Short-term Acclimation Research Articles

Integrated transcriptional and biochemical profiling suggests mechanisms associated with rapid cold hardening in adult Liriomyza trifolii (Burgess)

The leafminer Liriomyza trifolii causes severe economic damage on ornamental and horticultural crops in China. Rapid cold hardening (RCH) is a phenomenon where cold tolerance in insects can be significantly enhanced after a short-term acclimation to low temperatures. In this study, the regulation of transcription in response to cold hardening was investigated in L. trifolii adults, and fatty acids and cryoprotectant levels were measured. The composition of fatty acids changed after RCH treatment, and glucose and trehalose levels showed significant accumulation after acclimation, thus indicating that changes in fatty acids and cryoprotectants contribute to RCH in L. trifolii. RNA-seq was used to analyze transcriptional regulation after a 4 h hardening period and showed that differentially expressed genes clustered in multiple metabolic pathways, which indicates the importance of transcriptional regulation in RCH. This study expands our knowledge of biochemical and transcriptional changes in L. trifolii during cold hardening and provides a basis for further investigations aimed at understanding thermal adaptation in insects.

Short-term thermal acclimation improved the thermal tolerance of three species of scleractinian corals in the South China Sea

Investigating the potential and mechanisms of thermal adaptability in scleractinian corals is critical for aiding corals in dealing with global warming and improving the efficiency of coral reef restoration efforts. Although thermal acclimation facilitates the resistance of branching corals to thermal stress, little is known about the physiological processes of massive and platy corals in the South China Sea or their ability to adapt to heat stress. In this study, we conducted indoor short-term thermal acclimation simulation experiments on three types of corals: massive Porites lutea, platy Pavona decussata, and branching Pocillopora damicornis. Subsequently, we studied the responses and adaptive mechanisms of the three corals to heat stress and explored the effects of short-term thermal acclimation using physiological and biochemical markers. The results showed that the three corals exhibited comparable phenotypic and physiological responses to heat stress, including tentacle retraction and decreases in zooxanthellae density, maximum quantum efficiency of photosystem II, and glutathione content, along with increases in antioxidant activity (catalase and superoxide dismutase), ammonium assimilation (glutamine synthetase), and apoptosis (lipid peroxide and caspase-3). Additionally, heat tolerance differed among the different species of coral. Furthermore, the physiological markers performed better in all three coral types after acclimation, and the effects of short-term acclimation decreased from P. lutea to P. damicornis to P. decussata. We propose that short-term thermal acclimation enhances the heat tolerance of corals by affecting their metabolism and antioxidant capacity. Leveraging short-term thermal acclimation in coral reef restoration efforts could help corals adapt to the threats posed by global warming and enhance restoration efficiency.

Bees display limited acclimation capacity for heat tolerance.

Bees are essential pollinators and understanding their ability to cope with extreme temperature changes is crucial for predicting their resilience to climate change, but studies are limited. We measured the response of the critical thermal maximum (CTMax) to short-term acclimation in foragers of six bee species from the Greek island of Lesvos, which differ in body size, nesting habit, and level of sociality. We calculated the acclimation response ratio as a metric to assess acclimation capacity and tested whether bees' acclimation capacity was influenced by body size and/or CTMax. We also assessed whether CTMax increases following acute heat exposure simulating a heat wave. Average estimate of CTMax varied among species and increased with body size but did not significantly shift in response to acclimation treatment except in the sweat bee Lasioglossum malachurum. Acclimation capacity averaged 9% among species and it was not significantly associated with body size or CTMax. Similarly, the average CTMax did not increase following acute heat exposure. These results indicate that bees might have limited capacity to enhance heat tolerance via acclimation or in response to prior heat exposure, rendering them physiologically sensitive to rapid temperature changes during extreme weather events. These findings reinforce the idea that insects, like other ectotherms, generally express weak plasticity in CTMax, underscoring the critical role of behavioral thermoregulation for avoidance of extreme temperatures. Conserving and restoring native vegetation can provide bees temporary thermal refuges during extreme weather events.

Genetics of chilling response at early growth stage in rice: a recessive gene for tolerance and importance of acclimation.

Low-temperature adaptation in rice is mediated by the ability of a genotype to tolerate chilling temperatures. A genetic locus on chromosome 11 was analysed for chilling tolerance at the plumule stage in rice. The tolerant allele of A58, a japonica landrace in Japan, was inherited as a recessive gene (ctp-1A58), whereas the susceptible alleles from wild rice (Ctp-1W107) and modern variety (Ctp-1HY) were the dominant genes. Another recessive tolerant allele (ctp-1Silewah) was found in a tropical japonica variety (Silewah). Fine-mapping revealed that a candidate gene for the ctp-1 locus encoded a protein similar to the nucleotide-binding domain and leucine-rich repeat (NLR) protein, in which frameshift mutation by a 73 bp-deletion might confer chilling tolerance in ctp-1A58. Analysis of near-isogenic lines demonstrated that ctp-1A58 imparted tolerance effects only at severe chilling temperatures of 0.5 °C and 2 °C, both at plumule and seedling stages. Chilling acclimation treatments at a wide range of temperatures (8 °C-16 °C) for 72 h concealed the susceptible phenotype of Ctp-1W107 and Ctp-1HY. Furthermore, short-term acclimation treatment of 12 h at 8 °C was enough to be fully acclimated. These results suggest that the NLR gene induces a susceptible response upon exposure to severe chilling stress, however, another interacting gene(s) for acclimation response could suppress the maladaptive phenotype caused by the Ctp-1 allele. This study provides new insights for the adaptation and breeding of rice in a low-temperature environment.

Continuous short-term acclimation to moderate cold elicits cardioprotection in rats, and alters β-adrenergic signaling and immune status

Moderate cold acclimation (MCA) is a non-invasive intervention mitigating effects of various pathological conditions including myocardial infarction. We aim to determine the shortest cardioprotective regimen of MCA and the response of β1/2/3-adrenoceptors (β-AR), its downstream signaling, and inflammatory status, which play a role in cell-survival during myocardial infarction. Adult male Wistar rats were acclimated (9 °C, 1–3-10 days). Infarct size, echocardiography, western blotting, ELISA, mitochondrial respirometry, receptor binding assay, and quantitative immunofluorescence microscopy were carried out on left ventricular myocardium and brown adipose tissue (BAT). MultiPlex analysis of cytokines and chemokines in serum was accomplished. We found that short-term MCA reduced myocardial infarction, improved resistance of mitochondria to Ca2+-overload, and downregulated β1-ARs. The β2-ARs/protein kinase B/Akt were attenuated while β3-ARs translocated on the T-tubular system suggesting its activation. Protein kinase G (PKG) translocated to sarcoplasmic reticulum and phosphorylation of AMPKThr172 increased after 10 days. Principal component analysis revealed a significant shift in cytokine/chemokine serum levels on day 10 of acclimation, which corresponds to maturation of BAT. In conclusion, short-term MCA increases heart resilience to ischemia without any negative side effects such as hypertension or hypertrophy. Cold-elicited cardioprotection is accompanied by β1/2-AR desensitization, activation of the β3-AR/PKG/AMPK pathways, and an immunomodulatory effect.

Alpine plant species converge towards adopting elevation-specific resource-acquisition strategy in response to experimental early snow-melting

Snow-melt is one of the important factors limiting growth and survival of alpine plants. Changes in snow-melt timing have profound effects on eco-physiological characteristics of alpine plant species through alterations in growing season length. Here, we conducted a field experiment and studied species response to experimentally induced early snow-melting (ES) (natural vs. early) at an alpine site (Rohtang) in the western Himalaya region. Eco-physiological response of eight snow-bed restricted alpine plant species from different elevations (lower: 3850 m and upper: 4150 m amsl) and belonging to contrasting resource acquisition strategies (conservative and acquisitive) were studied after 2-years (2019 & 2020) of initiating ES field experiment. We estimated the functional traits related to leaf economic spectrum and physiological performance and assessed their pattern of phenotypic plasticity. Analysis by linear mixed effect model showed that both the ‘conservative’ and ‘acquisitive’ species had responded to ES with significant effects on species specific leaf area, leaf dry matter content, leaf thickness, leaf water content and sugar content. Our results also revealed that ES treatment induced significant increase in leaf C/N ratio (10.57 % to 13.65 %) and protein content (15.85 % to 20.76 %) at both the elevations, irrespective of species groups. The phenotypic plasticity was found to be low and was essentially species-specific. However, for leaf protein content, the upper elevation species exhibited a higher phenotypic plasticity (0.43 ± 0.18) than the lower elevation species (0.31 ± 0.21). Interestingly, we found that irrespective of species unique functional strategy, species adapt to perform more conservative at lower elevation and more acquisitive at upper elevation, in response to ES. We conclude that plants occurring at contrasting elevations respond differentially to ES. However, species showed capacity for short-term acclimation to future environmental conditions, but may be vulnerable, if their niche is occupied by new species with greater phenotypic plasticity and a superior competitive ability.

Long-term acclimation to warming improves the adaptive ability of Microcystis aeruginosa to high temperature: Based on growth, photosynthetic activity, and microcystin production

Gradually warming of water bodies caused by climate change is expected to intensify the expansion of Microcystis blooms causing a series of severe problems in waters. However, most predictions about global warming further promoting the dominance of Microcystis are dependent on the strains only experiencing short-term acclimation to high temperature. It still remains unknown whether long-term warming acclimation improves the adaptive ability of Microcystis to high temperature. The present study used Microcysits aeruginosa maintained at 25 °C, short- and long -term acclimated at 30 °C to explore the above knowledge gaps. The results showed that: (1) The growth rate of long-term warming acclimated M. aeruginosa was significantly enhanced, compared with those of low temperature cultured and short-term warming acclimated ones; (2) A faster decline rate of photosynthetic activity during growth phase and a higher ultimately stable photosynthetic activity during stationary phase of M. aeruginosa were caused by longer warming acclimation time; (3) high temperature reduced the microcystin production of long-term warming acclimated M. aeruginosa compared to that of low temperature cultured M. aeruginosa; (4) Warming acclimation time improved the driving effect of photosynthetic activity on the growth of M. aeruginosa but decreased the restriction ability of growth state to microcystin production of M. aeruginosa at high temperature; (5) Compared to low temperature cultured M. aeruginosa, high temperature improved the driving effect of photosynthetic activity on the growth of long-term warming acclimated M. aeruginosa, but decreased the sensitivity of photosynthetic activities to environmental resources and the regulative ability of microcystin production to photosynthetic activity. These findings indicated that long-term warming acclimation enhanced M. aeruginosa adaptive ability to high temperature and demonstrated the necessity of applying long-term warming acclimated strains in the future studies about the impact of global warming on cyanobacteria.

NTRC and thioredoxins m1/m2 underpin the light acclimation of plants on proteome and metabolome levels.

During photosynthesis, plants must manage strong fluctuations in light availability on different time scales, leading to long-term acclimation and short-term responses. However, little is known about the regulation and coordination of these processes and the modulators involved. In this study, we used proteomics, metabolomics, and reverse genetics to investigate how different light environmental factors, such as intensity or variability, affect long-term and short-term acclimation responses of Arabidopsis (Arabidopsis thaliana) and the importance of the chloroplast redox network in their regulation. In the wild type, high light, but not fluctuating light, led to large quantitative changes in the proteome and metabolome, accompanied by increased photosynthetic dynamics and plant growth. This finding supports light intensity as a stronger driver for acclimation than variability. Deficiencies in NADPH-thioredoxin reductase C (NTRC) or thioredoxins m1/m2, but not thioredoxin f1, almost completely suppressed the re-engineering of the proteome and metabolome, with both the induction of proteins involved in stress and redox responses and the repression of those involved in cytosolic and plastid protein synthesis and translation being strongly attenuated. Moreover, the correlations of protein or metabolite levels with light intensity were severely disturbed, suggesting a general defect in the light-dependent acclimation response, resulting in impaired photosynthetic dynamics. These results indicate a previously unknown role of NTRC and thioredoxins m1/m2 in modulating light acclimation at proteome and metabolome levels to control dynamic light responses. NTRC, but not thioredoxins m1/m2 or f1, also improves short-term photosynthetic responses by balancing the Calvin-Benson cycle in fluctuating light.

Long- and short-term acclimation of the photosynthetic apparatus to salinity in Chlamydomonas reinhardtii. The role of Stt7 protein kinase.

Salt stress triggers an Stt7-mediated LHCII-phosphorylation signaling mechanism similar to light-induced state transitions. However, phosphorylated LHCII, after detaching from PSII, does not attach to PSI but self-aggregates instead. Salt is a major stress factor in the growth of algae and plants. Here, our study mainly focuses on the organization of the photosynthetic apparatus to the long-term responses of Chlamydomonas reinhardtii to elevated NaCl concentrations. We analyzed the physiological effects of salt treatment at a cellular, membrane, and protein level by microscopy, protein profile analyses, transcripts, circular dichroism spectroscopy, chlorophyll fluorescence transients, and steady-state and time-resolved fluorescence spectroscopy. We have ascertained that cells that were grown in high-salinity medium form palmelloids sphere-shaped colonies, where daughter cells with curtailed flagella are enclosed within the mother cell walls. Palmelloid formation depends on the presence of a cell wall, as it was not observed in a cell-wall-less mutant CC-503. Using the stt7 mutant cells, we show Stt7 kinase-dependent phosphorylation of light-harvesting complex II (LHCII) in both short- and long-term treatments of various NaCl concentrations-demonstrating NaCl-induced state transitions that are similar to light-induced state transitions. The grana thylakoids were less appressed (with higher repeat distances), and cells grown in 150 mM NaCl showed disordered structures that formed diffuse boundaries with the flanking stroma lamellae. PSII core proteins were more prone to damage than PSI. At high salt concentrations (100-150 mM), LHCII aggregates accumulated in the thylakoid membranes. Low-temperature and time-resolved fluorescence spectroscopy indicated that the stt7 mutant was more sensitive to salt stress, suggesting that LHCII phosphorylation has a role in the acclimation and protection of the photosynthetic apparatus.

Short- and long-term consequences of heat exposure on mitochondrial metabolism in zebra finches (Taeniopygia castanotis)

Understanding the consequences of heat exposure on mitochondrial function is crucial as mitochondria lie at the core of metabolic processes, also affecting population dynamics. In adults, mitochondrial metabolism varies with temperature but can also depend on thermal conditions experienced during development. We exposed zebra finches to two alternative heat treatments during early development: “constant”, maintained birds at ambient 35 °C from parental pair formation to fledglings’ independence, while “periodic” heated broods at 40 °C, 6 h daily at nestling stage. Two years later, we acclimated birds from both experiments at 25 °C for 21 days, before exposing them to artificial heat (40 °C, 5 h daily for 10 days). After both conditions, we measured red blood cells’ mitochondrial metabolism using a high-resolution respirometer. We found significantly decreased mitochondrial metabolism for Routine, Oxidative Phosphorylation (OxPhos) and Electron Transport System maximum capacity (ETS) after the heat treatments. In addition, the birds exposed to “constant” heat in early life showed lower oxygen consumption at the Proton Leak (Leak) stage after the heat treatment as adults. Females showed higher mitochondrial respiration for Routine, ETS and Leak independent of the treatments, while this pattern was reversed for OxPhos coupling efficiency (OxCE). Our results show that short-term acclimation involved reduced mitochondrial respiration, and that the reaction of adult birds to heat depends on the intensity, pattern and duration of temperature conditions experienced at early-life stages. Our study provides insight into the complexity underlying variation in mitochondrial metabolism and raises questions on the adaptive value of long-lasting physiological adjustments triggered by the early-life thermal environment.

Short-term acclimation dynamics in a coldwater fish

Critical thermal maximum (CTmax) is widely used for measuring thermal tolerance but the strong effect of acclimation on CTmax is a likely source of variation within and among studies/species that makes comparisons more difficult. There have been surprisingly few studies focused on quantifying how quickly acclimation occurs or that combine temperature and duration effects. We studied the effects of absolute temperature difference and duration of acclimation on CTmax of brook trout (Salvelinus fontinalis), a well-studied species in the thermal biology literature, under laboratory conditions to determine how each of the two factors and their combined effects influence critical thermal maximum. Using an ecologically-relevant range of temperatures and testing CTmax multiple times between one and 30 days, we found that both temperature and duration of acclimation had strong effects on CTmax. As predicted, fish that were exposed to warmer temperatures longer had increased CTmax, but full acclimation (i.e., a plateau in CTmax) did not occur by day 30. Therefore, our study provides useful context for thermal biologists by demonstrating that the CTmax of fish can continue to acclimate to a new temperature for at least 30 days. We recommend that this be considered in future studies measuring thermal tolerance that intend to have their organisms fully acclimated to a given temperature. Our results also support using detailed thermal acclimation information to reduce uncertainty caused by local or seasonal acclimation effects and to improve the use of CTmax data for fundamental research and conservation planning.

Mechanisms underlying thermal breadth differ by species in insects from adjacent but thermally distinct streams – A test of the climate variability hypothesis

The Climate Variability Hypothesis (CVH) predicts that ectotherms from thermally variable climates should have wider thermal tolerances than their counterparts living in stable climates. Although the CVH has been widely supported, the mechanisms underlying wider tolerance traits remain unclear. We test the CVH along with three mechanistic hypotheses that may explain how differences in tolerance limits arise: 1) Short-term Acclimation Hypothesis (mechanism: rapid, reversible plasticity), 2) Long-term Effects Hypothesis (mechanisms: developmental plasticity, epigenetics, maternal effects, or adaptation), and 3) Trade-off Hypothesis (mechanism: trade-off between short- and long-term responses). We tested these hypotheses by measuring CTMIN, CTMAX, and thermal breadths (CTMAX - CTMIN) of aquatic mayfly and stonefly nymphs from adjacent streams with distinctly different levels of thermal variation following acclimation to either cool, control, and warm conditions. In one stream, daily mean temperature varied by about 5 °C annually, whereas in the other, it varied by more than 25 °C. In support of the CVH, we found that mayfly and stonefly nymphs from the thermally variable stream had broader thermal tolerances than those from the thermally stable stream. However, support for the mechanistic hypotheses differed by species. Mayflies appear to rely on long-term strategies for maintaining broader thermal limits, whereas stoneflies achieve broader thermal limits via short-term plasticity. We found no support for the Trade-off Hypothesis.

Effects of Body-Mounted Inertial Measurement Unit (IMU) Backpacks on Space Use and Behaviors of Laying Hens in a Perchery System

Body-mounted sensors have significantly enhanced our understanding of individual animals through location tracking, behavior monitoring, and activity determination. However, attaching sensors may alter the behavior of the tested animals, which would, potentially, invalidate the collected data. The objective of this study was to evaluate the effects of wearable backpacks on space use (feeder, nest box, and perch) and behaviors (aggressive, comfort, and locomotion behaviors) of laying hens in a perchery system. Nineteen laying hens were reared for 21 days, and each was fitted with a lightweight inertial measurement unit (IMU) backpack on day 0. Instantaneous scan samples were adopted to record the number of laying hens, using each space at a 5-min interval over the 16 h lights-on period at −6 d to −1 d, 1 d to 4 d, and 10 d to 15 d. Six hens were randomly selected for observation of behaviors during six 20-min periods at −5 d to −3 d, and 13 d to 15 d. Feeder use reduced at 1 d to 4 d, 11 d, and 13 d to 15 d, and nest box use reduced at 1 d, 3 d, and 10 d to 12 d, while it increased on 15 d. Hens perched more often at 1 d to 4 d and 10 d to 14 d. Space use was affected by wearing a backpack in the first few days after installation. As hens gradually accustomed to the devices, the effects on feeder, nest box, and perch use disappeared at 10 d, 13 d and 15 d, respectively. The diurnal pattern of hens using the nest box largely returned to the state before being backpacked, and there were slight recoveries in the use of feeder and perch use during the 15-day trial period. There was no observed difference in the amount of pecking, preening bouts, aerial ascent/descent, or the time spent on preening and walking at −5 d to −3 d and 13 d to 15 d. No differences were found in body weight and plumage condition score between 0 d and 16 d. The results demonstrated that the IMU backpack only had marginal and non-lasting effects on space use and behaviors of laying hens, and it seems suitable for further behavioral research after short-term acclimation. However, when the diurnal pattern serves as the variable of interest, researchers need to re-evaluate the effect of the device on birds, rather than implying there is no effect.

High Ecophysiological Plasticity of Desmarestia aculeata (Phaeophyceae) Present in an Arctic Fjord under Varying Salinity and Irradiance Conditions.

Simple SummaryThe Arctic region has been affected by rising temperatures, directly affecting the organisms living there. One of the organisms that inhabit this area is the seaweed Desmarestia aculeata (Phaeophyceae), widely distributed in the North Atlantic. It is exposed to the high Arctic light regime and fluctuating salinity conditions from glacial and terrestrial run-off. Despite its abundance, little is known about D. aculeata and how environmental drivers will affect it in a future altered by climate change. During the summer of 2019, D. aculeata was collected in Kongsfjorden, Svalbard (78.9° N, 11.9° E) to investigate its physiological and biochemical responses to salinities of 34, 28, and 18, and daily cycles of irradiance (50–500 μmol photons m−2s−1) at 0 °C over 21 days. Photosynthetic parameters and high pigment concentrations show how this species has an effective acclimation to irradiance changes, being unaffected by low salinity. The high concentration of antioxidant phlorotannins at low salinity show how D. aculeata can regulate its daily cycle despite the hyposaline conditions. Salinity and light are interacting factors in the acclimation process. Our work shows the high plasticity of D. aculeata, such that the species will probably be able to tolerate future changes in the Arctic.The seaweed Desmarestia aculeata (Phaeophyceae) is distributed in the temperate zone of the North Atlantic up to the Arctic, where it is exposed to a high Arctic light regime and fluctuating salinity conditions resulting from glacial and terrestrial run-off. Information on how this species is able to thrive under current and future Arctic conditions is scarce. During the Arctic summer of 2019, D. aculeata was collected in Kongsfjorden, Svalbard (78.9° N, 11.9° E) to investigate its physiological and biochemical responses to variations in salinity (salinities: 34, 28 and 18) and daily cycles of irradiance (50–500 μmol photons m−2s−1) at 0 °C over 21 days. The species revealed effective short-term acclimation to both abiotic drivers. Maximal quantum yield of PSII (Fv/Fm) fluctuated with the light cycle at a salinity of 34, while the maximum relative electron transport rate (rETRmax) significantly differed between salinities of 28 and 18. Chlorophyll a and β-Carotene remained at high concentrations in all treatments showing pronounced acclimation during the experiment. High mannitol concentrations were measured throughout the experiment, while phlorotannins were high at low salinity. Hyposalinity and light are interacting drivers of the physiological and biochemical acclimation process for D. aculeata. Our experiment highlights the high ecophysiological plasticity of D. aculeata, suggesting that the species will likely be capable of withstanding future habitat changes in the Arctic.

Plants acclimate to Photosystem I photoinhibition by readjusting the photosynthetic machinery.

Photosynthetic light reactions require strict regulation under dynamic environmental conditions. Still, depending on environmental constraints, photoinhibition of Photosystem (PSII) or PSI occurs frequently. Repair of photodamaged PSI, in sharp contrast to that of PSII, is extremely slow and leads to a functional imbalance between the photosystems. Slow PSI recovery prompted us to take advantage of the PSI‐specific photoinhibition treatment and investigate whether the imbalance between functional PSII and PSI leads to acclimation of photosynthesis to PSI‐limited conditions, either by short‐term or long‐term acclimation mechanisms as tested immediately after the photoinhibition treatment or after 24 h recovery in growth conditions, respectively. Short‐term acclimation mechanisms were induced directly upon inhibition, including thylakoid protein phosphorylation that redirects excitation energy to PSI as well as changes in the feedback regulation of photosynthesis, which relaxed photosynthetic control and excitation energy quenching. Longer‐term acclimation comprised reprogramming of the stromal redox system and an increase in ATP synthase and Cytochrome b6f abundance. Acclimation to PSI‐limited conditions restored the CO2 assimilation capacity of plants without major PSI repair. Response to PSI inhibition demonstrates that plants efficiently acclimate to changes occurring in the photosynthetic apparatus, which is likely a crucial component in plant acclimation to adverse environmental conditions.

Effects of a Short-Term Heat Acclimation Protocol in Elite Amateur Boxers

Stone, BL, Ashley, JD, Skinner, RM, Polanco, JP, Walters, MT, Schilling, BK, and Kellawan, JM. Effects of a short-term heat acclimation protocol in elite amateur boxers. J Strength Cond Res 36(7): 1966-1971, 2022-Boxing requires proficient technical and tactical skills coupled with high levels of physiological capacity. Although heat and humidity negatively affect acute exercise performance, short-term exercise training in hot and humid environments can lead to physiological adaptations that enhance exercise performance in both hot and thermoneutral conditions. In highly trained endurance athletes, exercise-induced acclimation can occur in as little as 5 days (known as short-term heat acclimation [STHA]). However, the impact of a 5-day heat acclimation (5-DayHA) in combat athletes, such as elite amateur boxers, is unknown. The aim of the present investigation was to determine whether a 5-DayHA improves aerobic performance in a thermoneutral environment and causes positive physiological adaptations in elite boxers. Seven elite amateur boxers underwent a 5-DayHA protocol, consisting of 60-minute exercise sessions in an environmental chamber at 32 °C and 70% relative humidity. Repeat sprint test (RST) evaluated aerobic performance in a thermoneutral environment 24 hours before and after the 5-DayHA. Presession and postsession hydration status (urine specific gravity) and body mass were assessed. After a 5-DayHA period, boxers significantly improved RST performance (13 ± 7 to 19 ± 7 sprints, d = 0.92, p = 0.03) but not pre-exercise hydration status (1.02 ± 0.01 to 1.01 ± 0.01, d = 0.82, p = 0.07). Therefore, these findings suggest 5-DayHA enhances aerobic performance in elite-level amateur boxers and may provide a viable training option for elite combat athletes.

Hyposalinity induces significant polar lipid remodeling in the marine microalga Dunaliella tertiolecta (Chlorophyceae)

Marine microalgae often live in a fluctuating environment including a decrease in salinity caused by global warming induced sea ice melting and freshwater inflows. Under conditions of fluctuating salinity, microalgae have evolved a variety of survival mechanisms such as lipid accumulation and remodeling. The purpose of this study was to investigated the membrane lipid remodeling of the marine green microalga Dunaliella tertiolecta as a short-term acclimation mechanism in response to hyposalinity (20 and 3 PSU) with respect to growth at optimal salinity (38 PSU). We identified 34 lipid species belonging to seven polar lipid classes. Dunaliella tertiolecta accumulates cell lipids and remodels polar lipid classes and their fatty acids composition as response to hypoosmotic stress at 3 PSU. We found that the unsaturation of most polar lipids decreases overall, indicating decreased membrane fluidity and altered permeability, whereas shortening the length of fatty acids of polar lipids is not one of the strategies of D. tertiolecta to cope with the decrease in salinity. Increase in relative content (%) and unsaturation of monogalactosyldiacylglycerols (MGDG) and decrease in relative content (%) and unsaturation of phosphatidylglycerols (PG), suggesting changes in photosynthetic membranes of thylakoids at 20 and 3 PSU. At a very low salinity of 3 PSU, the relative content (%) of phosphatidylinositols (PI) increases, suggesting increased lipid trafficking and signaling in the cells. These changes are statistically significant and we hypothesize that D. tertiolecta is genetically adapted to withstand large salinity fluctuations through polar lipid composition.

Consistently high heat tolerance acclimation in response to a simulated heatwave across species from the broadly distributed Acacia genus.

When leaves exceed their thermal threshold during heatwaves, irreversible damage to the leaf can accumulate. However, few studies have explored short-term acclimation of leaves to heatwaves that could help plants to prevent heat damage with increasing heatwave intensity. Here, we studied the heat tolerance of PSII (PHT) in response to a heatwave in Acacia species from across a strong environmental gradient in Australia. We compared PHT metrics derived from temperature-dependent chlorophyll fluorescence response curves (T-F 0 ) before and during a 4-day 38°C heatwave in a controlled glasshouse experiment. We found that the 15 Acacia species displayed surprisingly large and consistent PHT acclimation responses with a mean tolerance increase of 12°C (range, 7.7-19.1°C). Despite species originating from diverse climatic regions, neither maximum temperature of the warmest month nor mean annual precipitation at origin were clear predictors of PHT. To our knowledge, these are some of the largest measured acclimation responses of PHT from a controlled heatwave experiment. This remarkable capacity could partially explain why this genus has become more diverse and common as the Australian continent became more arid and suggests that the presence of Acacia in Australian ecosystems will remain ubiquitous with climate change.

Phenotypic plasticity in the energy metabolism of a small Andean rodent: Effect of short-term thermal acclimation and developmental conditions.

The study of phenotypic variation within species in response to different environments is a central issue in evolutionary and ecological physiology. Particularly, ambient temperature is one of the most important factors modulating interactions between animals and their environment. Phyllotis xanthopygus, a small Andean rodent, exhibits intraspecific differences along an altitudinal gradient in traits relevant to energy balance that persist after acclimation to common experimental temperatures. Therefore, we aim to explore geographic variations in energetic traits of P. xanthopygus and to assess the contribution of phenotypic plasticity to population differences. We compared metabolic rate and thermal conductance in response to different acclimation temperatures in animals collected at distinct altitudes (F0 generation) and in their offspring, born and raised under common-garden conditions (F1 generation). We found intraspecific differences in resting metabolic rate (RMR) of animals collected at different altitudes that were no longer evident in the F1 generation. Furthermore, although both generations showed the same pattern of RMR flexibility in response to acclimation temperature, its magnitude was lower for the F1 individuals. This suggests that developmental conditions affect the short-term acclimation capacity of this trait during adulthood. On the other hand, thermal conductance (C) showed irreversible plasticity, as animals raised in the laboratory at stable warm conditions had a relatively higher C than the animals from the field, showing no adjustments to thermal acclimation during adulthood in either group. In sum, our results support the hypothesis that the developmental environment shapes energetic traits, emphasizing the relevance of incorporating ontogeny in physiological studies.

Differential Response of Leafminer Flies Liriomyza trifolii (Burgess) and Liriomyza sativae (Blanchard) to Rapid Cold Hardening.

Simple SummaryLiriomyza trifolii (Burgess) and L. sativae (Blanchard) are closely-related, polyphagous leafminers that occur worldwide and presumably compete with each other. In this study, we evaluated the response of pupae and adults from both species to acute (2 h) cold exposures. The results were used to identify the lethal temperature for 80% of the population (LT80) for each species. In a separate set of experiments, insects were cooled to one of six nonlethal temperatures (0–5 °C) for 4 h and then cooled to the LT80 for 2 h to evaluate their rapid cold hardening (RCH) response. L. trifolii exhibited stronger cold tolerance than L. sativae; furthermore, the supercooling point of L. trifolii was significantly lower than that of L. sativae. RCH was induced in pupae of both species at a range of low temperatures (0–5 °C), and L. sativae pupae showed a more robust RCH response (e.g., lower supercooling pointand more durable RCH) than L. trifolii pupae. Our results indicate that subtle differences in RCH and basal cold tolerance impact the competitiveness of the two leafminers.Rapid cold hardening (RCH) is a rapid and critical adaption of insects to sudden temperature changes but is often overlooked or underestimated as a component of survival. Thus, interspecific comparisons of RCH are needed to predict how phenotypes will adapt to temperature variability. RCH not only enhances cold survival but also protects against non-lethal cold injury by preserving essential functions such as locomotion, reproduction, and energy balance. This study investigated the difference in basal cold tolerance and RCH capacity of L. trifolii and L. sativae. In both species, the cold tolerance of pupae was significantly enhanced after short-term exposure to moderately cold temperatures. The effect of RCH last for 4 h in L. sativae but only 2 h in L. trifolii. Interestingly, L. trifolii adults had a RCH response but L. sativae adults failed to acclimate. Short-term acclimation also lowered the supercooling point significantly in the pupae of both species. Based on these results, we propose a hypothesis that these differences will eventually affect their competition in the context of climate change. This study also provides the basis for future metabolomic and transcriptomic studies that may ultimately uncover the underlying mechanisms of RCH and interspecific competition between L. trifolii and L. sativae.