Evolutionary and acclimation-induced variation in the heat-shock responses of congeneric marine snails (genus Tegula) from different thermal habitats: implications for limits of thermotolerance and biogeography

Genetics and ontogeny are key factors influencing thermal resilience in a culturally and economically important bivalve

Increasing seawater temperatures coupled with more intense and frequent heatwaves pose an increasing threat to marine species. In this study, the New Zealand green-lipped mussel, Perna canaliculus, was used to investigate the effect of genetics and ontogeny on thermal resilience. The culturally and economically significant mussel P. canaliculus (Gmelin, 1971) has been selectively-bred in New Zealand for two decades, making it a unique biological resource to investigate genetic interactions in a temperate bivalve species. Six selectively-bred full sibling families and four different ages, from early juveniles (6, 8, 10 weeks post-fertilisation) to sub-adults (52 weeks post-fertilisation), were used for experimentation. At each age, each family was exposed to a three-hour heat challenge, followed by recovery, and survival assessments. The shell lengths of live and dead juvenile mussels were also measured. Gill tissue samples from sub-adults were collected after the thermal challenge to quantify the 70 kDa heat shock protein gene (hsp70). Results showed that genetics, ontogeny and size influence thermal resilience in P. canaliculus, with LT50 values ranging between 31.3 and 34.4 °C for all studied families and ages. Juveniles showed greater thermotolerance compared to sub-adults, while the largest individuals within each family/age class tended to be more heat sensitive than their siblings. Sub-adults differentially upregulated hsp70 in a pattern that correlated with net family survival following heat challenge, reinforcing the perceived role of inducible HSP70 protein in molluscs. This study provides insights into the complex interactions of age and genotype in determining heat tolerance of a key mussel species. As marine temperatures increase, equally complex selection pressure responses may therefore occur. Future research should focus on transcriptomic and genomic approaches for key species such as P. canaliculus to further understand and predict the effect of genetic variation and ontogeny on their survival in the context of climate change.

Heat tolerance, oxidative stress response tuning and robust gene activation in early-stage Drosophila melanogaster embryos

In organisms with complex life cycles, life stages that are most susceptible to environmental stress may determine species persistence in the face of climate change. Early embryos of Drosophila melanogaster are particularly sensitive to acute heat stress, yet tropical embryos have higher heat tolerance than temperate embryos, suggesting adaptive variation in embryonic heat tolerance. We compared transcriptomic responses to heat stress among tropical and temperate embryos to elucidate the gene regulatory basis of divergence in embryonic heat tolerance. The transcriptomes of tropical and temperate embryos differed in both constitutive and heat-stress-induced responses of the expression of relatively few genes, including genes involved in oxidative stress. Most of the transcriptomic response to heat stress was shared among all embryos. Embryos shifted the expression of thousands of genes, including increases in the expression of heat shock genes, suggesting robust zygotic gene activation and demonstrating that, contrary to previous reports, early embryos are not transcriptionally silent. The involvement of oxidative stress genes corroborates recent reports on the critical role of redox homeostasis in coordinating developmental transitions. By characterizing adaptive variation in the transcriptomic basis of embryonic heat tolerance, this study is a novel contribution to the literature on developmental physiology and developmental genetics.

Microhabitat acclimatization alters sea anemone-algal symbiosis and thermal tolerance across the intertidal zone

Contemporary symbioses in extreme environments can give an insight into mechanisms that stabilize species interactions during environmental change. The intertidal sea anemone, Anthopleura elegantissima, engages in a nutritional symbiosis with microalgae similar to tropical coral, but withstands more intense environmental fluctuations during tidal inundations. In this study, we compare baseline symbiotic traits and their sensitivity to thermal stress within and among anemone aggregations across the intertidal using a laboratory-based tank experiment to better understand how fixed genotypic and plastic environmental effects contribute to the successful maintenance of this symbiosis in extreme habitats. High intertidal anemones had lower baseline symbiont-to-host cell ratios under control conditions, but their symbionts had higher baseline photosynthetic efficiency compared to low intertidal anemone symbionts. Symbiont communities were identical across all samples, suggesting that shifts in symbiont density and photosynthetic performance could be an acclimatory mechanism to maintain symbiosis in different environments. Despite lower baseline symbiont-to-host cell ratios, high intertidal anemones maintained greater symbiont-to-host cell ratios under heat stress compared with low intertidal anemones, suggesting greater thermal tolerance of high intertidal holobionts. However, the thermal tolerance of clonal anemones acclimatized to different zones was not explained by tidal height alone, indicating additional environmental variables contribute to physiological differences. Host genotype significantly influenced anemone weight, but only explained a minor proportion of variation among symbiotic traits and their response to thermal stress, further implicating environmental history as the primary driver of holobiont tolerance. These results indicate that this symbiosis is highly plastic and may be able to acclimatize to climate change over ecological timescales, defying the convention that symbiotic organisms are more susceptible to environmental stress.

Flight or fight: different strategies of intertidal periwinkle Littoraria sinensis coping with high temperature across populations

Intertidal organisms usually live near their upper thermal limits, and are vulnerable to future global warming. As a vital response to thermal stress, thermoregulatory strategy in physiological and behavioral performance is essential for organisms coping with thermal stress and surviving the changing world. To investigate the relationship between the thermoregulatory strategy and habitat temperature, in the present study, we comparatively investigated the thermal responsive strategy among different geographic populations of the supralittoral snail Littoraria sinensis by determining snails' cardiac function and behavioral performance. Our results indicated that populations inhabiting high ambient temperatures had higher sublethal temperatures (i.e. Arrhenius breakpoint temperatures, ABTs, the temperature at which the heart rate shapely decreases with further heating) and lethal temperatures (i.e. Flatline temperatures, FLTs, the temperature at which heart rate ceases), and behaved less actively (e.g. shorter moving distances and shorter moving time) in the face of high and rising temperatures-a physiological fight strategy. On the other hand, populations at relatively low ambient temperatures had relatively lower physiological upper thermal limits with lower ABTs and FLTs and moved more actively in the face of high and rising temperatures-a behavioral flight strategy. These results demonstrate that the thermoregulatory strategies of the snails are closely related to their habitat temperatures and are different among populations surviving divergent thermal environments.

The effect of urbanization and temperature on thermal tolerance, foraging performance, and competition in cavity-dwelling ants

Human disturbance including rapid urbanization and increased temperatures can have profound effects on the ecology of local populations. Eusocial insects, such as ants, have adapted to stressors of increasing temperature and urbanization; however, these evolutionary responses are not consistent among populations across geographic space. Here we asked how urbanization and incubation temperature influence critical thermal maximum (CTmax) and various ecologically relevant behaviors in three ant species in urban and rural locations in Worcester, MA, USA. We did this by incubating colonies of three species of cavity dwelling ant (Aphaenogaster picea, Tapinoma sessile, and Temnothorax longispinosus) from 2 habitat types (Rural and Urban), for 60-days at multiple temperatures. We found that incubation temperature, urbanization, and species of ant all significantly affected overall colony critical thermal maximum. We also found that recruitment time, colonization time, and defense response were significantly affected by incubation temperature and varied between species of ant, while recruitment and colonization time were additionally affected by urbanization. These variable changes in performance and competitive traits across species suggest that responses to urbanization and shifting temperatures are not universal across species. Changes in behavioral responses caused by urbanization may disrupt biodiversity, creating unusual competitive environments as a consequence of natural adaptations and cause both direct and indirect mechanisms for which human disturbance can lead to local species extinction.

Differential metabolic responses in bold and shy sea anemones during a simulated heatwave

As climate change-induced heatwaves become more common, phenotypic plasticity at multiple levels is a key mitigation strategy by which organisms can optimise selective outcomes. In ectotherms, changes to both metabolism and behaviour can help alleviate thermal stress. Nonetheless, no study in any ectotherm has yet empirically investigated how changing temperatures affect among-individual differences in the associations between these traits. Using the beadlet anemone (Actinia equina), an intertidal species from a thermally heterogeneous environment, we investigated how individual metabolic rates, linked to morphotypic differences in A. equina, and boldness were related across changing temperatures. A crossed-over design and a temporal control were used to test the same individuals at a non-stressful temperature, 13°C, and under a simulated heatwave at 21°C. At each temperature, short-term repeated measurements of routine metabolic rate (RMR) and a single measurement of a repeatable boldness-related behaviour, immersion response time (IRT), were made. Individual differences, but not morphotypic differences, were highly predictive of metabolic plasticity, and the plasticity of RMR was associated with IRT. At 13°C, shy animals had the highest metabolic rates, while at 21°C, this relationship was reversed. Individuals that were bold at 13°C also exhibited the highest metabolic rates at 21°C. Additional metabolic challenges during heatwaves could be detrimental to fitness in bold individuals. Equally, lower metabolic rates at non-stressful temperatures could be necessary for optimal survival as heatwaves become more common. These results provide novel insight into the relationship between metabolic and behavioural plasticity, and its adaptive implications in a changing climate.

A snapshot of 100 years of discovery

With a century of literature behind Journal of Experimental Biology (JEB) in 2023, I look at some of the extraordinary papers contained within its archive. From publishing Nobel Prize-inspiring discoveries to founding fields and solving long-standing mysteries, the journal has been at the hub of experimental biology for 10 decades, leading the way and shining a light on the physiology of many remarkable animal species. In this Perspective, I highlight some of the key players in the field, summarise their seminal works and consider their long-term impact as JEB embarks on its next 100 years.

Roles of multi-level temperature-adaptive responses and microhabitat variation in establishing distributions of intertidal species

How intertidal species survive their harsh environment and how best to evaluate and forecast range shifts in species distribution are two important and closely related questions for intertidal ecologists and global change biologists. Adaptive variation in responses of organisms to environmental change across all levels of biological organization - from behavior to molecular systems - is of key importance in setting distribution patterns, yet studies often neglect the interactions of diverse types of biological variation (e.g. differences in thermal optima owing to genetic and acclimation-induced effects) with environmental variation, notably at the scale of microhabitats. Intertidal species have to cope with extreme and frequently changing thermal stress, and have shown high variation in thermal sensitivities and adaptive responses at different levels of biological organization. Here, I review the physiological and biochemical adaptations of intertidal species to environmental temperature on multiple spatial and temporal scales. With fine-scale datasets for the thermal limits of individuals and for environmental temperature variation at the microhabitat scale, we can map the thermal sensitivity for each individual in different microhabitats, and then scale up the thermal sensitivity analysis to the population level and, finally, to the species level by incorporating physiological traits into species distribution models. These more refined mechanistic models that include consideration of physiological variations have higher predictive power than models that neglect these variations, and they will be crucial to answering the questions posed above concerning adaptive mechanisms and the roles they play in governing distribution patterns in a rapidly changing world.

The environmental cellular stress response: the intertidal as a multistressor model

The wild poses a multifaceted challenge to the maintenance of cellular function. Therefore, a multistressor approach is essential to predict the cellular mechanisms which promote homeostasis and underpin whole-organism tolerance. The intertidal zone is particularly dynamic, and thus, its inhabitants provide excellent models to assess mechanisms underpinning multistressor tolerance. Here, we critically review our current understanding of the regulation of the cellular stress response (CSR) under multiple abiotic stressors in intertidal organisms and consider to what extent a multistressor approach brings us closer to understanding responses in the wild. The function of the CSR has been well documented in laboratory and field exposures with a view to understanding single-stressor thermal effects. Multistressor studies still remain relatively limited in comparison but have applied three main approaches: (i) laboratory application of multiple stressors in isolation, (ii) multiple stressors applied in combination, and (iii) field-based correlation of multiple stressors against the CSR. The application of multiple stressors in isolation has allowed the identification of putative, shared stress pathways but overlooks non-additive stressor interactions on the CSR. Combined stressor studies are relatively limited in number but already highlight variable effects on the CSR dependent upon stressor type, timing, and magnitude. Field studies have allowed the identification of responsive components of the CSR to various stressors in situ but are correlative, not causative. A combined approach involving laboratory multistressor studies linking the CSR to whole-organism tolerance as well as field studies is required if we are to understand the role of the CSR in the natural environment.

Metabolic and behavioural effects of hermit crab shell removal techniques: Is heating less invasive than cracking?

Hermit crabs (Paguroidea; Latreille 1802) offer great opportunities to study animal behaviour and physiology. However, the animals' size and sex cannot be determined when they are inside their shell; information crucial to many experimental designs. Here, we tested the effects of the two most common procedures used to make crabs leave their shells: heating the shell apex and cracking the shell with a bench press. We compared the effects of each of the two procedures on the metabolic rate, hiding time, and duration of the recovery time relative to unmanipulated hermit crabs. The hermit crabs forced to abandon their shell through heating increased their respiratory rate shortly after the manipulation (1 h) and recovered their metabolic rate in less than 24 h, as occurs in individuals suddenly exposed to high temperatures in the upper-intertidal zone. Hermit crabs removed from their shells via cracking spent more time hiding in their new shells; this effect was evident immediately after the manipulation and lasted more than 24 h, similar to responses exhibited after a life-threatening predator attack. Both methods are expected to be stressful, harmful, or fear-inducing; however, the temperature required to force the crabs to abandon the shell is below the critical thermal maxima of most inhabitants of tropical tide pools. The wide thermal windows of intertidal crustaceans and the shorter duration of consequences of shell heating compared to cracking suggest heating to be a less harmful procedure for removing tropical hermit crabs from their shells.

Integrated biochemical, transcriptomic and metabolomic analyses provide insight into heat stress response in Yangtze sturgeon (Acipenser dabryanus)

Temperature fluctuations caused by climate change and global warming pose a great threat to various species. Most fish are particularly vulnerable to elevated temperatures. Understanding the mechanism of high-temperature tolerance in fish can be beneficial for proposing effective strategies to help fish cope with global warming. In this study, we systematically studied the effects of high temperature on Acipenser dabryanus, an ancient living fossil and flagship species of the Yangtze River, at the histological, biochemical, transcriptomic and metabolomic levels. Intestinal and liver tissues from the control groups (18 °C) and acute heat stress groups (30 °C) of A. dabryanus were sampled for histological observation and liver tissues were assessed for transcriptomic and metabolomic profiling. Histopathological analysis showed that the intestine and liver tissues were damaged after heat stress. The plasma cortisol content and the levels of oxidative stress markers (catalase/glutathione reductase) and two aminotransferases (aspartate aminotransferase/alanine aminotransferase) increased significantly in response to acute heat stress. Transcriptomic and metabolomic methods showed 6707 upregulated and 4189 downregulated genes and 64 upregulated and 78 downregulated metabolites in the heat stress group. Heat shock protein (HSP) genes showed striking changes in expression under heat stress, with 21 genes belonging to the HSP30, HSP40, HSP60, HSP70 and HSP90 families significantly upregulated by short-term heat stress. The majority of genes associated with ubiquitin and various immune-related pathways were also markedly upregulated in the heat stress group. In addition, the combined analysis of metabolites and gene profiles suggested an enhancement of amino acid metabolism and glycometabolism and the suppression of fatty acid metabolism during heat stress, which could be a potential energy conservation strategy for A. dabryanus. To the best of our knowledge, the present study represents the first attempt to reveal the mechanisms of heat stress responses in A. dabryanus, which can provide insights into improved cultivation of fish in response to global warming.

Heat Shock Proteins (Hsps) in Cellular Homeostasis: A Promising Tool for Health Management in Crustacean Aquaculture

Heat shock proteins (Hsps) are a family of ubiquitously expressed stress proteins and extrinsic chaperones that are required for viability and cell growth in all living organisms. These proteins are highly conserved and produced in all cellular organisms when exposed to stress. Hsps play a significant role in protein synthesis and homeostasis, as well as in the maintenance of overall health in crustaceans against various internal and external environmental stresses. Recent reports have suggested that enhancing in vivo Hsp levels via non-lethal heat shock, exogenous Hsps, or plant-based compounds, could be a promising strategy used to develop protective immunity in crustaceans against both abiotic and biotic stresses. Hence, Hsps as the agent of being an immune booster and increasing disease resistance will present a significant advancement in reducing stressful conditions in the aquaculture system.

The influence of stochastic temperature fluctuations in shaping the physiological performance of the California mussel, Mytilus californianus

Climate change is forecasted to increase temperature variability and stochasticity. Most of our understanding of thermal physiology of intertidal organisms has come from laboratory experiments that acclimate organisms to submerged conditions and steady-state increases in temperatures. For organisms experiencing the ebb and flow of tides with unpredictable low tide aerial temperatures, the reliability of reported tolerances and thus predicted responses to climate change requires incorporation of environmental complexity into empirical studies. Using the mussel Mytilus californianus, our study examined how stochasticity of the thermal regime influences physiological performance. Mussels were acclimated to either submerged conditions or a tidal cycle that included either predictable, unpredictable or no thermal stress during daytime low tide. Physiological performance was measured through anaerobic metabolism, energy stores and cellular stress mechanisms just before low tide, and cardiac responses during a thermal ramp. Both air exposure and stochasticity of temperature change were important in determining thermal performance. Glycogen content was highest in the mussels from the unpredictable treatment, but there was no difference in the expression of heat shock proteins between thermal treatments, suggesting that mussels prioritise energy reserves to deal with unpredictable low tide conditions. Mussels exposed to fluctuating thermal regimes had lower gill anaerobic metabolism, which could reflect increased metabolic capacity. Our results suggest that while thermal magnitude plays an important role in shaping physiological performance, other key elements of the intertidal environment complexity such as stochasticity, thermal variability, and thermal history are also important considerations for determining how species will respond to climate warming.

Rapid Adjustments in Thermal Tolerance and the Metabolome to Daily Environmental Changes - A Field Study on the Arctic Seed Bug Nysius groenlandicus

Laboratory investigations on terrestrial model-species, typically of temperate origin, have demonstrated that terrestrial ectotherms can cope with daily temperature variations through rapid hardening responses. However, few studies have investigated this ability and its physiological basis in the field. Especially in polar regions, where the temporal and spatial temperature variations can be extreme, are hardening responses expected to be important. Here, we examined diurnal adjustments in heat and cold tolerance in the Greenlandic seed bug Nysius groenlandicus by collecting individuals for thermal assessment at different time points within and across days. We found a significant correlation between observed heat or cold tolerance and the ambient microhabitat temperatures at the time of capture, indicating that N. groenlandicus continuously and within short time-windows respond physiologically to thermal changes and/or other environmental variables in their microhabitats. Secondly, we assessed underlying metabolomic fingerprints using GC-MS metabolomics in a subset of individuals collected during days with either low or high temperature variation. Concentrations of metabolites, including sugars, polyols, and free amino acids varied significantly with time of collection. For instance, we detected elevated sugar levels in animals caught at the lowest daily field temperatures. Polyol concentrations were lower in individuals collected in the morning and evening and higher at midday and afternoon, possibly reflecting changes in temperature. Additionally, changes in concentrations of metabolites associated with energetic metabolism were observed across collection times. Our findings suggest that in these extreme polar environments hardening responses are marked and likely play a crucial role for coping with microhabitat temperature variation on a daily scale, and that metabolite levels are actively altered on a daily basis.

Ecological Leverage Points: Species Interactions Amplify the Physiological Effects of Global Environmental Change in the Ocean

Marine ecosystems are increasingly impacted by global environmental changes, including warming temperatures, deoxygenation, and ocean acidification. Marine scientists recognize intuitively that these environmental changes are translated into community changes via organismal physiology. However, physiology remains a black box in many ecological studies, and coexisting species in a community are often assumed to respond similarly to environmental stressors. Here, we emphasize how greater attention to physiology can improve our ability to predict the emergent effects of ocean change. In particular, understanding shifts in the intensity and outcome of species interactions such as competition and predation requires a sharpened focus on physiological variation among community members and the energetic demands and trophic mismatches generated by environmental changes. Our review also highlights how key species interactions that are sensitive to environmental change can operate as ecological leverage points through which small changes in abiotic conditions are amplified into large changes in marine ecosystems.

The Goldilocks Principle: A Unifying Perspective on Biochemical Adaptation to Abiotic Stressors in the Sea

The ability of marine organisms to thrive over wide ranges of environmental stressors that perturb structures of proteins, nucleic acids, and lipids illustrates the effectiveness of adaptation at the biochemical level. A critical role of these adaptations is to achieve a proper balance between structural rigidity, which is necessary for maintaining three-dimensional conformation, and flexibility, which is required to allow changes in conformation during function. The Goldilocks principle refers to this balancing act, wherein structural stability and functional properties are poised at values that are just right for the environment the organism faces. Achieving this balance involves changes in macromolecular sequence and adaptive change in the composition of the aqueous or lipid milieu in which macromolecules function. This article traces the development of the field of biochemical adaptation throughout my career and shows how comparative studies of marine animals from diverse habitats have shed light on fundamental properties of life common to all organisms.

Seasonal cellular stress phenomena and phenotypic plasticity in land snail Helix lucorum populations from different altitudes

Temperature, a major abiotic environmental factor, regulates various physiological functions in land snails and therefore determines their biogeographical distribution. Thus, species with different distributions may present different thermal tolerance limits. Additionally, the intense reactivation of snail metabolic rate upon arousal from hibernation or estivation may provoke stress. Land snails, Helix lucorum, display a wide altitudinal distribution resulting in populations being exposed to different seasonal temperature variations. The aim of the present study was to investigate the expression of heat shock proteins (Hsps), mitogen activated protein kinases (MAPKs) and proteins that are related to apoptosis (Bcl-2, ubiquitin), that have 'cytoprotective' roles and are also considered to be reliable indicators of stress because of their crucial role in maintaining cellular homeostasis. These proteins were assessed in H. lucorum individuals from two different populations, one at Axios (sea level, 0 m) and the other at Kokkinopilos (Olympus, 1250 m), as well as after mutual population exchanges, in order to find out whether the different responses of these stress-related proteins depend solely on the environmental temperature. The results showed seasonally altered levels in all studied proteins in the hepatopancreas and foot of snails, both among different populations and between the same populations exposed to varying altitudes. However, individuals of the same population in their native habitat or acclimatized to a different habitat showed a relatively similar pattern of expression, supporting the induction of the specific proteins according to the life history of each species.

Variation in thermal performance curves for oxygen consumption and loss of critical behaviors in co-occurring species indicate the potential for ecosystem stability under ocean warming

Species-level differences in responses to environmental factors may increase a community's ability to retain key functions under environmental change. We compared the oxygen consumption rates and maintenance of critical behaviors for three co-occurring intertidal gastropod species over a temperature range of 30 °C. Each species exhibited a distinct thermal performance curve (TPC) for oxygen consumption. The TPC of Lunella granulata was horizontally shifted to be significantly warmer than that of Chlorostoma argyrostoma. Monodonta labio's TPC was vertically shifted compared to the other two species, reflecting greater oxygen consumption overall. L. granulata and M. labio maintained critical behaviors at temperatures 3-5 °C warmer than C. argyrostoma. These differences in the thermal tolerances of similar, co-occurring species provide space for the insurance effect of biodiversity to occur. Understanding the degree to which co-occurring species respond differently to increased temperature may help us predict community resistance in the face of climate change.

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

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

De novo transcriptome assemblies of red king crab (Paralithodes camtschaticus) and snow crab (Chionoecetes opilio) molting gland and eyestalk ganglia - Temperature effects on expression of molting and growth regulatory genes in adult red king crab

Red king crab (Paralithodes camtschaticus) and snow crab (Chionoecetes opilio) are deep-sea crustaceans widely distributed in the North Pacific and Northwest Atlantic Oceans. These giant predators have invaded the Barents Sea over the past decades, and climate-driven temperature changes may influence their distribution and abundance in the sub-Arctic region. Molting and growth in crustaceans are strongly affected by temperature, but the underlying molecular mechanisms are little known, particularly in cold-water species. Here, we describe multiple regulatory factors in the two high-latitude crabs by developing de novo transcriptomes from the molting gland (Y-organ or YO) and eye stalk ganglia (ESG), in addition to the hepatopancreas and claw muscle of red king crab. The Halloween genes encoding the ecdysteroidogenic enzymes were expressed in YO, and the ESG contained multiple neuropeptides, including molt-inhibiting hormone (MIH), crustacean hyperglycemic hormone (CHH), and ion-transport peptide (ITP). Both crabs expressed a diversity of growth-related factors, such as mTOR, AKT, Rheb and AMPKα, and stress-responsive factors, including multiple heat shock proteins (HSPs). Temperature effects on the expression of key regulatory genes were quantified by qPCR in adult red king crab males kept at 4 °C or 10 °C for two weeks during intermolt. The Halloween genes tended to be upregulated in YO at high temperature, while the ecdysteroid receptor and several growth regulators showed tissue-specific responses to elevated temperature. Constitutive and heat-inducible HSPs were expressed in an inverse temperature-dependent manner, suggesting that adult red king crabs can acclimate to increased water temperatures.

Consequences of combined exposure to thermal stress and the plasticiser DEHP in Mytilus spp. differ by sex

Little is known about the combined effect of environmental factors and contaminants on commercially important marine species, and whether this effect differs by sex. In this study, blue mussels were exposed for seven days to both single and combined stressors (i.e., +3 °C elevated temperature and two environmentally relevant concentrations of the plastic softener DEHP, 0.5 and 50 μg/l) in a factorial design. Males were observed to be more sensitive to high temperature, demonstrated by the significant increase in out-of-season spawning gonads and higher gene expression of the antioxidant catalase and the estrogen receptor genes. On the other hand, while the gametogenesis cycle in females was more resilient than in males, DEHP exposure altered the estrogen-related receptor gene expression. We show that the combined stressors DEHP and increased temperature, in environmentally relevant magnitudes, have different consequences in male and female mussels, with the potential to impact the timing and breeding season success in Mytilus spp.

Divergence in Thermal Physiology Could Contribute to Vertical Segregation in Intertidal Ecotypes of Littorina saxatilis

AbstractThermal stress is a potentially important selective agent in intertidal marine habitats, but the role that thermal tolerance might play in local adaptation across shore height has been underexplored. Northwest Spain is home to two morphologically distinct ecotypes of the periwinkle Littorina saxatilis, separated by shore height and subject to substantial differences in thermal stress exposure. However, despite other biotic and abiotic drivers of ecotype segregation being well studied, their thermal tolerance has not been previously characterized. We investigated thermal tolerance across multiple life history stages by employing the thermal death time (TDT) approach to determine (i) whether the two ecotypes differ in thermal tolerance and (ii) how any differences vary with life history stage. Adults of the two ecotypes differed in their thermal tolerance in line with their shore position: the upper-shore ecotype, which experiences more extreme temperatures, exhibited greater endurance of thermal stress compared with the lower-shore ecotype. This difference was most pronounced at the highest temperatures tested. The proximate physiological basis for these differences is unknown but likely due to a multifarious interaction of traits affecting different parts of the TDT curve. Differences in tolerance between ecotypes were less pronounced in early life history stages but increased with ontogeny, suggesting partial divergence of this trait during development. Thermal tolerance could potentially play an important role in maintaining population divergence and genetic segregation between the two ecotypes, since the increased thermal sensitivity of the lower-shore ecotype may limit its dispersal onto the upper shore and so restrict gene flow.

Effects of Intertidal Position on Metabolism and Behavior in the Acorn Barnacle, Balanus glandula

The intertidal zone is characterized by persistent, tidally-driven fluctuations in both abiotic (e.g., temperature, oxygen, and salinity) and biotic (e.g., food availability and predation) factors, which make this a physiologically challenging habitat for resident organisms. The relative magnitude and degree of variability of environmental stress differ between intertidal zones, with the most extreme physiological stress often being experienced by organisms in the high intertidal. Given that so many of the constantly shifting parameters in this habitat are primary drivers of metabolic rate (e.g., temperature, [O₂], and food availability), we hypothesized that sessile conspecifics residing in different tidal zones would exhibit distinct “metabolic phenotypes,” a term we use to collectively describe the organisms’ baseline metabolic performance and capacity. To investigate this hypothesis, we collected acorn barnacles (Balanus glandula) from low, mid, and high intertidal positions in San Luis Obispo Bay, CA, and measured a suite of biochemical (whole-animal citrate synthase (CS) and lactate dehydrogenase (LDH) activity, and aerial [D-lactate]), physiological (O₂ consumption rates), morphological (body size), and behavioral (e.g., cirri beat frequency and percentage of time operculum open) indices of metabolism. We found tidal zone-dependent differences in B. glandula metabolism that primarily related to anaerobic capacity, cirral activity patterns, and body size. Barnacles from the low intertidal tended to have a greater capacity for anaerobic metabolism (i.e., increased LDH activity and increased baseline [D-lactate]), have reduced cirral beating activity—and presumably reduced feeding—when submerged, and be smaller in size compared to conspecifics in the high intertidal. We did not, however, see any D-lactate accumulation in barnacles from any tidal height throughout 96 h of air exposure. This trend indicates that the enhanced capacity of low intertidal barnacles for anaerobic metabolism may have evolved to support metabolism during more prolonged episodes of emersion or during events other than emersion (e.g., coastal hypoxia and predation). There were also no significant differences in CS activity or baseline O₂ consumption rates (in air or seawater at 14°C) across tidal heights, which imply that aerobic metabolic capacity may not be as sensitive to tidal position as anaerobic processes. Understanding how individuals occupying different shore heights differ in their metabolic capacity becomes increasingly interesting in the context of global climate change, given that the intertidal zone is predicted to experience even greater extremes in abiotic stress.

Survival and gene expression responses in immune challenged larval lake sturgeon

Larval lake sturgeon, Acipenser fulvescens, reared in hatcheries for stock enhancement of wild populations may be susceptible to early opportunistic bacterial infection. Thus, we examined survival and whole-body mRNA expression of both stress- and immune-related genes (MyD88, IL-1β, StAR, GR1, and HSP70) in 30 days post fertilization larval lake sturgeon following immune challenge with lipopolysaccharides (LPS). Larval sturgeon were exposed to 0, 25, 50, 100, 150, and 200 μg ml^-1 LPS and sampled after 30 min, 4 h, and 48 h. Mortality was zero in 0 and 25 μg ml^-1 LPS; 37.5% in 50 μg ml^-1 LPS and 100% in the higher concentrations. Expression of MyD88 and StAR mRNA were positively correlated and increased with time in the 50 μg ml^-1 LPS treatment. There was an influence of both treatment and time on IL-1β mRNA, with expression 10-fold higher than controls after 4 h. Expression of HSP70 mRNA was suppressed within 30 min of 50 μg ml^-1 LPS exposure and remained so throughout the time course. Correlated mRNA expression of GR1 with MyD88, StAR and IL-1β suggests a potential relationship between the innate immune and glucocorticoid responses of larval lake sturgeon during this early developmental stage. Data presented suggest that larval lake sturgeon largely responded with predicted changes in gene expression of immune related and stress response genes following LPS challenge. This study provides a foundation for future research examining the effects of hatchery and naturally occurring stressors on the immune responses of larval lake sturgeon.

Regulate or tolerate: Thermal strategy of a coral reef flat resident, the epaulette shark, Hemiscyllium ocellatum

Highly variable thermal environments, such as coral reef flats, are challenging for marine ectotherms and are thought to invoke the use of behavioural strategies to avoid extreme temperatures and seek out thermal environments close to their preferred temperatures. Common to coral reef flats, the epaulette shark (Hemiscyllium ocellatum) possesses physiological adaptations to hypoxic and hypercapnic conditions, such as those experienced on reef flats, but little is known regarding the thermal strategies used by these sharks. We investigated whether H. ocellatum uses behavioural thermoregulation (i.e., movement to occupy thermally favourable microhabitats) or tolerates the broad range of temperatures experienced on the reef flat. Using an automated shuttlebox system, we determined the preferred temperature of H. ocellatum under controlled laboratory conditions and then compared this preferred temperature to 6 months of in situ environmental and body temperatures of individual H. ocellatum across the Heron Island reef flat. The preferred temperature of H. ocellatum under controlled conditions was 20.7 ± 1.5°C, but the body temperatures of individual H. ocellatum on the Heron Island reef flat mirrored environmental temperatures regardless of season or month. Despite substantial temporal variation in temperature on the Heron Island reef flat (15-34°C during 2017), there was a lack of spatial variation in temperature across the reef flat between sites or microhabitats. This limited spatial variation in temperature creates a low-quality thermal habitat limiting the ability of H. ocellatum to behaviourally thermoregulate. Behavioural thermoregulation is assumed in many shark species, but it appears that H. ocellatum may utilize other physiological strategies to cope with extreme temperature fluctuations on coral reef flats. While H. ocellatum appears to be able to tolerate acute exposure to temperatures well outside of their preferred temperature, it is unclear how this, and other, species will cope as temperatures continue to rise and approach their critical thermal limits. Understanding how species will respond to continued warming and the strategies they may use will be key to predicting future populations and assemblages.

Blood biochemical status of deep-sea sharks following longline capture in the Gulf of Mexico

Prior to the Deepwater Horizon (DWH) oil spill, little research effort was focused on studying deep-sea sharks in the Gulf of Mexico (GoM). While the biology of these fishes remains virtually unknown, they are routinely captured in commercial fisheries as bycatch. In the absence of basic biological data, and with the probability of post-release survival unknown for most species, effective management plans cannot be formulated, making populations highly susceptible to overfishing. Any potential detrimental effects of the DWH oil spill, which occurred at 1500 m deep, are also unknown. Following longline capture, we characterized the physiological blood biochemical parameters related to secondary stress and compared them among seven shark species occurring on the continental shelf edge and slope in the GoM at depths ranging from 200 to 2000 m. We also investigated the relationship between blood parameters and depth as well as proximity to the oil spill site. The deep-sea sharks examined here exhibited variability in blood chemistry associated with the secondary stress response, with values falling within published records for previously studied elasmobranchs. Results suggested that there is greater relative physiological stress in shallower-dwelling sharks as well as smaller-bodied sharks. Further, the rate of core temperature warming was fastest in smaller bodied sharks, which likely contributes to greater physiological stress. The core temperatures of the larger-bodied, deeper-dwelling species were not altered as drastically as the smaller-bodied sharks after being hauled to the surface. Any chronic physiological effects of the oil spill were not detectable as there were no relevant correlations between blood chemistry metrics and proximity to the DWH oil spill site.

Allele-Specific Expression and Evolution of Gene Regulation Underlying Acute Heat Stress Response and Local Adaptation in the Copepod Tigriopus californicus

Geographic variation in environmental temperature can select for local adaptation among conspecific populations. Divergence in gene expression across the transcriptome is a key mechanism for evolution of local thermal adaptation in many systems, yet the genetic mechanisms underlying this regulatory evolution remain poorly understood. Here we examine gene expression in 2 locally adapted Tigriopus californicus populations (heat tolerant San Diego, SD, and less tolerant Santa Cruz, SC) and their F1 hybrids during acute heat stress response. Allele-specific expression (ASE) in F1 hybrids was used to determine cis-regulatory divergence. We found that the number of genes showing significant allelic imbalance increased under heat stress compared to unstressed controls. This suggests that there is significant population divergence in cis-regulatory elements underlying heat stress response. Specifically, the number of genes showing an excess of transcripts from the more thermal tolerant (SD) population increased with heat stress while that number of genes with an SC excess was similar in both treatments. Inheritance patterns of gene expression also revealed that genes displaying SD-dominant expression phenotypes increase in number in response to heat stress; that is, across loci, gene expression in F1's following heat stress showed more similarity to SD than SC, a pattern that was absent in the control treatment. The observed patterns of ASE and inheritance of gene expression provide insight into the complex processes underlying local adaptation and thermal stress response.

Spatial modeling of exposure of mangrove ecosystems to multiple environmental hazards

Determining the level of ecosystems exposure to multiple environmental hazards or risk factors is of paramount importance for developing, adopting, and planning management strategies to minimize the harmful effects of these hazards. We quantified the level of exposure of mangroves on the northern coasts of the Persian Gulf (PG) and the Gulf of Oman (GO) between 1986 and 2019 to eight environmental hazards, i.e., drought, maximum temperatures, rising sea levels, change of freshwater inflows to coasts, extreme storm surges, significant wave height (SWH), seaward edge retreat in the mangroves, and fishery intensity. Based on expert opinion, fuzzy weights were used to integrate these exposures into a single index (EI) for the region. Experts gave the greatest weight/importance to the risks posed by sea-level rise and seaward retreat of mangroves and the lowest risk to significant wave height and fishery intensity in coastal waters. The overall EI and six of eight individual variables (except fishery intensity and maximum temperatures) pointed to exposure levels of mangroves that increased from the coasts of the PG (EI 0.69) to the GO (EI 6.69). Since these hazards are expected to continue in the future, local/regional management responses should focus on minimizing regional anthropogenic threats and halt conversion of natural areas to agricultural and open areas to maintain freshwater inputs to coastal areas, particularly on the GO. Further, uplands that may serve as future refugia into which mangroves may expand over time as sea levels continue to rise should be protected from development. This was the first study that used an analytic framework to compute a mangrove exposure index to a suite of physical and socio-economic hazards across a region. This framework may provide insights into cost-effective resilience-based design and management of socio-ecologically coupled ecosystems in an era of increasing types and intensities of environmental hazards.

Effects of acclimation temperature on the thermal physiology in two geographically distinct populations of lake sturgeon (Acipenser fulvescens)

Temperature is one of the most important abiotic factors regulating development and biological processes in ectotherms. By 2050, climate change may result in temperature increases of 2.1-3.4°C in Manitoba, Canada. Lake sturgeon, Acipenser fulvescens, from both northern and southern populations in Manitoba were acclimated to 16, 20 and 24°C for 30 days, after which critical thermal maximum (CTmax) trials were conducted to investigate their thermal plasticity. We also examined the effects of temperature on morphological and physiological indices. Acclimation temperature significantly influenced the CTmax, body mass, hepatosomatic index, metabolic rate and the mRNA expression of transcripts involved in the cellular response to heat shock and hypoxia (HSP70, HSP90a, HSP90b, HIF-1α) in the gill of lake sturgeon. Population significantly affected the above phenotypes, as well as the mRNA expression of Na+/K+ ATPase-α1 and the hepatic glutathione peroxidase enzyme activity. The southern population had an average CTmax that was 0.71 and 0.45°C higher than the northern population at 20 and 24°C, respectively. Immediately following CTmax trials, mRNA expression of HSP90a and HIF-1α was positively correlated with individual CTmax of lake sturgeon across acclimation treatments and populations (r = 0.7, r = 0.62, respectively; P < 0.0001). Lake sturgeon acclimated to 20 and 24°C had decreased hepatosomatic indices (93 and 244% reduction, respectively; P < 0.0001) and metabolic suppression (27.7 and 42.1% reduction, respectively; P < 0.05) when compared to sturgeon acclimated to 16°C, regardless of population. Glutathione peroxidase activity and mRNA expression Na+/K+ ATPase-α1 were elevated in the northern relative to the southern population. Acclimation to 24°C also induced mortality in both populations when compared to sturgeon acclimated to 16 and 20°C. Thus, increased temperatures have wide-ranging population-specific physiological consequences for lake sturgeon across biological levels of organization.

Induction of Heat Shock Protein Genes is the Hallmark of Egg Heat Tolerance in Agasicles hygrophila (Coleoptera: Chrysomelidae)

Insects are ecotothermic organisms. Their development, survival, reproduction as well as distribution and abundance are affected by temperature. Heat shock protein (HSP) gene expression is closely associated with temperature variation and influences the adaptation of organisms to adverse environments. The beetle Agasicles hygrophila has successfully been used for biological control of the invasive plant alligator weed (Alternanthera philoxeroides). As A. hygrophila populations are substantially inhibited by high temperatures in the summer, increasing global temperatures may limit the efficacy of this control agent. We previously established that A. hygrophila eggs have low tolerance to heat and this factored into the decreased numbers of A. hygrophila beetles at temperatures of 37.5°C and above. Here, we identified 26 HSP genes in A. hygrophila and examined the relationship between the transcript levels of these genes and heat tolerance. The temperature at which the expression of these 21 HSP genes peaked (Tpeak) was 37.5°C, which is in line with the limit of the high temperatures that A. hygrophila eggs tolerate. Therefore, we speculate that the Tpeak of HSP gene expression in eggs indicates the upper limit of temperatures that A. hygrophila eggs tolerate. This study identifies HSP genes as potential robust biomarkers and emphasizes that determining species' heat tolerance in their natural habitats remains an important consideration for biocontrol. HSP gene expression data provide information about a species' heat tolerance and may be used to predict its geographical distribution.

Sub-lethal temperature thresholds indicate acclimation and physiological limits in brook trout Salvelinus fontinalis

The upper thermal tolerance of brook trout Salvelinus fontinalis was estimated using critical thermal maxima (CT_max ) experiments on fish acclimated to temperatures that span the species' thermal range (5-25°C). The CT_max increased with acclimation temperature but plateaued in fish acclimated to 20, 23 and 25°C. Plasma lactate was highest, and the hepato-somatic index (I_H ) was lowest at 23 and 25°C, which suggests additional metabolic costs at those acclimation temperatures. The results suggest that there is a sub-lethal threshold between 20 and 23°C, beyond which the fish experience reduced physiological performance.

Living on the upper intertidal mudflat: Different behavioral and physiological responses to high temperature between two sympatric cerithidea snails with divergent habitat-use strategies

Temperature plays a major role in controlling species' distributions, and small-scale variation in the thermal environment are potentially an important factor that governs distributions on a local scale. For untangling the roles of behavioral and physiological adaptations on species' distribution at a small-scale level, we carried out a comparative study of two mudflat snails (genus Cerithidea) by determining these congeners' burying behavior, lethal temperature, cardiac performance and heat-shock protein (hsp70) gene expression. These two sympatric snails occupy different microhabitats on the upper intertidal mudflat. During periods of emersion, C. cingulata inhabits the open mudflat and C. largillierti usually aggregates around small rocks on the upper intertidal mudflat. Our results indicate that the two Cerithidea congeners show different behavioral and physiological responses to high temperature. Compared to C. largillierti, C. cingulata prefers to bury into the mud, has a higher thermal limit and a higher level of inducible expression of hsp70 mRNA, implying important roles of behavioral and physiological adaptations to the harsh thermal environment on the open mudflat. Furthermore, results of generalized additive modelling (GAM) analysis of cardiac performance and coefficient of variation (CV) of hsp70 mRNA expression showed high inter-individual variation in C. cingulata. These results highlight the importance of behavioral and physiological adaptions in sympatric species' distributions on the mudflat and help to shed light on the mechanisms of how small-scale differences in the thermal environment shape sympatric species' distributions.

Characterizing biogeochemical fluctuations in a world of extremes: A synthesis for temperate intertidal habitats in the face of global change

Coastal and intertidal habitats are at the forefront of anthropogenic influence and environmental change. The species occupying these habitats are adapted to a world of extremes, which may render them robust to the changing climate or more vulnerable if they are at their physiological limits. We characterized the diurnal, seasonal and interannual patterns of flux in biogeochemistry across an intertidal gradient on a temperate sandstone platform in eastern Australia over 6 years (2009-2015) and present a synthesis of our current understanding of this habitat in context with global change. We used rock pools as natural mesocosms to determine biogeochemistry dynamics and patterns of eco-stress experienced by resident biota. In situ measurements and discrete water samples were collected night and day during neap low tide events to capture diurnal biogeochemistry cycles. Calculation of pH_T using total alkalinity (TA) and dissolved inorganic carbon (DIC) revealed that the mid-intertidal habitat exhibited the greatest flux over the years (pH_T 7.52-8.87), and over a single tidal cycle (1.11 pH_T units), while the low-intertidal (pH_T 7.82-8.30) and subtidal (pH_T 7.87-8.30) were less variable. Temperature flux was also greatest in the mid-intertidal (8.0-34.5°C) and over a single tidal event (14°C range), as typical of temperate rocky shores. Mean TA and DIC increased at night and decreased during the day, with the most extreme conditions measured in the mid-intertidal owing to prolonged emersion periods. Temporal sampling revealed that net ecosystem calcification and production were highest during the day and lowest at night, particularly in the mid-intertidal. Characterization of biogeochemical fluctuations in a world of extremes demonstrates the variable conditions that intertidal biota routinely experience and highlight potential microhabitat-specific vulnerabilities and climate change refugia.

Ecological change in dynamic environments: Accounting for temporal environmental variability in studies of ocean change biology

The environmental conditions in the ocean have long been considered relatively more stable through time compared to the conditions on land. Advances in sensing technologies, however, are increasingly revealing substantial fluctuations in abiotic factors over ecologically and evolutionarily relevant timescales in the ocean, leading to a growing recognition of the dynamism of the marine environment as well as new questions about how this dynamism may influence species' vulnerability to global environmental change. In some instances, the diurnal or seasonal variability in major environmental change drivers, such as temperature, pH and seawater carbonate chemistry, and dissolved oxygen, can exceed the changes expected with continued anthropogenic global change. While ocean global change biologists have begun to experimentally test how variability in environmental conditions mediates species' responses to changes in the mean, the extensive literature on species' adaptations to temporal variability in their environment and the implications of this variability for their evolutionary responses has not been well integrated into the field. Here, we review the physiological mechanisms underlying species' responses to changes in temperature, pCO₂ /pH (and other carbonate parameters), and dissolved oxygen, and discuss what is known about behavioral, plastic, and evolutionary strategies for dealing with variable environments. In addition, we discuss how exposure to variability may influence species' responses to changes in the mean conditions and highlight key research needs for ocean global change biology.

High Heat Tolerance Is Negatively Correlated with Heat Tolerance Plasticity in Nudibranch Mollusks

Rapid ocean warming may alter habitat suitability and population fitness for marine ectotherms. Susceptibility to thermal perturbations will depend in part on plasticity of a species' upper thermal limits of performance (CT_max). However, we currently lack data regarding CT_max plasticity for several major marine taxa, including nudibranch mollusks, thus limiting predictive responses to habitat warming for these species. In order to determine relative sensitivity to future warming, we investigated heat tolerance limits (CT_max), heat tolerance plasticity (acclimation response ratio), thermal safety margins, temperature sensitivity of metabolism, and metabolic cost of heat shock in nine species of nudibranchs collected across a thermal gradient along the northeastern Pacific coast of California and held at ambient and elevated temperature for thermal acclimation. Heat tolerance differed significantly among species, ranging from 25.4 ° ± 0.5 ° C to 32.2 ° ± 1.8 ° C ( x ¯ ± SD ), but did not vary with collection site within species. Thermal plasticity was generally high ( 0.52 ± 0.06 , x ¯ ± SE ) and was strongly negatively correlated with CT_max in accordance with the trade-off hypothesis of thermal adaptation. Metabolic costs of thermal challenge were low, with no significant alteration in respiration rate of any species 1 h after exposure to acute heat shock. Thermal safety margins, calculated against maximum habitat temperatures, were negative for nearly all species examined ( -8.5 ° ± 5.3 ° C , x ¯ ± CI [confidence interval]). From these data, we conclude that warm adaptation in intertidal nudibranchs constrains plastic responses to acute thermal challenge and that southern warm-adapted species are likely most vulnerable to future warming.

Climate Change Impact in the Ria de Aveiro Lagoon Ecosystem: A Case Study

Climate change and global sea-level rise are major issues of the 21st century. The main goal of this study is to assess the physical and biogeochemical status of the Ria de Aveiro lagoon (Portugal) under future climate scenarios, using a coupled physical/ eutrophication model. The impact on the lagoon ecosystem status of the mean sea level rise (MSLR), the amplitude rise of the M2 tidal constituent (M2R), the changes in the river discharge, and the rising of the air temperature was investigated. Under MSLR and M2R, the results point to an overall salinity increase and water temperature decrease, revealing ocean water dominance. The main lagoon areas presented salinity values close to those of the ocean waters (~34 PSU), while a high range of salinity was presented for the river and the far end areas (20–34 PSU). The water temperature showed a decrease of approximately 0.5–1.5 °C. The responses of the biogeochemical variables reflect the increase of the oceanic inflow (transparent and nutrient-poor water) or the reduction of the river flows (nutrient-rich waters). The results evidenced, under the scenarios, an overall decreasing of the inorganic nitrogen concentration and the carbon phytoplankton concentrations. A warm climate, although increasing the water temperature, does not seem to affect the lagoon’s main status, at least in the frame of the model used in the study.

Differences in induced thermotolerance among populations of Olympia oysters

An organism's ability to cope with thermal stress is an important predictor of survival in a changing climate. One way in which organisms may acclimatize to thermal stress in the short-term is through induced thermotolerance, whereby exposure to a sublethal heat shock enables the organism to subsequently survive what might otherwise be a lethal event. Whether induced thermotolerance is related to basal thermotolerance is not well understood for marine organisms. Furthermore, whether populations often differ in their capacity for induced thermotolerance is also unclear. Here, we tested for differences in basal thermotolerance and induced thermotolerance among six populations of Olympia oysters (Ostrea lurida) from three California estuaries. Oysters were raised under common-garden laboratory conditions for a generation and then exposed to two treatments (control or sublethal heat shock) followed by a spectrum of temperatures that bound the upper critical temperature in order to determine LT₅₀ (temperature at which 50% of the population dies). All populations exhibited induced thermotolerance by increasing their LT₅₀ to a similar maximum temperature when extreme thermal stress was preceded by a sublethal heat shock. However, populations differed in their basal thermotolerance and their plasticity in thermotolerance. Populations with the highest basal thermotolerance were least able to modify upper critical temperature, while the population with the lowest basal thermotolerance exhibited the greatest plasticity in the upper critical temperature. Our results highlight that populations with high basal thermotolerance may be most vulnerable to climate warming because they lack the plasticity required to adjust their upper thermal limits.

Sirtuins as regulators of the cellular stress response and metabolism in marine ectotherms

The effects of climate change are altering the environmental landscape of marine habitats and exposing organisms to stressful conditions that may exceed their tolerance limits. Marine intertidal organisms are well adapted to fluctuating environments by adjusting energy metabolism and inducing the cellular stress response (CSR). Recent studies have shown that food availability can influence stress tolerance of marine ectotherms where a well-fed organism is more "robust" and more likely to survive a stressor than an animal under a low-food regime. We propose that the link between food availability and stress tolerance in marine ectotherms may be regulated by sirtuins, NAD⁺-dependent deacylases. In model organisms sirtuins act as energy sensors and are active under calorie restricted states where they target and regulate cellular metabolism, minimize oxidative stress, and influence the CSR. However, we know little regarding sirtuins in marine ectotherms. Herein we review the current literature on sirtuins in marine ectotherms including marine teleosts, limpets, and mussels. We show that the role of sirtuins in marine ectotherms is conserved from model organisms in regulating the CSR and energy, but the direct connection to NAD⁺ status under fed and starved conditions requires more attention. Although there is a beginning foundation of research regarding sirtuins in marine organisms, it is limited and would benefit from targeted studies investigating sirtuin activity in various tissues and animals under multiple stressors, NAD⁺/NADH levels under various fed states, and by using known sirtuin inhibitors and activators to elucidate the potential targets of sirtuins in marine animals.

An intertidal fish shows thermal acclimation despite living in a rapidly fluctuating environment

The co-evolution of acclimation capacity and thermal performance breadth has been a contentious issue for decades, and little is known regarding the extent to which acclimation alters the shape of acute thermal performance curves. Current acclimation theory suggests that when daily variation is large and unpredictable ectotherms should not acclimate but should evolve wide performance breadths, allowing maintenance of performance across a wide thermal range. The subtropical intertidal zone, however, experiences a large amount of daily thermal variation, but daily means and ranges shift in predictable ways with season, where daily and seasonal variation is roughly equal. We predicted that animals in this habitat would maintain their capacity to acclimate and that performance breadth would not be altered by acclimation to maintain function with rapidly fluctuating daily temperatures. We tested our prediction using a subtropical goby, Bathygobius cocosensis, which lives in tide pools that vary widely, over days and seasons. We exposed B. cocosensis to winter (12-17 °C) and summer (30-35 °C) thermal conditions for six weeks and then measured the thermal dependence of burst swimming speed, routine and maximum metabolic rate, and ventilation rate between 12 and 36 °C. B. cocosensis exhibited an acclimation response for burst swimming speed, maximum metabolic rate and metabolic scope, but acclimation did not alter the shape of acute thermal performance curves. These results indicate that thermal acclimation can occur when short-term thermal variability is large and equal to seasonal variation, and wide performance breadths can be maintained with acclimation in heterogeneous environments.

Behavioural effects of psychoactive pharmaceutical exposure on European perch (Perca fluviatilis) in a multi-stressor environment

With the ability to resist biodegradation and exert therapeutic effects at low concentrations, pharmaceutical contaminants have become environmental stressors for wildlife. One such contaminant is the anxiolytic oxazepam, a psychoactive pharmaceutical that is frequently detected in surface waters globally. Despite growing interest in understanding how wildlife respond to anxiolytics, synergistic effects of pharmaceuticals and other abiotic (e.g. temperature) and biotic (e.g. predation risk) stressors remain unclear. Here, using a multi-stressor approach, we investigated effects of 7-day oxazepam exposure (6.5 μg/L) on anxiety-related behaviours in juvenile European perch (Perca fluviatilis). The multi-stressor approach was achieved by exposing perch to oxazepam at two temperatures (10 °C and 18 °C), and at two predation risk regimes-generated using chemical cues from the northern pike (Esox lucius). Our exposures resulted in a successful uptake of the drug from the water, i.e., oxazepam was measured in perch muscle tissue at 50 ± 17 ng/g (mean ± SD). We found significant oxazepam-induced effects on boldness, with 76.7% of the treated fish entering the white background (i.e. 'exposed' area where exposure to presumed risks are higher) within the first 5 min, compared to 66.6% of the control fish. We also found a significant effect of temperature on total time spent freezing (i.e. staying motionless). Specifically, fish in the low temperature treatments (oxazepam, predation) froze for longer than fish in high temperatures. Our multi-stressor study is the first to uncover how anxiety-related behaviours in wild juvenile fish are altered by changes in water temperature and perceived predation risk. Importantly, our findings highlight the need to focus on multiple stressors to improve understanding of how organisms not only survive, but adapt to, human-induced environmental change.

Non-reversible and Reversible Heat Tolerance Plasticity in Tropical Intertidal Animals: Responding to Habitat Temperature Heterogeneity

The theory for thermal plasticity of tropical ectotherms has centered on terrestrial and open-water marine animals which experience reduced variation in diurnal and seasonal temperatures, conditions constraining plasticity selection. Tropical marine intertidal animals, however, experience complex habitat thermal heterogeneity, circumstances encouraging thermal plasticity selection. Using the tropical rocky-intertidal gastropod, Echinolittorina malaccana, we investigated heat tolerance plasticity in terms of laboratory acclimation and natural acclimatization of populations from thermally-dissimilar nearby shorelines. Laboratory treatments yielded similar capacities of snails from either population to acclimate their lethal thermal limit (LT50 variation was ∼2°C). However, the populations differed in the temperature range over which acclimatory adjustments could be made; LT50 plasticity occurred over a higher temperature range in the warm-shore snails compared to the cool-shore snails, giving an overall acclimation capacity for the populations combined of 2.9°C. In addition to confirming significant heat tolerance plasticity in tropical intertidal animals, these findings reveal two plasticity forms, reversible (laboratory acclimation) and non-reversible (population or shoreline specific) plasticity. The plasticity forms should account for different spatiotemporal scales of the environmental temperature variation; reversible plasticity for daily and tidal variations in microhabitat temperature and non-reversible plasticity for lifelong, shoreline temperature conditions. Non-reversible heat tolerance plasticity, likely established after larvae settle on the shore, should be energetically beneficial in preventing heat shock protein overexpression, but also should facilitate widespread colonization of coasts that support thermally-diverse shorelines. This first demonstration of different plasticity forms in benthic intertidal animals supports the hypothesis that habitat heterogeneity (irrespective of latitude) drives thermal plasticity selection. It further suggests that studies not making reference to different spatial scales of thermal heterogeneity, nor seeking how these may drive different thermal plasticity forms, risk misinterpreting ectothermic responses to environmental warming.

High thermal stress responses of Echinolittorina snails at their range edge predict population vulnerability to future warming

Populations at the edge of their species' distribution ranges are typically living at the physiological extreme of the environmental conditions they can tolerate. As a species' response to global change is likely to be largely determined by its physiological performance, subsequent changes in environmental conditions can profoundly influence populations at range edges, resulting in range extensions or retractions. To understand the differential physiological performance among populations at their distribution range edge and center, we measured levels of mRNA for heat shock protein 70 (hsp70) as an indicator of temperature sensitivity in two high-shore littorinid snails, Echinolittorina malaccana and E. radiata, between 1°N to 36°N along the NW Pacific coast. These Echinolittorina snails are extremely heat-tolerant and frequently experience environmental temperatures in excess of 55 °C when emersed. It was assumed that animals exhibiting high temperature sensitivity will synthesize higher levels of mRNA, which will thus lead to higher energetic costs for thermal defense. Populations showed significant geographic variation in temperature sensitivity along their range. Snails at the northern range edge of E. malaccana and southern range edge of E. radiata exhibited higher levels of hsp70 expression than individuals collected from populations at the center of their respective ranges. The high levels of hsp70 mRNA in populations at the edge of a species' distribution range may serve as an adaptive response to locally stressful thermal environments, suggesting populations at the edge of their distribution range are potentially more sensitive to future global warming.

Comparing mutagenesis and simulations as tools for identifying functionally important sequence changes for protein thermal adaptation

Comparative studies of orthologous proteins of species evolved at different temperatures have revealed consistent patterns of temperature-related variation in thermal stabilities of structure and function. However, the precise mechanisms by which interspecific variations in sequence foster these adaptive changes remain largely unknown. Here, we compare orthologs of cytosolic malate dehydrogenase (cMDH) from marine molluscs adapted to temperatures ranging from -1.9 °C (Antarctica) to ∼55 °C (South China coast) and show how amino acid usage in different regions of the enzyme (surface, intermediate depth, and protein core) varies with adaptation temperature. This eukaryotic enzyme follows some but not all of the rules established in comparisons of archaeal and bacterial proteins. To link the effects of specific amino acid substitutions with adaptive variations in enzyme thermal stability, we combined site-directed mutagenesis (SDM) and in vitro protein experimentation with in silico mutagenesis using molecular dynamics simulation (MDS) techniques. SDM and MDS methods generally but not invariably yielded common effects on protein stability. MDS analysis is shown to provide insights into how specific amino acid substitutions affect the conformational flexibilities of mobile regions (MRs) of the enzyme that are essential for binding and catalysis. Whereas these substitutions invariably lie outside of the MRs, they effectively transmit their flexibility-modulating effects to the MRs through linked interactions among surface residues. This discovery illustrates that regions of the protein surface lying outside of the site of catalysis can help establish an enzyme's thermal responses and foster evolutionary adaptation of function.

Evolution in chronic cold: varied loss of cellular response to heat in Antarctic notothenioid fish

Background

Confined within the freezing Southern Ocean, the Antarctic notothenioids have evolved to become both cold adapted and cold specialized. A marked signature of cold specialization is an apparent loss of the cellular heat shock response (HSR). As the HSR has been examined in very few notothenioid species to-date, it remains unknown whether HSR loss pervades the Antarctic radiation, or whether the broader cellular responses to heat stress has sustained similar loss. Understanding the evolutionary status of these responses in this stenothermal taxon is crucial for evaluating its adaptive potential to ocean warming under climate change.

Results

In this study, we used an acute heat stress protocol followed by RNA-Seq analyses to study the evolution of cellular-wide transcriptional responses to heat stress across three select notothenioid lineages - the basal temperate and nearest non-Antarctic sister species Eleginops maclovinus serving as ancestral proxy, the cryopelagic Pagothenia borchgrevinki and the icefish Chionodraco rastrospinosus representing cold-adapted red-blooded and hemoglobinless Antarctic notothenioids respectively. E. maclovinus displayed robust cellular stress responses including the ER Unfolded Protein Response and the cytosolic HSR, cementing the HSR as a plesiomorphy that preceded Antarctic notothenioid radiation. While the transcriptional response to heat stress was minimal in P. borchgrevinki, C. rastrospinosus exhibited robust responses in the broader cellular networks especially in inflammatory responses despite lacking the classic HSR and UPR.

Conclusion

The disparate patterns observed in these two archetypal Antarctic species indicate the evolutionary status in cellular ability to mitigate acute heat stress varies even among Antarctic lineages, which may affect their adaptive potential in coping with a warming world.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1254-6) contains supplementary material, which is available to authorized users.

Influence of respiratory mode on the thermal tolerance of intertidal limpets

Predicting ecological responses to climate change requires an understanding of the mechanisms that influence species' tolerances to temperature. Based on the idea that air and water breathing animals are differentially suited to life in either medium due to differences in their respiratory morphology, we examined the possibility that the thermal tolerances of co-existing intertidal pulmonate and patellogastropod limpets may differ in different breathing media. We tested this by determining each species' median lethal temperature (LT50) and cardiac Arrhenius breakpoint temperature (ABT) as measures of upper thermal tolerance limits, in air and water. Although all these species can survive in air and water, we hypothesised that the pulmonate limpets, Siphonaria capensis and S. serrata, would have higher thermal limits than the patellogastropod limpets, Cellana capensis and Scutellastra granularis, in air and vice versa in water. The results did not support our hypotheses, since C. capensis had similar thermal tolerance limits to the pulmonate limpets in air and the pulmonate limpets had thermal tolerance limits similar to or higher than S. granularis in water. Thus, considering pulmonate and patellid limpets as groups, we found no differences in their collective upper thermal tolerance limits in either medium. We conclude that differences between these two limpet groups in their respiratory morphology do not influence thermal tolerance, but that tolerances are species-specific.