Thermal tolerance in the keystone species Daphnia magna-a candidate gene and an outlier analysis approach

The analysis of inducible family members in the water flea Daphnia magna led to the identification of an uncharacterized lineage of heat shock protein 70

To explore the function and evolutionary relationships of inducible heat shock protein 70 (Hsp70) in Daphnia magna, cDNAs of four Hsp70 family members (DmaHsp70, DmaHsp70-2, DmaHsp70-12, DmaHsp70-14) were cloned. While all DmaHsp70s possess three function domains, it is noteworthy that only DmaHsp70 ends with a "EEVD" motif. Phylogenetic analysis indicates that the Hsp70-12 lineage is distanced from the rest, and therefore it is an uncharacterized lineage of Hsp70. The differences in isoelectric point and 3-dimensional (3D) conformation of the N-terminal nucleotide binding domain (NBD) of DmaHsp70s further support the theory. DmaHsp70s exhibit varied motif distribution patterns and the logo sequences of motifs have diverse signature characteristics, indicating that different mechanisms are involved in the regulation of ATP binding and hydrolysis for the DmaHsp70s. Protein-protein network together with the predicted subcellular locations of DmaHsp70s suggest that they likely fulfill distinct roles in cells. The transcription of four DmaHsp70s were changed during the recovery stage after thermal stress or oxidative stress. But the expression pattern of them were dissimilar. Collectively, these results collectively elucidated the identification of a previously uncharacterizedHsp70 lineage in animal and extended our understanding of the Hsp70 family.

Genomics for monitoring and understanding species responses to global climate change

All life forms across the globe are experiencing drastic changes in environmental conditions as a result of global climate change. These environmental changes are happening rapidly, incur substantial socioeconomic costs, pose threats to biodiversity and diminish a species' potential to adapt to future environments. Understanding and monitoring how organisms respond to human-driven climate change is therefore a major priority for the conservation of biodiversity in a rapidly changing environment. Recent developments in genomic, transcriptomic and epigenomic technologies are enabling unprecedented insights into the evolutionary processes and molecular bases of adaptation. This Review summarizes methods that apply and integrate omics tools to experimentally investigate, monitor and predict how species and communities in the wild cope with global climate change, which is by genetically adapting to new environmental conditions, through range shifts or through phenotypic plasticity. We identify advantages and limitations of each method and discuss future research avenues that would improve our understanding of species' evolutionary responses to global climate change, highlighting the need for holistic, multi-omics approaches to ecosystem monitoring during global climate change.

Increased virulence due to multiple infection in Daphnia leads to limited growth in 1 of 2 co-infecting microsporidian parasites

Recent outbreaks of various infectious diseases have highlighted the ever-present need to understand the drivers of the outbreak and spread of disease. Although much of the research investigating diseases focuses on single infections, natural systems are dominated by multiple infections. These infections may occur simultaneously, but are often acquired sequentially, which may alter the outcome of infection. Using waterfleas (Daphnia magna) as a model organism, we examined the outcome of sequential and simultaneous multiple infections with 2 microsporidian parasites (Ordospora colligata and Hamiltosporidium tvaerminnensis) in a fully factorial design with 9 treatments and 30 replicates. We found no differences between simultaneous and sequential infections. However, H. tvaerminnensis fitness was impeded by multiple infection due to increased host mortality, which gave H. tvaerminnensis less time to grow. Host fecundity was also reduced across all treatments, but animals infected with O. colligata at a younger age produced the fewest offspring. As H. tvaerminnensis is both horizontally and vertically transmitted, this reduction in offspring may have further reduced H. tvaerminnensis fitness in co-infected treatments. Our findings suggest that in natural populations where both species co-occur, H. tvaerminnensis may evolve to higher levels of virulence following frequent co-infection by O. colligata.

Disturbances in growth, oxidative stress, energy reserves and the expressions of related genes in Daphnia magna after exposure to ZnO under thermal stress

The toxicological effects of metal contamination are influenced by the ambient temperature. Therefore, global warming affects the toxicity of metal contamination in aquatic ecosystems. ZnO is widely used as a catalyst in many industries, and causes contamination in aquatic ecosystems. Here, we investigated the effects of ZnO concentration under elevated temperature by observing growth, oxidative stress, energy reserves and related gene expression in exposed Daphnia magna. Body length and growth rate increased in neonates exposed to ZnO for 2 days but decreased at 9 and 21 days under elevated temperature. ZnO concentration and elevated temperature induced oxidative stress in mature D. magna by reducing superoxide dismutase (SOD) activity and increasing malondialdehyde (MDA) levels. In contrast, juveniles were unaffected. Carbohydrate, protein and caloric contents were reduced throughout development in D. magna treated with ZnO and elevated temperature in all exposure periods (2, 9 and 21 days). However, lipid content also decreased in mature D. magna treated with ZnO cultured under elevated temperature, while that of juveniles showed an increase in lipid content. Therefore, energy was perhaps allocated to physiological processes for detoxification and homeostasis. Moreover, expression patterns of genes related to physiological processes changed under elevated temperature and ZnO exposure. Taken together, our results highlight that the combination of temperature and ZnO concentration induced toxicity in D. magna. This conclusion was confirmed by the Integrated Biological Response (IBR) index. This study shows that changes in biological levels of organization could be used to monitor environmental change using D. magna as a bioindicator.

Thermal stress and mutation accumulation increase heat shock protein expression in Daphnia

Understanding the short- and long-term consequences of climate change is a major challenge in biology. For aquatic organisms, temperature changes and drought can lead to thermal stress and habitat loss, both of which can ultimately lead to higher mutation rates. Here, we examine the effect of high temperature and mutation accumulation on gene expression at two loci from the heat shock protein (HSP) gene family, HSP60 and HSP90. HSPs have been posited to serve as 'mutational capacitors' given their role as molecular chaperones involved in protein folding and degradation, thus buffering against a wide range of cellular stress and destabilization. We assayed changes in HSP expression across 5 genotypes of Daphnia magna, a sentinel species in ecology and environmental biology, with and without acute exposure to thermal stress and accumulated mutations. Across genotypes, HSP expression increased ~ 6× in response to heat and ~ 4× with mutation accumulation, individually. Both factors simultaneously (lineages with high mutation loads exposed to high heat) increased gene expression ~ 23×-much more than that predicted by an additive model. Our results corroborate suggestions that HSPs can buffer against not only the effects of heat, but also mutations-a combination of factors both likely to increase in a warming world.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10682-022-10209-1.

Long-term adverse effects of microplastics on Daphnia magna reproduction and population growth rate at increased water temperature and light intensity: Combined effects of stressors and interactions

In many ecosystems, the zooplankton community has been pressured simultaneously by microplastic pollution and alterations resulting from global climate changes. The potential influence of light intensity rise (from 10,830 lx to 26,000 lx) and water temperature rise (from 20 °C to 25 °C) on the long term-toxicity of microplastics (MPs) to Daphnia magna were investigated. Three 21-day laboratory bioassays with model MPs (1-5 μm diameter) were carried out at (i) 20 °C/10830 lx, (ii) 20 °C/26000 lx, and (iii) 25 °C/10830 lx. In each bioassay, one control (no MPs) and three MP concentrations (0.04, 0.09, 0.19 mg/L) were tested. In all the bioassays, MPs caused parental and juvenile mortality, and reduced the somatic growth, reproduction and population growth rate. The MP EC₅₀s on living offspring (95% confidence interval within brackets) were 0.146 mg/L (0.142-0.151 mg/L) at 20 °C/10830 lx, 0.102 mg/L (0.099-0.105 mg/L) at 20 °C/26000 lx, and 0.101 mg/L (0.098-0.104 mg/L) at 25 °C/10830 lx. Relatively to the respective control group, 0.19 mg/L of MPs decreased the mean of the population growth rate by 27% at 20 °C/10830 lx, 38% at 20 °C/26000 lx and 59% at 25 °C/10830 lx. Based on the population growth rate and in relation to 20 °C/10830 lx (control, no MPs), the interaction between increased light intensity (26,000 lx) and MPs was synergism (at all the MP concentrations tested). The interaction between water temperature rise (25 °C) and MPs was antagonism at 0.04 mg/L of MPs and synergism at 0.09 and 0.19 mg/L of MPs. In the present scenario of climate changes and global MP pollution such findings raise high concern because zooplankton communities are crucial for aquatic biodiversity conservation, ecosystem functioning and services provided to humans. Further studies on the combined effects of MPs, other common pollutants, and alterations due to climate changes are needed.

False and true positives in arthropod thermal adaptation candidate gene lists

Genome-wide studies are prone to false positives due to inherently low priors and statistical power. One approach to ameliorate this problem is to seek validation of reported candidate genes across independent studies: genes with repeatedly discovered effects are less likely to be false positives. Inversely, genes reported only as many times as expected by chance alone, while possibly representing novel discoveries, are also more likely to be false positives. We show that, across over 30 genome-wide studies that reported Drosophila and Daphnia genes with possible roles in thermal adaptation, the combined lists of candidate genes and orthologous groups are rapidly approaching the total number of genes and orthologous groups in the respective genomes. This is consistent with the expectation of high frequency of false positives. The majority of these spurious candidates have been identified by one or a few studies, as expected by chance alone. In contrast, a noticeable minority of genes have been identified by numerous studies with the probabilities of such discoveries occurring by chance alone being exceedingly small. For this subset of genes, different studies are in agreement with each other despite differences in the ecological settings, genomic tools and methodology, and reporting thresholds. We provide a reference set of presumed true positives among Drosophila candidate genes and orthologous groups involved in response to changes in temperature, suitable for cross-validation purposes. Despite this approach being prone to false negatives, this list of presumed true positives includes several hundred genes, consistent with the "omnigenic" concept of genetic architecture of complex traits.

Breaking free from thermodynamic constraints: thermal acclimation and metabolic compensation in a freshwater zooplankton species

Respiration rates of ectothermic organisms are affected by environmental temperatures, and sustainable metabolism at high temperatures sometimes limits heat tolerance. Organisms are hypothesized to exhibit acclimatory metabolic compensation effects, decelerating their metabolic processes below Arrhenius expectations based on temperature alone. We tested the hypothesis that either heritable or plastic heat tolerance differences can be explained by metabolic compensation in the eurythermal freshwater zooplankton crustacean Daphnia magna We measured respiration rates in a ramp-up experiment over a range of assay temperatures (5-37°C) in eight genotypes of D. magna representing a range of previously reported acute heat tolerances and, at a narrower range of temperatures (10-35°C), in D. magna with different acclimation history (either 10 or 25°C). We discovered no difference in temperature-specific respiration rates between heat-tolerant and heat-sensitive genotypes. In contrast, we observed acclimation-specific compensatory differences in respiration rates at both extremes of the temperature range studied. Notably, there was a deceleration of oxygen consumption at higher temperature in 25°C-acclimated D. magna relative to their 10°C-acclimated counterparts, observed in active animals, a pattern corroborated by similar changes in filtering rate and, partly, by changes in mitochondrial membrane potential. A recovery experiment indicated that the reduction of respiration was not caused by irreversible damage during exposure to a sublethal temperature. Response time necessary to acquire the respiratory adjustment to high temperature was lower than for low temperature, indicating that metabolic compensation at lower temperatures requires slower, possibly structural changes.

Linking multiple biomarker responses in Daphnia magna under thermal stress

Temperature is an important abiotic variable that greatly influences the performance of aquatic ectotherms, especially under current anthropogenic global warming and thermal discharges. The aim of the present study was to evaluate thermal stress (20 °C vs 28 °C) in Daphnia magna over 21 d, focusing on the linkage among molecular and biochemical biomarker responses. Thermal stress significantly increased the levels of reactive oxygen species (ROS) and lipid peroxidation, especially in the 3-d short-term exposure treatment. This change in the ROS level was also correlated with mitochondrial membrane damage. These findings suggest that oxidative stress is the major pathway for thermally-induced toxicity of D. magna. Additionally, the expression levels of genes related to hypoxia (Hb), development (Vtg1), and sex determination (Dsx1-α, Dsx1-β, and Dsx2) were greatly increased by elevated temperature in a time-dependent manner. The cellular energy allocation was markedly decreased at the elevated temperature in the 3-d exposure treatment, mainly due to carbohydrates consumption for survival (oxidative stress defense). The present study showed that linking multiples biomarker responses are crucial for understanding the underlying mechanism of thermal stress on D. magna.

Transgenerational response to early spring warming in Daphnia

Temperature and photoperiod regulate key fitness traits in plants and animals. However, with temperature increase due to global warming, temperature cue thresholds are experienced at shorter photoperiods, disrupting the optimal seasonal timing of physiological, developmental and reproductive events in many species. Understanding the mechanisms of adaptation to the asynchrony between temperature and photoperiod is key to inform our understanding of how species will respond to global warming. Here, we studied the transgenerational mechanisms of responses of the cyclical parthenogen Daphnia magna to different photoperiod lengths co-occurring with warm temperature thereby assessing the impact of earlier spring warming on its fitness. Daphnia uses temperature and photoperiod cues to time dormancy, and to switch between sexual and asexual reproduction. Daphnia life cycle offers the opportunity to measure the relative contribution of plastic and genetic responses to environmental change across generations and over evolutionary time. We use transgenerational common garden experiments on three populations 'resurrected' from a biological archive experiencing temperature increase over five decades. Our results suggest that response to early spring warming evolved underpinned by a complex interaction between plastic and genetic mechanisms while a positive maternal contribution at matching environments between parental and offspring generation was also observed.

Functional responses of Daphnia magna to zero-mean flow turbulence

Daphnia are important to understanding the biogeochemistry of aquatic ecosystems, mainly because of their ability to filter bacteria, algae and inorganic particles as well. Although there are many studies on the general effects that biotic and abiotic stressors, increased temperature and hypoxia, salinity, metals, pharmaceuticals, pesticides, etc., have on Daphnia populations, little is known about the impact elevated turbulence has. Here, we show that turbulence affects Daphnia magna survival, swimming behaviour and filtering capacity. Our data demonstrate that altering their habitat by induced mixing from turbulence, induces an increased filtering capacity of the Daphnia magna individuals, provided the level of background turbulence (defined by the dissipation of turbulent kinetic energy) is lower than ε = 0.04 cm² s⁻³. The filtering capacity reduced exponentially with increasing ε, and at ε > 1 cm² s⁻³ both mobility and filtration were suppressed and eventually led to the death of all the Daphnia magna individuals.

Temperature-driven response reversibility and short-term quasi-acclimation of Daphnia magna

Analysing the effect water temperature has on Daphnia magna is essential in anticipating the impact climate change will have on this freshwater zooplanktonic keystone species. While many authors have followed this line of research, few have covered an extensive temperature range or complex temperature change scenarios. Global warming is mostly associated with increased extreme temperature events, such as heat waves, as well as earlier and more intense thermal stratification. Both of these events may directly influence D. magna fitness, especially in those populations performing diel vertical migration (DVM). We analysed the effect water temperatures, ranging from 11 to 29°C, have on the filtration capacity (FC) of D. magna, to anticipate the effects of acclimation, temperature change rate (TCR) and potential reversibility of responses to such conditions. Results show that sudden temperature changes have an immediate negative impact on the FC of D. magna and is more severe at higher temperatures and higher TCRs. However, D. magna individuals have shown themselves to be capable of quasi-acclimating to temperatures ranging from 11 to 25°C in around a week and achieving much higher FCs; albeit never reaching the optimal FC achieved at 20°C. That said, 29°C is lethal for D. magna individuals within approximately five days. Finally, non-optimal temperature acclimated individuals can recover maximal FC within 2–4 days of the optimal long-term acclimation temperature (20°C) being re-established, thus proving temperature responses to be reversible.

Predictability of the impact of multiple stressors on the keystone species Daphnia

Eutrophication and climate change are two of the most pressing environmental issues affecting up to 50% of aquatic ecosystems worldwide. Mitigation strategies to reduce the impact of environmental change are complicated by inherent difficulties of predicting the long-term impact of multiple stressors on natural populations. Here, we investigated the impact of temperature, food levels and carbamate insecticides, in isolation and in combination, on current and historical populations of the freshwater grazer Daphnia. We used common garden and competition experiments on historical and modern populations of D. magna ‘resurrected’ from a lake with known history of anthropogenic eutrophication and documented increase in ambient temperature over time. We found that these populations response dramatically differed between single and multiple stressors. Whereas warming alone induced similar responses among populations, warming combined with insecticides or food limitation resulted in significantly lower fitness in the population historically exposed to pesticides. These results suggest that the negative effect of historical pesticide exposure is magnified in the presence of warming, supporting the hypothesis of synergism between chemical pollution and other stressors.

Stoichiometric responses to nano ZnO under warming are modified by thermal evolution in Daphnia magna

Effects of stressors on body stoichiometry are important as these may cascade through food webs. Contamination and global warming are two key anthropogenic stressors, yet their effects on body stoichiometry have been rarely tested. Further, while thermal evolution may increase the ability to deal with warming, it is unknown how thermal evolution modifies the effect of contaminants under warming. Using resurrection ecology, we studied two Daphnia magna subpopulations (old/recent) of which the recent subpopulation evolved a higher heat tolerance. We exposed both subpopulations to a sublethal concentration of nano zinc oxide (nZnO) and 4 °C warming and quantified their effects on body stoichiometry: carbon (C), nitrogen (N), phosphorus (P) contents and their ratios (C:N, C:P, N:P). In the old subpopulation, nZnO only marginally decreased the C content and had no effect on N and P contents and their ratios. In contrast, in the recent subpopulation nZnO strongly increased the body P content (+51%) and reduced the C:P (-34%) and N:P (-34%) ratios at 24 °C but not at 20 °C. Moreover, these stoichiometric changes were not explained by changes of corresponding macromolecules as assumed by theory. Our results indicate that the stoichiometric responses to nZnO in Daphnia are temperature-dependent and modified by rapid evolution. The observed changes in body stoichiometry may affect the food quality of this important prey and have the potential to cascade through food webs and shape nutrients cycling.

Thermal evolution offsets the elevated toxicity of a contaminant under warming: A resurrection study in Daphnia magna

Synergistic interactions between temperature and contaminants are a major challenge for ecological risk assessment, especially under global warming. While thermal evolution may increase the ability to deal with warming, it is unknown whether it may also affect the ability to deal with the many contaminants that are more toxic at higher temperatures. We investigated how evolution of genetic adaptation to warming affected the interactions between warming and a novel stressor: zinc oxide nanoparticles (nZnO) in a natural population of Daphnia magna using resurrection ecology. We hatched resting eggs from two D. magna subpopulations (old: 1955-1965, recent: 1995-2005) from the sediment of a lake that experienced an increase in average temperature and in recurrence of heat waves but was never exposed to industrial waste. In the old "ancestral" subpopulation, exposure to a sublethal concentration of nZnO decreased the intrinsic growth rate, metabolic activity, and energy reserves at 24°C but not at 20°C, indicating a synergism between warming and nZnO. In contrast, these synergistic effects disappeared in the recent "derived" subpopulation that evolved a lower sensitivity to nZnO at 24°C, which indicates that thermal evolution could offset the elevated toxicity of nZnO under warming. This evolution of reduced sensitivity to nZnO under warming could not be explained by changes in the total internal zinc accumulation but was partially associated with the evolution of the expression of a key metal detoxification gene under warming. Our results suggest that the increased sensitivity to the sublethal concentration of nZnO under the predicted 4°C warming by the end of this century may be counteracted by thermal evolution in this D. magna population. Our results illustrate the importance of evolution to warming in shaping the responses to another anthropogenic stressor, here a contaminant. More general, genetic adaptation to an environmental stressor may ensure that synergistic effects between contaminants and this environmental stressor will not be present anymore.

Temperature gradient affects differentiation of gene expression and SNP allele frequencies in the dominant Lake Baikal zooplankton species

Local adaptation and phenotypic plasticity are main mechanisms of organisms' resilience in changing environments. Both are affected by gene flow and are expected to be weak in zooplankton populations inhabiting large continuous water bodies and strongly affected by currents. Lake Baikal, the deepest and one of the coldest lakes on Earth, experienced epilimnion temperature increase during the last 100 years, exposing Baikal's zooplankton to novel selective pressures. We obtained a partial transcriptome of Epischura baikalensis (Copepoda: Calanoida), the dominant component of Baikal's zooplankton, and estimated SNP allele frequencies and transcript abundances in samples from regions of Baikal that differ in multiyear average surface temperatures. The strongest signal in both SNP and transcript abundance differentiation is the SW-NE gradient along the 600+ km long axis of the lake, suggesting isolation by distance. SNP differentiation is stronger for nonsynonymous than synonymous SNPs and is paralleled by differential survival during a laboratory exposure to increased temperature, indicating directional selection operating on the temperature gradient. Transcript abundance, generally collinear with the SNP differentiation, shows samples from the warmest, less deep location clustering together with the southernmost samples. Differential expression is more frequent among transcripts orthologous to candidate thermal response genes previously identified in model arthropods, including genes encoding cytoskeleton proteins, heat-shock proteins, proteases, enzymes of central energy metabolism, lipid and antioxidant pathways. We conclude that the pivotal endemic zooplankton species in Lake Baikal exists under temperature-mediated selection and possesses both genetic variation and plasticity to respond to novel temperature-related environmental pressures.

Resurrection of Dormant Daphnia magna: Protocol and Applications

Long-term studies enable the identification of eco-evolutionary processes that occur over extended time periods. In addition, they provide key empirical data that may be used in predictive modelling to forecast evolutionary responses of natural ecosystems to future environmental changes. However, excluding a few exceptional cases, long-term studies are scarce because of logistic difficulties associated with accessing temporal samples. Temporal dynamics are frequently studied in the laboratory or in controlled mesocosm experiments with exceptional studies that reconstruct the evolution of natural populations in the wild.

Here, a standard operating procedure (SOP) is provided to revive or resurrect dormant Daphnia magna, a widespread zooplankton keystone species in aquatic ecosystems, to dramatically advance the state-of-the-art longitudinal data collection in natural systems. The field of Resurrection Ecology was defined in 1999 by Kerfoot and co-workers, even though the first attempts at hatching diapausing zooplankton eggs date back to the late 1980s. Since Kerfoot's seminal paper, the methodology of resurrecting zooplankton species has been increasingly frequently applied, though propagated among laboratories only via direct knowledge transfer. Here, an SOP is described that provides a step-by-step protocol on the practice of resurrecting dormant Daphnia magna eggs.

Two key studies are provided in which the fitness response of resurrected Daphnia magna populations to warming is measured, capitalizing on the ability to study historical and modern populations in the same settings. Finally, the application of next generation sequencing technologies to revived or still dormant stages is discussed. These technologies provide unprecedented power in dissecting the processes and mechanisms of evolution if applied to populations that have experienced changes in selection pressure over time.

Paleolimnology and resurrection ecology: The future of reconstructing the past

Paleolimnologists have utilized lake sediment records to understand historical lake and landscape development, timing and magnitude of environmental change at lake, watershed, regional and global scales, and as historical datasets to target watershed and lake management. Resurrection ecologists have long recognized lake sediments as sources of viable propagules ("seed or egg banks") with which to explore questions of community ecology, ecological response, and evolutionary ecology. Most researchers consider Daphnia as the primary model organism in these efforts, but many other aquatic biota, from viruses to macrophytes, similarly produce viable propagules that are incorporated in the sediment record but have been underutilized in resurrection ecology. The common goals shared by these two disciplines have led to mutualistic and synergistic collaborations-a development that must be encouraged to expand. We give an overview of the achievements of paleolimnology and the reconstruction of environmental history of lakes, review the untapped diversity of aquatic organisms that produce dormant propagules, compare Daphnia as a model of resurrection ecology with other organisms amenable to resurrection studies, especially diatoms, and consider new research directions that represent the nexus of these two fields.

Haemoglobin-mediated response to hyper-thermal stress in the keystone species Daphnia magna

Anthropogenic global warming has become a major geological and environmental force driving drastic changes in natural ecosystems. Due to the high thermal conductivity of water and the effects of temperature on metabolic processes, freshwater ecosystems are among the most impacted by these changes. The ability to tolerate changes in temperature may determine species long‐term survival and fitness. Therefore, it is critical to identify coping mechanisms to thermal and hyper‐thermal stress in aquatic organisms. A central regulatory element compensating for changes in oxygen supply and ambient temperature is the respiratory protein haemoglobin (Hb). Here, we quantify Hb plastic and evolutionary response in Daphnia magna subpopulations resurrected from the sedimentary archive of a lake with known history of increase in average temperature and recurrence of heat waves. By measuring constitutive changes in crude Hb protein content among subpopulations, we assessed evolution of the Hb gene family in response to temperature increase. To quantify the contribution of plasticity in the response of this gene family to hyper‐thermal stress, we quantified changes in Hb content in all subpopulations under hyper‐thermal stress as compared to nonstressful temperature. Further, we tested competitive abilities of genotypes as a function of their Hb content, constitutive and induced. We found that Hb‐rich genotypes have superior competitive abilities as compared to Hb‐poor genotypes under hyper‐thermal stress after a period of acclimation. These findings suggest that whereas long‐term adjustment to higher occurrence of heat waves may require a combination of plasticity and genetic adaptation, plasticity is most likely the coping mechanism to hyper‐thermal stress in the short term. Our study suggests that with higher occurrence of heat waves, Hb‐rich genotypes may be favoured with potential long‐term impact on population genetic diversity.