Competition Increases Risk of Species Extinction during Extreme Warming.

AbstractTemperature and interspecific competition are fundamental drivers of community structure in natural systems and can interact to affect many measures of species performance. However, surprisingly little is known about the extent to which competition affects extinction temperatures during extreme warming. This information is important for evaluating future threats to species from extreme high-temperature events and heat waves, which are rising in frequency and severity around the world. Using experimental freshwater communities of rotifers and ciliates, this study shows that interspecific competition can lower the threshold temperature at which local extinction occurs, reducing time to extinction during periods of sustained warming by as much as 2 weeks. Competitors may lower extinction temperatures by altering biochemical characteristics of the natural environment that affect temperature tolerance (e.g., levels of dissolved oxygen, nutrients, and metabolic wastes) or by accelerating population decline through traditional effects of resource depletion on life history parameters that affect population growth rates. The results suggest that changes in community structure in space and time could drive variability in upper thermal limits.

How do outside-hosts-overwintering parasitoids, at the adult stage, cope with cold?

INTRODUCTION: When overwintering, most endoparasitoids are protected from the cold inside their hosts. However, some endoparasitoids, along with ectoparasitoids, fall into the category called outside-hosts-overwintering parasitoids (OHOP) at immature or adult stages. We compared the cold-hardiness capacity and strategy between adult OHOP and their hosts (HOST) by examining their supercooling points (SCP), with acclimation periods and acclimation temperatures, and their lower lethal temperatures at 50% mortality (LLT50). We hypothesized that OHOP are more cold-hardy than their HOST, with lower SCP and LLT50. MATERIALS AND METHODS: Throughout the summers of 2020, 2021, and 2022, adult cabbage seedpod weevils (HOST) were sampled with a sweep net at the canola pod stage, and thousands of pods were collected and placed in emergence boxes to retrieve the adult OHOP Trichomalus perfectus. Regarding SCP measures, OHOP and HOST were separated according to various treatments. Each treatment considered a target exposure temperature (5, 10, or 20 °C) or a target exposure period (5, 15 or 25 days) at 5 °C. Regarding LLT measures, OHOP and HOST were categorized into five treatments, each corresponding to a specific exposure temperature (-5, -10, -15, -20 or -25 °C). RESULTS AND CONCLUSION: Acclimations to a lower temperature (5 °C) and a longer period (25 days) led to a significantly lower SCP of OHOP than HOST. Regarding OHOP, the average SCP was -19.71 °C when the acclimation temperature was 20 °C and significantly decreased to -23.20 °C when it was 5 °C. The average SCP was -18.82 °C when the acclimation period was five days and significantly decreased to -23.20 °C when it was 25 days. Conversely, the average SCP for HOST was never below -20 °C. At 20 °C acclimation temperature, HOST exhibited a significantly higher SCP of -14.64 °C compared to acclimations at 5 °C (-19.19 °C) and 10 °C (-20.00 °C), but there were no significant differences between 5 and 10 °C nor between acclimation periods. Therefore, the adult OHOP is more cold-hardy than its HOST. OHOP also exhibited a lower LLT50 than HOST, with -19.20 °C versus -17.59 °C. Finally, OHOP and HOST employ the same freeze-avoidance strategy, as evidenced by their SCP values (-19.57 °C versus -16.80 °C) which closely align with their respective LLT50. Adult OHOP better survive winter than their HOST in cold environments.

Cold tolerance and overwintering survival of Aphelinus certus (Hymenoptera: Aphelinidae), a parasitoid of the soybean aphid (Hemiptera: Aphididae) in North America.

Broad-spectrum insecticides are the main control measure of the invasive and economically damaging soybean aphid (Aphis glycines) in North America, although biological control by resident natural enemies can also greatly diminish population levels. One such natural enemy is the accidentally introduced Eurasian parasitoid Aphelinus certus (Hymenoptera: Aphelinidae), though its impact appears to be limited by low rates of parasitism early in the growing season. We tested the hypothesis that A. certus might experience high overwintering mortality. In the laboratory, we used thermocouple thermometry to measure the supercooling points of diapausing parasitoids and assessed parasitoid survival after exposure to ecologically relevant durations of low temperature. We found A. certus to be freeze-intolerant with a median supercooling point of -28°C. When exposed to temperatures of 0°C for up to 7 months, adults emerged only after exposures of at least 60 days and survival decreased with durations beyond 150 days. We also conducted in-field studies at sites from northern Minnesota to southern Iowa to determine if diapausing A. certus could overwinter above and below the snowpack. Survival was negatively correlated with increasing latitude and was greater for parasitoids placed on the ground than 1 meter off the ground, likely due to the warmer and stabler temperatures of the subnivean microclimate. Our results suggest that A. certus is capable of overwintering in the region inhabited by soybean aphid but may experience substantial mortality even under ideal conditions. Climate change is predicted to bring warmer, drier winters to the North American Midwest, with decreased depth and duration of snow cover, which may further reduce overwintering survival.

Late lactation in small mammals is a critically sensitive window of vulnerability to elevated ambient temperature.

Predicted increases in global average temperature are physiologically trivial for most endotherms. However, heat waves will also increase in both frequency and severity, and these will be physiologically more important. Lactating small mammals are hypothesized to be limited by heat dissipation capacity, suggesting high temperatures may adversely impact lactation performance. We measured reproductive performance of mice and striped hamsters (Cricetulus barabensis), including milk energy output (MEO), at temperatures between 21 and 36 °C. In both species, there was a decline in MEO between 21 and 33 °C. In mice, milk production at 33 °C was only 18% of that at 21 °C. This led to reductions in pup growth by 20% but limited pup mortality (0.8%), because of a threefold increase in growth efficiency. In contrast, in hamsters, MEO at 33 °C was reduced to 78.1% of that at 21 °C, yet this led to significant pup mortality (possibly infanticide) and reduced pup growth by 12.7%. Hamster females were more able to sustain milk production as ambient temperature increased, but they and their pups were less capable of adjusting to the lower supply. In both species, exposure to 36 °C resulted in rapid catastrophic lactation failure and maternal mortality. Upper lethal temperature was lowered by 3 to 6 °C in late lactation, making it a critically sensitive window to high ambient temperatures. Our data suggest future heat wave events will impact breeding success of small rodents, but this is based on animals with a long history in captivity. More work should be performed on wild rodents to confirm these impacts.

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.

Biogeography of the theileriosis vector, Rhipicephalus appendiculatus under current and future climate scenarios of Zimbabwe.

Climate directly influences the epidemiology of vector-borne diseases at various spatial and temporal scales. Following the recent increased incidences of theileriosis in Zimbabwe, a disease mainly transmitted by Rhipicephalus appendiculatus, we determined lethal temperatures for the species and current and possible future distribution using the machine learning algorithm 'Maxent'. Rhipicephalus appendiculatus larvae had an upper lethal temperature (ULT50) of about 44 ± 0.5 °C and this was marginally higher for nymphs and adults at 46 ± 0.5 °C. Environmental temperatures recorded in selected zonal tick microhabitats were below the determined lethal limits, indicating the ability of the tick to survive these regions. The resultant model under current climatic conditions showed areas with high suitability indices to the eastern, northeastern and southeastern parts of the country, mainly in Masvingo, Manicaland and Mashonaland Central provinces. Future predictions as determined by 2050 climatic conditions indicate a reduction in suitable habitats with the tick receding to presently cooler high elevation areas such as the eastern Highlands of Zimbabwe and a few isolated pockets in the interior of the country. Lowveld areas show low suitability under current climatic conditions and are expected to remain unsuitable in future. Overall, the study shows that R. appendiculatus distribution is constrained by climatic factors and helps identify areas of where occurrence of the species and the disease it transmits is highly likely. This will assist in optimizing disease surveillance and vector management strategies targeted at the species.

Nano-cryospray: An adjuvant assisted approach to increase the efficacy of cryospray.

The present study proposes a novel approach to treat skin cancer. It is an amalgamation of two techniques; (i) Cryospray in which necrosis is achieved through local application of liquid nitrogen spray on lesions (occurring on superficial skin) and (ii) Transdermal Drug Delivery systems (TDDS) in which drugs are administered through the superficial skin. It focuses on increasing the cryoablation through the administration of nanoparticles in the skin. Biodegradable Magnesium Oxide (MgO) nanoparticles are selected to make nano-phantom. TEM and XRD results reveal the crystalline nature of MgO nanoparticle with particle diameter 10-40 nm. A comparative study of cryoablation is carried out between the nano-phantom and the normal-phantom while spraying liquid nitrogen through a commercial 0.8 mm diameter single hole nozzle. Quantitative and qualitative improvements in cryoablation are observed due to the presence of nanoparticle. Necrotic zone in nano-phantom is twice larger than in the normal-phantom up to an axial depth of 2 mm from the centre of spray for the same spraying distance. Minimum spraying distance for nano-phantom is estimated to be 13 mm. Among the three spraying distances selected for the study, it has been observed that cryoablation decreases as the spraying distance increases. The proposed approach can be used to enhance the scope of cryospray in the treatment of larger lesions like Squamous cell carcinoma, keloids etc. without incorporating the device modifications.

Freezing: how do water mites (Acari: Hydrachnidia) survive exposure to sub-zero temperatures?

Until now, very little is known about the ability of adult and deutonymph water mites (Acari, Hydrachnidia) to survive in sub-zero temperatures. Information concerns mainly water mites from vernal astatic waters, and the knowledge has never been experimentally verified. To determine the sensitivity of water mites to freezing, experiments were conducted on (1) the impact of acclimatization, (2) temperature, and (3) duration of freezing on survival, (4) the survival rate of water mites from various types of water bodies, and (5) the survival rate of water mites from different climatic zones. The experiments were carried out in a phytotron chamber, and water mites were placed in containers (10 × 10 × 5 cm) filled with 4/5 of water for 10 specimens each. Water mites were identified to the species level after finishing the experiments. The temperature was lowered 1 °C every hour until the target temperature was reached. After a certain period of freezing (depending on the treatment) the temperature was raised by 1 °C every hour until it reached 4 °C. The time of the experiment was measured from the moment the desired temperature was reached (below 0 °C) until the ice thawed and the temperature of 4 °C was reached again. The highest survival rates had Limnochares aquatica, Piona nodata, Sperchon clupeifer and Lebertia porosa, followed by L. insignis, Hygrobates longipalpis, H. setosus, Limnesia undulatoides, Piona pusilla, Arrenurus globator, Hydrodroma despiciens, Piona longipalpis, Sperchonopsis verrucosa, Unionicola crassipes and Mideopsis crassipes; no specimens of Torrenticola amplexa survived. The following conclusions were drawn: (1) water mites can survive freezing to -2 °C, lower temperatures are lethal for them; (2) they survived better the short period of freezing (24-48 h) than the long period (168 h); (3) resistance to freezing seems to be an evolutionary trait of individual species, only partly related to the living environment; and (4) freezing survival rates are linked to the region of Europe and are much lower in Southern than in Central Europe.

Effects of constant and fluctuating incubation temperatures on hatching success and hatchling traits in the diamondback terrapin (Malaclemys terrapin) in the context of the warming climate.

As global temperatures continue to rise, so too will the nest temperatures of many species of turtles. Yet for most turtle species, including the estuarine diamondback terrapin (Malaclemys terrapin), there is limited information on embryonic sensitivity to elevated temperature. We incubated eggs of M. terrapin at three, mean temperatures (31, 34, 37 °C) under two thermal exposure regimes (constant or semi-naturally fluctuating temperature) and measured hatching success, developmental rate, and hatchling size. Hatching success was 100% at 31 °C and 67% at 34 °C, respectively; at 37 °C, all eggs failed early in the incubation period. These values were unaffected by exposure regime. The modeled LT50 (temperature that was lethal to 50% of the test population) was 34.0 °C in the constant and 34.2 °C in the fluctuating thermal regime, reflecting a steep decline in survival between 33 and 35 °C. Hatchlings having been incubated at a constant 34 °C hatched sooner than those incubated at 31 °C under either constant or fluctuating temperature. Hatchlings were smaller in straight carapace length (CL) and width after having been incubated at 34 °C compared to 31 °C. Larger (CL) hatchlings resulted from fluctuating temperature conditions relative to constant temperature conditions, regardless of mean temperature. Based upon recent temperatures in natural nests, the M. terrapin population studied here appears to possess resiliency to several degrees of elevated mean nest temperatures, beyond which, embryonic mortality will likely sharply increase. When considered within the mosaic of challenges that Maryland's M. terrapin face as the climate warms, including ongoing habitat losses due to sea level rise and impending thermal impacts on bioenergetics and offspring sex ratios, a future increase in embryonic mortality could be a critical factor for a population already experiencing ecological and physiological challenges due to climate change.

Cold tolerance and supercooling points of two ladybird beetles (Col.: Coccinellidae): Impact of the diet.

Ladybird beetles have successfully been used to control different pests. Cheilomenes sexmaculata (Fabricius) and Oenopia conglobata contaminata)Menetries((Coleoptera: Coccinellidae) are two dominant and efficient predators of the common pistachio psylla, Agonoscena pistaciae (Hem.: Psyllidae) in Iran. In the current study, the impact of two diets, i.e., nymphs of A. pistaciae and eggs of Ephestia kuehniella Zeller (Lep.: Pyralidae), were investigated on the cold hardiness, supercooling point (SCP), and lethal temperature of different life stages of the coccinellids. The results suggested that the eggs of E. kuehniella are a suitable diet for both predators. In general, beetles of O. conglobata contaminata were more cold tolerant than those of C. sexmaculata. The SCP of the adults of C. sexmaculata, feeding on psyllid was about -15 °C, whereas the SCP of the beetles, feeding on the eggs of flour moth, was about -19 °C. However, the diets had no significant effects on the SCP of O. conglobata contaminata. For both ladybird beetles, eggs were the most sensitive stage, and adulthood was the most tolerant developmental stage. No eggs survived at zero and subzero temperatures. The survival of C. sexmaculata increased from 6.25% for adults fed on psyllids to 13.75% for those fed on flour moth eggs after 24 h exposure to cold at -4 °C. The survival of O. conglobata contaminata adults after exposure to cold at -4 °C for 24 h raised from 28.75% for adults fed on psyllids to 42.50% for those fed on flour moth eggs. Regardless of the diet, both beetles were considered to be chill-intolerant insects as the most mortality occurred above the SCP.

Testing the climatic variability hypothesis in edaphic and subterranean Collembola (Hexapoda).

The climatic variability hypothesis was applied to the thermal tolerance of edaphic and cave Collembola occupying contrasting environments. Collembola belonged to four categories - trogloxene, subtroglophile, eutroglophile and troglobiont - with a different degree of affinity to subterranean habitats. Altogether, specimens of 17 species were exposed to a one-hour laboratory survival test. The impact of temperature, species and species-temperature interaction on cold and heat survival was statistically significant. There was a decrease trend in cold and heat tolerance from trogloxenes, over subtroglophiles and eutroglophiles to troglobionts. It was shown that obligate cave species, restricted to climatic-stable cave conditions, retain a functional thermal resistance, i.e. the genetically determined ability to tolerate relatively broader temperature ranges. Our results outlined the direct relationship between the thermal tolerances of species and the size of their geographic distributions. It was also observed that cold resistance of Collembola decreased significantly with increasing species body length, indicating that body size plays an important role in temperature tolerances of arthropods inhabiting soil and subterranean habitats.

Upper lethal temperatures in three cold-tolerant insects are higher in winter than in summer.

Upper lethal temperatures (ULTs) of cold-adapted insect species in winter have not been previously examined. We anticipated that as the lower lethal temperatures (LLTs) decreased (by 20-30°C) with the onset of winter, the ULTs would also decrease accordingly. Consequently, given the recent increases in winter freeze-thaw cycles and warmer winters due to climate change, it became of interest to determine whether ambient temperatures during thaws were approaching ULTs during the cold seasons. However, beetle Dendroides canadensis (Coleoptera: Pyrochroidae) larvae had higher 24 and 48 h ULT50 (the temperature at which 50% mortality occurred) in winter than in summer. The 24 and 48 h ULT50 for D. canadensis in winter were 40.9 and 38.7°C, respectively. For D. canadensis in summer, the 24 and 48 h ULT50 were 36.7 and 36.4°C. During the transition periods of spring and autumn, the 24 h ULT50 was 37.3 and 38.5°C, respectively. While D. canadensis in winter had a 24 h LT50 range between LLT and ULT of 64°C, the summer range was only 41°C. Additionally, larvae of the beetle Cucujus clavipes clavipes (Coleoptera: Cucujidae) and the cranefly Tipula trivittata (Diptera: Tipulidae) also had higher ULTs in winter than in summer. This unexpected phenomenon of increased temperature survivorship at both lower and higher temperatures in the winter compared with that in the summer has not been previously documented. With the decreased high temperature tolerance as the season progresses from winter to summer, it was observed that environmental temperatures are closest to upper lethal temperatures in spring.

Effect of salinity on the upper lethal temperature tolerance of early-juvenile red drum.

Previous work investigating the temperature tolerance of juvenile red drum ranging 18-50mm TL found evidence for positive size dependence (smaller fish less tolerant to higher temperatures) suggesting smaller size classes (<18mm TL) potentially may succumb to extreme summer water temperatures. Here, we explored the upper lethal temperature tolerance (ULT) in smaller-sized red drum which ranged from 10 to 20mm TL across multiple salinities to further understand the thermal limitations of this propagated game fish. In order to investigate the combined effect of temperature and salinity on ULT, temperature trials were conducted under three levels of salinity which commonly occur along the coast of Texas (25, 35, and 45ppt). The rate of temperature increase (+0.25°C/h) was designed to mimic a natural temperature increase of a summer day in Texas. We determined that the lethal temperature at 50% (LT50) did not differ between the three salinities examined statistically; median lethal temperature for individuals exposed to 25ppt ranged from 36.4 to 37.7°C, 35ppt ranged from 36.4 to 37.7°C, and 45ppt ranged from 36.1 to 37.4°C. Further, LT50 data obtained here for early-juvenile red drum did not differ from data of a similar experiment examining 25mm TL sized fish.

An invitation to measure insect cold tolerance: Methods, approaches, and workflow.

Insect performance is limited by the temperature of the environment, and in temperate, polar, and alpine regions, the majority of insects must face the challenge of exposure to low temperatures. The physiological response to cold exposure shapes the ability of insects to survive and thrive in these environments, and can be measured, without great technical difficulty, for both basic and applied research. For example, understanding insect cold tolerance allows us to predict the establishment and spread of insect pests and biological control agents. Additionally, the discipline provides the tools for drawing physiological comparisons among groups in wider studies that may not be focused primarily on the ability of insects to survive the cold. Thus, the study of insect cold tolerance is of a broad interest, and several reviews have addressed the theories and advances in the field. Here, however, we aim to clarify and provide rationale for common practices used to study cold tolerance, as a guide for newcomers to the field, students, and those wishing to incorporate cold tolerance into a broader study. We cover the 'tried and true' measures of insect cold tolerance, the equipment necessary for these measurement, and summarize the ecological and biological significance of each. Finally, we suggest a framework and workflow for measuring cold tolerance and low temperature performance in insects.

Supercooling capacity and cold hardiness of band-winged grasshopper eggs (Orthoptera: Acrididae).

The band-winged grasshopper, Oedaleus asiaticus Bei-Bienko, is one of the most dominant and economically important grasshopper species in the steppe grasslands and farming-pastoral ecotone in northern China. It is a univoltine species and overwinters as eggs in soil. The cold hardiness of its eggs was examined in the laboratory. Water content in soil significantly affected the supercooling points (SCPs), water content and fat content of prediapause eggs. With the increase of water content in soil, the SCP, and water content of prediapause eggs rose whereas the fat content declined. There was a significant relationship between the SCP and water content or fat content of prediapause eggs. The SCPs of prediapause and diapause eggs varied from -7.6 to -28.4°C and the SCPs of eggs 30 d after oviposition could be divided into two groups. The means of high SCP group (-11.0 to -11.9°C) were much higher than those of low SCP group (-21.8 to -21.9°C), and the majority belonged to the latter (90.48-93.33%). The SCPs of prediapause eggs and early-diapause eggs 30 d after oviposition were significantly higher than those of deep-diapause eggs 60 d after oviposition. The survival rates of diapause eggs were significantly different among different temperature treatments. The survival rate was higher than 88% at greater than -20°C and declined significantly to 57% at -25°C, and suddenly dropped to zero at -30°C. The lower lethal temperature (Ltemp50) for 12 h exposure was -25.3°C and the lower lethal time (Ltime50) at -20°C was 32.8 d. As the mean SCPs of diapause eggs were similar to their Ltemp50, the SCP of eggs can be considered as a good indicator of cold hardiness for O. asiaticus and that this grasshopper is a freeze-intolerant insect.

Experimental investigation of freeze injury temperatures in trees and their contributing factors based on electrical impedance spectroscopy.

In trees, injuries resulting from subfreezing temperatures can cause damage to the cellular biofilm system, metabolic functions, and fibrous reticulum, and even cell death. Investigating the occurrence of freezing damage and its contributing factors could help understand the mechanisms underlying freezing injury and prevent the subsequent damage in trees. To achieve this, a laboratory experiment was conducted using cut wood samples from Korean pine (Pinus koraiensis Siebold & Zucc) and Simon poplar (Populus simonii Carr.), and the effects of environmental freezing factors, including freezing temperatures, freezing duration, and cooling rate, on the temperature at which freezing injuries occur were examined using the electrical impedance spectroscopy (EIS) method. The semi-lethal temperature (LT50), as an indicator of freezing injury in wood tissue, was theoretically deduced based on the measured extracellular resistance (r e) using EIS. The contributory factors to changes in LT50 were determined and their relationship was established. The results revealed that all freezing factors exhibited significant effects on electrical impedance characteristics (r e, r i, and τ), significantly influencing the LT50 of the wood. Random forest (RF) and support vector machine (SVM) models were used to assess the contribution of the freezing factors and moisture content (MC). Among the factors examined, freezing duration had the greatest impact on LT50, followed by the MC, whereas the contribution of the cooling rate was minimal. The model accuracies were 0.89 and 0.86 for Korean pine and Simon poplar, respectively. The findings of our study illustrate that the occurrence of freezing injury in trees is primarily influenced by the duration of freezing at specific subzero temperatures. Slow cooling combined with prolonged freezing at low subzero temperatures leads to earlier and more severe freezing damage.

Frost Damage Mitigation in Flowers and Fruitlets of Peach and Almond from the Application of a Multi-Attribute Approach Biostimulant.

To prevent frost damage in fruit trees, growers employ passive and active methods, and one of these second methods is the use of biostimulant compounds against abiotic stress. In this study, two trials were conducted to evaluate the effectiveness of a multi-attribute approach biostimulant-containing α-tocopherol, boron, and glycols, in peach ('UFO-4' cultivar) and almond ('Vairo' cultivar) trees. In a first trial, one-year-old shoots with flowers were collected after 24 h, 48 h, and 96 h of the biostimulant applications. Two different application rates of the product (1000 and 2000 cc ha-1) were tested and compared to an untreated control. In a second trial, one-year-old shoots with fruitlets were collected after 24 h of the biostimulant applications. In this case, only an application rate (2000 cc ha-1) was tested. In the two trials, the collected one-year-old shoots were subjected to different frost temperatures using a controlled environment chamber. The damage level was assessed by a morphological analysis of the flowers and fruitlets 96 h after each frost cycle simulation. The lethal temperatures (LT10, LT50, and LT90) of each treatment were calculated by probit analysis. The product applied 24 h and 48 h before the frost simulations significantly decreased the LT10 and LT50 in 1.5 °C in peach flowers, and 2.5 °C in almond flowers (a temperature reduction of 50% and 75%, respectively). These results were more consistent when the application volume was 2000 cc ha-1, instead of 1000 cc ha-1. Significant differences between treated and non-treated fruitlets were observed only in almond fruitlets, with LT10 and LT50 being 0.5 °C lower in treated fruitlets (20% reduction). In conclusion, the multi-attribute approach biostimulant applied 24 or 48 h before the frost reduced the mortality of peach and almond flowers, but its effectiveness to protect fruitlets after bloom was inconsistent.

Insufficient Cold Resistance as a Possible Reason for the Absence of Darkling Beetles (Coleoptera, Tenebrionidae) in Pleistocene Sediments of Siberia.

The level of diversity and abundance of darkling beetles (Coleoptera, Tenebrionidae) is the main difference between the late Pleistocene and modern insect faunas of arid regions. In the Pleistocene assemblages they are extremely rare, whereas in the modern ones they predominate. It is assumed that the reason for their rarity in fossil entomological complexes is their lack of cold resistance. The supercooling points (SCP) and low lethal temperatures (LLT) of adults from five species of Altai darkling beetles that overwinter in the soil and larvae from one such species were measured in the laboratory. All beetles supercooled at negative temperatures but could not survive freezing, with the average SCP of the most cold-resistant species between -25.7 and -21.7 °C (Bioramix picipes, Anatolica dashidorzsi, and Penthicus altaicus). However, 50% of the individuals from different species in the experiment died after exposure during two days at temperatures ranging from -22 to -20 °C. The focal species are distributed in parts of Central Asia with an extreme continental climate, and the temperatures measured in the soil of these natural areas turned out to be lower than or close to the limit of cold resistance of the beetles. Overwintering of darkling beetles is therefore only possible in areas with deep snow: in hollows, under bushes, and under large cereals. Darkling beetles with poor cold resistance could not have existed in the colder climate of the late Pleistocene, which explains their absence from fossil fauna.

Survival and arm abscission are linked to regional heterothermy in an intertidal sea star.

Body temperature is a more pertinent variable to physiological stress than ambient air temperature. Modeling and empirical studies on the impacts of climate change on ectotherms usually assume that body temperature within organisms is uniform. However, many ectotherms show significant within-body temperature heterogeneity. The relationship between regional heterothermy and the response of ectotherms to sublethal and lethal conditions remains underexplored. We quantified within-body thermal heterogeneity in an intertidal sea star (Pisaster ochraceus) during aerial exposure at low tide to examine the lethal and sublethal effects of temperatures of different body regions. In manipulative experiments, we measured the temperature of the arms and central disc, as well as survival and arm abscission under extreme aerial conditions. Survival was related strongly to central disc temperature. Arms were generally warmer than the central disc in individuals that survived aerial heating, but we found the reverse in those that died. When the central disc reached sublethal temperatures of 31-35°C, arms reached temperatures of 33-39°C, inducing arm abscission. The absolute temperature of individual arms was a poor predictor of arm abscission, but the arms lost were consistently the hottest at the within-individual scale. Therefore, the vital region of this sea star may remain below the lethal threshold under extreme conditions, possibly through water movement from the arms to the central disc and/or evaporative cooling, but at the cost of increased risk of arm abscission. Initiation of arm abscission seems to reflect a whole-organism response while death occurs as a result of stress acting directly on central disc tissues.

Ocean acidification increases susceptibility to sub-zero air temperatures in ecosystem engineers and limits poleward range shifts.

Ongoing climate change has caused rapidly increasing temperatures and an unprecedented decline in seawater pH, known as ocean acidification. Increasing temperatures are redistributing species toward higher and cooler latitudes that are most affected by ocean acidification. While the persistence of intertidal species in cold environments is related to their capacity to resist sub-zero air temperatures, studies have never considered the interacting impacts of ocean acidification and freeze stress on species survival and distribution. Here, a full-factorial experiment was used to study whether ocean acidification increases mortality in subtidal Mytilus trossulus and subtidal M. galloprovincialis, and intertidal M. trossulus following sub-zero air temperature exposure. We examined physiological processes behind variation in freeze tolerance using 1H NMR metabolomics, analyses of fatty acids, and amino acid composition. We show that low pH conditions (pH = 7.5) significantly decrease freeze tolerance in both intertidal and subtidal populations of Mytilus spp. Under current day pH conditions (pH = 7.9), intertidal M. trossulus was more freeze tolerant than subtidal M. trossulus and subtidal M. galloprovincialis. Conversely, under low pH conditions, subtidal M. trossulus was more freeze tolerant than the other mussel categories. Differences in the concentration of various metabolites (cryoprotectants) or in the composition of amino acids and fatty acids could not explain the decrease in survival. These results suggest that ocean acidification can offset the poleward range expansions facilitated by warming and that reduced freeze tolerance could result in a range contraction if temperatures become lethal at the equatorward edge.