The use of stress-70 proteins in physiology: a re-appraisal

Evaluation of the osmoregulatory capacity and three stress biomarkers in white shrimp Penaeus vannamei exposed to different temperature and salinity conditions: Na+/K+ ATPase, Heat Shock Proteins (HSP), and Crustacean Hyperglycemic Hormones (CHHs)

Salinity and temperature influence growth, survival, and reproduction of crustacean species such as Penaeus vannamei where Na +/K+-ATPase plays a key role in maintaining osmotic homeostasis in different salinity conditions. This ability is suggested to be mediated by other proteins including neuropeptides such as the crustacean hyperglycemic hormones (CHHs), and heat shock proteins (HSPs). The mRNA expression of Na+/K+-ATPase, HSP60, HSP70, CHH-A, and CHH-B1, was analyzed by qPCR in shrimp acclimated to different salinities (10, 26, and 40 PSU) and temperature conditions (20, 23, 26, 29, and 32 °C) to evaluate their uses as molecular stress biomarkers. The results showed that the hemolymph osmoregulatory capacity in shrimp changed with exposure to the different salinities. From 26 to 32 °C the Na+/K+-ATPase expression increased significantly at 10 PSU relative to shrimp acclimated at 26 PSU and at 20 °C increased at similar values independently of salinity. The highest HSP expression levels were obtained by HSP70 at 20 °C, suggesting a role in protecting proteins such as Na+/K+ -ATPase under low-temperature and salinity conditions. CHH-A was not expressed in the gill under any condition, but CHH-B1 showed the highest expression at the lowest temperatures and salinities, suggesting its participation in the Na+/K+-ATPase induction. Since Na+/K+-ATPase, HSPs, and CHHs seem to participate in maintaining the osmo-ionic balance and homeostasis in P. vannamei, their expression levels may be used as a stress biomarkers to monitor marine crustacean health status when acclimated in low salinity and temperature conditions.

A Review on the Involvement of Heat Shock Proteins (Extrinsic Chaperones) in Response to Stress Conditions in Aquatic Organisms

Heat shock proteins (HSPs) encompass both extrinsic chaperones and stress proteins. These proteins, with molecular weights ranging from 14 to 120 kDa, are conserved across all living organisms and are expressed in response to stress. The upregulation of specific genes triggers the synthesis of HSPs, facilitated by the interaction between heat shock factors and gene promoter regions. Notably, HSPs function as chaperones or helper molecules in various cellular processes involving lipids and proteins, and their upregulation is not limited to heat-induced stress but also occurs in response to anoxia, acidosis, hypoxia, toxins, ischemia, protein breakdown, and microbial infection. HSPs play a vital role in regulating protein synthesis in cells. They assist in the folding and assembly of other cellular proteins, primarily through HSP families such as HSP70 and HSP90. Additionally, the process of the folding, translocation, and aggregation of proteins is governed by the dynamic partitioning facilitated by HSPs throughout the cell. Beyond their involvement in protein metabolism, HSPs also exert a significant influence on apoptosis, the immune system, and various characteristics of inflammation. The immunity of aquatic organisms, including shrimp, fish, and shellfish, relies heavily on the development of inflammation, as well as non-specific and specific immune responses to viral and bacterial infections. Recent advancements in aquatic research have demonstrated that the HSP levels in populations of fish, shrimp, and shellfish can be increased through non-traumatic means such as water or oral administration of HSP stimulants, exogenous HSPs, and heat induction. These methods have proven useful in reducing physical stress and trauma, while also facilitating sustainable husbandry practices such as vaccination and transportation, thereby offering health benefits. Hence, the present review discusses the importance of HSPs in different tissues in aquatic organisms (fish, shrimp), and their expression levels during pathogen invasion; this gives new insights into the significance of HSPs in invertebrates.

Temperature alters the oxidative and metabolic biomarkers and expression of environmental stress-related genes in chocolate mahseer (Neolissochilus hexagonolepis)

Long-term acclimation temperature effects on biomarkers of oxidative stress, metabolic stress, expression of heat shock proteins (Hsps), and warm-temperature acclimation related 65-kDa protein (Wap65) were evaluated in the threatened chocolate mahseer (Neolissochilus hexagonolepis). Fifteen-day-old larvae were acclimated to different water temperatures (15, 19, 23-control group, 27, and 31 °C) for 60 days prior to the sampling for quantification of mRNA, enzyme, nitric oxide, and malondialdehyde (MDA) content. Acclimation to 31 °C increased the basal mRNA level of glutathione S-transferase alpha 1 (GSTa1), and activities of catalase (CAT), glutathione reductase (GR), and GST enzymes and but downregulated the expression of superoxide dismutase 1 (SOD1) in the whole-body homogenate. Other antioxidant genes, i.e., CAT and GPx1a, were unaffected at 31 °C, and nitric oxide (NO) concentration was significantly lower. In contrast, fish acclimated to 15 °C showed an upregulated transcript level of all the antioxidant genes and no significant difference in the CAT, GR, and GST enzymes. Activities of the metabolic enzymes, aspartate transaminase (AST) and alanine transaminase (ALT), were significantly lower at 15 °C. The expression of Hsp47 was upregulated at both 15 and 31 °C groups, whereas Hsp70 was elevated at 27 and 31 °C groups. Wap65-1 transcription did not show significant variation in treatment groups compared to control. Fish in the high (31 °C) and low-temperature (15 °C) acclimation groups were capable of maintaining oxidative stress by modulating their antioxidant transcripts, enzymes, and Hsps.

Do predator (Mystus gulio) and prey (Penaeus monodon) have differential response against heatwaves? Unveiling through oxidative stress biomarkers and thermal tolerance estimation

Extreme climatic events such as heatwaves are anticipated to intensify in future and impose additional thermal stress to aquatic animals. Knowledge regarding an organism's thermal tolerance or sensitivity is therefore important in determining the effects of fluctuating water temperature on physiological responses. Thus, thermal tolerance tests can serve as a first step in understanding the present and future effects of climate warming. Climatic variability will alter prey-predator attributes differentially and impact their subsequent interactions. The key objective of this study was to compare and decode the stress responses, resistance and vulnerability of two economically important species from Sundarbans estuarine system- Penaeus monodon (prey) and Mystus gulio (predator) subjected to acute thermal challenges such as sudden heatwaves. Both the species were subjected to an increasing thermal ramp of 1°C h^-1 from 22°C to 42°C. Organisms were observed continuously throughout the ramping period and changes in the locomotory behaviour were followed until their loss of equilibrium. The digestive tissue samples were dissected out from both M. gulio and P. monodon at every 2°C and also after a recovery period of 48 h. The SOD, CAT, GST, LPO were measured and integrated biomarker response (IBR) was analysed. The results from thermal tolerance maxima estimation, biomarker study, IBR responses indicated more intense stress response in fish M. gulio whereas recovery potential was greater in shrimp P. monodon. Our findings corroborate the 'trophic sensitivity hypothesis' which advocates predators to be less tolerant in aggravated environmental stress than their prey.

Trimethylamine N-Oxide (TMAO) and Trimethylamine (TMA) Determinations of Two Hadal Amphipods

Hadal trenches are a unique habitat with high hydrostatic pressure, low temperature and scarce food supplies. Amphipods are the dominant scavenging metazoan species in this ecosystem. Trimethylamine (TMA) and trimethylamine oxide (TMAO) have been shown to play important roles in regulating osmotic pressure in mammals, hadal dwellers and even microbes. However, the distributions of TMAO and TMA concentrations of hadal animals among different tissues have not been reported so far. Here, the TMAO and TMA contents of eight tissues of two hadal amphipods, Hirondellea gigas and Alicella gigantea from the Mariana Trench and the New Britain Trench, were detected by using the ultrahigh performance liquid chromatography–mass spectrometry (UPLC-MS/MS) method. Compared with the shallow water Decapoda, Penaeus vannamei, the hadal amphipods possessed significantly higher TMAO concentrations and a similar level of TMA in all the detected tissues. A higher level of TMAO was detected in the external organs (such as the eye and exoskeleton) for both of the two hadal amphipods, which indicated that the TMAO concentration was not evenly distributed, although the same hydrostatic pressure existed in the outer and internal organs. Moreover, a strong positive correlation was found between the concentrations of TMAO and TMA in the two hadal amphipods. In addition, evolutionary analysis regarding FMO3, the enzyme to convert TMA into TMAO, was also conducted. Three positive selected sites in the conserved region and two specific mutation sites in two conserved motifs were found in the A. gigantea FMO3 gene. Combined together, this study supports the important role of TMAO for the environmental adaptability of hadal amphipods and speculates on the molecular evolution and protein structure of FMO3 in hadal species.

Can heat shock protein 70 (HSP70) serve as biomarkers in Antarctica for future ocean acidification, warming and salinity stress?

The Antarctic Peninsula is one of the fastest-warming places on Earth. Elevated sea water temperatures cause glacier and sea ice melting. When icebergs melt into the ocean, it “freshens” the saltwater around them, reducing its salinity. The oceans absorb excess anthropogenic carbon dioxide (CO2) causing decline in ocean pH, a process known as ocean acidification. Many marine organisms are specifically affected by ocean warming, freshening and acidification. Due to the sensitivity of Antarctica to global warming, using biomarkers is the best way for scientists to predict more accurately future climate change and provide useful information or ecological risk assessments. The 70-kilodalton (kDa) heat shock protein (HSP70) chaperones have been used as biomarkers of stress in temperate and tropical environments. The induction of the HSP70 genes (Hsp70) that alter intracellular proteins in living organisms is a signal triggered by environmental temperature changes. Induction of Hsp70 has been observed both in eukaryotes and in prokaryotes as response to environmental stressors including increased and decreased temperature, salinity, pH and the combined effects of changes in temperature, acidification and salinity stress. Generally, HSP70s play critical roles in numerous complex processes of metabolism; their synthesis can usually be increased or decreased during stressful conditions. However, there is a question as to whether HSP70s may serve as excellent biomarkers in the Antarctic considering the long residence time of Antarctic organisms in a cold polar environment which appears to have greatly modified the response of heat responding transcriptional systems. This review provides insight into the vital roles of HSP70 that make them ideal candidates as biomarkers for identifying resistance and resilience in response to abiotic stressors associated with climate change, which are the effects of ocean warming, freshening and acidification in Antarctic organisms.

Acclimation to cyclic hypoxia improves thermal tolerance and copper survival in the caridean shrimp Palaemon varians

In response to the continuous variation of environmental parameters, species must be able to adjust their physiology to overcome stressful conditions, a process known as acclimatization. Numerous laboratory studies have been conducted to understand and describe the mechanisms of acclimation to one environmental stressor (e.g. cyclic hypoxia), but currently our understanding of how acclimation to one stressor can change tolerance to a subsequent stressor is limited. Here, in two different experiments, we used the shrimp Palaemon varians to test how, following 28-days acclimation to cyclic hypoxia (mimicking a cyclic hypoxic regime currently found in its natural habitat), critical thermal maximum (CT_max) and sensitivity to copper (Cu²⁺) exposure (30 mgL^-1) changed in comparison to shrimp acclimated to normoxic conditions and then exposed to thermal stress or Cu²⁺. Acclimation to cyclic hypoxia improved both CT_max (~1 °C higher than controls) and survival to acute Cu²⁺ exposure (~30% higher than controls) and induced significant gene expression changes (i.e. up-regulation of heat shock protein 70 - HSP70, hypoxia inducible factor - HIF, phosphoenolpyruvate carboxykinase - PEPCK, glucose 6-P transporter - G6Pt, metallothionein - Mt, and down-regulation of hemocyanin - Hem) in animals acclimated to cyclic hypoxia. Our results demonstrate how acclimation to cyclic hypoxia improved tolerance to subsequent stressors, highlighting the complexity of predicting organismal performance in variable (i.e. where multiple parameters can simultaneously change during the day) environments.

Variable protein expression in marine-derived filamentous fungus Penicillium chrysogenum in response to varying copper concentrations and salinity

Copper is one of the essential trace dietary minerals for all living organisms, but is potentially toxic at higher concentrations, mainly due to the redox reactions in its transition state. Tolerance of microbes towards copper is primarily attributed to chelation and biosorption. In this study, marine-derived filamentous fungi were evaluated for their ability to remove Cu(ii) from a culture medium. Further, the cellular response of a select isolate to salinity stress (0, 35 and 100 PSU) and Cu(ii) stress (0, 100, and 500 ppm) was studied using the peptide mass fingerprinting technique, which revealed expression of 919 proteins, of which 55 proteins were commonly expressed across all conditions. Housekeeping proteins such as citrate synthase, pyruvate carboxylase, ribosomal proteins, ATP synthases, and more were expressed across all conditions. Reactive oxygen species scavenging proteins such as glutaredoxin, mitochondrial peroxiredoxins and thioredoxins were expressed under Cu(ii) and salinity stresses individually as well as in combination. Up-regulation of glutaredoxin under Cu(ii) stress with fold change values of 18.3 and 13.9 under 100 ppm and 500 ppm of Cu(ii) indicated active scavenging of free radicals to combat oxidative damage. The common mechanisms reported were enzymatic scavenging of free radicals, activation of DNA damage and repair proteins and probable intracellular metal chelation. This indicated multiple stress mechanisms employed by the isolate to combat the singular and synergistic effects of Cu(ii) and salinity stress.

Evaluating bivalve cytoprotective responses and their regulatory pathways in a climate change scenario

Temperature is a relevant abiotic factor affecting physiological performance and distribution of marine animals in natural environments. The changes in global seawater temperatures make it necessary to understand how molecular mechanisms operate under the cumulative effects of global climate change and chemical pollution to promote/hamper environmental acclimatization. Marine mussels are excellent model organisms to infer the impacts of those anthropogenic threats on coastal ecosystems. In this study, Mediterranean mussels (Mytilus galloprovincialis) were exposed to different concentrations of the metal copper (Cu as CuCl₂: 2.5, 5, 10, 20, 40 μg/L) or the antibiotic oxytetracycline (OTC: 0.1, 1, 10, 100, 1000 μg/L) at increasing seawater temperatures (16 °C, 20 °C, 24 °C). Transcriptional modulation of a 70-kDa heat shock protein (HSP70) and of the ABC transporter P-glycoprotein (P-gp, encoded by the ABCB gene) was assessed along with the cAMP/PKA signaling pathway regulating both gene expressions. At the physiological temperature of mussels (16 °C), Cu and OTC induced bimodal changes of cAMP levels and PKA activities in gills of exposed animals. A correlation between OTC- or Cu- induced changes of PKA activity and expression of hsp70 and ABCB was observed. Temperature increases (up to 24 °C) altered ABCB and hsp70 responses to the pollutants and disrupted their relationship with cAMP/PKA modulation, leading to loss of correlation between the biological endpoints. On the whole, the results indicate that temperature may impair the effects of inorganic and organic chemicals on the cAMP/PKA signaling pathway of mussels, in turn altering key molecular mediators of physiological plasticity and cytoprotection.

Evolution of cellular stress response mechanisms

The cellular stress response (CSR) is pervasive to all domains of life. It has shaped the interaction between organisms and their environment since the origin of the first cell. Although the CSR has been subject to a myriad of nuanced modifications in the various branches of life present today, its core features remain preserved. The scientific literature covering the CSR is enormous and the broad scope of this brief overview was challenging. However, it is critical to conceptually understand how cells respond to stress in a holistic sense and to point out how fundamental aspects of the CSR framework are integrated. It was necessary to be extremely selective and not feasible to even mention many interesting and important developments in this expansive field. The purpose of this overview is to sketch out general and emerging CSR concepts with an emphasis on the initial cellular strain resulting from stress (macromolecular damage) and the evolutionarily most highly conserved elements of the CSR. Examples emphasize fish and aquatic invertebrates to highlight what is known in organisms beyond mammals, yeast, and other common models. Nonetheless, select pioneering studies using canonical models are also considered and the concepts discussed are applicable to all cells. More detail on important aspects of the CSR in aquatic animals is provided in the accompanying articles of this special issue.

Histopatology and HSP70 analysis of the midgut of Rhinocricus padbergi (Diplopoda) in the evaluation of the toxicity of two new metallic-insecticides

Millipedes are organisms of the edaphic fauna and have been used as bioindicators for the evaluation of pollutants in the environment, as they are in constant contact with the soil. This study used the millipede Rhinocricus padbergi as surrogate to evaluate the toxicity of two metallic-insecticides that has been developed for leaf-cutting ants management. Millipedes were exposed in terrariums containing different concentrations of the metallic-insecticides and, after periods of 21 and 90 days, three individuals from each terrarium were dissected in order to remove the midgut, the organ where absorption of nutrients and, consequently, toxic substances occurs. The toxic action of the metallic-insecticides was analyzed through qualitative and semi-quantitative analysis of morphophysiological alterations and by quantitative analysis of the HSP70 stress protein. The results showed that the metallic-insecticides may increase HSP70 labeling, although not at all concentrations and periods of exposure. Histopathological alterations were not significant at any concentration, indicating that the cytoprotective action of HSP70 is able to prevent severe damage to the midgut. It is therefore suggested that the metallic-insecticides are not toxic to the species studied here as no toxicity was observed under the conditions tested. In addition, stress protein localization in midgut helps understand how morphophysiological processes can potentially be affected by pesticide exposure.

Applying sunscreens on earthworms: Molecular response of Eisenia fetida after direct contact with an organic UV filter

The use of organic Ultraviolet (UV) filters has increased in the last years, either in sunscreens, other cosmetics, or even food packaging. These filters may end up in soil and water since the Wastewater Treatment Plants may not successfully remove them. Among them, benzophenones are known to act as endocrine disruptors. However, most of the studies are directed towards vertebrates and aquatic invertebrates, while there is a lack of information on the molecular mechanisms affected by these compounds on soil dwelling invertebrates. Here, we study the impact of direct acute (48 h) contact of 4-hydroxybenzophenone (4-OHBP) at two sublethal concentrations (0.02 and 0.2 mg/mL) on gene expression of the earthworm Eisenia fetida. Investigated genes were involved in endocrine pathways, stress response, detoxification mechanisms, genotoxicity, energy metabolism and epigenetics. Three of them were identified for the first time in earthworms. Our results suggest that exposure to 4-OHBP affected endocrine pathways, causing an increase in the Ecdysone receptor gene (EcR) expression. Moreover, the UV filter induced changes in the CuZn superoxide dismutase gene (CuZn SOD), indicating an effect in the stress response. Finally, significant changes were detected for glyceraldehyde-3-phosphate dehydrogenase gene (GAPDH) expression, indicating that energy metabolism is influenced by the 4-OHBP and highlighting the risks of using GAPDH as an internal reference for Real Time PCR.

Description of strongly heat-inducible heat shock protein 70 transcripts from Baikal endemic amphipods

Heat shock proteins/cognates 70 are chaperones essential for proper protein folding. This protein family comprises inducible members (Hsp70s) with expression triggered by the increased concentration of misfolded proteins due to protein-destabilizing conditions, as well as constitutively expressed cognate members (Hsc70s). Previous works on non-model amphipod species Eulimnogammarus verrucosus and Eulimnogammarus cyaneus, both endemic to Lake Baikal in Eastern Siberia, have only revealed a constitutively expressed form, expression of which was moderately further induced by protein-destabilizing conditions. Here we describe heat-inducible hsp70s in these species. Contrary to the common approach of using sequence similarity with hsp/hsc70 of a wide spectrum of organisms and some characteristic features, such as absence of introns within genes and presence of heat shock elements in their promoter areas, the present study is based on next-generation sequencing for the studied or related species followed by differential expression analysis, quantitative PCR validation and detailed investigation of the predicted polypeptide sequences. This approach allowed us to describe a novel type of hsp70 transcripts that overexpress in response to heat shock. Moreover, we propose diagnostic sequence features of this Hsp70 type for amphipods. Phylogenetic comparisons with different types of Hsp/Hsc70s allowed us to suggest that the hsp/hsc70 gene family in Amphipoda diversified into cognate and heat-inducible paralogs independently from other crustaceans. Thus, the cognate and inducible hsp70 types in distant taxa may not be recognized by sequence similarity.

Assessing a species thermal tolerance through a multiparameter approach: the case study of the deep-sea hydrothermal vent shrimp Rimicaris exoculata

Assessing species thermal tolerance requires identification of their thermal strategies and evaluation of their ability to cope with temperature fluctuations. The mobilization of the molecular heat stress response (HSR), which is a proxy for the thermal tolerance, would be part of the strategy of species colonizing highly variable thermal environments. We here investigate multiple parameters of the HSR in the deep-sea vent shrimp Rimicaris exoculata that colonizes such environments. The set points of the HSR induction, compared to those of the coastal species Palaemonetes varians, clearly reflect a high thermotolerance in this species, while the HSR is proved to be rarely mobilized in the R. exoculata natural populations. Finally, the compilation of multiple parameters such as the upper thermal limit and several thresholds of the HSR, as well as thermal behavior observations, allows us to provide a more accurate picture of the combination and complementarity of strategies that can account for the overall thermal tolerance of the species.

Impact of a Heat Shock Protein Impurity on the Immunogenicity of Biotherapeutic Monoclonal Antibodies

Purpose

Anti-drug antibodies can impair the efficacy of therapeutic proteins and, in some circumstances, induce adverse health effects. Immunogenicity can be promoted by aggregation; here we examined the ability of recombinant mouse heat shock protein 70 (rmHSP70) - a common host cell impurity - to modulate the immune responses to aggregates of two therapeutic mAbs in mice.

Methods

Heat and shaking stress methods were used to generate aggregates in the sub-micron size range from two human mAbs, and immunogenicity assessed by intraperitoneal exposure in BALB/c mice.

Results

rmHSP70 was shown to bind preferentially to aggregates of both mAbs, but not to the native, monomeric proteins. Aggregates supplemented with 0.1% rmHSP70 induced significantly enhanced IgG2a antibody responses compared with aggregates alone but the effect was not observed for monomeric mAbs. Dendritic cells pulsed with mAb aggregate showed enhanced IFNγ production on co-culture with T cells in the presence of rmHSP70.

Conclusion

The results indicate a Th1-skewing of the immune response by aggregates and show that murine rmHSP70 selectively modulates the immune response to mAb aggregates, but not monomer. These data suggest that heat shock protein impurities can selectively accumulate by binding to mAb aggregates and thus influence immunogenic responses to therapeutic proteins.

Electronic supplementary material

The online version of this article (10.1007/s11095-019-2586-7) contains supplementary material, which is available to authorized users.

Assessment of muscular energy metabolism and heat shock response of the green abalone Haliotis fulgens (Gastropoda: Philipi) at extreme temperatures combined with acute hypoxia and hypercapnia

The interaction between ocean warming, hypoxia and hypercapnia, suggested by climate projections, may push an organism earlier to the limits of its thermal tolerance window. In a previous study on juveniles of green abalone (Haliotis fulgens), combined exposure to hypoxia and hypercapnia during heat stress induced a lowered critical thermal maximum (CT_max), indicated by constrained oxygen consumption, muscular spams and loss of attachment. Thus, the present study investigated the cell physiology in foot muscle of H. fulgens juveniles exposed to acute warming (18 °C to 32 °C at +3 °C day^-1) under hypoxia (50% air saturation) and hypercapnia (~1000 μatm PCO₂), alone and in combination, to decipher the mechanisms leading to functional loss in this tissue. Under exposure to either hypoxia or hypercapnia, citrate synthase (CS) activity decreased with initial warming, in line with thermal compensation, but returned to control levels at 32 °C. The anaerobic enzymes lactate and tauropine dehydrogenase increased only under hypoxia at 32 °C. Under the combined treatment, CS overcame thermal compensation and remained stable overall, indicating active mitochondrial regulation under these conditions. Limited accumulation of anaerobic metabolites indicates unchanged mode of energy production. In all treatments, upregulation of Hsp70 mRNA was observed already at 30 °C. However, lack of evidence for Hsp70 protein accumulation provides only limited support to thermal denaturation of proteins. We conclude that under combined hypoxia and hypercapnia, metabolic depression allowed the H. fulgens musculature to retain an aerobic mode of metabolism in response to warming but may have contributed to functional loss.

Variability in Protein Expression in Marine-Derived Purpureocillium lilacinum Subjected to Salt and Chromium Stresses

Abiotic factors can cause substantial limitation of growth of microbes. A combination of salinity stress along with chromium (Cr+6), one of the carcinogen, can pose an immediate threat to any living system. To understand how salinity (0, 35 and 100 PSU) and Cr(VI) stress (0, 100 and 500 ppm), affects cells at the molecular level, the cellular response of Purpureocillium lilacinum to the individual as well the combination of both the stresses were studied by peptide mass fingerprinting technique. The study reports 1412 proteins, of which 105 proteins were found to be present across all conditions. The most prevalent functional class expressed was genetic information processing. Proteins involved in free radical scavenging were up-regulated in response to the oxidative stress generated due to both the applied stresses while expression of metal chelators, transporters systems, indicated towards multiple stress tolerance mechanisms to combat synergistic effects of salt and Cr stress.

Transcriptional response of the heat shock gene hsp70 aligns with differences in stress susceptibility of shallow-water corals from the Mediterranean Sea

Shallow-water corals of the Mediterranean Sea are facing a dramatic increase in water temperature due to climate change, predicted to increase the frequency of bleaching and mass mortality events. However, supposedly not all corals are affected equally, as they show differences in stress susceptibility, as suggested by physiological outputs of corals along temperature gradients and under controlled conditions in terms of reproduction, demography, growth, calcification, and photosynthetic efficiency. In this study, gene expression and induction of a 70-kDa heat shock protein (HSP70) was analyzed in five common shallow-water hard corals in the Mediterranean Sea, namely Astroides calycularis, Balanophyllia europaea, Caryophyllia inornata, Cladocora caespitosa, and Leptopsammia pruvoti. The main aim was to assess the contribution of this evolutionary conserved cytoprotective mechanism to the physiological plasticity of these species that possess different growth modes (solitary vs colonial) and trophic strategies (zooxanthellate vs azooxanthellate). Using quantitative real-time PCR, in situ hsp70 baseline levels and expression profiles after a heat-shock exposure were assessed. Levels of hsp70 and heat stress induction were higher in zooxanthellate than in azooxanthellate species, and different heat stress transcriptional profiles were observed between colonial and solitary zooxanthellate corals. On the whole, the hsp70 transcriptional response to heat stress aligns with stress susceptibility of the species and suggests a contribution of trophic strategy and morphology in shaping coral resilience to stress. Understanding these molecular processes may contribute to assess the potential effects and relative resilience of Mediterranean corals under climate change.

Climate change as a possible driver of invasion and differential in HSP70 expression in two genetically distinct populations of the invasive killer shrimp, Dikerogammarus villosus

Global climate change is known to affect physiological processes in charge of cellular stress response. That often results in forcing many organisms to shift their biogeographic distribution ranges. It also holds true for euryoecious and highly invasive species like the killer shrimp, Dikerogammarus villosus. In this study we compare the level of response to thermal stress in two genetically diversified populations of the amphipod D. villosus on the cellular level, namely HSP70 expression. The results show clear difference in HSP70 expression, that can be a direct consequence of the different climatic conditions both populations faced along their invasion routes. We conclude that the eastern population of D. villosus is more sensitive to thermal stress than the western population, hence its invasion potential may be lower than that of the latter. Considering the thermal tolerance of both populations and global warming, we can make some predictions about further spread of D. villosus, including the possibility of an emergence of the super-invader that may arise after cross-breeding of both populations, imposing even larger threat to the freshwater ecosystems.

Seasonal plasticity in photoprotection modulates UV-induced hsp gene expression in copepods from a clear lake

Zooplankton from clear alpine lakes is exposed to stressful levels of solar UV radiation (UVR). As these pelagic organisms experience high UVR and large changes in solar radiation conditions between ice-free and ice-cover periods, they have evolved various strategies to minimize UVR exposure and damage. Here, we studied the relation between photoprotection levels (mycosporine-like amino acids, carotenoids), antioxidant capacities, and gene expression of heat shock proteins (hsps) as indicator of stress in the copepod Cyclops abyssorum tatricus during the course of a year. Expression of hsp60, hsp70, and hsp90 was measured in the field (baseline expression [BE]) and after UVR exposure in the laboratory. The BE differed among genes and seasons (hsp60: high during summer, hsp70 and hsp90: high during the ice-cover period). The gene expression of hsp70 was upregulated after exposure to UVR (up to 5.2-fold change), while hsp60 and hsp90 were only constitutively expressed. A strong seasonal pattern was found in the photoprotective compounds and antioxidant capacities, with highest levels during the ice-free period. The extent of upregulation of hsp70 gene expression increased with decreasing photoprotection levels and peaked 24 h post UVR exposure (9.6-fold change) at the time of lowest photoprotection (February). Our data suggest that hsp70 gene expression is modulated by seasonal plasticity in photoprotection. This ability of adequate stress response is essential for survival in highly variable ecosystems such as alpine lakes.

Metabolic costs imposed by hydrostatic pressure constrain bathymetric range in the lithodid crab Lithodes maja

The changing climate is shifting the distributions of marine species, yet the potential for shifts in depth distributions is virtually unexplored. Hydrostatic pressure is proposed to contribute to a physiological bottleneck constraining depth range extension in shallow-water taxa. However, bathymetric limitation by hydrostatic pressure remains undemonstrated, and the mechanism limiting hyperbaric tolerance remains hypothetical. Here, we assess the effects of hydrostatic pressure in the lithodid crab Lithodes maja (bathymetric range 4-790 m depth, approximately equivalent to 0.1 to 7.9 MPa hydrostatic pressure). Heart rate decreased with increasing hydrostatic pressure, and was significantly lower at ≥10.0 MPa than at 0.1 MPa. Oxygen consumption increased with increasing hydrostatic pressure to 12.5 MPa, before decreasing as hydrostatic pressure increased to 20.0 MPa; oxygen consumption was significantly higher at 7.5-17.5 MPa than at 0.1 MPa. Increases in expression of genes associated with neurotransmission, metabolism and stress were observed between 7.5 and 12.5 MPa. We suggest that hyperbaric tolerance in Lmaja may be oxygen-limited by hyperbaric effects on heart rate and metabolic rate, but that Lmaja's bathymetric range is limited by metabolic costs imposed by the effects of high hydrostatic pressure. These results advocate including hydrostatic pressure in a complex model of environmental tolerance, where energy limitation constrains biogeographic range, and facilitate the incorporation of hydrostatic pressure into the broader metabolic framework for ecology and evolution. Such an approach is crucial for accurately projecting biogeographic responses to changing climate, and for understanding the ecology and evolution of life at depth.

RNA sequencing analysis of transcriptional change in the freshwater mussel Elliptio complanata after environmentally relevant sodium chloride exposure

To identify potential biomarkers of salt stress in a freshwater sentinel species, we examined transcriptional responses of the common mussel Elliptio complanata to controlled sodium chloride (NaCl) exposures. Ribonucleic acid sequencing (RNA-Seq) of mantle tissue identified 481 transcripts differentially expressed in adult mussels exposed to 2 ppt NaCl (1.2 ppt chloride) for 7 d, of which 290 had nonoverlapping intervals. Differentially expressed gene categories included ion and transmembrane transport, oxidoreductase activity, maintenance of protein folding, and amino acid metabolism. The rate-limiting enzyme for synthesis of taurine, an amino acid frequently linked to osmotic stress in aquatic species, was upregulated, as was the transmembrane ion pump sodium/potassium adenosine 5'-triphosphatase. These patterns confirm a primary transcriptional response to the experimental dose, albeit likely overlapping with nonspecific secondary stress responses. Substantial involvement of the heat shock protein 70 chaperone family and the water-transporting aquaporin family was not detected, however, in contrast to some studies in other bivalves. A subset of the most significantly regulated genes was confirmed by quantitative polymerase chain reaction in an independent sample. Cluster analysis showed separation of mussels exposed to 2 ppt NaCl from control mussels in multivariate space, but mussels exposed to 1 ppt NaCl were largely indistinguishable from controls. Transcriptome-scale analysis of salt exposure under laboratory conditions efficiently identified candidate biomarkers for further functional analysis and field validation. Environ Toxicol Chem 2017;36:2352-2366. © Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Physiological plasticity related to zonation affects hsp70 expression in the reef-building coral Pocillopora verrucosa

This study investigates for the first time the transcriptional regulation of a stress-inducible 70-kDa heat shock protein (hsp70) in the scleractinian coral Pocillopora verrucosa sampled at three locations and two depths (3 m and 12 m) in Bangka Island waters (North Sulawesi, Indonesia). Percentage of coral cover indicated reduced habitat suitability with depth and at the Tanjung Husi (TA) site, which also displayed relatively higher seawater temperatures. Expression of the P. verrucosa hsp70 transcript evaluated under field conditions followed a depth-related profile, with relatively higher expression levels in 3-m collected nubbins compared to the 12-m ones. Expression levels of metabolism-related transcripts ATP synthase and NADH dehydrogenase indicated metabolic activation of nubbins to cope with habitat conditions of the TA site at 3 m. After a 14-day acclimatization to common and fixed temperature conditions in the laboratory, corals were subjected for 7 days to an altered thermal regime, where temperature was elevated at 31°C during the light phase and returned to 28°C during the dark phase. Nubbins collected at 12 m were relatively more sensitive to thermal stress, as they significantly over-expressed the selected transcripts. Corals collected at 3 m appeared more resilient, as they showed unaffected mRNA expressions. The results indicated that local habitat conditions may influence transcription of stress-related genes in P. verrucosa. Corals exhibiting higher basal hsp70 levels may display enhanced tolerance towards environmental stressors.

Ultraviolet filters differentially impact the expression of key endocrine and stress genes in embryos and larvae of Chironomus riparius

Several organic UV filters have hormonal activity in vertebrates, as demonstrated in fishes, rodents and human cells. Despite the accumulation of filter contaminants in aquatic systems, research on their effects on the endocrine systems of freshwaters invertebrates is scarce. In this work, the effects of five frequently used UV filters were investigated in embryos and larvae of Chironomus riparius, which is a reference organism in ecotoxicology. LC50 values for larvae as well as the percentage of eclosion of eggs were determined following exposures to: octyl-p-methoxycinnamate (OMC) also known as 2-ethylhexyl-4-methoxycinnamate (EHMC); 4-methylbenzylidene camphor (4MBC); 4-hydroxybenzophenone (4HB); octocrylene (OC); and octyldimethyl-p-aminobenzoate (OD-PABA). To assess sublethal effects, expression levels of the genes coding for the ecdysone receptor (EcR) and heat shock protein HSP70 were investigated as biomarkers for endocrine and stress effects at the cellular level. Life-stage-dependent sensitivity was found. In embryos, all of the UV filters provoked a significant overexpression of EcR at 24h after exposure. OC, 4MBC and OD-PABA also triggered transcriptional activation of the hsp70 stress gene in embryos. In contrast, in larvae, only 4MBC and OMC/EHMC increased EcR and hsp70 mRNA levels and OD-PABA upregulated only the EcR gene. These results revealed that embryos are particularly sensitive to UV filters, which affect endocrine regulation during development. Most UV filters also triggered the cellular stress response, and thus exhibit proteotoxic effects. The differences observed between embryos and larvae and the higher sensitivity of embryos highlight the importance of considering different life stages when evaluating the environmental risks of pollutants, particularly when analyzing endocrine effects.

The evolution of heat shock protein sequences, cis-regulatory elements, and expression profiles in the eusocial Hymenoptera

Background

The eusocial Hymenoptera have radiated across a wide range of thermal environments, exposing them to significant physiological stressors. We reconstructed the evolutionary history of three families of Heat Shock Proteins (Hsp90, Hsp70, Hsp40), the primary molecular chaperones protecting against thermal damage, across 12 Hymenopteran species and four other insect orders. We also predicted and tested for thermal inducibility of eight Hsps from the presence of cis-regulatory heat shock elements (HSEs). We tested whether Hsp induction patterns in ants were associated with different thermal environments.

Results

We found evidence for duplications, losses, and cis-regulatory changes in two of the three gene families. One member of the Hsp90 gene family, hsp83, duplicated basally in the Hymenoptera, with shifts in HSE motifs in the novel copy. Both copies were retained in bees, but ants retained only the novel HSE copy. For Hsp70, Hymenoptera lack the primary heat-inducible orthologue from Drosophila melanogaster and instead induce the cognate form, hsc70-4, which also underwent an early duplication. Episodic diversifying selection was detected along the branch predating the duplication of hsc70-4 and continued along one of the paralogue branches after duplication. Four out of eight Hsp genes were heat-inducible and matched the predictions based on presence of conserved HSEs. For the inducible homologues, the more thermally tolerant species, Pogonomyrmex barbatus, had greater Hsp basal expression and induction in response to heat stress than did the less thermally tolerant species, Aphaenogaster picea. Furthermore, there was no trade-off between basal expression and induction.

Conclusions

Our results highlight the unique evolutionary history of Hsps in eusocial Hymenoptera, which has been shaped by gains, losses, and changes in cis-regulation. Ants, and most likely other Hymenoptera, utilize lineage-specific heat inducible Hsps, whose expression patterns are associated with adaptive variation in thermal tolerance between two ant species. Collectively, our analyses suggest that Hsp sequence and expression patterns may reflect the forces of selection acting on thermal tolerance in ants and other social Hymenoptera.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0573-0) contains supplementary material, which is available to authorized users.

Comparative physiological, biochemical, and molecular thermal stress response profiles for two Unionid freshwater mussel species

Freshwater mussels, aquatic keystone species, are in global decline. Long life spans, sedentary lifestyles, and unique reproductive strategies involving obligate parasitic stages make unionid freshwater mussels particularly sensitive to environmental perturbations resulting from global climate change. A greater understanding of the mechanisms by which closely related species differ in their response to thermal challenge is critical for successful conservation and management practices. As such, both an acute heat shock and a chronic warming simulation were conducted in order to evaluate responses between hypothesized thermally tolerant, Villosa lienosa, and thermally sensitive, Villosa nebulosa, freshwater mussels in response to predicted thermal warming. Multiple biological responses were quantified, including mortality, condition index, growth rates, glycogen and triglyceride content, and candidate gene expression. During acute heat shock, both species upregulated HSP90 and HSP70, though V. lienosa showed consistently greater transcript levels during upregulation. This pattern was consistent during the chronic warming simulation, with V. nebulosa showing greater induction of HSP60. Chronic warming stimulated increases in condition index for V. nebulosa, however declines in growth rates during a recovery period were observed with no concurrent tissue glycogen levels changes. This contrasts with V. lienosa, where tissue glycogen significantly increased during chronic warming, though no response was observed for condition index or growth rates. These differences might indicate disparate thermal stress response mechanisms correlated with metabolic demands and resource utilization. These biological differences could thus be a factor influencing current ranges and these two species‘ future ability to cope with persistent warming in their native habitats.

Towards multi-level biomonitoring of nematodes to assess risk of nitrogen and phosphorus pollution in Jinchuan Wetland of Northeast China

Cultivation for agricultural production often poses threats to nearby wetlands ecosystems in fertile landscapes. In this study, nematode ecological indexes were assessed through the main soil properties of the wetlands, farmlands, and edges of wetlands and farmlands in Jinchuan Wetland by the random sampling. Behavior and reproduction in Caenorhabditis elegans (C. elegans) exposed to the sampled waters were also examined. Stress proteins Hsp70 and Hsp90 were measured both in the living field samples of C. elegans and the lab-tested C. elegans. Our results suggested that disturbance to wetland ecosystems by nitrogen and phosphorus reduced nematode richness and proportions of bacterivore nematodes. Bacterivore nematode diversity and plant-parasitic ecological index were proven to be sensitive indicators of the ecological health of wetlands. Nematode Hsp70 were useful biosensors to monitor and assess the levels of nitrogen and phosphorus pollutions in wetlands. Furthermore, multi-level soil faunal assessments by canonical correspondence analysis showed that Jinchuan Wetland is threatened with non-point source pollution from nearby farmlands.

Diversification, evolution and sub-functionalization of 70kDa heat-shock proteins in two sister species of antarctic krill: differences in thermal habitats, responses and implications under climate change

BACKGROUND

A comparative thermal tolerance study was undertaken on two sister species of Euphausiids (Antarctic krills) Euphausia superba and Euphausia crystallorophias. Both are essential components of the Southern Ocean ecosystem, but occupy distinct environmental geographical locations with slightly different temperature regimes. They therefore provide a useful model system for the investigation of adaptations to thermal tolerance.

METHODOLOGY/PRINCIPAL FINDING

Initial CTmax studies showed that E. superba was slightly more thermotolerant than E. crystallorophias. Five Hsp70 mRNAs were characterized from the RNAseq data of both species and subsequent expression kinetics studies revealed notable differences in induction of each of the 5 orthologues between the two species, with E. crystallorophias reacting more rapidly than E. superba. Furthermore, analyses conducted to estimate the evolutionary rates and selection strengths acting on each gene tended to support the hypothesis that diversifying selection has contributed to the diversification of this gene family, and led to the selective relaxation on the inducible C form with its possible loss of function in the two krill species.

CONCLUSIONS

The sensitivity of the epipelagic species E. crystallorophias to temperature variations and/or its adaptation to cold is enhanced when compared with its sister species, E. superba. These results indicate that ice krill could be the first of the two species to be impacted by the warming of coastal waters of the Austral ocean in the coming years due to climate change.

Physiological, cellular and biochemical thermal stress response of intertidal shrimps with different vertical distributions: Palaemon elegans and Palaemon serratus

The ability to cope with high temperature variations is a critical factor in intertidal communities. Two species of intertidal rocky shore shrimps (Palaemon sp.) with different vertical distributions were collected from the Portuguese coast in order to test if they were differentially sensitive to thermal stress. Three distinct levels of biological organization (organismal, biochemical, and cellular) were surveyed. The shrimp were exposed to a constant rate of temperature increase of 1°C x h(-1), starting at 20°C until reaching the CTMax (critical thermal maximum). During heat stress, two biomarkers of protein damage were quantified in the muscle via enzyme-linked immunosorbent assays: heat shock proteins HSP70 (hsp70/hsc70) and total ubiquitin. Muscle histopathological alterations caused by temperature were also evaluated. CTMax values were not significantly different between the congeners (P. elegans 33.4 ± 0.5 °C; P. serratus 33.0 ± 0.5 °C). Biomarker levels did not increase along the temperature trial, but P. elegans (higher intertidal) showed higher amounts of HSP70 and total ubiquitin than P. serratus (lower intertidal). HSP70 and total ubiquitin levels showed a positive significant correlation in both species, suggesting that their association is important in thermal tolerance. Histopathological observations of muscle tissue in P. serratus showed no gross alterations due to temperature but did show localized atrophy of muscle fibers at CTMax. In P. elegans, alterations occurred at a larger scale, showing multiple foci of atrophic muscular fascicles caused by necrotic or autolytic processes. In conclusion, Palaemon congeners displayed different responses to stress at a cellular level, with P. elegans having greater biomarker levels and histopathological alterations.

Characterising multi-level effects of an acute pressure exposure on a shallow-water invertebrate: insights into the kinetics and hierarchy of the stress response

Hydrostatic pressure is an important, ubiquitous, environmental variable of particular relevance in the marine environment. However, it is widely overlooked despite recent evidence that some marine ectotherms may be demonstrating climate-driven bathymetric range shifts. Wide ranging effects of increased hydrostatic pressure have been observed from the molecular level through to the behavioural level. Still, no study has simultaneously examined these multiple levels of organisation in a single experiment in order to understand the kinetics, hierarchy, and interconnected nature of such responses during an acute exposure, and over a subsequent recovery period. Herein, we quantify the transcription of a set of previously characterised genes during, and following, an acute pressure exposure in adults of the shrimp Palaemonetes varians. Further, we perform respiratory rate and behavioural analysis over the same period. Increases in gene expression were observed during, and following, exposure in genes associated with stress and metabolism. Respiratory rate increased during exposure, and into the recovery period. Finally, differential behaviour was observed under elevated hydrostatic pressure in comparison to ambient pressure. Characterising generalised responses to acute elevated pressure is a vital pre-cursor to longer–term, acclimation-based pressure studies. Results provide a novel insight into what we term the overall stress response (OSR) to elevated pressure; a concept that we suggest to be applicable to other environmental stressors. We highlight the importance of considering more than a single component of the stress response in physiological studies, particularly in an era where environmental multi-stressor studies are proliferating.

The UV filter benzophenone 3 (BP-3) activates hormonal genes mimicking the action of ecdysone and alters embryo development in the insect Chironomus riparius (Diptera)

Numerous studies have evaluated the endocrine effects of UV filters in vertebrates, but little attention has been paid to their possible hormonal activity in invertebrates. We examined the effects of benzophenone-3 (BP-3), one of the most common sunscreen agents, in Chironomus riparius (Insecta), a reference organism in aquatic toxicology. Salivary glands from larvae were treated with either the hormone ecdysone or BP-3 to compare the response of endocrine genes. It was found that BP-3 elicits the same effects as the natural hormone activating the expression of a set of ecdysone responsive genes. BP-3 also activated the stress gene hsp70. Interestingly, similar effects have been confirmed in vivo in embryos. Moreover, BP-3 also altered embryogenesis delaying hatching. This is the first demonstration of hormonal activity of UV filters in invertebrates, showing a mode of action similar to ecdysteroid hormones. This finding highlights the potential endocrine disruptive effects of these emergent pollutants.

An intron-containing, heat-inducible stress-70 gene in the millipede Tachypodoiulus niger (Julidae, Diplopoda)

The highly conserved part of the nucleotide-binding domain of the hsp70 gene family was amplified from the soil diplopod Tachypodoiulus niger (Julidae, Diplopoda). Genomic DNA yielded 701, 549 and 540 bp sequences, whereas cDNA from heat shocked animals produced only one distinct fragment of 543 bp. The sequences could be classified as a 70 kDa heat shock protein (hsp70), the corresponding 70 kDa heat shock cognate (hsc70) and a glucose-related hsp70 homologue (grp78). Comparisons of genomic and cDNA sequences of hsc70 identified two introns within the consensus sequence. Generally, stress-70 expression levels were low, which hampered successful RT-PCR and subsequent subcloning. Following experimental heat shock, however, the spliced hsc70 was amplified predominantly, instead of its inducible homologue hsp70. This finding suggests that microevolution in this soil-dwelling arthropod is directed towards low constitutive stress-70 levels and that the capacity for stress-70 induction presumably is limited. hsc70, albeit having introns, apparently is inducible and contributes to the stress-70 response.

Sex differences in the acute in vivo effects of different human SP-A variants on the mouse alveolar macrophage proteome

Surfactant protein A (SP-A) is involved in lung innate immunity. Humans have two SP-A genes, SFTPA1 and SFTPA2, each with several variants. We examined the in vivo effects of treatment with specific SP-A variants on the alveolar macrophage (AM) proteome from SP-A knockout (KO) mice. KO mice received either SP-A1, SP-A2, or both. AM were collected and their proteomes examined with 2D-DIGE. We identified 90 proteins and categorized them as related to actin/cytoskeleton, oxidative stress, protease balance/chaperones, regulation of inflammation, and regulatory/developmental processes. SP-A1 and SP-A2 had different effects on the AM proteome and these effects differed between sexes. In males more changes occurred in the oxidative stress, protease/chaperones, and inflammation groups with SP-A2 treatment than with SP-A1. In females most SP-A1-induced changes were in the actin/cytoskeletal and oxidative stress groups. We conclude that after acute SP-A1 and SP-A2 treatment, sex-specific differences were observed in the AM proteomes from KO mice, and that these sex differences differ in response to SP-A1 and SP-A2. Females are more responsive to SP-A1, whereas the gene-specific differences in males were minimal. These observations not only demonstrate the therapeutic potential of exogenous SP-A, but also illustrate sex- and gene-specific differences in the response to it.

BIOLOGICAL SIGNIFICANCE

This study shows that changes occur in the alveolar macrophage proteome in response to a single in vivo treatment with exogenous SP-A1 and/or SP-A2. We demonstrate that SP-A1 and SP-A2 have different effects on the AM proteome and that sex differences exist in the response to each SP-A1 and SP-A2 gene product. This study illustrates the potential of exogenous SP-A1 and SP-A2 treatment for the manipulation of macrophage function and indicates that the specific SP-A variant used for treatment may vary with sex and with the cellular functions being modified. The observed changes may contribute to sex differences in the incidence of some lung diseases.

Widespread phenotypic and genetic divergence along altitudinal gradients in animals

Altitudinal gradients offer valuable study systems to investigate how adaptive genetic diversity is distributed within and between natural populations and which factors promote or prevent adaptive differentiation. The environmental clines along altitudinal gradients tend to be steep relative to the dispersal distance of many organisms, providing an opportunity to study the joint effects of divergent natural selection and gene flow. Temperature is one variable showing consistent altitudinal changes, and altitudinal gradients can therefore provide spatial surrogates for some of the changes anticipated under climate change. Here, we investigate the extent and patterns of adaptive divergence in animal populations along altitudinal gradients by surveying the literature for (i) studies on phenotypic variation assessed under common garden or reciprocal transplant designs and (ii) studies looking for signatures of divergent selection at the molecular level. Phenotypic data show that significant between-population differences are common and taxonomically widespread, involving traits such as mass, wing size, tolerance to thermal extremes and melanization. Several lines of evidence suggest that some of the observed differences are adaptively relevant, but rigorous tests of local adaptation or the link between specific phenotypes and fitness are sorely lacking. Evidence for a role of altitudinal adaptation also exists for a number of candidate genes, most prominently haemoglobin, and for anonymous molecular markers. Novel genomic approaches may provide valuable tools for studying adaptive diversity, also in species that are not amenable to experimentation.