Stine Slotsbo

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

Thermal performance curves (TPCs), which quantify how an ectotherms 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.

Body metal concentrations and glycogen reserves in earthworms (Dendrobaena octaedra) from contaminated and uncontaminated forest soil.

Stress originating from toxicants such as heavy metals can induce compensatory changes in the energy metabolism of organisms due to increased energy expenses associated with detoxification and excretion processes. These energy expenses may be reflected in the available energy reserves such as glycogen. In a field study the earthworm, Dendrobaena octaedra, was collected from polluted areas, and from unpolluted reference areas. If present in the environment, cadmium, lead and copper accumulated to high concentrations in D. octaedra. In contrast, other toxic metals such as aluminium, nickel and zinc appeared to be regulated and kept at low internal concentrations compared to soil concentrations. Lead, cadmium and copper accumulation did not correlate with glycogen reserves of individual worms. In contrast, aluminium, nickel and zinc were negatively correlated with glycogen reserves. These results suggest that coping with different metals in earthworms is associated with differential energy demands depending on the associated detoxification strategy.

Freeze tolerance and accumulation of cryoprotectants in the enchytraeid Enchytraeus albidus (Oligochaeta) from Greenland and Europe.

The freeze tolerance and accumulation of cryoprotectants was investigated in three geographically different populations of the enchytraeid Enchytraeus albidus (Oligochaeta). E. albidus is widely distributed from the high Arctic to temperate Western Europe. Our results show that E. albidus is freeze tolerant, with freeze tolerance varying extensively between Greenlandic and European populations. Two populations from sub Arctic (Nuuk) and high Arctic Greenland (Zackenberg) survived freezing at -15 degrees C, whereas only 30% of a German population survived this temperature. When frozen, E. albidus responded by catabolising glycogen to glucose, which likely acted as a cryoprotectant. The average glucose concentrations were similar in the three populations when worms were frozen at -2 degrees C, approximately 50 microg glucose mg(-1) tissue dry weight (DW). At -14 degrees C the glucose concentrations increased to between 110 and 170 microg mg(-1) DW in worms from Greenland. The average glycogen content of worms from Zackenberg and Nuuk were about 300 microg mg(-1) DW, but only 230 microg mg(-1) DW in worms from Germany showing that not all glycogen was catabolised during the experiment. Nuclear magnetic resonance spectrometry (NMR) was used to screen for other putative cryoprotectants. Proline, glutamine and alanine were up regulated in frozen worms at -2 degrees C but only in relatively small concentrations suggesting that they were of little significance for freeze survival. The present study confirms earlier reports that freeze tolerant enchytraeids, like other freeze tolerant oligochaete earthworms, accumulate high concentrations of glucose as a primary cryoprotectant.

Exposure to mercury reduces heat tolerance and heat hardening ability of the springtail Folsomia candida

We investigated the combined effects of mercury (HgCl(2)) and acute heat on survival of the springtail Folsomia candida. The springtails were exposed to a range of aqueous concentrations (0-48 mg Hg(2+)/L) of HgCl(2) for 24 h. Subsequently, the same individuals were exposed to a range of high temperatures, from 20 to 35.5 degrees C. We found a highly significant synergistic interaction between effects of mercury and heat, with a reduced tolerance to heat after exposure to sublethal concentrations of mercury. Further, the heat hardening ability of F. candida was studied at sublethal concentrations of mercury. F. candida was able to heat harden (exposure to a mild heat treatment increasing survival of subsequent severe heat); however, when the springtails experienced a previous exposure to as little as 1 mg Hg(2+)/L, heat hardening failed to improve survival of heat shock at 34.5 degrees C, even though this was much lower than concentrations affecting survival without heat stress. Mild heat stress is known to induce the heat shock protein, HSP70, and real-time quantitative PCR confirmed that pre-acclimation to 32 degrees C did indeed cause >5-fold up-regulation of HSP70 expression. This up-regulation was not affected by previous exposure to 1 mg Hg(2+)/L.

Lipophilic Contaminants Influence Cold Tolerance of Invertebrates through Changes in Cell Membrane Fluidity

Contaminants taken up by living organisms in the environment as a result of anthropogenic contamination can reduce the tolerance of natural stressors, e.g., low temperatures, but the physiological mechanisms behind these interactions of effects are poorly understood. The tolerance to low temperatures of organisms that cannot regulate their body temperature (ectotherms) depends on their ability to increase the fluidity of their cellular membranes at low temperatures. Our study shows that contaminants accumulating in lipids of organisms alter the physical state of their membranes simply by being present. Contaminants of varying chemical structures can alter the membrane fluidity in either direction and correspondingly modulate the cold tolerance of intact animals.

Accumulation of free amino acids during exposure to drought in three springtail species

Springtails are closely related to insects, but they differ from these with respect to water balance, in particular because springtails are small and have high integumental permeability to water. Here we report a series of experiments addressing the dynamics of osmoregulation, water content and accumulation of free amino acids (FAAs) in three springtail species during exposure to a gradually increasing environmental desiccation simulating conditions in drought exposed soil. Folsomia candida and Protaphorura fimata (both living in the deeper soil layers; euedaphic species) were active throughout the 3week exposure, with the developing drought regime ending at -3.56MPa (the soil water activity at the permanent wilting point of plants is -1.5MPa) and remained hyperosmotic (having an body fluid osmolality higher than the corresponding environment) to their surrounding air. Sinella curviseta (living in upper soil/litter layers; hemiedaphic species) also survived this exposure, but remained hypoosmotic throughout (i.e. with lower osmolality than the environment). The body content of most FAAs increased in response to drought in all three species. Alanine, proline and arginine were the most significantly upregulated FAAs. By combining our results with data in the literature, we could account for 82% of the observed osmolality at -3.56MPa in F. candida and 92% in P. fimata. The osmolality of S. curviseta was only slightly increased under drought, but here FAAs were considerably more important as osmolytes than in the two other species. We propose that FAAs probably have general importance in drought tolerance of springtails.

Cold tolerance and freeze-induced glucose accumulation in three terrestrial slugs.

Cold tolerance and metabolic responses to freezing of three slug species common in Scandinavia (Arion ater, Arion rufus and Arion lusitanicus) are reported. Autumn collected slugs were cold acclimated in the laboratory and subjected to freezing conditions simulating likely winter temperatures in their habitat. Slugs spontaneously froze at about -4 °C when cooled under dry conditions, but freezing of body fluids was readily induced at -1 °C when in contact with external ice crystals. All three species survived freezing for 2 days at -1 °C, and some A. rufus and A. lusitanicus also survived freezing at -2 °C. (1)H NMR spectroscopy revealed that freezing of body fluids resulted in accumulation of lactate, succinate and glucose. Accumulation of lactate and succinate indicates that ATP production occurred via fermentative pathways, which is likely a result of oxygen depletion in frozen tissues. Glucose increased from about 6 to 22 μg/mg dry tissue upon freezing in A. rufus, but less so in A. ater and A. lusitanicus. Glucose may thus act as a cryoprotectant in these slugs, although the concentrations are not as high as reported for other freeze tolerant invertebrates.

Reversibility of developmental heat and cold plasticity is asymmetric and has long-lasting consequences for adult thermal tolerance

ABSTRACT The ability of insects to cope with stressful temperatures through adaptive plasticity has allowed them to thrive under a wide range of thermal conditions. Developmental plasticity is generally considered to be a non-reversible phenotypic change, e.g. in morphological traits, while adult acclimation responses are often considered to be reversible physiological responses. However, physiologically mediated thermal acclimation might not follow this general prediction. We investigated the magnitude and rate of reversibility of developmental thermal plasticity responses in heat and cold tolerance of adult flies, using a full factorial design with two developmental and two adult temperatures (15 and 25°C). We show that cold tolerance attained during development is readily adjusted to the prevailing conditions during adult acclimation, with a symmetric rate of decrease or increase. In contrast, heat tolerance is only partly reversible during acclimation and is thus constrained by the temperature during development. The effect of adult acclimation on heat tolerance was asymmetrical, with a general loss of heat tolerance with age. Surprisingly, the decline in adult heat tolerance at 25°C was decelerated in flies developed at low temperatures. This result was supported by correlated responses in two senescence-associated traits and in accordance with a lower rate of ageing after low temperature development, suggesting that physiological age is not reset at eclosion. The results have profound ecological consequences for populations, as optimal developmental temperatures will be dependent on the thermal conditions faced in the adult stage and the age at which they occur. Summary: Using Drosophila melanogaster, we show how developmental plasticity of cold tolerance is completely reversible in the adult stage, while adult acclimation in heat tolerance is constrained by developmental temperature.

Importance of Freeze–Thaw Events in Low Temperature Ecotoxicology of Cold Tolerant Enchytraeids

Due to global warming it is predicted that freeze-thaw cycles will increase in Arctic and cold temperate regions. The effects of this variation becomes of particular ecological importance to freeze-tolerant species when it is combined with chemical pollutants. We compared the effect of control temperature (2 °C), daily freeze-thaw cycles (2 to -4 °C) and constant freezing (-2 °C) temperatures on the cold-tolerance of oligochaete worms (Enchytraeus albidus) and tested how survival was influenced by pre-exposure to 4-nonylphenol (4-NP), a common nonionic detergent found in sewage sludge amended soils. Results showed that combined effect of 4-NP and daily freeze-thaw cycles can cause higher mortality to worms as compared with sustained freezing or control temperature. Exposure to 4-NP caused a substantial depletion of glycogen reserves which is catabolized during freezing to produce cryoprotective concentrations of free glucose. Further, exposure to freeze-thaw cycles resulted in higher concentrations of 4-NP in worm tissues as compared to constant freezing or control temperature (2 °C). Thus, worms exposed to combined effect of freeze-thaw cycles and 4-NP suffer higher consequences, with the toxic effect of the chemical potentiating the deleterious effects of freezing and thawing.

Low temperature survival in different life stages of the Iberian slug, Arion lusitanicus☆

The slug Arion lusitanicus Mabille (Gastropoda: Pulmonata: Arionidae) is an invasive species which has spread to most parts of Europe. The area of origin is unknown, but A. lusitanicus seems to cope well with the local conditions in the countries to which it has migrated. It spreads rapidly, occurs often in high densities and has become a serious pest in most European countries. Therefore there is an urgent need for better knowledge of the ecophysiology of A. lusitanicus, such as the influence of climatic conditions, in order to develop prognostic models and strategies for novel pest management practises. The aim of our study was to investigate the influence of subzero temperatures in relation to winter survival. A. lusitanicus is shown to be freeze-tolerant in some life stages. Most juveniles and some adult slugs survived being frozen at -1.3°C for 3days, but none of the slugs survived freezing at -3°C. The eggs survived subzero temperatures (down to -2°C) probably by supercooling. Juveniles and adults may also survive in a supercooled state (down to -3°C) but are generally poor supercoolers. Therefore, the winter survival of A. lusitanicus depends to a high degree on migration to habitats protected from low winter temperatures, e.g. under plant litter, buried in the soil or in compost heaps.