A moderate change in temperature induces changes in fatty acid composition of storage and membrane lipids in a soil arthropod

A moderate change in ambient temperature can lead to vital physiological and biochemical adjustments in ectotherms, one of which is a change in fatty acid composition. When temperature decreases, the composition of membrane lipids (phospholipid fatty acids) is expected to become more unsaturated to be able to maintain homeoviscosity. Although different in function, storage lipids (triacylglycerol fatty acids) are expected to respond to temperature changes in a similar way. Age-specific differences, however, could influence this temperature response between different life stages. Here, we investigate if fatty acid composition of membrane and storage lipids responds similarly to temperature changes for two different life stages of Orchesella cincta. Juveniles and adults were cold acclimated (15 °C → 5 °C) for 28 days and then re-acclimated (5 °C → 15 °C) for another 28 days. We found adult membranes had a more unsaturated fatty acid composition than juveniles. Membrane lipids became more unsaturated during cold acclimation, and a reversed response occurred during warm acclimation. Membrane lipids, however, showed no warm acclimation, possibly due to the moderate temperature change. The ability to adjust storage lipid composition to moderate changes in ambient temperature may be an underestimated fitness component of temperature adaptation because fluidity of storage lipids permits accessibility of enzymes to energy reserves.     

Acclimation responses to temperature vary with vertical stratification: implications for vulnerability of soil‐dwelling species to extreme temperature events

The occurrence of summer heat waves is predicted to increase in amplitude and frequency in the near future, but the consequences of such extreme events are largely unknown, especially for belowground organisms. Soil organisms usually exhibit strong vertical stratification, resulting in more frequent exposure to extreme temperatures for surface‐dwelling species than for soil‐dwelling species. Therefore soil‐dwelling species are expected to have poor acclimation responses to cope with temperature changes. We used five species of surface‐dwelling and four species of soil‐dwelling Collembola that habituate different depths in the soil. We tested for differences in tolerance to extreme temperatures after acclimation to warm and cold conditions. We also tested for differences in acclimation of the underlying physiology by looking at changes in membrane lipid composition. Chill coma recovery time, heat knockdown time and fatty acid profiles were determined after 1 week of acclimation to either 5 or 20 °C. Our results showed that surface‐dwelling Collembola better maintained increased heat tolerance across acclimation temperatures, but no such response was found for cold tolerance. Concordantly, four of the five surface‐dwelling Collembola showed up to fourfold changes in relative abundance of fatty acids after 1 week of acclimation, whereas none of the soil‐dwelling species showed a significant adjustment in fatty acid composition. Strong physiological responses to temperature fluctuations may have become redundant in soil‐dwelling species due to the relative thermal stability of their subterranean habitat. Based on the results of the four species studied, we expect that unless soil‐dwelling species can temporarily retreat to avoid extreme temperatures, the predicted increase in heat waves under climatic change renders these soil‐dwelling species more vulnerable to extinction than species with better physiological capabilities. Being able to act under a larger thermal range is probably costly and could reduce maximum performance at the optimal temperature.     

The costs of phenotypic adaptation to repeatedly fluctuating temperatures in a soil arthropod

Costs of phenotypic adaptation to changing environments have often been studied in morphological structures. Such structures typically are irreversible for at least some stage in the organism's life. In this study we investigated whether recurrent and reversible adaptation to changes in the thermal environment incurs a cost in terms of some key life-history traits in the collembolan Orchesella cincta. We exposed juvenile O. cincta to two treatments differing in the frequency of temperature fluctuation but with equal total temperature sums. In the high frequency treatment temperature fluctuated daily between 10 and 20 °C, while in the low frequency treatment temperature fluctuated on a weekly schedule. During the treatments we measured juvenile growth rate and juvenile mortality, and after six weeks the animals were transferred to constant 15 °C and adult starvation resistance was assessed. We found no significant differences between the treatments in juvenile growth rate or juvenile survival. Also, adults that had grown up under high frequency temperature fluctuations did not suffer from reduced starvation resistance compared to animals growing under low frequency temperature fluctuations. This finding supports the hypothesis that selection minimizes the production costs of inducible phenotypes and suggests that the development of optimal phenotypes and evolution of temperature reaction norms are not constrained by such costs.     

Effects of exposure to short-term heat stress on male reproductive fitness in a soil arthropod

Ambient temperature is a key environmental factor influencing a variety of aspects of the ecology and evolution of ectotherms. Reproductive traits have been suggested to be more sensitive to thermal stress than other life history traits. This study investigated the direct and indirect effects of heat shock on male reproductive success in the widespread springtail Orchesella cincta. Male springtails were exposed to four temperature treatments: heat hardening (35.2 °C for 1 h), heat shock (37.2 °C for 1 h), heat hardening + heat shock (35.2 °C for 1 h, followed 15 h later by 37.2 °C for 1 h), and control (20 °C). The heat shock gene Hsp70 showed high expression in all the heat treatments, indicating that the treatments indeed induced thermal stress. Significant mortality was only found in the treatment with heat shock, both with and without heat hardening. A direct effect of heat treatment was found on time to first reproduction, which was significantly longer after heat shock (with or without heat hardening) than in the control treatment. There was no difference among treatments in the number of spermatophores produced in the first reproductive instar. Heat treatment also had indirect effects on male reproductive success. Females chose significantly more spermatophores from control males than from males that received heat shock, heat hardening or both. A high percentage of spermatophores produced by heat shocked males caused reproductive failure in females, but no significant differences among treatments were found.Our results suggest that not all traits were equally affected by the heat stress. Heat hardening did not protect reproductive traits against the negative effects of heat shock. The indirect effects of heat shock on reproduction may be equally important as the direct effects.     

Effects of acclimation temperature on thermal tolerance, locomotion performance and respiratory metabolism in Acheta domesticus L. (Orthoptera: Gryllidae)

The effects of acclimation temperature on insect thermal performance curves are generally poorly understood but significant for understanding responses to future climate variation and the evolution of these reaction norms. Here, in Acheta domesticus, we examine the physiological effects of 7-9 days acclimation to temperatures 4 °C above and below optimum growth temperature of 29 °C (i.e. 25, 29, 33 °C) for traits of resistance to thermal extremes, temperature-dependence of locomotion performance (jumping distance and running speed) and temperature-dependence of respiratory metabolism. We also examine the effects of acclimation on mitochondrial cytochrome c oxidase (CCO) enzyme activity. Chill coma recovery time (CRRT) was significantly reduced from 38 to 13 min with acclimation at 33-25 °C, respectively. Heat knockdown resistance was less responsive than CCRT to acclimation, with no significant effects of acclimation detected for heat knockdown times (25 °C: 18.25, 29 °C: 18.07, 33 °C: 25.5 min). Thermal optima for running speed were higher (39.4-40.6 °C) than those for jumping performance (25.6-30.9 °C). Acclimation temperature affected jumping distance but not running speed (general linear model, p = 0.0075) although maximum performance (U_MAX) and optimum temperature (T_OPT) of the performance curves showed small or insignificant effects of acclimation temperature. However, these effects were sensitive to the method of analysis since analyses of T_OPT, U_MAX and the temperature breadth (T_BR) derived from non-linear curve-fitting approaches produced high inter-individual variation within acclimation groups and reduced variation between acclimation groups. Standard metabolic rate (SMR) was positively related to body mass and test temperature. Acclimation temperature significantly influenced the slope of the SMR-temperature reaction norms, whereas no variation in the intercept was found. The CCO enzyme activity remained unaffected by thermal acclimation. Finally, high temperature acclimation resulted in significant increases in mortality (60-70% at 33 °C vs. 20-30% at 25 and 29 °C). These results suggest that although A. domesticus may be able to cope with low temperature extremes to some degree through phenotypic plasticity, population declines with warmer mean temperatures of only a few degrees are likely owing to the limited plasticity of their performance curves.     

Cold tolerance in relation to developmental and adult temperature in a butterfly

Abstract. Larvae of the butterfly Lycaena tityrus (Poda) are reared at 20 or 27 °C until adult eclosion, after which they are maintained at the same temperature or are transferred to the alternate temperature. The resulting adults are exposed to −20 °C for 8 min, returned to ambient temperature, and the recovery time to standing position is recorded. On the day of eclosion, individuals reared at 20 °C show 19% shorter recovery times than individuals reared at 27 °C. This effect of developmental temperature disappears when the same animals are tested 3 and 6 days later. However, adult temperature did not affect recovery time in these animals, presumably due to over-riding effects of previous cold shocks. This is suggested by another set of animals, not having experienced previous cold shocks, demonstrating recovery times that are 28% shorter in individuals maintained as adults for 3 days at 20 compared to 27 °C. Thus, L. tityrus appears to be capable of adapting to local temperatures.     

松天牛小首螨对极端温度耐受性的驯化效应及低温存储研究

[目的]松天牛小首螨是近年发现的首个能够寄生致死松墨天牛卵的一个螨类新种,研究该螨对极端温度耐受性的驯化效应和低温存储条件,有助于进一步评估该螨的潜在地理分布或应用区域,并为该螨的规模化运输和存储提供基础依据。[方法]通过不同温度条件驯化后,测定松天牛小首螨暴露在极端温度下的存活率,同时比较不同低温条件下存储的松天牛小首螨膨腹体涌出的成螨数量,以及存储的雌成螨的生存情况。[结果]高温驯化可显著提高雌成螨高温暴露存活率,其中30℃ 36 h驯化后的存活率提高了1.26倍;低温驯化可显著提高雌成螨极端低温暴露存活率,其中10℃ 96 h、10℃ 120 h驯化后的存活率分别提高了2.08和2.13倍。以膨腹体为存储对象,低温存储后涌出成螨的数量随着存储时间延长而逐渐显著减少;以雌成螨为存储对象,在10℃条件下存储30 d,存活率为65.10%,在4℃条件下存储30 d,存活率达84.21%。[结论]松天牛小首螨具有很强的温度适应性,短期温度驯化即可大幅提升其对极端温度的耐受性。膨腹体适合作为该螨短期低温存储对象,雌成螨则适合作为中长期低温存储对象。     

Unusual tolerance to high temperatures in a new herbicide-resistant D1 mutant from Glycine max (L.) Merr. cell cultures deficient in fatty acid desaturation

The unusual tolerance to heat stress of STR7, an atrazine-resistant mutant isolated from photosynthetic cell-suspension cultures of soybean (Glycine max L. Merr. cv. Corsoy) and characterized previously [M. Alfonso et al. (1996) Plant Physiol 112:1499–1508] has been studied. The STR7 mutant maintained normal growth and fluorescence parameters at higher temperatures than the wild type (WT). The temperature for 50% inactivation of the oxygen-evolving activity of STR7 thylakoids was 13 °C higher than in the WT. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis with specific antibodies revealed that the integrity of photosystem II in the STR7 mutant was maintained at higher temperatures than in the WT. This unusual intrinsic tolerance to high temperatures contrasted with the higher sensitivity to heat stress reported as a feature linked to the triazine-resistance trait. The chloroplast membrane of STR7 accumulated an unusually high content of saturated C16:0 and reduced levels of C16:1 and C18:3 unsaturated fatty acids compared with the WT. Among all the lipid classes, chloroplastic lipids synthesized via the prokaryotic pathway (mono-galactosyl-diacyl-glycerol, phosphatidylglycerol and di-galactosyl-diacyl-glycerol), which represented more than 75% of the total lipid classes, showed the most substantial differences in C16:0 and C18:3 levels. In addition, changes in the physico-chemical properties of the thylakoid membrane and chloroplast ultrastructure were also detected. Received: 11 April 2000 / Accepted: 16 August 2000     

Diurnal variation in methane emission in relation to the water table,soil temperature,climate and vegetation cover in a Swedish acid mire

Diurnal variation in the rate of methane emission and its relation to water table depth and macro climate was studied in several plant communities within an acid,Sphagnum dominated, mixed mire in Northern Sweden. Provided that diurnal variation in solar radiation and air temperature occurred, methane fluxes differed during day and night. Diurnal patterns in methane emission rates were found to differ among mire plant communities. In relatively dry plant communities (ridges, minerotrophic lawn), the average nighttime emission rates were 2–3 times higher than the daytime rates during the two periods with high diurnal variation in solar radiation and air temperature. Methane emission was significantly (p < 0.05) related to solar radiation and soil temperature at depths of 5 and 10 cm at all sampling points in the dry plant communities. In the wetter plant communities, no significant difference between daytime and nighttime average methane emission rates were found even though methane emissions were significantly related with radiation and soil temperature at approximately 70% of the sampling points. The increased emission rate for methane at night in the comparatively dry plant communities was probably caused by an inhibition of methane oxidation, owing to the lower nighttime temperatures or to a delay in the supply of root-exuded substrate for the anaerobic bacteria, or by both. The pattern observed in the wet plant communities indicated that methane production were positively related either to soil temperature or light-regulated root exudation.