroborate observations in vertebrates, perhaps suggesting a fundamental connection between ketocarotenoid pigmentation and mitochondrial function that should be explored further.

The excessive worldwide production of plastic materials results in omnipresent microplastic pollution. Scientific studies dealing with the impacts of microplastics on aquatic ecosystems focus mainly on the marine environment, documenting the effect on the functional traits of various organisms. Polystyrene, one of the most commonly used plastics, has become a widely used model in this respect. In our study, freshwater shrimps (Neocardina heteropoda) were exposed to virgin polystyrene particles (size 0.5 mm; nominal concentration 8 mgL−1), and their behavioral and physiological responses were compared to control shrimp. The exposed shrimps exhibited modified activity patterns (greater speeds, accelerations and distances moved), accompanied by a lowered standard metabolic rate (SMR). The observed effects differed in their progression from the 7th to 14th day of exposure, from undetectable changes (distance, SMR) to significant differences (speed, acceleration). Significant differences were also detected in the behavioral syndromes expressed by the exposed and controlled shrimps, indicating that the microplastics influence not only the particular traits, but also their functional relationships. As such, our study contributes to the integration of behavioral ecotoxicology in risk assessment, documenting the adverse performance of freshwater invertebrates exposed to microplastics with the potential to transpose the problem to higher levels of the food web.

Ocean acidification (OA) resulting from anthropogenic CO2 emissions is impairing the reproduction of marine organisms. While parental exposure to OA can protect offspring via carryover effects, this phenomenon is poorly understood in many marine invertebrate taxa. Here, we examined how parental exposure to acidified (pH 7.40) versus ambient (pH 7.72) seawater influenced reproduction and offspring performance across six gametogenic cycles (13 weeks) in the estuarine sea anemone Nematostella vectensis. Females exhibited reproductive plasticity under acidic conditions, releasing significantly fewer but larger eggs compared to ambient females after 4 weeks of exposure, and larger eggs in two of the four following spawning cycles despite recovering fecundity, indicating long-term acclimatization and greater investment in eggs. Males showed no changes in fecundity under acidic conditions but produced a greater percentage of sperm with high mitochondrial membrane potential (MMP; a proxy for elevated motility), which corresponded with higher fertilization rates relative to ambient males. Finally, parental exposure to acidic conditions did not significantly influence offspring development rates, respiration rates, or heat tolerance. Overall, this study demonstrates that parental exposure to acidic conditions impacts gamete production and physiology but not offspring performance in N. vectensis, suggesting that increased investment in individual gametes may promote fitness.

Many insect species harbour heritable bacterial endosymbionts. Some facultative endosymbionts provide benefits to their hosts under certain environmental conditions. Facultative endosymbionts are expected to impose additional energetic expenditures to their host, reducing host fitness. While there is accumulating evidence in plant sucking insects that facultative endosymbionts reduce the fitness of their host under permissive conditions, no direct energy costs associated with facultative endosymbionts have been identified. Using the standard metabolic rate (SMR) as a measure of the energy cost of self-maintenance, we investigated whether two common facultative endosymbionts Hamiltonella defensa or Regiella insecticola increase the maintenance cost of the pea aphid Acyrthosiphon pisum which could translate into host fitness reduction ('compensation hypothesis'). In addition, we tested if there was a link between SMR and the aphid fitness and whether it depended on endosymbiont density and aphid energetic reserves. Finally, we measured SMR at different temperatures to assess the impact of suboptimal thermal conditions on physiological cost of endosymbionts. In the presence of facultative endosymbionts, aphids expressed generally a lower fitness and a higher SMR compared to uninfected ones, in accordance with the 'compensation hypothesis'. However, the SMR difference between infected and uninfected aphids tended to decrease with increasing temperature. Complex host genotype-by-symbiont genotype-by-temperature interactions on SMR were also revealed. Energetic budget of adult aphids appeared weakly influenced by the aphid genotype and endosymbiont species, suggesting that facultative endosymbionts primarily impact the consumption of energy resources rather than their acquisition. Density of facultative endosymbionts varied largely among aphid lines but was not associated with the fitness nor metabolic rate of aphids. This work supports the energy basis of facultative endosymbiont associated fitness costs and raises new questions about the effect of facultative endosymbionts on the energy metabolism of their host.

p-Toluene sulfonamide (p-TSA), a small molecular drug with antineoplastic activity is widely gaining interest from researchers because of its pharmacological activities. In this study, we explored the potential cardio and neural toxicity of p-TSA in sublethal concentrations by using zebrafish as an in vivo animal model. Based on the acute toxicity assay, the 96hr LC50 was estimated as 204.3 ppm, suggesting the overall toxicity of p-TSA is relatively low in zebrafish larvae. For the cardiotoxicity test, we found that p-TSA caused only a minor alteration in treated larvae after no overall significant alterations were observed in cardiac rhythm and cardiac physiology parameters, as supported by the results from expression level measurements of several cardiac development marker genes. On the other hand, we found that acute p-TSA exposure significantly increased the larval locomotion activity during the photomotor test while prolonged exposure (4 days) reduced the locomotor startle reflex activities in zebrafish. In addition, a higher respiratory rate and blood flow velocity was also observed in the acutely treated fish groups compared to the untreated group. Finally, by molecular docking, we found that p-TSA has a moderate binding affinity to skeletal muscle myosin II subfragment 1 (S1), ATPase activity, actin- and Ca2+-stimulated myosin S1 ATPase, and v-type proton ATPase. These binding interactions between p-TSA and proteins offer insights into the potential molecular mechanism of action of p-TSA on observed altered responses toward photo and vibration stimuli and minor altered vascular performance in the zebrafish larvae.

Competition and metabolism should be linked. Intraspecific variation in metabolic rates and, hence, resource demands covary with competitive ability. The effects of metabolism on conspecific interactions, however, have mostly been studied under laboratory conditions. We used a trait‐specific response‐surface design to test for the effects of metabolism on pairwise interactions of the marine colonial invertebrate, Bugula neritina in the field. Specifically, we compared the performance (survival, growth, and reproduction) of focal individuals, both in the presence and absence of a neighbor colony, both of which had their metabolic phenotype characterized. Survival of focal colonies depended on the metabolic phenotype of the neighboring individual, and on the combination of both the focal and neighbor colony metabolic phenotypes that were present. Surprisingly, we found pervasive effects of neighbor metabolic phenotypes on focal colony growth and reproduction, although the sign and strength of these effects showed strong microenvironmental variability. Overall, we find that the metabolic phenotype changes the strength of competitive interactions, but these effects are highly contingent on local conditions. We suggest future studies explore how variation in metabolic rate affects organisms beyond the focal organism alone, particularly under field conditions.

As coral reefs face warming oceans and increased coral bleaching, a whitening of the coral due to loss of microalgal endosymbionts, the possibility of evolutionary rescue offers some hope for reef persistence. In tightly linked mutualisms, evolutionary rescue may occur through evolution of one or both partners. Many obligate mutualisms are composed of relatively small, fast-growing symbionts with greater potential to evolve on ecologically relevant time scales than their relatively large, slower growing hosts. We examined the potential for adaptation of the upside-down sea jelly Cassiopea xamachana to increased temperature via evolution of its microalgal endosymbiont, Symbiodinium microadriaticum. We quantified trait variation among five algal genotypes in response to three temperatures and fitness of hosts infected with each genotype. All genotypes had positive growth rates at each temperature, but rates of respiration and photosynthesis decreased with increasing temperature. Responses varied among genotypes but were unrelated to genetic similarity. The effect of temperature on asexual reproduction and the timing of development in the host also depended on the genotype of the symbiont. Natural selection could favor different algal genotypes at different temperatures, affecting host fitness. This eco-evolutionary interaction may be a critical component of understanding species resilience in increasingly stressful environments.

Increasing ocean temperatures have been demonstrated to have a range of negative impacts on coral reef fishes. However, despite a wealth of studies of juvenile/adult reef fish, studies of how early developmental stages respond to ocean warming are limited. As overall population persistence is influenced by the development of early life stages, detailed studies of larval responses to ocean warming are essential. Here, in an aquaria-based study we investigate how temperatures associated with future warming and present-day marine heatwaves (+3 °C) impact the growth, metabolic rate, and transcriptome of 6 discrete developmental stages of clownfish larvae (Amphiprion ocellaris). A total of 6 clutches of larvae were assessed, with 897 larvae imaged, 262 larvae undergoing metabolic testing and 108 larvae subject to transcriptome sequencing. Our results show that larvae reared at +3 °C grow and develop significantly faster and exhibit higher metabolic rates than those in control conditions. Finally, we highlight the molecular mechanisms underpinning the response of larvae from different developmental stages to higher temperatures, with genes associated with metabolism, neurotransmission, heat stress and epigenetic reprogramming differentially expressed at +3 °C. Overall, these results indicate that clownfish development could be altered under future warming, with developmental rate, metabolic rate, and gene expression all affected. Such changes may lead to altered larval dispersal, changes in settlement time and increased energetic costs.

In this study we investigated potential impacts of Cu exposure at low, environmentally relevant, concentrations on early live stages of Atlantic cod ( Gadus morhua ). Cod embryos and larvae were exposed to 0.5 μg/L (low), 2 μg/L (medium), and 6 μg/L (high) Cu from 4 to 17 days post fertilisation (dpf). Hatching success, mortality, oxygen consumption, biometric traits, and malformations were determined. A dynamic energy budget (DEB) model was applied to identify potential impacts on bioenergetics. A positive correlation was found between Cu exposure concentrations and Cu body burden in eggs, but not in larvae. The tested concentrations did not increase mortality in neither embryos nor larvae, or larvae deformations. Further, the DEB model did not indicate effects of the tested Cu concentrations.

Anthropogenic releases of plastics, persistent organic pollutants (POPs), and heavy metals can impact the environment, including aquatic ecosystems. Nanoplastics (NPs) have recently emerged as pervasive environmental pollutants that have the ability to adsorb POPs and can cause stress in organisms. Among POPs, DDT and its metabolites are ubiquitous environmental pollutants due to their long persistence. Despite the discontinued use of DDT in Europe, DDT and its metabolites (primarily p,p'-DDE) are still found at detectable levels in fish feed used in salmon aquaculture. Our study aimed to look at the individual and combined toxicity of NPs (50 mg/L polystyrene) and DDE (100 μg/L) using zebrafish larvae as a model. We found no significant morphological, cardiac, respiratory, or behavioural changes in zebrafish larvae exposed to NPs alone. Conversely, morphological, cardiac and respiratory alterations were observed in zebrafish larvae exposed to DDE and NPs + DDE. Interestingly, behavioural changes were only observed in zebrafish larvae exposed to NPs + DDE. These findings were supported by RNA-seq results, which showed that some cardiac, vascular, and immunogenic pathways were downregulated only in zebrafish larvae exposed to NPs + DDE. In summary, we found an enhanced toxicological impact of DDE when combined with NPs.

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is the most widely used antioxidant in automobile tyres and many rubber products. We investigated the impact of 6PPD and 6PPD quinone on acute toxicity, morphology, swimming behaviour, heart rate, and oxygen consumption in zebrafish larvae. Zebrafish embryos were exposed to 6PPD and 6PPD quinone at concentrations of 1, 10, and 25 µg/L during the development period of 1-96 hpf. In the present study, 6PPD quinone was found to be toxic to zebrafish larvae with a 24 h LC 50 of 308.67 µg/L. No significant mortality was observed at any of the tested concentrations. A dose-dependent reduction in swimming performance was observed in the exposed larvae at 116 hpf for both toxicants. Overall, our study shows that exposure of zebrafish embryos to 6PPD and 6PPD quinone at environmentally relevant concentrations (1 µg/L) does not affect its behaviour. However, exposure to higher but still sublethal concentrations of 6PPD and 6PPD quinone (10 and 25 µg/L) can affect behavioural endpoints. These findings reveal the toxicity of 6PPD and 6PPD quinone to early life stages of fish.

Copepods dominate zooplankton biomass of the upper ocean, especially in the highly seasonal northern boreal and Polar Regions, for which specific life-cycle traits such as the accumulation of lipid reserves, migration into deep water, and diapause, are key adaptations. Understanding such traits is central to determining the energetic consequences of high latitude range shifts related to climate change and ultimately, biogeochemical models of carbon flow. Using the calanoid copepod Calanus finmarchicus, we explore a new indicator of diapause, swimming activity, and assess its relationship with respiration. Stage CV copepods were sampled in late summer from shallow (epipelagic) and deep (mesopelagic) water at both on-shelf and off-shelf locations within the Fram Strait at a time when the animals had entered diapause. Using high-throughput quantitative behaviour screening on ex situ swimming activity, we found that irrespective of sampling station copepods from the mesopelagic show highly reduced activity (88.5 ± 3.4 % reduction) when compared to those from the epipelagic. This was supported by morphometric analyses which found that copepods from the mesopelagic were generally larger (12.4 ± 8.8 % increase) and had more lipid reserves (19.3 ± 2.2 % increase) than epipelagic individuals. On average, copepods from the off-shelf station exhibited respiration rates similar to overwintering rates observed elsewhere (1.23 ± 0.76 µg C d-1), while respiration rates of copepods from the shelf station were more consistent with active metabolism (2.46 ± 1.02 µg C d-1). Nevertheless, active and diapausing rates were observed in individuals from both stations at both epi- and mesopelagic depths. We suggest that rapid screening of activity may provide an early indicator of diapause before it becomes fully apparent and consistent in other physiological indicators. Ultimately, swimming activity may provide a useful tool to assess the putative endogenous and exogenous factors involved in diapause onset, provide a handle on the energetics of diapause, and input to biogeochemical carbon models on C. finmarchicus.

In many cases, understanding species’ responses to climate change requires understanding variation among individuals in response to such change. For species with strong symbiotic relationships, such as many coral reef species, genetic variation in symbiont responses to temperature may affect the response to increased ocean temperatures. To assess variation among symbiont genotypes, we examined the population dynamics and physiological responses of genotypes of Breviolum antillogorgium in response to increased temperature. We found broad temperature tolerance across genotypes, with all genotypes showing positive growth at 26, 30, and 32°C. Genotypes differed in the magnitude of the response of growth rate and carrying capacity to increasing temperature, suggesting that natural selection could favor different genotypes at different temperatures. However, the historical temperature at which genotypes were reared (26 or 30°C) was not a good predictor of contemporary temperature response. We found increased photosynthetic rates and decreased respiration rates with increasing contemporary temperature, and differences in physiology among genotypes, but found no significant differences in the response of these traits to temperature among genotypes. In species with such broad thermal tolerance, selection experiments on symbionts outside of the host may not yield results sufficient for evolutionary rescue from climate change.

Aim Although zebrafish are gaining popularity as biomedical models of cardiovascular disease, our understanding of their cardiac control mechanisms is fragmentary. Our goal was to clarify the controversial role of the ß1‐adrenergic receptor (AR) in the regulation of heart rate in zebrafish. Methods CRISPR‐Cas9 was used to delete the adrb1 gene in zebrafish allowing us to generate a stable adrb1 −/− line. Larval heart rates were measured during pharmacological protocols and with exposure to hypercapnia. Expression of the five zebrafish adrb genes were measured in larval zebrafish hearts using qPCR. Results Compared with genetically matched wild‐types ( adrb1 +/+ ), adrb1 −/− larvae exhibited ~20 beats min −1 lower heart rate, measured from 2 to 21 days post‐fertilization (dpf). Nevertheless, adrb1 −/− larvae exhibited preserved positive chronotropic responses to pharmacological treatment with AR agonists (adrenaline, noradrenaline, isoproterenol), which were blocked by propranolol (general ß‐AR antagonist). Regardless of genotype, larvae exhibited similar increases in heart rate in response to hypercapnia (1% CO 2 ) at 5 dpf, but tachycardia was blunted in adrb1 −/− larvae at 6 dpf. adrb1 gene expression was abolished in the hearts of adrb1 −/− larvae, confirming successful knockout. While gene expression of adrb2a and adrb3a was unchanged, adrb2b and adrb3b mRNA levels increased in adrb1 −/− larval hearts. Conclusion Despite adrb1 contributing to the setting of resting heart rate in larvae, it is not strictly essential for zebrafish, as we generated a viable and breeding adrb1 −/− line. The chronotropic effects of adrenergic stimulation persist in adrb1 −/− zebrafish, likely due to the upregulation of other ß‐AR subtypes.

Significance Biology has long-standing rules about how metabolism and demography should covary. These rules connect physiology to ecology but remarkably, these rules have only ever been tested indirectly. Using a model marine invertebrate, we created experimental field populations that varied in metabolic rate but not body size. We show that metabolism qualitatively affects population growth and carrying capacity in ways predicted by theory but that scaling relationships for these parameters, as well as estimates of energy use at carrying capacity, depart from classic predictions. That metabolism affects demography in ways that depart from canonical theory has important implications for predicting how populations may respond to global change and size-selective harvesting. Metabolism should drive demography by determining the rates of both biological work and resource demand. Long-standing “rules” for how metabolism should covary with demography permeate biology, from predicting the impacts of climate change to managing fisheries. Evidence for these rules is almost exclusively indirect and in the form of among-species comparisons, while direct evidence is exceptionally rare. In a manipulative field experiment on a sessile marine invertebrate, we created experimental populations that varied in population size (density) and metabolic rate, but not body size. We then tested key theoretical predictions regarding relationships between metabolism and demography by parameterizing population models with lifetime performance data from our field experiment. We found that populations with higher metabolisms had greater intrinsic rates of increase and lower carrying capacities, in qualitative accordance with classic theory. We also found important departures from theory—in particular, carrying capacity declined less steeply than predicted, such that energy use at equilibrium increased with metabolic rate, violating the long-standing axiom of energy equivalence. Theory holds that energy equivalence emerges because resource supply is assumed to be independent of metabolic rate. We find this assumption to be violated under real-world conditions, with potentially far-reaching consequences for the management of biological systems.

The UAB Nathan Shock Center focuses on comparative energetics and aging. Energetics, as defined for this purpose, encompasses the causes, mechanisms, and consequences of the acquisition, storage, and use of metabolizable energy. Comparative energetics is the study of metabolic processes at multiple scales and across multiple species as it relates to health and aging. The link between energetics and aging is increasingly understood in terms of dysregulated mitochondrial function, altered metabolic signaling, and aberrant nutrient responsiveness with increasing age. The center offers world-class expertise in comprehensive, integrated energetic assessment and analysis from the level of the organelle to the organism and across species from the size of worms to rats as well as state-of-the-art data analytics. The range of services offered by our three research cores, (1) The Organismal Energetics Core, (2) Mitometabolism Core, and (3) Data Analytics Core, is described herein.

The purpose of this study was to investigate if the cardiovascular system is important for ammonia excretion in the early life stages of zebrafish. Morpholino knockdowns of cardiac troponin T (TNNT2) or vascular endothelial growth factor A (VEGFA) provided morphants with nonfunctional circulation. At the embryonic stage [30–36 h postfertilization (hpf)], ammonia excretion was not constrained by a lack of cardiovascular function. At 2 days postfertilization (dpf) and 4 dpf, morpholino knockdowns of TNNT2 or VEGFA significantly reduced ammonia excretion in all morphants. Expression of rhag, rhbg, and rhcgb showed no significant changes but the mRNA levels of the urea transporter ( ut) were upregulated in the 4 dpf morphants. Taken together, rhag, rhbg, rhcgb, and ut gene expression and an unchanged tissue ammonia concentration but an increased tissue urea concentration, suggest that impaired ammonia excretion led to increased urea synthesis. However, in larvae anesthetized with tricaine or clove oil, ammonia excretion was not reduced in the 4 dpf morphants compared with controls. Furthermore, oxygen consumption was reduced in morphants regardless of anesthesia. These results suggest that cardiovascular function is not directly involved in ammonia excretion, but rather reduced activity and external convection may explain reduced ammonia excretion and compensatory urea accumulation in morphants with reduced cardiovascular function.

Mining and processing of minerals produce large quantities of tailings as waste. Some countries, including Norway, allow disposal of mine tailings in the sea. In this study we investigated the impacts of tailings from a calcium carbonate (CaCO 3 ) processing plant on early live stages of haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua). Fish eggs (3 days post fertilisation; dpf) were exposed for 48 h to three concentrations of tailings, nominally 1 mg L -1 (low, L); 10 mg L -1 (medium, M) and 100 mg L -1 (high, H); with L and M representing concentrations occurring at tailing release points. Results show that tailings rapidly adhered to eggs of both species, causing negative buoyancy (sinking of eggs) in M and H exposures. While tailings remained on egg surfaces in both species also after exposure termination, adhesion seemed more pronounced in cod, leading to larger impacts on buoyancy even after exposure. Tailing exposure further induced early hatching and significantly reduced survival in M and H exposed embryos in both fish species, and in cod from the L exposure group. Moreover, tailing exposure caused reduced survival and malformations in larvae, potentially related to premature hatching. This study shows that mineral particles adhere to haddock and cod eggs, affecting egg buoyancy, survival and development.

Marine tailing disposal (MTD) is sometimes practiced as an alternative to traditional mine tailing deposition on land. Environmental challenges connected to MTD include spreading of fine particulate matter in the water column and the potential release of metals and processing chemicals. This study investigated if tailing exposure affects the marine copepod Calanus finmarchicus, and whether effects are related to exposure to mineral particles or the presence of metals and/or processing chemicals in the tailings. We investigated the impacts of three different tailing compositions: calcium carbonate particles with and without processing chemicals and fine-grained tailings from a copper ore. Early life stages of C. finmarchicus were exposed over several developmental stages to low and high suspension concentrations for 15 days, and their development, oxygen consumption and biometry determined. The data was fitted in a dynamic energy budget (DEB) model to determine mechanisms underlying responses and to understand the primary modes of action related to mine tailing exposure. Results show that copepods exposed to tailings generally exhibited slower growth and accumulated less lipids. The presence of metals and processing chemicals did not influence these responses, suggesting that uptake of mineral particles was responsible for the observed effects. This was further supported by the applied DEB model, confirming that ingestion of tailing particles while feeding can result in less energy being available for growth and development.

Previous studies have demonstrated that hypoxia tolerance is improved in zebrafish (Danio rerio) larvae after prior exposure to lowered ambient O2 levels. Such improved hypoxia performance was attributed in part, to increased levels of hypoxia-inducible factor 1α (Hif-1α) exerting downstream effects on various physiological processes including promotion of trunk skin angiogenesis. Since O2 uptake ( $$\dot{M}{\text{O}}_{2}$$ ) in larvae is facilitated largely by O2 diffusion across the skin, enhanced cutaneous vascularization is expected to enhance $$\dot{M}{\text{O}}_{2}$$ during hypoxia and thus contribute to improved hypoxia tolerance. In this study, we used the scanning micro-optrode technique together with quantification of cutaneous vascularity in wild types (WT) and Hif-1α knockouts (hif1aa−/−ab−/−) to test the hypothesis that improved hypoxia tolerance after hypoxia acclimation in larvae at 4 or 7 days post-fertilization (dpf) was associated with Hif-1α-dependent increases in skin vascularity and regional cutaneous O2 fluxes (JO2). Hypoxia tolerance, as determined by measurements of critical PO2 (Pcrit), was unaltered by hypoxia pre-exposure in larvae at 4 dpf and there were no significant differences in Pcrit between WT and hif1aa−/−ab−/− larvae at this developmental stage. However, at 7 dpf there was a significant effect of genotype with WT larvae showing a lower Pcrit than hif1aa−/−ab−/− larvae, an effect that was being driven by a reduced Pcrit in the WT larvae after hypoxia pre-exposure (19.2 ± 1.9 mmHg) compared to hif1aa−/−ab−/− fish (35.5 ± 3.5 mmHg). Regardless of genotype, pre-exposure status or developmental age, JO2 decreased along the body in the anterior-to-posterior direction. Neither hypoxia pre-exposure nor genotype affected JO2 at any region along the body. The lack of any effect of hypoxia pre-exposure or genotype on JO2 was consistent with the lack of any effect on skin vascularity as measured in Tg(fli1:EGFP)yl transgenic larvae. Thus, the decreased hypoxia performance (increased Pcrit) at 7 dpf in the hif1aa−/−ab−/− larvae did not appear to be reliant on changes in trunk vascularity or cutaneous O2 diffusion.

Fishes living in fresh water counter the passive loss of salts by actively absorbing ions through specialized cells termed ionocytes. Ionocytes contain ATP-dependent transporters, are enriched with mitochondria, and therefore ionic regulation is an energy-consuming process. The purpose of this study was to assess the aerobic costs of ion transport in larval zebrafish (Danio rerio). We hypothesized that changes in rates of Na+ uptake evoked by acidic or low Na+ rearing conditions would result in corresponding changes in whole-body oxygen consumption (ṀO2) and/or cutaneous oxygen flux (JO2), measured at the ionocyte-expressing yolk sac epithelium using the scanning micro-optrode technique (SMOT). Larvae at 4 days post-fertilisation (dpf) that were reared under low pH (pH 4) exhibited a higher rate of Na+ uptake compared to fish reared under control conditions (pH 7.6) yet displayed a lower ṀO2 and no difference in cutaneous JO2. Despite a higher Na+ uptake capacity in larvae reared under low Na+ conditions, there were no differences in ṀO2 ­and JO2 at 4 dpf. Furthermore, although Na+ uptake was nearly abolished in 2 dpf larvae lacking ionocytes after morpholino knockdown of the ionocyte proliferation regulating transcription factor foxi3a, ṀO2 ­and JO2 were unaffected. Finally, laser ablation of ionocytes did not affect cutaneous JO2. Thus, we conclude that the aerobic costs of ion uptake by ionocytes in larval zebrafish, at least in the case of Na+, are below detection using whole-body respirometry or cutaneous SMOT scans, providing evidence that ion regulation in zebrafish larvae incurs a low aerobic cost.

Establishing relationships between parasite infection and physiological condition of the host can be difficult and therefore are often neglected when describing factors causing population declines. Using the parasite–host system between the parasitic nematode Contracaecum osculatum and the Eastern Baltic cod Gadus morhua, we here shed new light on how parasite load may relate to the physiological condition of a transport host. The Eastern Baltic cod is in distress, with declining nutritional conditions, disappearance of the larger fish, high natural mortality and no signs of recovery of the population. During the latest decade, high infection levels with C. osculatum have been observed in fish in the central and southern parts of the Baltic Sea. We investigated the aerobic performance, nutritional condition, organ masses, and plasma and proximate body composition of wild naturally infected G. morhua in relation to infection density with C. osculatum. Fish with high infection densities of C. osculatum had (i) decreased nutritional condition, (ii) depressed energy turnover as evidenced by reduced standard metabolic rate, (iii) reduction in the digestive organ masses, and alongside (iv) changes in the plasma, body and liver composition, and fish energy source. The significantly reduced albumin to globulin ratio in highly infected G. morhua suggests that the fish suffer from a chronic liver disease. Furthermore, fish with high infection loads had the lowest Fulton’s condition factor. Yet, it remains unknown whether our results steam from a direct effect of C. osculatum, or because G. morhua in an already compromised nutritional state are more susceptible towards the parasite. Nevertheless, impairment of the physiological condition can lead to reduced swimming performance, compromising foraging success while augmenting the risk of predation, potentially leading to an increase in the natural mortality of the host. We hence argue that fish–parasite interactions must not be neglected when implementing and refining strategies to rebuild deteriorating populations.

Ocean acidification is occurring in conjunction with warming and deoxygenation as a result of anthropogenic greenhouse gas emissions. Multistressor experiments are critically needed to better understand the sensitivity of marine organisms to these concurrent changes. Growth and survival responses to acidification have been documented for many marine species, but studies that explore underlying physiological mechanisms of carbon dioxide (CO2) sensitivity are less common. We investigated oxygen consumption rates as proxies for metabolic responses in embryos and newly hatched larvae of an estuarine forage fish (Atlantic silverside, Menidia menidia) to factorial combinations of CO2×temperature or CO2×oxygen. Metabolic rates of embryos and larvae significantly increased with temperature, but partial pressure of CO2 (PCO2) alone did not affect metabolic rates in any experiment. However, there was a significant interaction between PCO2 and partial pressure of oxygen (PO2) in embryos, because metabolic rates were unaffected by PO2 level at ambient PCO2, but decreased with declining PO2 under elevated PCO2. For larvae, however, PCO2 and PO2 had no significant effect on metabolic rates. Our findings suggest high individual variability in metabolic responses to high PCO2, perhaps due to parental effects and time of spawning. We conclude that early life metabolism is largely resilient to elevated PCO2 in this species, but that acidification likely influences energetic responses and thus vulnerability to hypoxia.

Metabolism is linked with the pace-of-life, co-varying with survival, growth, and reproduction. Metabolic rates should therefore be under strong selection and, if heritable, become less variable over time. Yet intraspecific variation in metabolic rates is ubiquitous, even after accounting for body mass and temperature. Theory predicts variable selection maintains trait variation, but field estimates of how selection on metabolism varies are rare. We use a model marine invertebrate to estimate selection on metabolic rates in the wild under different competitive environments. Fitness landscapes varied among environments separated by a few centimeters: interspecific competition selected for higher metabolism, and a faster pace-of-life, relative to competition-free environments. Populations experience a mosaic of competitive regimes; we find metabolism mediates a competition-colonization trade-off across these regimes. Although high metabolic phenotypes possess greater competitive ability, in the absence of competitors, low metabolic phenotypes are better colonizers. Spatial heterogeneity and the variable selection on metabolic rates that it generates is likely to maintain variation in metabolic rate, despite strong selection in any single environment.

Fish increase ventilation during hypoxia, a reflex termed the hypoxic ventilatory response (HVR). The HVR is an effective mechanism to increase O2 uptake, but at a high metabolic cost. Therefore, when hypoxia becomes severe enough, ventilation declines, as its benefit is diminished. The water oxygen partial pressure (PwO2) at which this decline occurs is expected to be near the critical PwO2 (Pcrit), the PwO2 at which O2 consumption begins to decline. Our results indicate that in zebrafish (Danio rerio), the relationship between peak HVR and Pcrit was dependent on developmental stage. Peak ventilation occurred at PwO2’s higher than Pcrit in larvae, but at a PwO2 significantly lower than Pcrit in adults. Larval zebrafish use cutaneous respiration to a greater extent than branchial respiration and the cost of sustaining the HVR may outweigh the benefit, whereas adult zebrafish, which rely on branchial respiration, may benefit from using HVR at PwO2 below Pcrit.

Organisms with annual life cycles are exposed to life stage specific thermal environments across seasons. Seasonal variation in thermal environments can vary across years and among sites. We investigated how organisms with annual life cycles respond to predictable seasonal changes in temperature and unpredictable thermal variation between habitats and years throughout their lives. Field surveys and historical records reveal that the spatially and temporally heterogeneous thermal environments inhabited by the annual mayfly Ephemerella maculata (Ephemerellidae) shift the date for transition to the next, life stage, so that the thermal phenotype of each life stage matches the thermal environment of the specific habitat and year. Laboratory studies of three distinct life stages of this mayfly reveal that life stage transitions are temperature dependent, facilitating timing shifts that are synchronized with the current season’s temperatures. Each life stage exhibited specific thermal sensitivity and performance phenotypes that matched the ambient temperature typically experienced during that life stage. Our study across the whole life cycle reveals mechanisms that allow organisms to achieve lifetime eurythermy in a dynamic seasonal environment, despite having narrower thermal ranges for growth and development in each life stage.

The ability to measure oxygen consumption rates of a living organism in real-time provides an indirect method of monitoring dynamic changes in metabolism reflecting organismal level mitochondrial function. In this study, we assessed the Loligo Systems microplate system for measuring individual respiration in small organisms. This included adult nematodes (Caenorhabditis elegans, N2), zebrafish embryos (Danio rerio, AB), and adult fruit flies (Drosophila melanogaster, w1118). Organisms were placed inside 80 µL glass chambers on a 24-well microplate atop a 24-channel optical fluorescence oxygen reading device. Adult nematodes and zebrafish embryos were in liquid culture, M9 buffer and egg water respectively, and the adult flies were in room air. The microplate and reader were placed inside an incubator for temperature control. A silicone gasket with a thin liner was used to seal the chambers. Reference standard oxygen consumption (respiration) of single and multiple adult nematodes (n=1–4 animals/well), zebrafish embryos (n=1–4 animals/well), and adult flies (n=1–2 animals/well) in the microplate system were achieved. Significant differences across numbers of animals/well and by sex were observed. Validation experiments of the oxygen consumption rates measured in C. elegans in parallel with Seahorse extracellular flux (XF) experiments are underway. The Loligo Systems microplate system offers a non-invasive, non-destructive method to measure real-time respiration in smaller organisms. These data provide preliminary evidence for utility of the system for a variety of biomedical applications that relate to organismal and mitochondrial function/dysfunction, including research in the basic biology of aging in these highly-utilized, pre-clinical, genetic model organisms.

Aquatic ectotherms face a challenge of obtaining sufficient oxygen, and it is commonly claimed that this challenge increases with increasing environmental temperature, causing concerns about the fate of aquatic ecosystems under climate change. However, the oxygen challenge hypothesis often ignores the effect of known phenotypic plastic responses. These can occur on either a within‐ or multigenerational scale, where multiple reactions act in concert to increase oxygen supply in response to increased temperature in a wide range of traits (molecular, egg content, behavioural, cell structure, morphological). Here, we combine a novel modelling approach with empirical measurements that enable quantification of how both the oxygen supply (maximum oxygen diffusion rate) and demand (metabolic rate) are affected by temperature while allowing for phenotypic plasticity. We exposed the aquatic ectotherm Daphnia magna to a range of temperatures (17–28°C) over several asexual generations and confirm that phenotypic plasticity contributes to an increased ability to obtain oxygen on the whole‐organism level at high temperatures. This response is strongest within the highest temperature range (22–28°C), where the change in oxygen challenge is expected to be most pronounced. However, the observed thermal plasticity in oxygen supply failed to compensate for the increased demand. Thus, we provide empirical evidence that the oxygen challenge in aquatic ectotherms increases with increasing temperature, even in the presence of phenotypic plasticity in oxygen supply.

3-ketodihydrosphingosine reductase (KDSR) is the key enzyme in the de novo sphingolipid synthesis. We identified a novel missense kdsrI105R mutation in zebrafish that led to a loss of function, and resulted in progression of hepatomegaly to steatosis, then hepatic injury phenotype. Lipidomics analysis of the kdsrI105R mutant revealed compensatory activation of the sphingolipid salvage pathway, resulting in significant accumulation of sphingolipids including ceramides, sphingosine and sphingosine 1-phosphate (S1P). Ultrastructural analysis revealed swollen mitochondria with cristae damage in the kdsrI105R mutant hepatocytes, which can be a cause of hepatic injury in the mutant. We found elevated sphingosine kinase 2 (sphk2) expression in the kdsrI105R mutant. Genetic interaction analysis with the kdsrI105R and the sphk2wc1 mutants showed that sphk2 depletion suppressed liver defects observed in the kdsrI105R mutant, suggesting that liver defects were mediated by S1P accumulation. Further, both oxidative stress and ER stress were completely suppressed by deletion of sphk2 in kdsrI105R mutants, linking these two processes mechanistically to hepatic injury in the kdsrI105R mutants. Importantly, we found that the heterozygous mutation in kdsr induced predisposed liver injury in adult zebrafish. These data point to kdsr as a novel genetic risk factor for hepatic injury.

Much is known about the genetic variance in certain components of metabolism, most notably resting and maximum metabolic rate. This is in stark contrast to the lack of information on genetic variance in the metabolic rate of individuals that feed and express routine activity, and how this rate correlates with other components of the energy budget or life history traits. Here we quantify genetic variance in metabolic rate (MR) under such conditions, as well as food consumption, juvenile somatic growth rate and age at maturation under ad lib food availability in a set of 10 clones of Daphnia magna from a natural population. Broad sense evolvabilities (0.16–0.56%) were on the same order of magnitude as those typically observed for physiological and life history traits, and suggest that all these traits have the potential to evolve within this population. We did not find support for the previously hypothesized positive genetic correlation between metabolic rate and growth rate. Rather, the patterns of genetic correlations suggest that genetic variance in food consumption is the single most influential trait shaping somatic growth rate, but that additional variance in growth can be explained by considering the joint effect of consumption and MR. The genetic variance in consumption and MR also translated into genetic variance in age at maturation, creating a direct link between these energy budget components and a life history trait with strong fitness effects. Moreover, a weak positive correlation between MR and food consumption suggests the presence of substantial amounts of independent genetic control of these traits, consistent with results obtained using genomic approaches.

Understanding whether populations and communities can evolve fast enough to keep up with ongoing climate change is one of the most pressing issues in biology today. A growing number of studies have documented rapid evolutionary responses to warming, suggesting that populations may be able to persist despite temperature increases. The challenge now is to better understand how species interactions, which are ubiquitous in nature, mediate these population responses to warming. Here, we use laboratory natural selection experiments in a freshwater community to test hypotheses related to how thermal evolution of Daphnia pulex to two selection temperatures (12 and 18°C) is mediated by rapid thermal evolution of its algal resource ( Scenedesmus obliquus ) or by the presence of the zooplankton predator Chaoborus americanus. We found that cold‐evolved algae (a high‐quality resource) facilitated the evolution of increased thermal plasticity in Daphnia populations selected at 12°C, for both body size and per capita growth rates ( r ). Conversely, warm‐evolved algae facilitated the evolution of increased r thermal plasticity for Daphnia selected at 18°C. Lastly, we found that the effect of selection temperature on evolved Daphnia body size was more pronounced when Daphnia were also reared with predators. These data demonstrate that trait evolution of a focal population to the thermal environment can be affected by both bottom‐up and top‐down species interactions and that rapid temperature evolution of a resource can have cascading effects on consumer thermal evolution. Our study highlights the importance of incorporating species interactions when estimating ecological and evolutionary responses of populations and communities to ongoing temperature warming.

Adult males of Calanus copepods in the Arctic are mainly observed between late autumn and late spring, and are seldom recorded during summer. Due to logistical constraints, there are still relatively few studies on zooplankton in high-latitude regions during the winter, and subsequently, little is known about Calanus males. Here, we present data on abundance, spatial distribution, prosome length, lipid content, respiration and swimming activity of i>Calanus adults, along with adult sex ratios in i>Calanus populations from 5 Arctic fjords in Svalbard, Norway (78-80° N) during the polar night in January 2015, 2016 and 2017. Adult males and females of i>Calanus were observed at all locations and occurred throughout the entire water column. Morphological examination and molecular identification of i>Calanus males proved that all males encountered belong to Calanus glacialis, even in the fjords where overwintering copepodite stage CV of C. finmarchicus dominated at the time. Adult sex ratios in C. glacialis populations varied from 1 male per 4 females to 2 males per female. From 3 to 18% of females carried spermatophores attached to the genital segment. Lipid content in males was slightly higher than in females. Shipboard experiments showed that males had higher swimming activity and respiration rates than females. Our observations indicate that adult males of C. glacialis stay active and demonstrate active mating behavior in mid-winter, and that the mating phenology of C. glacialis is decoupled from that of C. finmarchicus in the study area in January.

Volatile organic compounds (VOCs) are known to potentially cause a severe change in the respiratory metabolism of freshwater species, however the effect of these contaminants on groundwater-obligate species has not been investigated to date. Tetrachloroethylene (TCE) is a VOC frequently found in the groundwater bodies of industrialized areas, even years after a contamination event because TCE degradation takes several decades to occur. Contamination from TCE is considered persistent and difficult to remediate. Its high density favors a gravity-driven vertical infiltration into groundwater bodies. The TCE threshold value is 1.1 μg/L in groundwater bodies of Italy. TCE concentration in many Italian groundwater bodies is widely over this legal limit. In this study, we investigated the effect of 1.1 μg/L TCE on the survival, oxygen consumption, and locomotory activities of a groundwater-obligate copepod species. The specimens required for the trials were collected in the Antro del Corchia Cave (Tuscany). We measured the individual-based oxygen consumption of this species as a proxy of possible metabolic reactions to long-term (5 days) exposures to TCE at 8.0°C that is the mean annual temperature of groundwater flowing in the cave. To this end, we used a sealed glass microplate equipped with 24-planar oxygen sensor spots with optical isolation glued onto the bottom of 80-μL wells (Loligo Systems, Denmark) integrated with a 24-channel fluorescence-based respirometry system (SDR Sensor Dish Reader, PreSens, Germany). The system allows simultaneous measurement of 20 replicates and 4 controls. Survival and locomotory activity assessments were performed by counting the number of alive individuals and measuring the number of moving animals in 5 mL glass vials each containing 20 individuals. Preliminary results showed a decreasing in oxygen consumption of the organisms exposed to 1.1 μg/L TCE for 5 days at 8°C respect to the control. However, neither survival nor locomotory activities appeared to have been affected by exposure to TCE. See Suppl. material 1.

The average global temperature is predicted to increase by 3 °C by the end of this century due to human-induced climate change. The overall metabolism of the aquatic biota will be directly affected by rising temperatures and associated changes. Since thermal stability is a characteristic of groundwater ecosystems, global warming is expected to have a profound effect on the groundwater fauna. The prediction that stygobitic (obligate groundwater dweller) species are vulnerable to climate change includes assumptions about metabolic effects that can only be tested by comparisons across a thermal gradient. To this end, we investigated the effects of two different thermal regimes on the metabolism of the stygobitic copepod species Diacyclops belgicus (Kiefer, 1936). We measured the individual-based oxygen consumption of this species as a proxy of possible metabolic reactions to temperature rising from 14 to 17 °C. We used a sealed glass microplate equipped with planar oxygen sensor spots with optical isolation glued onto the bottom of 80-μL wells integrated with a 24-channel fluorescence-based respirometry system. The tests have provided controversial results according to which the D. belgicus populations should be prudently considered at risk under a global warming scenario.

Environmental change may cause phenotypic changes that are inherited across generations through transgenerational plasticity (TGP). If TGP is adaptive, offspring fitness increases with an increasing match between parent and offspring environment. Here we test for adaptive TGP in somatic growth and metabolic rate in response to temperature in the clonal zooplankton Daphnia pulex. Animals of the first focal generation experienced thermal transgenerational ‘mismatch’ (parental and offspring temperatures differed), whereas conditions of the next two generations matched the (grand)maternal thermal conditions. Adjustments of metabolic rate occurred during the lifetime of the first generation (i.e. within-generation plasticity). However, no further change was observed during the subsequent two generations, as would be expected under TGP. Furthermore, we observed no tendency for increased juvenile somatic growth (a trait highly correlated with fitness in Daphnia ) over the three generations when reared at new temperatures. These results are inconsistent with existing studies of thermal TGP, and we describe how previous experimental designs may have confounded TGP with within-generation plasticity and selective mortality. We suggest that the current evidence for thermal TGP is weak. To increase our understanding of the ecological and evolutionary role of TGP, future studies should more carefully identify possible confounding factors.

For ectotherms, temperature modifies the rate of physiological function across a temperature tolerance window depending on thermal history, ontogeny, and evolutionary history. Some adult Antarctic fishes, with comparatively narrow thermal windows, exhibit thermal plasticity in standard metabolic rate; however, little is known about the shape or breadth of thermal performance curves of earlier life stages of Antarctic fishes. We tested the effects of acute warming (− 1 to 8 °C) and temperature acclimation (2 weeks at − 1, 2, 4 °C) on survival and standard metabolic rate in early embryos of the dragonfish Gymnodraco acuticeps from McMurdo Sound, Ross Island, Antarctica. Contrary to predictions, embryos acclimated to warmer temperatures did not experience greater mortality and nearly all embryos survived acute warming to 8 °C. Metabolic performance curve height and shape were both significantly altered after 2 weeks of development at − 1 °C, with further increase in curve height, but not alteration of shape, with warm temperature acclimation. Overall metabolic rate temperature sensitivity (Q 10) from − 1 to 8 °C varied from 2.6 to 3.6, with the greatest thermal sensitivity exhibited by embryos at earlier developmental stages. Interclutch variation in metabolic rates, mass, and development of simultaneously collected embryos was also documented. Taken together, metabolic performance curves provide insight into the costs of early development under warming temperatures, with the potential for thermal sensitivity to be modified by dragonfish phenology and magnitude of seasonal changes in temperature.

Within many species, larger offspring have higher fitness. While the presence of an offspring size–fitness relationship is canonical in life‐history theory, the mechanisms that determine why this relationship exists are unclear. Linking metabolic theory to life‐history theory could provide a general explanation for why larger offspring often perform better than smaller offspring. In many species, energy reserves at the completion of development drive differences in offspring fitness. Development is costly, so any factor that decreases energy expenditure during development should result in higher energy reserves and thus subsequently offspring fitness. Metabolic theory predicts that larger offspring should have relatively lower metabolic rates and thus emerge with a higher level of energy reserves (assuming developmental times are constant). The increased efficiency of development in larger offspring may therefore be an underlying driver of the relationship between offspring size and offspring fitness, but this has not been tested within species. To determine how the costs of development scale with offspring size, we measured energy expenditure throughout development in the model organism Danio rerio across a range of natural offspring sizes. We also measured how offspring size affects the length of the developmental period. We then examined how hatchling size and condition scale with offspring size. We find that larger offspring have lower mass‐specific metabolic rates during development, but develop at the same rate as smaller offspring. Larger offspring also hatch relatively heavier and in better condition than smaller offspring. That the relative costs of development decrease with offspring size may provide a widely applicable explanation for why larger offspring often perform better than smaller offspring. A plain language summary is available for this article.

The effects of multiple stressors on the early life stages of reef-building corals are poorly understood. Elevated temperature is the main physiological driver of mass coral bleaching events, but increasing evidence suggests that other stressors, including elevated dissolved inorganic nitrogen (DIN), may exacerbate the negative effects of thermal stress. To test this hypothesis, we investigated the performance of larvae of Orbicella faveolata and Porites astreoides, two important Caribbean reef coral species with contrasting reproductive and algal transmission modes, under increased temperature and/or elevated DIN. We used a fluorescence-based microplate respirometer to measure the oxygen consumption of coral larvae from both species, and also assessed the effects of these stressors on P. astreoides larval settlement and mortality. Overall, we found that (1) larvae increased their respiration in response to different factors (O. faveolata in response to elevated temperature and P. astreoides in response to elevated nitrate) and (2) P. astreoides larvae showed a significant increase in settlement as a result of elevated nitrate, but higher mortality under elevated temperature. This study shows how microplate respirometry can be successfully used to assess changes in respiration of coral larvae, and our findings suggest that the effects of thermal stress and nitrate enrichment in coral larvae may be species specific and are neither additive nor synergistic for O. faveolata or P. astreoides. These findings may have important consequences for the recruitment and community reassembly of corals to nutrient-polluted reefs that have been impacted by climate change.

Metabolic rate reflects the ‘pace of life’ in every organism. Metabolic rate is related to an organism's capacity for essential maintenance, growth and reproduction—all of which interact to affect fitness. Although thousands of measurements of metabolic rate have been made, the microevolutionary forces that shape metabolic rate remain poorly resolved. The relationship between metabolic rate and components of fitness are often inconsistent, possibly because these fitness components incompletely map to actual fitness and often negatively covary with each other. Here we measure metabolic rate across ontogeny and monitor its effects on actual fitness (lifetime reproductive output) for a marine bryozoan in the field. We also measure key components of fitness throughout the entire life history including growth rate, longevity and age at the onset of reproduction. We found that correlational selection favours individuals with higher metabolic rates in one stage and lower metabolic rates in the other—individuals with similar metabolic rates in each developmental stage displayed the lowest fitness. Furthermore, individuals with the lowest metabolic rates lived for longer and reproduced more, but they also grew more slowly and took longer to reproduce initially. That metabolic rate is related to the pace of the life history in nature has long been suggested by macroevolutionary patterns but this study reveals the microevolutionary processes that probably generated these patterns.

Population density has recently been suggested to be an important factor influencing metabolic rates and to represent an important ‘third axis’ explaining variation beyond that explained by body mass and temperature. In situations where population density influences food consumption, the immediate effect on metabolism acting through specific dynamic action ( SDA ), and downregulation due to fasting over longer periods, is well understood. However, according to a recent review, previous studies suggest a more general effect of population density per se, even in the absence of such effects. It has been hypothesized that this results from animals performing anticipatory responses (i.e. reduced activity) to expected declines in food availability. Here, we test the generality of this finding by measuring density effects on metabolic rates in 10 clones from two different species of the zooplankton Daphnia ( Daphnia pulex Leydig and D. magna Straus). Using fluorescence‐based respirometry, we obtain high‐precision measures of metabolism. We also identify additional studies on this topic that were not included in the previous review, compare the results and evaluate the potential for measurement bias in all previous studies. We demonstrate significant variation in mass‐specific metabolism among clones within both species. However, we find no evidence for a negative relationship between population density and mass‐specific metabolism. The previously reported pattern also disappeared when we extended the set of studies analysed. We discuss potential reasons for the discrepancy among studies, including two main sources of potential bias (microbial respiration and declining oxygen consumption due to reduced oxygen availability). Only one of the previous studies gives sufficient information to conclude the absence of such biases, and consistent with our results, no effect of density on metabolism was found. We conclude that population density per se does not have a general effect on mass‐specific metabolic rate.

Within species, larger offspring typically outperform smaller offspring. While the relationship between offspring size and performance is ubiquitous, the cause of this relationship remains elusive. By linking metabolic and life-history theory, we provide a general explanation for why larger offspring perform better than smaller offspring. Using high-throughput respirometry arrays, we link metabolic rate to offspring size in two species of marine bryozoan. We found that metabolism scales allometrically with offspring size in both species: while larger offspring use absolutely more energy than smaller offspring, larger offspring use proportionally less of their maternally derived energy throughout the dependent, non-feeding phase. The increased metabolic efficiency of larger offspring while dependent on maternal investment may explain offspring size effects—larger offspring reach nutritional independence (feed for themselves) with a higher proportion of energy relative to structure than smaller offspring. These findings offer a potentially universal explanation for why larger offspring tend to perform better than smaller offspring but studies on other taxa are needed.