Heat-sensitive Species Research Articles

Establishment of Efficient Method for Evaluation of Heat Stress Tolerance of Herbaceous Plant Species and Selection of Heat-Tolerant Plants

Due to climate change, heat-tolerant species have become increasingly important; however, the selection system for herbaceous plants has yet to be well established. This study aimed to establish a selection system for heat-tolerant plant species and to identify such species. Heat stress at 50 °C for 120 min was applied to 27 plant species using a heat treatment and recovery model. Among them, four herbaceous species—Hemerocallis fulva, Heliopsis longipes, Hosta plantagines, and Scilla scilloides—were selected by measuring their electrolyte leakage index (ELI). Additionally, species with high ELI values (Centaurea cyanus) and low ELI values (S. scilloide) were selected to determine the optimal temperature and time for the heat treatment using linear regression analysis. The selected heat-tolerant herbaceous plants survived under optimal heat stress conditions (120 min at 50 °C). The degree of cell death in the selected plant species was measured using Evans blue staining. The results showed that the cell death indexes of heat-tolerant species were less than 22% after heat treatment, compared to over 57% in heat-sensitive species. Furthermore, the recovery ability at room temperature after heat treatment was assessed using the DAB staining method. The selected heat-tolerant plant species recovered quickly (within 90 min), whereas the heat-sensitive species required over 480 min for recovery. The analytical method developed in this study can more accurately determine the response of various plants to heat stress and has high reproducibility. Therefore, it is considered an excellent method for establishing a heat-tolerant plant selection system.

The impact of climate and potassium nutrition on crop yields: Insights from a 30-year Swiss long-term fertilization experiment

Climate change will strongly influence agricultural practices in the future. In order to promote resource-efficient agriculture, it is important to analyse the impact of climate variation on crop yields. In this study, we report yields of spring wheat, winter barley, maize, potato and sugar beet from the long-term crop rotation and fertilization experiment Demo in Switzerland and analyze their response to different climate variables (e.g., annual and seasonal temperature, precipitation, evapotranspiration, number of heat days and days of heavy rainfall). In addition, we investigate the impact of readily plant-available soil potassium (K) on the relationship of crop yields and precipitation. Annual and summer temperatures increased by 1 °C and 1.5 °C, respectively, over the observation period, and both the number of heat days and days of heavy rainfall increased in summer. Rising summer temperatures have a negative impact on all crop yields, which was most prominent for spring wheat, potato and maize. Annual, spring and summer precipitation show varying effects on different crops. For maize, soil K has a mediating effect on yield reductions under low spring precipitation. Yields are significantly reduced by 1 t ha−1 per 100 mm reduction of precipitation below a soil K threshold of 7 mg K kg−1 soil. Based on these results and the future climate scenarios for Switzerland, crop rotations with less heat-sensitive species and early-maturing varieties should be considered. In order to keep future irrigation demands and costs as low as possible, the soil K fertility classes in the Swiss K fertilization guidelines might need to be revisited. Our study is one of a few long-term observations that show the impact of climate variation on crop yields and highlights the potential of K management as a climate change adaptation measure.

Urban Heat Island and Reduced Habitat Complexity Explain Spider Community Composition by Excluding Large and Heat-Sensitive Species

Along with worldwide urbanization, upheavals in habitat and temperature are major threats for biodiversity. However, due to their interdependence, their relative roles as drivers of animal community composition remain entangled. Here, we investigated how taxonomic and functional compositions of arthropod communities were related to uncorrelated habitat and temperature gradients, and compared landscape (i.e., urbanization, Urban Heat Island (UHI)) to local variables (i.e., vegetation height and cover, near-ground temperature). We sampled 20,499 spiders (137 species) on 36 grasslands in Rennes (northwestern France). Unlike rural areas, urban sites were characterized by short vegetation and intense UHI, hosted species-poor communities, and were composed of small thermophilic species. UHI intensification and local loss of habitat complexity (short and dense vegetation) were associated with declining large and heat-sensitive species. These results highlight the prevalent role of urban warming, rather than land cover change, as an urban filter. Further, we show that landscape-scale UHI, not local temperature, filters species according to their functional attributes. UHI can therefore be considered as a thermal barrier, filtering species according to their physiological capacity to cope with urban thermal conditions. Finally, to counterbalance biotic homogenization, we argue for the importance of implementing complex habitat structures at the local scale within urban green infrastructure.

Leaf thermal tolerance and sensitivity of temperate tree species are correlated with leaf physiological and functional drought resistance traits

Climate change is causing more frequent and severe climatic events, such as extreme heat and co-occurring drought, potentially accelerating tree mortality. Which tree species will cope better with those extreme events is still being researched. This study focuses on heat as a physiological stress factor and interspecific variation of thermal tolerance and sensitivity traits in 15 temperate coniferous and broad-leaved tree species. We investigate (1) whether thermal tolerance and sensitivity traits correlate with a drought-related physiological trait, particularly the leaf turgor loss point (πtlp, wilting point), and (2) how thermal tolerance and sensitivity traits co-vary within different tree-functional types classified by morphological and physiological traits of the leaf, i.e., leaf mass per area (LMA) and percentage loss of area (PLA). The study was carried out in the Traunstein Forest Dynamics Plot of the ForestGEO network in Germany. The temperature response of the maximum quantum yield of photosystem II (Fv/Fm) on leaf discs was determined, from which various physiological leaf traits were estimated, one of which is the breaking point temperature (T5), the temperature at which Fv/Fm declines by 5%. Additionally, the temperature of 50% (T50) and 95% (T95) decline in Fv/Fm was evaluated. The decline width between T50 and T5 (DWT50−T5) was taken as an indicator of the species’ thermal sensitivity. The breaking point temperature ranged from 35.4 ± 3.0 to 47.9 ± 3.9 °C among the investigated tree species and T50 ranged between 46.1 ± 0.4 and 53.6 ± 0.7 °C. A large interspecific variation of thermal tolerance and sensitivity was found. European ash (Fraxinus excelsior L.) was the most heat-sensitive species, while Wild cherry (Prunus avium L.) was the least heat-sensitive species. Species with a more negative πtlp tended to have a higher breaking point temperature than species with a less negative πtlp. A lower thermal sensitivity characterized species with a higher LMA, and high PLA was found in species with low thermal sensitivity. Accordingly, species with thicker and tougher leaves have lower thermal sensitivity which coincides with a lower wilting point. We conclude that species that develop drought-adapted foliage can cope better with heat stress. Further, they might be able to maintain transpirational cooling during combined heat and drought stress, which could lessen their mortality risk during climatic extremes.

Marine Heat Waves over Natural and Urban Coastal Environments of South Florida

Marine Heat Wave (MHW) events are increasingly recognized as an important factor in the sustainability of coastal environments (both natural and urban), in the context of climate change. They are related to increasing trends of Sea Surface Temperature (SST) at the adjacent ocean waters. SST is an important parameter of the earth’s climate and increasing SST trends have been associated with adverse effects on coastal ecosystems, with important environmental and socioeconomic implications. This study focuses on the SST interannual variability over the coastal marine environment of South Florida, which contains several fragile ecosystems, and draws associate effects with adjacent large urban coastal settlements. The methodology is based on high-resolution satellite-derived SST data during a 40-year period (1982–2021), augmented by recent high-resolution model simulations (2012–2020). A generally increasing trend has been detected in the observations over the entire region (0.19 °C/decade). The unusual temperature levels have been associated with the formation of extensive MHW events, which showed interannual positive trends (0.75 events/decade) during the 40-year study period. Specifically, the six most recent years (2015–2021) were characterized by the strongest formation of MHWs with a peak in 2015, 2019 and 2020, with more than 8 events/year and approximately 70 to 110 days/year duration in total. The Florida Keys, especially along the Straits of Florida (southern island coasts), revealed very strong increasing trends. Miami Beach is also characterized by strong interannual trends (1.1 events/decade and 10 days/decade) compared to the enclosed basin of Biscayne Bay. In addition to the influence of atmospheric conditions over all regions around South Florida, the formation of MHWs near the eastern Florida coasts was also controlled by ocean dynamics, related to the warm Florida Current (FC). The evolution of the FC close to the eastern coasts (e.g., Miami Beach) was found to be a pre-condition of MHW formation. Several disastrous events on the biotic environment of South Florida near large urban settlements have been related to the formation of MHWs. The detected positive trends, and especially the recent high peaks of MHW events, may enhance the loss of specific heat-sensitive species, damaging the biodiversity of this tropical coastal environment and weakening the natural coastal protection against tropical storms. Urban planning for sustainable development in South Florida’s coastal cities must take into account MHW trends.

Correlations between photosynthetic heat tolerance and leaf anatomy and climatic niche in Asian mangrove trees.

Photosynthetic heat tolerance (PHT ) is a key predictor of plant response to climate change. Mangroves are an ecologically and economically important coastal plant community comprised of trees growing at their physiological limits. Mangroves are currently impacted by global warming, yet the PHT of mangrove trees is poorly understood. In this study, we provide the first assessment of PHT in 13 Asian mangrove species, based on the critical temperature that causes the initial damage (TCrit ) and the temperature that causes 50% damage (T50 ) to photosystem II. We tested the hypotheses that the PHT in mangroves is: (i) correlated with climatic niche and leaf traits, and (ii) higher than in plants from other tropical ecosystems. Our results demonstrated correlations between PHT and multiple key climate variables, the palisade to spongy mesophyll ratio and the leaf area. The two most heat-sensitive species were Kandelia obovata and Avicennia marina. Our study also revealed that mangrove trees show high heat tolerance compared to plants from other tropical ecosystems. The high PHT of mangroves thus demonstrated a conservative evolutionary strategy in heat tolerance, and highlights the need for integrative and comparative studies on thermoregulatory traits and climatic niche in order to understand the physiological response of mangrove trees to climate change-driven heatwaves and rising global temperatures.

Effect of Nutrient Solution Cooling in Summer and Heating in Winter on the Performance of Baby Leafy Vegetables in Deep-Water Hydroponic Systems

Hydroponics has become a popular production technology for leafy greens in greenhouses. However, year-round production of cool-season leafy greens remains challenging due to costly heating and cooling during winter and summer seasons, depending on location. Therefore, the objective of this study is to investigate the effect of nutrient solution cooling and heating in deep-water hydroponic systems on the performance of several leafy green vegetables. Two experiments of nutrient solution cooling during the summer season and another two experiments of nutrient solution heating during the winter season were conducted in Texas, USA in 2020–2021. Lettuce (Lactuca sativa L.) ‘Bergams Green’ and ‘Red Mist’, Pak Choi (Brassica rapa subsp. chinensis) ‘Purple Magic’ and ‘White Stem’, and spinach (Spinacia oleracea L.) ‘Mandolin’ and ‘Seaside’ were grown in the summer experiments, and only the two lettuce cultivars were grown for the winter experiments. For both cooling and heating studies, six deep-water culture systems were used with two treatments: cooling (23 °C) vs. no cooling, and heating (22 °C) vs. no heating, with three replications in each experiment. In the nutrient solution cooling study, spinach was the most heat-sensitive species, and ‘Mandolin’ was more heat-tolerant than ‘Seaside,’ as evidenced by its lower mortality rate in both experiments. Lettuce and pak choi grew well and solution cooling increased shoot fresh weight in both lettuce cultivars and in ‘White Stem’ pak choi but not in ‘Purple Magic’ pak choi. Conversely, during the winter season, solution heating increased shoot fresh weight of both lettuce cultivars; however, ‘Red Mist’ was more responsive than ‘Bergams Green’ lettuce. These results indicate the potential to increase crop yield by controlling nutrient solution temperature throughout the year, depending on the season. Also, there were genotypic differences in both cooling and heating experiments, indicating that more research is needed to determine the species-dependent and even cultivar-dependent nutrient solution temperature control strategies to achieve optimum year-round production.

Effects of Heat Stress on Mating Behavior and Colony Development in Bombus terrestris (Hymenoptera: Apidae)

Climate change is related to an increase in the frequency and intensity of extreme events such as heatwaves. In insect pollinators, heat exposure is associated with direct physiological perturbations, and in several species, could lead to a decrease of fitness related to a decrease in fertility. Here we developed a new experimental protocol in controlled conditions to assess if the exposure to high temperatures could modify the attractiveness and fertility of Bombus terrestris males. Our results show that virgin queens of B. terrestris do not have preferences between the pheromonal secretions of heat-exposed and control males. Moreover, mating with a heat-exposed male has no impact on the copulation behavior and the development of the nest (brood composition). We advise to extend trials to cover a range of wild and heat-sensitive species on multiple generations to better understand the impact of heat waves on the bumblebee communities.

Sensitivity of Photosynthesis to Warming in Two Similar Species of the Aquatic Angiosperm Ruppia from Tropical and Temperate Habitats

Climate change-related events, such as marine heatwaves, are increasing seawater temperatures, thereby putting pressure on marine biota. The cosmopolitan distribution and significant contribution to marine primary production by the genus Ruppia makes them interesting organisms to study thermal tolerance and local adaptation. In this study, we investigated the photosynthetic responses in Ruppia to the predicted future warming in two contrasting bioregions, temperate Sweden and tropical Thailand. Through DNA barcoding, specimens were determined to Ruppia cirrhosa for Sweden and Ruppia maritima for Thailand. Photosynthetic responses were assessed using pulse amplitude-modulated fluorometry, firstly in short time incubations at 18, 23, 28, and 33 °C in the Swedish set-up and 28, 33, 38, and 43 °C in the Thai set-up. Subsequent experiments were conducted to compare the short time effects to longer, five-day incubations in 28 °C for Swedish plants and 40 °C for Thai plants. Swedish R. cirrhosa displayed minor response, while Thai R. maritima was more sensitive to both direct and prolonged temperature stress with a drastic decrease in the photosynthetic parameters leading to mortality. The results indicate that in predicted warming scenarios, Swedish R. cirrhosa may sustain an efficient photosynthesis and potentially outcompete more heat-sensitive species. However, populations of the similar R. maritima in tropical environments may suffer a decline as their productivity will be highly reduced.

Comparative analyses of extreme dry seed thermotolerance in five Cactaceae species

Extreme dry seed thermotolerance is an important trait in the context of plant adaptation to desert environments, yet the mechanisms underlying interspecific differences in seed extremophily remain little understood. Seeds of a selection of desert Cactaceae species (Leucostele litoralis, Leucostele skottsbergii, Eulychnia breviflora, Eriosyce paucicostata and Ferocactus wislizeni) were subjected to comparative biophysical and molecular analyses prior to (mature dry seeds) and post (imbibing seeds) heat treatment (103 °C).Biophysical properties of mature dry seeds, such as seed coat hardness and thermal transitions, were characterized through puncture force resistance and differential scanning calorimetry, respectively. In addition, the protein composition of dry seeds was compared by 2-D electrophoresis and de novo sequencing. Finally, oxidative DNA damage repair and gene expression during seed imbibition were analysed via ELISA (8-oxo-dG levels) and comparative transcriptomics.Results revealed that enhanced dry seed thermotolerance could not be explained by seed coat hardness, seed thermal transitions or (ROS-induced oxidative) DNA damage repair. Comparative proteomic analysis showed that the majority of overlapping proteins were more abundant in relatively heat sensitive species, suggesting that higher basal levels of (stress) proteins do not underly improved heat resilience in Cactaceae. However, comparative transcriptomics during imbibition following heat stress detected consistent expression patterns of heat- and drying-responsive genes that correlated with dry seed thermotolerance. These patterns included upregulation of positive (HSP101/CLPB1, MGE2, MBF1c, HSFB2A, RPN1a, RPT2a, DEGP14/PARK13, XPO1A, MAIGO2/MAG2, CAMTA1, ADH1) and downregulation of negative (RCF3, VOZ1, FAD7, ZAT12, RNP1) heat and drought tolerance regulators.Thus, our comparative analyses of extremophile Cactaceae species suggest that higher dry seed thermotolerance is realised through enhanced recovery from heat stress during imbibition, which is a critical stage in the plant life cycle.

Temperature-dependent life history and transcriptomic responses in heat-tolerant versus heat-sensitive Brachionus rotifers

Thermal stress response is an essential physiological trait that determines occurrence and temporal succession in nature, including response to climate change. We compared temperature-related demography in closely related heat-tolerant and heat-sensitive Brachionus rotifer species. We found significant differences in heat response, with the heat-sensitive species adopting a strategy of long survival and low population growth, while the heat-tolerant followed the opposite strategy. In both species, we examined the genetic basis of physiological variation by comparing gene expression across increasing temperatures. Comparative transcriptomic analyses identified shared and opposing responses to heat. Interestingly, expression of heat shock proteins (hsps) was strikingly different in the two species and mirrored differences in population growth rates, showing that hsp genes are likely a key component of a species’ adaptation to different temperatures. Temperature induction caused opposing patterns of expression in further functional categories including energy, carbohydrate and lipid metabolism, and in genes related to ribosomal proteins. In the heat-sensitive species, elevated temperatures caused up-regulation of genes related to meiosis induction and post-translational histone modifications. This work demonstrates the sweeping reorganizations of biological functions that accompany temperature adaptation in these two species and reveals potential molecular mechanisms that might be activated for adaptation to global warming.

Temperature shapes movement and habitat selection by a heat-sensitive ungulate

Warmer weather caused by climate change poses increasingly serious threats to the persistence of many species, but animals can modify behavior to mitigate at least some of the threats posed by warmer temperatures. Identifying and characterizing how animals modify behavior to avoid the negative consequences of acute heat will be crucial for understanding how animals will respond to warmer temperatures in the future. We studied the extent to which moose (Alces alces), a species known to be sensitive to heat, mitigates heat on hot summer days via multiple different behaviors: (1) reduced movement, (2) increased visitation to shade, (3) increased visitation to water, or (4) a combination of these behaviors. We used GPS telemetry and a step-selection function to analyze movement and habitat selection by moose in northeastern Minnesota, USA. Moose reduced movement, used areas of the landscape with more shade, and traveled nearer to mixed forests and bogs during periods of heat. Moose used shade far more than water to ameliorate heat, and the most pronounced changes in behavior occurred between 15 and 20 °C. Research characterizing the behaviors animals use to facilitate thermoregulation will aid conservation of heat-sensitive species in a warming world. The modeling framework presented in this study is a promising method for evaluating the influence of temperature on movement and habitat selection.

Proteome and transcriptome reveal the involvement of heat shock proteins and antioxidant system in thermotolerance of Clematis florida

Clematis florida Thun (CfT) is an ornamental and medicinal plant. It is a cold resistant but heat sensitive species and deserves to be further investigated to improve its adaptability to heat stress. Exploring the molecular mechanism potential via an omic-analysis constitutes a promising approach towards improving heat tolerance of CfT. Two CfT lines, heat resistance (HR) and heat sensitive (HS), with differential thermotolerance capacities were used for the integrative analyses of proteomics and transcriptomes. Transcriptomes analysis showed that various pathways were significantly enriched including plant hormone signal transduction and carbon fixation pathways in prokaryotes. Proteomics study revealed the enrichment of some other pathways comprising antioxidant activity and carbohydrates metabolism. Based on combined transcriptomes and proteomics analyses and following heat stress treatment, a total of 1724 annotated genes were overlapped between both CfT lines. Particularly, 84 differential expressed genes (DEGs) were overlapped in both CfT lines. Fifteen out of these 84 genes were up-regulated solely for HR line (PS) but not for HS one (SG). This strongly suggests a potential prominent role for these genes in the thermotolerance process in PS line. We corroborate that two Hsps (Hsp18 and Hsp70) out of 20 detected proteins with higher expression levels in PS than in SG based on either global transcripts or proteins levels. According to the transcriptomes and proteomics analyses, 6 proteins and their corresponding genes were found to be significantly abundant in HR line (PS). Data are available via ProteomeXchange with identifier PXD018192. The expressions levels of these 6 genes were checked also for both CfT lines to evaluate their potential contributions in the heat tolerance process. Thus, their expression levels were approximately 2~4 times higher in HR than in HS line. We provided as well a representative schematic model to highlight the key genes involved in ROS scavenging and photorespiratory pathway in CfT. This model could be helpful also in understanding the mechanism of heat tolerance in CfT.

Obligate bacterial endosymbionts limit thermal tolerance of insect host species

The thermal tolerance of an organism limits its ecological and geographic ranges and is potentially affected by dependence on temperature-sensitive symbiotic partners. Aphid species vary widely in heat sensitivity, but almost all aphids are dependent on the nutrient-provisioning intracellular bacterium Buchnera, which has evolved with aphids for 100 million years and which has a reduced genome potentially limiting heat tolerance. We addressed whether heat sensitivity of Buchnera underlies variation in thermal tolerance among 5 aphid species. We measured how heat exposure of juvenile aphids affects later survival, maturation time, and fecundity. At one extreme, heat exposure of Aphis gossypii enhanced fecundity and had no effect on the Buchnera titer. In contrast, heat suppressed Buchnera populations in Aphis fabae, which suffered elevated mortality, delayed development and reduced fecundity. Likewise, in Acyrthosiphon kondoi and Acyrthosiphon pisum, heat caused rapid declines in Buchnera numbers, as well as reduced survivorship, development rate, and fecundity. Fecundity following heat exposure is severely decreased by a Buchnera mutation that suppresses the transcriptional response of a gene encoding a small heat shock protein. Similarly, absence of this Buchnera heat shock gene may explain the heat sensitivity of Ap. fabae Fluorescent in situ hybridization revealed heat-induced deformation and shrinkage of bacteriocytes in heat-sensitive species but not in heat-tolerant species. Sensitive and tolerant species also differed in numbers and transcriptional responses of heat shock genes. These results show that shifts in Buchnera heat sensitivity contribute to host variation in heat tolerance.

Ecological responses of periphyton dry mass and epilithic diatom community structure for different atrazine and temperature scenarios

Climate change–induced temperature increase may influence the ecotoxicity of agricultural herbicides such as atrazine and consequently negatively impact aquatic biota. The objective of this study was to assess the effects of increased temperature on the ecotoxicity of atrazine to diatom community structure and stream periphyton load using laboratory microcosm experiments. A natural periphyton community from the Mukwadzi River, Zimbabwe, was inoculated into nine experimental systems containing clean glass substrates for periphyton colonisation. Communities were exposed to 0 µg∙L-1 (control), 15 µg∙L-1 and 200 µg∙L-1 atrazine concentrations at 3 temperature levels of 26°C, 28°C and 30°C. Periphyton dry weight and community taxonomic composition were analysed on samples collected after 1, 2 and 3 weeks of colonisation. A linear mixed-effects model was used to analyse the main and interactive effects of atrazine and temperature on dry mass, species diversity, evenness and richness. Temperature and atrazine had significant additive effects on species diversity, richness and dry mass. As temperature increased, diatom species composition shifted from heat-sensitive species such as Achnanthidium affine to heat-tolerant species such as Achnanthidium exiguum and Epithemia adnata. Increasing temperature in aquatic environments contaminated with atrazine results in sensitive and temperature-intolerant diatoms being eliminated from periphyton communities. Climate change will exacerbate effects of atrazine on periphyton dry mass and diatom community structure.

Transcriptomic resilience, symbiont shuffling, and vulnerability to recurrent bleaching in reef-building corals.

As climate change progresses and extreme temperature events increase in frequency, rates of disturbance may soon outpace the capacity of certain species of reef-building coral to recover from bleaching. This may lead to dramatic shifts in community composition and ecosystem function. Understanding variation in rates of bleaching recovery among species and how that translates to resilience to recurrent bleaching is fundamental to predicting the impacts of increasing disturbances on coral reefs globally. We tracked the response of two heat sensitive species in the genus Acropora to repeated bleaching events during the austral summers of 2015 and 2017. Despite a similar bleaching response, the species Acropora gemmifera recovered faster based on transcriptome-wide gene expression patterns and had a more dynamic algal symbiont community than Acropora hyacinthus growing on the same reef. Moreover, A.gemmifera had higher survival to repeated heat extremes, with six-fold lower mortality than A.hyacinthus. These patterns suggest that speed of recovery from a first round of bleaching, based on multiple mechanisms, contributes strongly to sensitivity to a second round of bleaching. Furthermore, our data uncovered intragenus variation in a group of corals thought generally to be heat-sensitive and therefore paint a more nuanced view of the future health of coral reef ecosystems against a backdrop of increasing thermal disturbances.

Forecasting the response to global warming in a heat-sensitive species

Avoiding hyperthermia entails considerable metabolic costs for endotherms. Such costs increase in warm conditions, when endotherms may trade food intake for cooler areas to avoid heat stress and maximize their energy balance. The need to reduce heat stress may involve the adoption of tactics affecting space use and foraging behaviour, which are important to understand and predict the effects of climate change and inform conservation. We used resource selection models to examine the behavioural response to heat stress in the Alpine ibex (Capra ibex), a cold-adapted endotherm particularly prone to overheating. Ibex avoided heat stress by selecting the space based on the maximum daily temperature rather than moving hourly to ‘surf the heat wave’, which minimised movement costs but prevented optimal foraging. By integrating these findings with new climate forecasts, we predict that rising temperatures will force mountain ungulates to move upward and overcrowd thermal refugia with reduced carrying capacity. Our approach helps in identifying priority areas for the conservation of mountain species.

Genomic changes associated with adaptation to arid environments in cactophilic Drosophila species

BackgroundInsights into the genetic capacities of species to adapt to future climate change can be gained by using comparative genomic and transcriptomic data to reconstruct the genetic changes associated with such adaptations in the past. Here we investigate the genetic changes associated with adaptation to arid environments, specifically climatic extremes and new cactus hosts, through such an analysis of five repleta group Drosophila species.ResultsWe find disproportionately high rates of gene gains in internal branches in the species’ phylogeny where cactus use and subsequently cactus specialisation and high heat and desiccation tolerance evolved. The terminal branch leading to the most heat and desiccation resistant species, Drosophila aldrichi, also shows disproportionately high rates of both gene gains and positive selection. Several Gene Ontology terms related to metabolism were enriched in gene gain events in lineages where cactus use was evolving, while some regulatory and developmental genes were strongly selected in the Drosophila aldrichi branch. Transcriptomic analysis of flies subjected to sublethal heat shocks showed many more downregulation responses to the stress in a heat sensitive versus heat resistant species, confirming the existence of widespread regulatory as well as structural changes in the species’ differing adaptations. Gene Ontology terms related to metabolism were enriched in the differentially expressed genes in the resistant species while terms related to stress response were over-represented in the sensitive one.ConclusionAdaptations to new cactus hosts and hot desiccating environments were associated with periods of accelerated evolutionary change in diverse biochemistries. The hundreds of genes involved suggest adaptations of this sort would be difficult to achieve in the timeframes projected for anthropogenic climate change.

Comparison of thermal tolerance in Collembola (Hexapoda) inhabiting soil and subterranean habitats

We hypothesized that trogloxenes inhabiting surface habitats, thermally fluctuating environment, would tolerate wide temperature ranges. We expected that the temperature tolerances would diminish over categories trogloxene - subtroglophile - eutroglophile - troglobiont as a result of the degree of adaptation to subterranean environment that is characteristic with thermally stable conditions. We also assumed that body size may play crucial role in tolerance of Collembola to high and low temperature. Eighteen species of all four categories were exposed to one-hour survival laboratory test. The impact of temperature, species and species-temperature interaction on the cold and heat survival was statistically significant. The species heat tolerance significantly increased with increasing cold tolerance. In general, decrease in cold and heat tolerance was shown from trogloxenes, over subtroglophiles and eutroglophiles to troglobionts. Cryptic species Folsomia sp. among trogloxenes and Ceratophysella sigillata, Hypogastrura crassaegranulata among subtroglophiles were highly heat- and also cold-resistant, showing wide ecological plasticity. Subtroglophilous Tetrodontophora bielanensis and Lepidocyrtus violaceus , eutroglophilous Heteromurus nitidus and troglobiont Protaphorura janosik were the most cold-sensitive species, and all troglobionts and eutroglophilous Pygmarrhopalites pygmaeus as the most heat-sensitive species. Species belonging to ecological groups not or less associated to cave environment (trogloxenes and subtroglophiles) showed wider range of temperature tolerance in comparison with more cave adapted species (eutroglophiles and troglobionts), tested by ANOVA. Cold resistance decreased significantly with increasing body length, indicating that body size plays an important role in temperature tolerances of arthropods inhabiting soil and subterranean habitats.

Differential ecophysiological responses and resilience to heat wave events in four co-occurring temperate tree species

Extreme summer heat waves are known to induce foliar and stem mortality in temperate forest ecosystems, yet our mechanistic knowledge of physiological thresholds for damage is lacking. Current spatiotemporal simulations of forest growth responses to climate change fail to explain the variability between co-occurring tree species to climate extremes, indicating a need for new model frameworks that include mechanistic understanding of trait-specific responses. In this context, using manipulative heat wave (hw) experiments we investigated ecophysiological responses and physiological recovery in four co-occurring temperate tree species of the southeastern United States including three deciduous angiosperms: southern red oak (Quercus falcata Michx.), shumard oak (Q. shumardii Buckl.) and, tulip-poplar (Liriodendron tulipifera L.) and one evergreen conifer: eastern white pine (Pinus strobus L.). The objectives were to investigate inter-specific differences in ecophysiological responses to hw events to understand mechanistic differences in resilience that may be useful for future model development. Two-year-old, well-irrigated potted saplings were exposed to progressively increasing extreme hw diurnal cycles followed by a recovery cycle, with peak midday air temperature increasing from 37 °C to a maximum of 51 °C on the third day of the hw. Plants were assessed for various photosynthetic and water use responses, chlorophyll fluorescence and photosystem-II (PSII) activity, leaf temperature and foliar pigments. Intense heat caused progressive down-regulation in net photosynthesis, but the stomata remained operational, which helped cool leaves through loss of latent heat. Even though whole plant transpiration increased for all species, the rate plateaued at higher hw events that allowed leaf temperature to exceed 45 °C, well beyond the optimal range. A significant increase in non-photochemical quenching over the hw cycles was evident in all species though indications of both transient and chronic PSII damage were evident in the most heat sensitive species, pine and tulip poplar. The oaks, especially Q. falcata, showed greater thermotolerance than other species with a higher threshold for photodamage to PSII, rapid overnight recovery of photoinhibition and minimal heat-induced canopy necrosis. We conclude that these co-occurring tree species exhibit large variability in thermotolerance and in their capability to repair both transient and chronic photodamage. Our results indicate that extreme heat induced damage to PSII within the leaf chloroplasts may be a mechanistic trait that can be used to project how different species respond to extreme weather events.