Exposure to teflubenzuron reduces drought tolerance of collembolans.

Chitin synthesis inhibitors (CSIs) are commonly used insecticides compromising cuticle formation and structure in arthropods. Arthropods rely on intact cuticles to maintain water balance and cellular homeostasis to survive in different weather conditions. We hypothesized that physiological impacts of CSIs may make arthropods more vulnerable to harsh environmental conditions, such as extreme heat, cold or drought. The aim of this study was to investigate if pre-exposure to teflubenzuron (a common CSI) would influence Folsomia candida's (Collembola: Isotomidae) sensitivity to natural stressors. Here, we exposed adult collembolans to teflubenzuron through food for two weeks, then survivors were immediately divided into three groups for subsequent acute heat, cold, and drought exposure. After acute exposure to these natural stressors, the collembolans were moved to optimal conditions for a one-week recovery period during which their survival, time to regain reproduction, and egg production were examined. We analyzed the interaction between effects of teflubenzuron and natural stressors using a multiplicative model. No interaction between effects of teflubenzuron and heat was observed in any test endpoints. A synergistic interaction between effects of teflubenzuron and cold was observed in the time to regain reproduction. Both survival and egg production, on the other hand, showed synergistic interaction between effects of teflubenzuron and drought, as well as a tendency for longer reproduction recovery times. Our results suggest that pre-exposure to teflubenzuron reduces drought tolerance in F. candida, while its impact on heat or cold tolerance is minor or absent. This study is among the first to explore the combined effects of CSI and natural stressors on soil arthropods, providing more insight on potential risks posed by such chemicals in the environment.

Chronic Effects of an Insect Growth Regulator (teflubenzuron) on the Life Cycle and Population Growth Rate of Folsomia candida.

Current standard toxicity tests on nontarget soil invertebrates mainly focus on the endpoints survival and reproduction. Such results are likely insufficient to predict effects at higher organizational levels, for example, the population level. We assessed the effects of exposure to the pesticide teflubenzuron on the collembolan Folsomia candida, by performing a full life-cycle experiment exposing single individuals via contaminated food (uncontaminated control and 0.2, 0.32, 0.48, 0.72, 1.08, and 1.6 mg/kg dry yeast). Several life-history traits were considered by following the growth and development of newly hatched individuals over a period of 65 days. We assessed survival, body length, time to first oviposition, cumulative egg production, and hatchability of eggs. A two-stage model was applied to calculate the population growth rate (λ) combined with elasticity analysis to reveal the relative sensitivity of λ to the effects of teflubenzuron on each life-history parameter. Body length was the least sensitive life-history parameter (median effective concentration = 1.10 mg teflubenzuron/kg dry yeast) followed by time to first oviposition (0.96 mg/kg), survival (median lethal concentration = 0.87 mg/kg), cumulative egg production (0.32 mg/kg), and egg hatchability (0.27 mg/kg). Population growth decreased with increasing concentrations of teflubenzuron (λ = 1.162/day in control to 1.005/day in 0.72 mg/kg dry yeast, with populations going extinct at 1.08 and 1.6 mg/kg dry yeast). Elasticity analysis showed that changes in juvenile survival had a greater impact on the population growth rate compared with the other life-history traits. Our study provides a comprehensive overview of individual-level effects of long-term exposure to teflubenzuron and integrates these effects to assess the potential risk to collembolan populations. Environ Toxicol Chem 2024;43:1173-1183. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Low soil Moisture Slows Uptake and Elimination Rates of Phenanthrene in Springtails.

This study investigated the influence of soil water status on the toxicokinetics of phenanthrene in the springtail Folsomia candida allowing estimation of uptake and elimination rates at two contrasting soil water potentials. Fitting a three-phase model to the observations showed that uptake rate (ku) was almost two times higher in moist soil (-2 kPa) than in dry soil (-360 kPa). During the first days of the exposure, elimination rate (ke) was not significantly different in moist and dry soil, but after eight days ke had increased significantly more in moist soil than in dry soil. Our results confirm the general notion that the exposure route via soil pore water is important. Understanding the significance of soil moisture in exposure and effects of contaminants on soil invertebrates is crucial for assessing the ecological risks associated with soil pollution in a changing climate.

Copper-contaminated soil compromises thermal performance in the springtail Folsomia candida (Collembola).

The widespread agricultural and industrial emissions of copper-based chemicals have increased copper levels in soils worldwide. Copper contamination can cause a range of toxic effects on soil animals and influence thermal tolerance. However, toxic effects are commonly investigated using simple endpoints (e.g., mortality) and acute tests. Thus, how organisms respond to ecological realistic sub-lethal and chronic exposures across the entire thermal scope of an organism is not known. In this study, we investigated the effects of copper exposure on the thermal performance of a springtail (Folsomia candida), regarding its survival, individual growth, population growth, and the composition of membrane phospholipid fatty acids. Folsomia candida (Collembola) is a typical representative of soil arthropods and a model organism that has been widely used for ecotoxicological studies. In a full-factorial soil microcosm experiment, springtails were exposed to three levels of copper (ca. 17 (control), 436, and 1629 mg/kg dry soil) and ten temperatures from 0 to 30 °C. Results showed that three-week copper exposure at temperatures below 15 °C and above 26 °C negatively influenced the springtail survival. The body growth was significantly lower for the springtails in high-dose copper soils at temperatures above 24 °C. A high copper level reduced the number of juveniles by 50 %, thereby impairing population growth. Both temperature and copper exposure significantly impacted membrane properties. Our results indicated that high-dose copper exposure compromised the tolerance to suboptimal temperatures and decreased maximal performance, whereas medium copper exposure partially reduced the performance at suboptimal temperatures. Overall, copper contamination reduced the thermal tolerance of springtails at suboptimal temperatures, probably by interfering with membrane homeoviscous adaptation. Our results show that soil organisms living in copper-contaminated areas might be more sensitive to thermally stressful periods.

Tolerance of high temperature and associated effects on reproduction in euedaphic Collembola.

Studies show that tropical and mid-latitude terrestrial ectotherms are more vulnerable to global warming than species from high latitudes. However, thermal tolerance studies from these regions still lack soil invertebrates. In the present study, we investigated six euedaphic species of Collembola (of the genera Onychiurus and Protaphorura) sampled across latitudes ranging from 31° N to 64° N and determined their upper thermal limit (UTL) by static assays. In another experiment, we submitted springtails to high temperatures for exposure times, causing 5% to 30% mortality within each species. Survivors from this series of increasing heat injuries were used to determine the time-to-first-oviposition and the number of eggs produced following heat exposure. Two hypotheses are tested in this study: 1) heat tolerance of species correlates positively with the environmental temperature of their habitat; 2) the most heat-tolerant species require less time to regain reproduction and produce more eggs than the least heat-tolerant species. Results showed that the UTL positively correlates to the soil temperature of the sampling site. The sequence of UTL60 (the temperature causing 50% mortality after 60 min of exposure) from highest to least was O. yodai > P. fimata > P. armata ≈ P. tricampata > P. macfadyeni > P. pseudovanderdrifti. Heat stress inflicted on springtails can delay reproduction in all species, and two species showed a reduced egg production rate after heat exposure. For heat stress causing up to 30% mortality, the most heat-tolerant species did not have advantages over the least heat-tolerant species for what concerns the recovery of reproduction. The relation between UTL and recovery from heat stress is not linear. Our study provides evidence for a potential long-term effect of high-temperature exposure on euedaphic species of Collembola and highlights the need for further studies on the effects of global warming on soil-living organisms.

Evaluation of life-history traits in Folsomia candida exposed to combined repeated mild heat shocks with phenanthrene.

Climate change increases the frequency and intensity of extreme weather events. In nature, organisms are often exposed to climatic stressors and contaminants simultaneously, and the effects of contaminants may be modified by climate change and vice versa. Here, the effects of repeated mild heat shocks (0-5 times, 30 °C for 6 h), alone or combined with phenanthrene (PHE) (80 mg kg-1 dry soil), on life-history traits of the springtail Folsomia candida were investigated. The survival, growth, maturation, and reproduction of single juvenile springtails were assessed over a period of 37 days. Increasing number of heat bouts or PHE exposure did not have significant negative effects on overall survival at the termination of the experiment, but the interaction between the two stressors led to complex interactions for the dynamics of survival during the test. Neither body growth nor time to first oviposition was influenced by heat or PHE, but a reduction of egg production with increasing number of heat bouts was observed, and there was an interaction between the two stressors. Further, a trade-off between the number of eggs produced and egg size was observed, indicating that females invested the same amount of energy in reproduction despite exposure to stressful temperature and PHE. These results indicate that egg production (in terms of the number of eggs) was a more sensitive indicator of the combined effects of mild heat shocks and PHE than growth, and there was a trade-off between survival and egg production.

Influence of Soil Moisture on Bioaccumulation, Growth, and Recruitment of Folsomia candida Exposed to Phenanthrene-Polluted Soil.

Climate change has resulted in an increased occurrence of summer droughts in large parts of the world. Low soil moisture has marked impacts on the physiology of soil invertebrates and lowers degradation rates of organic contaminants in soil. Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic contaminants that readily accumulate in the lipids of soil organisms. Here, we exposed springtails (Collembola, small soil living arthropods) to phenanthrene (a common PAH) in combination with a range of soil water contents to investigate the combined effects of these factors on the bioaccumulation, survival, recruitment, and body growth in a full factorial experiment. The results showed that phenanthrene up to 60 mg/kg dry soil had moderate effects on survival (<20%), whereas dry soil (4% soil water content) caused approximately 60% mortality. The bioaccumulation of phenanthrene increased almost 3-fold when soil water content decreased from 22 to 4%. We observed a joint effect of low soil water content and phenanthrene on recruitment, suggesting a synergistic interaction. The recruitment EC50 values of phenanthrene decreased from approximately 40 mg/kg dry soil at 22% soil water content to approximately 10 mg/kg dry soil at 12% soil water content. Our results show that the effects of phenanthrene are more pronounced in dry soil partly because bioaccumulation is enhanced when soils become dry.

Increased daily temperature fluctuations exacerbate the toxicity of phenanthrene in Enchytraeus albidus (Enchytraeidae).

Temperature variability in soils is expected to increase due to the more frequent occurrence of heat waves, putting species under thermal stress. In addition, organic pollutants such as polycyclic aromatic hydrocarbons (PAHs) are released into the environment due to anthropogenic activities. Both stressors negatively impact terrestrial organisms and may interact with each other. Here, we subjected the soil living enchytraeid, Enchytraeus albidus, to combined exposure to phenanthrene (PHE; 0, 10, 20, 40, and 80 mg kg-1 dry soil) and a range of temperature treatments (constant temperature (CT): 10, 15 and 20 °C; different mean temperature with the same daily temperature fluctuation (DTF-5): 10 ± 5, 15 ± 5 and 20 ± 5 °C; daily temperature fluctuation with the same mean, but different amplitudes (DTF-A): 20, 20 ± 2, 20 ± 5 and 20 ± 7 °C). We measured internal PHE concentration in adults and found that an increase in mean temperature significantly increased the internal PHE concentration. The production of juveniles was measured using a standardized test. We found a synergistic interaction between the temperature amplitude (DTF-A treatments) and PHE on the reproduction of E. albidus. The EC50 of reproduction decreased with increasing amplitude. These results show that the negative effects of PHE on E. albidus can be magnified if stressful temperatures are reached (although briefly) during diurnal fluctuations of soil temperature. Our results highlight the importance and inclusion of extreme thermal events in the risk assessment of pollutants.

Heat stress delays detoxification of phenanthrene in the springtail Folsomia candida.

Climate change has intensified the occurrence of heat waves, resulting in organisms being exposed to thermal and chemical stress at the same time. The effects of mild heat shock combined with sublethal concentrations of phenanthrene (PHE) on defense mechanisms in springtails Folsomia candida were investigated. The transcription of Heat Shock Protein 70 (HSP70) was significantly upregulated by heat shock but tended to reach the control levels after 42 h of recovery. The transcription of cytochrome P450 3A13 (CYP3A13) was upregulated 3-13 fold by PHE but suppressed by heat shock. The suppression by heat shock might contribute to the reduced detoxification of PHE during high-temperature exposure. In line with this, we found that the internal PHE concentration was approximately 70% higher in heat-shocked springtails than in animals kept at control temperature. In general, the transcription of genes encoding enzymes of detoxification phase Ⅱ (glutathione S-transferase 3) and phase Ⅲ (ABC transporter 1) and the activity of antioxidant defense enzymes (superoxide dismutase and catalase) were less influenced than genes encoding phase I detoxification mechanisms (CYP3A13). These results indicate that heat shock delays the detoxification of PHE in springtails.

Analysis of heat and cold tolerance of a freeze-tolerant soil invertebrate distributed from temperate to Arctic regions: evidence of selection for extreme cold tolerance.

Tolerance to thermal extremes is critical for the geographic distributions of ectotherm species, many of which are probably going to be modified by future climatic changes. To predict species distributions it is important to understand the potential of species to adapt to changing thermal conditions. Here, we tested whether the thermal tolerance traits of a common freeze-tolerant potworm were correlated with climatic conditions and if adaptation to extreme cold constrains the evolutionary potential for high temperature tolerance. Further, we tested if evolution of thermal tolerance traits is associated with costs in other fitness traits (body size and reproduction). Lastly, we tested if slopes of temperature-survival curves (i.e., the sensitivity distribution) are related to tolerance itself. Using 24 populations of the potworm, Enchytraeus albidus Henle (Enchytraeidae), collected from a wide range of climatic conditions, we established a common garden experiment in which we determined high and low temperature tolerance (using survival as endpoint), average reproductive output and adult body size. Heat tolerance was not related to environmental temperatures whereas lower lethal temperature was about 10 °C lower in Arctic populations than in populations from temperate regions. Reproduction was not related to environmental temperature, but was negatively correlated with cold tolerance. One explanation for the trade-off between cold tolerance and reproduction could be that the more cold-hardy populations need to channel energy to large glycogen reserves at the expense of less energy expenditure for reproduction. Adult body size was negatively related to environmental temperature. Finally, the slopes of temperature-survival curves were significantly correlated with critical temperature limits for heat and cold tolerance; i.e., slopes increased with thermal tolerance. Our results suggest that relatively heat-sensitive populations possess genetic variation, leaving room for improved heat tolerance through evolutionary processes, which may alleviate the effects of a warmer future climate in the Arctic. On the other hand, we observed relatively narrow sensitivity distributions (i.e., less variation) in the most heat tolerant populations. Taken together, our results suggest that both cold and heat tolerance can only be selected for (and improved) until a certain limit has been reached.

Thermal optimum for mass production of the live feed organism Enchytraeus albidus.

Live feed organisms are essential for the larval stages of many fish species grown in aquaculture, and juvenile fish reared on live feeds often exhibit higher survival and growth than those reared on formulated feed. The terrestrial enchytraeid (white worm), Enchytraeus albidus, has potential as a sustainable source of live feed because it can easily be mass produced, feeds on a wide range of organic waste materials and has high contents of protein and long-chain poly-unsaturated fatty acids. In the present study, we observed the effect of temperature on population growth over five months using soil microcosms. At the outset, each microcosm was supplied with approximately the same number of cocoons. Hatched enchytraeids were given rolled oats ad libitum as feed. We followed the population growth at seven temperatures in the range of 4-25 °C and investigated body composition in order to find optimal temperature for mass production. Results showed that E. albidus has a broad thermal optimum range and displays almost similar biomass production in the range of 15-22 °C with specific growth rates between 6.5 and 6.8%. In this temperature range, protein contents were 40-45%, glycogen contents 20-25% and total fatty acid contents 15-20% of dry weight. The temperature had a highly significant effect on fatty acid composition. In particular, the abundance of omega-3 fatty acids (18:3ω3 and 20:5ω3) was largest at low temperature. For what concerns achievable density of worms in mass cultures, our results surpassed previous results and showed that densities close to 100 g L-1 substrate are realistic. Maximum production of biomass can likely reach 80 g live worms L-1 month-1 at temperatures between 15 and 22 °C.

Temperature-Dependent Toxicokinetics of Phenanthrene in Enchytraeus albidus (Oligochaeta).

Although the toxicokinetics of organic pollutants in soil invertebrates under optimal and constant temperature has been widely reported, their uptake, elimination, and bioaccumulation under suboptimal temperatures, and especially daily fluctuating temperature (FT) regimes have received only little research attention. In this study, the uptake, elimination, and bioaccumulation of phenanthrene (PHE) in Enchytraeus albidus (Oligochaeta) under different constant temperatures, and an FT regime were investigated in a natural soil. In general, the PHE concentrations in worm tissues reached steady state within 14 days at different temperatures. The uptake (ku) and elimination (ke) rate constants and the bioaccumulation increased with increasing temperature likely because of an increased diffusivity of PHE into the worms and an increased metabolic rate. Interestingly, the bioaccumulation factor of PHE in E. albidus showed a positive relationship with temperature because the slope of the ku-temperature relationship was larger than that of the ke-temperature relationship. Further, the uptake and elimination rate constants were larger under the FT regime than at the constant average of the fluctuating temperature. These findings suggest that, climatic conditions, especially daily fluctuating temperatures, should be considered for the assessment of the toxicokinetics of organic pollutants in terrestrial organisms.

Compartmentation and effects of lead (Pb) in the collembolan, Folsomia candida.

The impact of soil lead (Pb) pollution on survival, growth, and reproduction of the collembolan, Folsomia candida, and Pb compartmentation in its gut and remaining body parts were studied by exposing animals to laboratory-spiked soil. The survival, growth, and reproduction of F. candida were significantly reduced by increasing soil Pb concentration. The LC50 values of survival based on total and CaCl2-extractable Pb concentration in soil were 2562 mg kg-1 and 351 mg kg-1, respectively. The EC50 values of reproduction were 1244 mg kg-1 and 48 mg kg-1, respectively. The Pb concentration in whole body, gut, and remaining body parts was significantly increased with the increase of soil Pb concentration and followed an exponential increase when the soil Pb concentration was equal to or above a threshold (1000 mg kg-1 for whole body and remaining body part, 500 mg kg-1 for gut). Below this threshold, these relationships were linear. The Pb concentration in the gut was higher than whole body and remaining body part of F. candida, and the threshold of internal Pb concentration at which F. candida can compensate was in the range 7-13 mg Pb kg-1 dry animal (corresponding to soil Pb concentration 500-1000 mg Pb kg-1 dry soil). The results indicate that reproduction of F. candida was a more sensitive indicator of lead toxicity than survival and growth. Pb was mainly accumulated in the gut of F. candida. We discuss the internal Pb concentration as an indicator of adverse effects in the risk assessment of soil Pb pollution.

Mercury (Hg2+) interferes with physiological adaptations to freezing in the arctic earthworm Enchytraeus albidus.

Freezing temperatures is an important stressor in the arctic regions and has a significant influence on the population dynamics and geographic distribution of terrestrial invertebrates. Toxic metals in the environment can interfere with protective cold-acclimation responses of organisms. It is therefore important to evaluate the combined effects of cold stress and environmental contaminants. Here, we aimed to investigate the effects of Hg (HgCl2) on various physiological aspects of freeze-tolerance in the earthworm (Enchytraeus albidus). We measured the levels of the cryoprotectant glucose, the glycogen content (source of glucose molecules for cryoprotection and fuel for metabolism), and changes in the composition of membrane phospholipid fatty acids (PLFA) as an indicator of lipid peroxidation. Freezing at -6 °C had no effect on survival in uncontaminated soil, however, survival of freezing in Hg contaminated soil was clearly reduced, especially at extended exposure times. Thus, the LC50 value in frozen soil decreased from 8.3 mg Hg kg-1 (when exposed for 17 days) to only 4.2 mg Hg kg-1 after 36 days' exposure indicating that combined effects of Hg and freezing became larger at prolonged exposure times. Hg caused a depletion of glycogen reserves (almost 50% at 12 mg kg-1 dry soil), but despite this effect worms were able to maintain a constant cryoprotectant level (about 0.12 mg glucose mg-1 dry weight) at all Hg concentrations. Hg had clear negative effects on the proportion of unsaturated PLFAs, which could be an indication of lipid peroxidation. Since a high proportion of unsaturated fatty acids in the membrane is important for invertebrate freeze-tolerance, our results suggest that the negative effect of Hg on freeze-tolerance in E. albidus is related to degraded membrane functionality at low temperature.

Plant Secondary Compounds in Soil and Their Role in Belowground Species Interactions.

Knowledge of the effect of plant secondary compounds (PSCs) on belowground interactions in the more diffuse community of species living outside the rhizosphere is sparse compared with what we know about how PSCs affect aboveground interactions. We illustrate here that PSCs from foliar tissue, root exudates, and leaf litter effectively influence such belowground plant-plant, plant-microorganism, and plant-soil invertebrate interactions. Climatic factors can induce PSC production and select for different plant chemical types. Therefore, climate change can alter both quantitative and qualitative PSC production, and how these compounds move in the soil. This can change the soil chemical environment, with cascading effects on both the ecology and evolution of belowground species interactions and, ultimately, soil functioning.

Effects of α-pinene on life history traits and stress tolerance in the springtail Folsomia candida.

Volatile monoterpenes are emitted in large quantities to both air and soil by many plant species. While studies have addressed effects of monoterpenes on aboveground invertebrates, we have much poorer understanding of the possible effects of monoterpenes on soil invertebrates. Monoterpenes play a protective role in some plant species during heat and water stress, and therefore may provide similar protection against abiotic stress to soil invertebrates. The aim of the present study was to investigate the effects of the common monoterpene, α-pinene, on the soil living springtail, Folsomia candida (Collembola; Isotomidae). We hypothesized that exposure to α-pinene would lower the transition temperature of membranes, and thereby improve cold tolerance. Controlled exposure to α-pinene, which is a volatile liquid at room temperature, was made possible by passive dosing through the air-phase using a lipid donor. This lipid-based passive dosing approach also allows linking observed effects to concentrations in membrane when equilibrium is achieved. Equilibrium membrane concentrations above 116 mmol kg-1 caused springtails to become comatose, and coma recovery time was proportional to exposure concentration. Alpha-pinene delayed time to first egg laying, while the number of eggs laid and hatchability was unaffected. Springtails exposed to α-pinene showed increased survival of cold shock (-6 °C, 2 h), but no effects on heat (34 °C, 2 h) or drought tolerance (98.2% relative humidity, 7d) were observed. The present study has demonstrated that α-pinene has direct toxic effects to F. candida, but on the other hand can improve their cold tolerance considerably at membrane concentrations above 87 mmol kg-1.

Synergistic interaction between effects of phenanthrene and dynamic heat stress cycles in a soil arthropod.

Climatic stressors and chemicals should not be treated as isolated problems since they often occur simultaneously, and their combined effects must be evaluated including their possible interactive effects. In the present study we subjected springtails (Folsomia candida) to combined exposure to phenanthrene and dynamic heat cycles in a full factorial experiment. In a microcosm experiment, we studied the population growth of springtails subjected to a range of sub-lethal concentrations of phenanthrene. During the 28-day experiment we further subjected microcosms to varying numbers of repeated dynamic heat cycles (0-5 cycles) simulating repeated heat waves. We found a synergistic interaction between the effects of phenanthrene and the number of heat waves on both body mass of adults and juvenile production of F. candida showing that the negative effects of phenanthrene were intensified when animals were heat stressed, and/or vice versa. This interaction was not related to internal concentrations of phenanthrene in adult springtails, nor was it due to altered degradation of phenanthrene in soil. We argue that both phenanthrene (by its partitioning into membrane bilayers) and heat have detrimental effects on the physical conditions of cellular membranes in a dose-dependent manner, which, under extreme circumstances, can increase membrane fluidity to a level which is sub-optimal for normal membrane functioning. We discuss the possibility that the synergistic interactions subsequently reduce life-history parameters such as growth and reproduction.

Comparing Enchytraeus albidus populations from contrasting climatic environments suggest a link between cold tolerance and metabolic activity.

Basal metabolic activity and freezing of body fluids create reactive oxygen species (ROS) in freeze-tolerant organisms. These sources of ROS can have an additive negative effect via oxidative stress. In cells, antioxidant systems are responsible for removing ROS in order to avoid damage due to oxidative stress. Relatively little is known about the importance of metabolic rate for the survival of freezing, despite a good understanding of several cold tolerance related physiological mechanisms. We hypothesized that low basal metabolism would be selected for in freeze-tolerant organisms where winter survival is important for fitness for two reasons. First, avoidance of the additive effect of ROS production from metabolism and freezing, and second, as an energy-saving mechanism under extended periods of freezing where the animal is metabolically active, but unable to feed. We used the terrestrial oligochaete, Enchytraeus albidus, which is widely distributed from Spain to the high Arctic and compared eight populations originating across a broad geographical and climatic gradient after they had been cold acclimated at 5 °C in a common garden experiment. Cold tolerance (lower lethal temperature: LT50) and the potential metabolic activity (PMA, an estimator of the maximal enzymatic potential of the mitochondrial respiration chain) of eight populations were positively correlated amongst each other and correlated negatively with latitude and positively with average yearly temperature and the average temperature of the coldest month. These results indicate that low PMA in cold tolerant populations is important for survival in extremely cold environments.

Combined effects of drought and cold acclimation on phospholipid fatty acid composition and cold-shock tolerance in the springtail Protaphorura fimata.

Terrestrial arthropods' ability to survive sub-zero winter temperatures is an important factor influencing their abundance and geographic distribution. It is, therefore, important to understand their physiological mechanisms of low-temperature survival. Acclimation to moderate-low temperature can improve cold tolerance, and pre-acclimation to mild desiccation can also improve survival of a subsequent cold exposure. However, very few studies have assessed the combined actions of cold and drought acclimations. In the present study, we combined cold acclimation with drought acclimation making it possible to assess the interactions between effects of these two stressors using the springtail Protaphorura fimata as a model organism. We investigated the interacting effects of drought and cold acclimation on body fluid osmolality, membrane phospholipid fatty acid (PLFA) composition, and cold-shock tolerance. Acclimation to mild drought (- 2.46 MPa) increased body fluid osmolality from 0.33 to 1.25 Osm at all acclimation temperatures (5, 10, 15, or 20 °C) likely due to accumulation of the compatible osmolytes, trehalose, and alanine. Interestingly, the expected positive effect of drought acclimation on cold-shock tolerance was only evident at high acclimation temperature (20 °C), whereas at intermediate temperatures (10 and 15 °C), there was an interaction between acclimation temperature and drought. At 5 °C, no effect of drought acclimation on cold-shock tolerance was observed despite high osmolality. The positive effect of drought acclimation at 20 °C on subsequent cold-shock survival coincided with a drought-induced effect on PLFA composition only detectable at high temperature. We discuss the possible roles of drought-induced compatible osmolytes and an altered PLFA composition in the cold-shock tolerance of arthropods.

Can we predict ectotherm responses to climate change using thermal performance curves and body temperatures?

Thermal performance curves (TPCs), which quantify how an ectotherm's body temperature (Tb ) affects its performance or fitness, are often used in an attempt to predict organismal responses to climate change. Here, we examine the key - but often biologically unreasonable - assumptions underlying this approach; for example, that physiology and thermal regimes are invariant over ontogeny, space and time, and also that TPCs are independent of previously experienced Tb. We show how a critical consideration of these assumptions can lead to biologically useful hypotheses and experimental designs. For example, rather than assuming that TPCs are fixed during ontogeny, one can measure TPCs for each major life stage and incorporate these into stage-specific ecological models to reveal the life stage most likely to be vulnerable to climate change. Our overall goal is to explicitly examine the assumptions underlying the integration of TPCs with Tb , to develop a framework within which empiricists can place their work within these limitations, and to facilitate the application of thermal physiology to understanding the biological implications of climate change.