Longevity and temperature response of pollen as affected by elevated growth temperature and carbon dioxide in peanut and grain sorghum

It is important to understand the effects of environmental conditions during plant growth on longevity and temperature response of pollen. Objectives of this study were to determine the influence of growth temperature and/or carbon dioxide (CO₂) concentration on pollen longevity and temperature response of peanut and grain sorghum pollen. Plants were grown at daytime maximum/nighttime minimum temperatures of 32/22, 36/26, 40/30 and 44/34 °C at ambient (350 μmol mol⁻¹) and at elevated (700 μmol mol⁻¹) CO₂ from emergence to maturity. At flowering, pollen longevity was estimated by measuring in vitro pollen germination at different time intervals after anther dehiscence. Temperature response of pollen was measured by germinating pollen on artificial growth medium at temperatures ranging from 12 to 48 °C in incubators at 4 °C intervals. Elevated growth temperature decreased pollen germination percentage in both crop species. Sorghum pollen had shorter longevity than peanut pollen. There was no influence of CO₂ on pollen longevity. Pollen longevity of sorghum at 36/26 °C was about 2 h shorter than at 32/22 °C. There was no effect of growth temperature or CO₂ on cardinal temperatures (T_min, T_opt, and T_max) of pollen in both crop species. The T_min, T_opt, and T_max identified at different growth temperatures and CO₂ levels were similar at 14.9, 30.1, and 45.6 °C, respectively for peanut pollen. The corresponding values for sorghum pollen were 17.2, 29.4, and 41.7 °C. In conclusion, pollen longevity and pollen germination percentage was decreased by growth at elevated temperature, and pollen developed at elevated temperature and/or elevated CO₂ did not have greater temperature tolerance.     

Combined ventilatory responses to aerial hypoxia and temperature in the South American lungfish Lepidosiren paradoxa

The control of pulmonary ventilation in South American lungfish Lepidosiren paradoxa is poorly understood. Interactions between temperature and hypoxia are particularly relevant due to large seasonal variations of its habitat. Therefore, we tested the hypothesis that the ventilatory responses to aerial hypoxia of Lepidosiren are highly dependent on ambient temperature. We used a pneumotachograph to measure pulmonary ventilation (V_E), tidal volume (V_T) and respiratory frequency (f_R) during normoxic (21% O₂) and hypoxic (12%, 10% and 7% O₂) conditions at two temperatures (25 and 35 °C). Blood gases, arterial PO₂ (PaO₂), arterial PCO₂ (PaCO₂) and arterial pH (pH_a) were also evaluated. At 25 °C, V_E increased significantly at 10% and 7% hypoxic levels when compared to the control value (21% O₂). At 35 °C, all hypoxic levels elicited a significant increase of V_E relative to control values. V_E is augmented mostly by increases of respiratory frequency (f_R), and there were significant interactions (p<0.001) between aerial hypoxia and temperature. PaCO₂ increased from ∼22 mmHg (normoxic value at 25 °C) to ∼32 mmHg (normoxic value at 35 °C). Concomitantly, the pH_a decreased from 7.51 (25 °C) to 7.38 (35 °C). Hypoxia-induced hyperventilation caused a reduction in PaCO₂ and an increase in pH_a, which were more pronounced at 35 °C than at 25 °C, reflecting an increased hyperventilation under the high temperature. In conclusion, the magnitude of ventilatory response is highly temperature-dependent in L. paradoxa, which is important for an animal experiencing large seasonal variations.     

Thermogenic characteristics and evaporative water loss in the tree shrew (Tupaia belangeri)

Thermogenic characteristics and evaporative water loss were measured at different temperatures in Tupaia belangeri. The thermal neutral zone (TNZ) of T. belangeri was 30–35 °C. Mean body temperature was 39.76±0.27 °C and mean body mass was 100.86±9.09 g. Basal metabolic rate (BMR) was 1.38±0.03 ml O₂/g h. Average minimum thermal conductance (C_m) was 0.13±0.01 ml O₂/g h °C. Evaporative water loss in T. belangeri increased when the temperature rose; the maximal evaporative water loss was 3.88±0.41 mg H₂O/g h at 37.5 °C. The results may reflect features of small mammals in the sub-tropical plateau region: T. belangeri had high basal metabolic rate and high total thermal conductance, compared with the predicted values based on their body mass whilst their body temperatures are relatively high; T. belangeri has high levels of evaporative water loss and poor water-retention capacity. Evaporative water loss plays an important role in temperature regulation.     

A cryoprotective and cold-adapted 1,3-β-endoglucanase from cherimoya (Annona cherimola) fruit

A 1,3-β-glucanase with potent cryoprotective activity was purified to homogeneity from the mesocarp of CO₂-treated cherimoya fruit (Annona cherimola Mill.) stored at low temperature using anion exchange and chromatofocusing chromatography. This protein was characterized as a glycosylated endo-1,3-β-glucanase with a M_r of 22.07 kDa and a pI of 5.25. The hydrolase was active and stable in a broad acidic pH range and it exhibited maximum activity at pH 5.0. It had a low optimum temperature of 35 °C and it retained 40% maximum activity at 5 °C. The purified 1,3-β-glucanase was relatively heat unstable and its activity declined progressively at temperatures above 50 °C. Kinetic studies revealed low k_cat (3.10 ± 0.04 s⁻¹) and K_m (0.32 ± 0.03 mg ml⁻¹) values, reflecting the intermediate efficiency of the protein in hydrolyzing laminarin. Moreover, a thermodynamic characterization revealed that the purified enzyme displayed a high k_cat at both 37 and 5 °C, and a low E_a (6.99 kJ mol⁻¹) within this range of temperatures. In vitro functional studies indicated that the purified 1,3-β-glucanase had no inhibitory effects on Botrytis cinerea hyphal growth and no antifreeze activity, as determined by thermal hysteresis analysis using differential scanning calorimetry. However, a strong cryoprotective activity was observed against freeze-thaw inactivation of lactate dehydrogenase. Indeed, the PD₅₀ was 8.7 μg ml⁻¹ (394 nM), 9.2-fold higher (3.1 on a molar basis) than that of the cryoprotective protein BSA. Together with the observed accumulation of glycine-betaine in CO₂-treated cherimoya tissues, these results suggest that 1,3-β-glucanase could be functionally implicated in low temperature-defense mechanism activated by CO₂.     

Metabolism,thermoregulation and evaporative water loss in the Chaotung Vole (Eothenomys olitor) in Yunnan-Kweichow Plateau in summer

Proper adjustment of thermoregulatory mechanisms ensures the survival of mammals when they are subjected to seasonal changes in their natural environment. To understand the physiological and ecological adaptations of Eothenomys olitor, we measured their metabolic rate, thermal conductance, body temperature (T_b) and evaporative water loss at a temperature range of 5–30 °C in summer. The thermal neutral zone (TNZ) of E. olitor was 20–27.5 °C, and the mean body temperature was 35.81±0.15 °C. Basal metabolic rate (BMR) was 2.81±0.11 ml O₂/g h and mean minimum thermal conductance (C_m) was 0.18±0.01 ml O₂/g h °C. Evaporative water loss (EWL) in E. olitor increased when the ambient temperature increased. The maximal evaporative water loss was 6.74±0.19 mg H₂O/g h at 30 °C. These results indicated that E. olitor have relatively high BMR, low body temperature, low lower critical temperature, and normal thermal conductance. EWL plays an inportant role in temperature regulation. These characteristics are closely related to the living habitat of the species, and represent its adaptive strategy to the climate of the Yunnan-Kweichow Plateau, a low-latitude, high-altitude region where annual temperature fluctuations are small, but daily temperature fluctuations are greater.     

Hot hypoxic flies: Whole-organism interactions between hypoxic and thermal stressors in Drosophila melanogaster

The upper critical thermal maximum (CT_max) of metazoans varies over a wide range, and its determinative factors, such as oxygen limitation, remain controversial. Induction of thermoprotective mechanisms after challenge by sublethal heat stress has been well documented in many organisms, including the model fly Drosophila melanogaster. Interestingly, however, other challenges—notably a period of anoxia—induce post-exposure thermoprotective effects in some organisms such as locusts and houseflies. Here I show, using thermolimit respirometry, that acute hypoxia during thermal stress significantly reduced the CT_max of D. melanogaster, but only below an oxygen partial pressure of about 10 kPa (39.0±0.4 SE °C at 9.3 kPa vs. 36.0±0.2 SE °C at 3.5 kPa). Likewise, the scope for voluntary motor activity declined sharply below 10 kPa and was essentially eliminated at 2.3 kPa. Respiratory water loss increased highly significantly below about 10 kPa. The post-CT_max release of a large quantity of CO₂ is shown to be independent of loss of spiracular control, but dependent at least in part on oxygen availability. The results are broadly in accord with Pörtner's oxygen limitation hypothesis, but suggest that acute oxygen limitation only becomes an important factor at partial pressures less than half of typical atmospheric levels.     

Water transport in epididymal and ejaculated rhesus monkey (Macaca mulatta) sperm during freezing

In the present study, we report the effects of cooling ejaculated and epididymal rhesus monkey (Macacamulatta) sperm with and without the presence of a cryoprotective agent, glycerol. Water transport data during freezing of ejaculated and epididymal sperm cell suspensions were obtained at a cooling rate of 20 °C/min in the absence of any cryoprotective agents and in the presence of 0.7 M of glycerol, as well. Using previously published values, the macaque sperm cell was modeled as a cylinder of length 73.83 μm with a radius of 0.40 μm and an osmotically inactive cell volume, V_b, of 0.772V_o, where V_o is the isotonic cell volume. This translated to a surface area, SA to initial water volume, WV ratio of ∼22 μm⁻¹. By fitting a model of water transport to the experimentally determined volumetric shrinkage data, the best-fit membrane permeability parameters (reference membrane permeability to water at 0 °C, L_pg or L_pg[cpa] and the activation energy, E_Lp or E_Lp[cpa]) were found to range from: L_pg or L_pg[cpa] = 0.0020-0.0029 μm/min-atm; E_Lp or E_Lp[cpa]) = 10.6-18.3 kcal/mole. By incorporating these membrane permeability parameters in a recently developed equation (optimal cooling rate, ; where the units of B_opt are °C/min, E_Lp or E_Lp[cpa] are kcal/mole, L_pg or L_pg[cpa] are μm/min-atm and SA/WV are μm⁻¹), we determined the optimal rates of freezing macaque sperm to be ∼23 °C/min (ejaculated sperm in the absence of CPAs), ∼29 °C/min (ejaculated sperm in the presence of glycerol), ∼24 °C/min (epididymal sperm in the absence of CPAs) and ∼24 °C/min (epididymal sperm in the presence of glycerol). In conclusion, the subzero water transport response and consequently the subzero water transport parameters are not significantly different between the ejaculated and epididymal macaque spermatozoa under corresponding cooling conditions.     

The physiological response of reef corals to diel fluctuations in seawater temperature

An opportunity to explore the effects of fluctuating temperatures on tropical scleractinian corals arose when diurnal warming (as large as 4.7 °C) was detected over the rich coral communities found within the back reef of Moorea, French Polynesia. In April and May 2007, experiments were completed to determine the effects of fluctuating temperature on Pocillopora meandrina and Porites rus, and consecutive trials were used to expose them for 13 days to 26 °C, 28 °C (ambient conditions), 30 °C, or a fluctuating treatment ranging from 26 to 30 °C over 24 h. The multivariate response was assessed using maximum dark-adapted quantum yield of PSII (F_V/F_M), Symbiodinium density, chlorophyll-a content, and calcification. In trial 1, multivariate physiology of both species was significantly affected by treatments, with the fluctuating temperature resulting in a 17-45% decline in Symbiodinium density (relative to the ambient) matching that occurring at a constant 30 °C; F_V/F_M, chlorophyll-a content, and calcification, did not differ between the fluctuating and the steady treatments. In contrast, in trial 2 that utilized corals collected two weeks after those used in trial 1, the corals were unaffected by the treatments, likely due to an environment × trial interaction caused by seasonal declines in Symbiodinium density. Together, these results demonstrate that short transgressions to ecologically relevant high and low temperatures can elicit a potentially detrimental response equivalent to that occurring upon exposure to a constant high temperature. The dissimilar responses among dependent variables and consecutive trials underscore the importance of temporal replication and multivariate approaches in coral ecophysiology. It is likely that recent history has a stronger effect on the response of corals to treatments than is currently recognized.     

Hydrogen production by sorption-enhanced steam reforming of glycerol

Catalytic steam reforming of glycerol for H₂ production has been evaluated experimentally in a continuous flow fixed-bed reactor. The experiments were carried out under atmospheric pressure within a temperature range of 400–700 °C. A commercial Ni-based catalyst and a dolomite sorbent were used for the steam reforming reactions and in situ CO₂ removal. The product gases were measured by on-line gas analysers. The results show that H₂ productivity is greatly increased with increasing temperature and the formation of methane by-product becomes negligible above 500 °C. The results suggest an optimal temperature of ∼500 °C for the glycerol steam reforming with in situ CO₂ removal using calcined dolomite as the sorbent, at which the CO₂ breakthrough time is longest and the H₂ purity is highest. The shrinking core model and the 1D-diffusion model describe well the CO₂ removal under the conditions of this work.     

A novel alkaline lipase from Ralstonia with potential application in biodiesel production

With the aim of isolating a biocatalyst able to catalyze biodiesel production from microbial source, Ralstonia sp. CS274 was isolated and a lipase from the strain (RL74) was purified. Molecular weight of RL74 was estimated to be 28,000 Da by SDS-PAGE. The activity was highest at 50-55 °C and pH 8.0-9.5 and was stable at pH 7.0-12.0 and up to 45 °C. It was resistant to oxidizing and reducing agents and the activity was enhanced by detergents. RL74 was 1,3 specific and K_m and V_max for p-nitrophenyl palmitate were 2.73 ± 0.6 mM and 101.4 ± 1.9 mM/min mg, respectively. N-terminal amino acid sequence showed partial homology with that of Penicillium lipases. RL74 produced biodiesel more efficiently in palm oil than in soybean oil; and the production was highest at pH 8.0, at 5% methanol and at 20% water content.     

Evaporative water loss and energy metabolic in two small mammals,voles (Eothenomys miletus) and mice (Apodemus chevrieri), in Hengduan mountains region

Evaporative water loss (EWL) and energy metabolism were measured at different temperatures in Eothenomys miletus and Apodemus chevrieri in dry air. The thermal neutral zone (TNZ) of E. miletus was 22.5–30 °C and that of A. chevrieri was 20–27.5 °C. Mean body temperatures of the two species were 35.75±0.5 and 36.54±0.61 °C. Basal metabolic rates (BMR) were 1.92±0.17 and 2.7±0.5 ml O₂/g h, respectively. Average minimum thermal conductance (C_m) were 0.23±0.08 and 0.25±0.06 ml O₂/g h °C. EWL in E. miletus and A. chevrieri increased with the increase in temperature; the maximal EWL at 35 °C was 4.78±0.6 mg H₂O/g h in E. miletus, and 5.92±0.43 mg H₂O/g h in A. chevrieri. Percentage of evaporative heat loss to total heat production (EHL/HP) increased with the increase in temperature; the maximal EHL/HP was 22.45% at 30 °C in E. miletus, and in A. chevrieri it was 19.96% at 27.5 °C. The results may reflect features of small rodents in the Hengduan mountains region: both E. miletus and A. chevrieri have high levels of BMR and high levels of total thermal conductance, compared with the predicted values based on their body masses, while their body temperatures are relatively low. EWL plays an important role in temperature regulation.     

Ventilatory responses to temperature variation in the fresh water turtle,Mauremys caspica leprosa

A study of lung gas exchange in the fresh water turtle Mauremys caspica leprosa at normal physiological body temperatures (15, 25 and 35 °C) was extended to extreme temperatures (5 and 40 °C) to determine whether the direct relationship between body temperature and ventilatory response found in many lung-breathing ectotherms including other chelonian species was maintained. From 5 to 35 °C the lung ventilation per unit of O₂ uptake and CO₂ removed declined with temperature. Consequently, lung CO₂ partial pressure increased with temperature. Its value was maintained within narrow limits at each thermal constant, suggesting a suitable control throughout the complete ventilatory cycle. At 40 °C the ventilatory response showed the opposite trend. The ratios of ventilation to lung gas exchange increased compared to their values at 35 °C. The impact of this increased breathing-lowering the estimated mean alveolar CO₂ partial pressure-was nevertheless less than expected due to an increase in calculated physiological dead space. This suggests that the relative hyperventilation in response to hyperthermia found in Mauremys caspica leprosa is related to evaporative heat loss.Abbreviations BTPS body temperature, ambient pressure, saturated with water vapour - CTM critical thermal maximum - F_N2 fractional concentration of nitrogen - PA _CO2or PL _CO2 alveolar or lung CO₂ pressure - PA_O2or PL_O2 alveolar or lung O₂ pressure - PI_O2 inspired O₂ pressure - R respiratory exchange ratio - STPD standard temperature, standard pressure, dry - T _a ambient temperature - T _b body temperature - VA alveolar ventilation - VA/VCO₂ relative alveolar ventilation (alveolar ventilation per unit of CO₂ removed) - VO₂ O₂ uptake - VCO₂ CO₂ output - V _D anatomical dead space volume - V _D physiological dead space volume - VE/VO₂ ventilatory equivalent for O₂ - VE pulmonary ventilation or expiratory minute volume - VE/VCO₂ ventilatory equivalent for CO₂ - V _T tidal volume     

Seed germination of Lasia spinosa as a function of temperature,light, desiccation,and storage

Lasia spinosa seeds were not dormant at maturity in early spring. The most favorable temperatures for germination were between 25 and 30 °C, and final percentage and rate of germination decreased with an increase or decrease in temperature. When L. spinosa seeds were transferred to 25 °C, after 60 days at 10 °C (where none of the seeds germinated), final germination increased from 0% to 78%. Seeds germinated to high percentage both in light and in dark, although dark germination took more than twice as long as in the light. During desiccation of seeds at 15 °C and 45% relatively humidity, moisture loss decreased exponentially from 2.02 to 0.13 g H₂O g⁻¹ dry wt within 16 days, and only a few seeds (12%) survived 0.13 g H₂O g⁻¹ dry wt moisture content. Seeds stored at 0.58 g H₂O g⁻¹ dry wt moisture content at four constant temperatures (4, 10, 15, and −18 °C) for up to 6 months exhibited a well-defined trend of decreasing viability with decreasing temperature. Thus, we concluded that freshly harvested L. spinosa seeds are non-dormant and recalcitrant. Also, the seeds with 0.58 g H₂O g⁻¹ dry wt moisture content could be effectively stored for a few months between 10 and 15 °C although the most appropriate temperature for wet storage appears to be 10 °C, as it is close to the minimum temperature for germination and so there will be less pre-sprouting compared to 15 °C.     

Elevated temperature, per se, does not limit the ability of rainbow trout to increase stroke volume

Key questions remain about the regulation and limits of cardiac function in fish challenged with elevated temperature, and to what extent sex differences influence cardiac performance. In this study, we investigated the in vivo relationship between heart rate (f_H), stroke volume (S_V), and cardiac output (Q) in quiescent, sexually immature rainbow trout (Oncorhynchus mykiss Walbaum) when challenged with: (1) an acute increase in water temperature from 14 to 24 °C at 2 °C h⁻¹ and (2) a 50% reduction in f_H at 24 °C, achieved through the incremental administration of zatebradine hydrochloride (total dose 2 mg kg body mass⁻¹). There were no statistically significant (P<0.05) sex differences in cardiovascular function as temperature was raised to 24 °C. In males (N=10) and females (N=9), f_H increased in a linear fashion with water temperature (from ∼60 beats min⁻¹ at 14 °C to ∼125 beats min⁻¹ at 24 °C; Q₁₀=2.1), S_V was largely unchanged, and systemic blood pressure (P_DA) increased only slightly (by approx. 0.5 kPa) because the potential effect of increased Q on P_DA was mostly offset by a 35% decrease in systemic vascular resistance (R_sys). At 24 °C, zatebradine treatment halved f_H in both sexes, and yet Q was maintained at pre-treatment levels due to a doubling of S_V. Overall, these results: (1) indicate that the in vivo cardiovascular response of quiescent, immature, male and female trout to elevated temperature is similar and (2) challenge the current dogma about how temperature affects cardiac function in fishes. Specifically, unlike previous in vitro or in situ studies, our data demonstrate that fish are capable of maintaining or even increasing S_V at high temperatures. This suggests that aspects of cardiac control favor an increase in f_H as temperatures rise, or that increases in cardiac output to meet the fish’s metabolic demands at high temperatures are met solely through an increase in f_H because tachycardia is a requisite (unavoidable) physiological response.     

The effects of CO2 and chronic cold exposure on fecundity of female Drosophila melanogaster

Carbon dioxide and chilling are sometimes used to immobilise insects for laboratory research. Both of these methods are known to have short-term effects on behaviour and physiology in Drosophila, but their long-term impacts are unknown. We exposed female D. melanogaster adults to high CO₂ concentrations (4 h at 18,000 ppm) and chronic cold (72 h at 4 °C). The carbon dioxide exposure increased chill coma recovery time, but did not result in changes in offspring number, sex ratio, or size. By contrast, the cold exposure resulted in fewer, smaller offspring, and resulted in a male-biased sex ratio compared to controls. There was no significant interaction between CO₂ and cold. We conclude that although caution must be used in choosing an immobilisation method, CO₂ appears to have less long-term impact than cold.     

Intraspecific tolerance of Metarhizium anisopliae conidia to the upper thermal limits of summer with a description of a quantitative assay system

Conidial tolerance to the upper thermal limits of summer is important for fungal biocontrol agents, whose conidia are formulated into mycoinsecticides for field application. To develop an efficient assay system, aerial conidia of eight Metarhizium anisopliae, four M. anisopliae var. anisopliae, and six M. anisopliae var. acridum isolates with different host and geographic origins were wet-stressed for ≤180 min at 48 °C or incubated for 14 d colony growths at 10-35 °C. The survival ratios (relative to unstressed conidia) of each isolate, examined at 15-min intervals, fit a logistic equation (r² ≥ 0.975), yielding median lethal times (LT₅₀s) of 14.3-150.3 min for the 18 isolates stressed at 48 °C. Seven grasshopper isolates from Africa had a mean LT₅₀ of 110 (73-150) min, but could not grow at 10 or 15 °C. The mean LT₅₀ of five non-grasshopper isolates capable of growing at 10-35 °C was 16 (10-26) min only. Three isolates with typically low (type I), medium (type II), and high (type III) levels of tolerance to 48 °C were further assayed for ≤4-d tolerance of their conidia to the wet stress at 38, 40, 42, or 45 °C. The resultant LT₅₀s decreased to 20, 53 and 167 min at 48 °C from 507, 1612, and 8256 min at 38 °C for types I, II and III, respectively. For the distinguished types, the logarithms of the LT₅₀s were significantly correlated to the temperatures of 38-48 °C with an inverse linearity (r² ≥ 0.88). The method developed to assay quantitatively fungal thermotolerance would be useful for screening of fungal candidates for improved pest control in summer.     

Metabolic thermogenesis and evaporative water loss in the Hwamei Garrulax canorus

Basal metabolic rate (BMR) is thought to be a major hub in the network of physiological mechanisms connecting life history traits. Evaporative water loss (EWL) is a physiological indicator that is widely used to measure water relations in inter- or intraspecific studies of birds in different environments. In this study, we examined the physiological responses of summer-acclimatized Hwamei Garrulax canorus to temperature by measuring their body temperature (T_b), metabolic rate (MR) and EWL at ambient temperatures (T_a) between 5 and 40 °C. Overall, we found that mean body temperature was 42.4 °C and average minimum thermal conductance (C) was 0.15 ml O₂ g⁻¹ h⁻¹ °C⁻¹ measured between 5 and 20 °C. The thermal neutral zone (TNZ) was 31.8–35.3 °C and BMR was 181.83 ml O₂ h⁻¹. Below the lower critical temperature, MR increased linearly with decreasing T_a according to the relationship: MR (ml O₂ h⁻¹)=266.59–2.66 T_a. At T_as above the upper critical temperature, MR increased with T_a according to the relationship: MR (ml O₂ h⁻¹)=−271.26+12.85 T_a. EWL increased with T_a according to the relationship: EWL (mg H₂O h⁻¹)=−19.16+12.64 T_a and exceeded metabolic water production at T_a>14.0 °C. The high T_b and thermal conductance, low BMR, narrow TNZ, and high evaporative water production/metabolic water production (EWP/MWP) ratio in the Hwamei are consistent with the idea that this species is adapted to warm, mesic climates, where metabolic thermogenesis and water conservation are not strong selective pressures.     

Partitioning of transpiratory water loss of the desert scorpion, Hadrurus arizonensis (Iuridae)

Terrestrial arthropods lose body water to the environment mainly through transpiration. The aim of this study was to determine the fraction of respiratory losses from total transpiratory water loss in scorpions, as relatively high respiratory losses would indicate a fitness benefit from regulation of gas-exchange rate under stressful desiccating conditions. We measured metabolic rates and water-loss rates of Hadrurus arizonensis (Iuridae) at a range of ecologically-relevant temperatures. Calculation of respiratory water losses was based on increased metabolic and water-loss rates during nocturnal activity (assuming no change in cuticular resistance at a given constant experimental temperature). Respiratory losses accounted for 9.0 ± 1.7% of total transpiratory losses at 25 °C, doubled to 17.9 ± 1.8% at 30 °C and increased to 31.0 ± 2.0% at 35 °C (n = 5, 15 and 15, respectively). Furthermore, the relative importance of respiratory transpiration is likely to be higher at temperatures above 35 °C, which have been recorded even within the burrows of H. arizonensis. Measurements of cuticular lipid melting points do not provide evidence for increased cuticular resistance to water loss at higher temperatures. However, the relatively high fraction of respiratory water losses reported here for H. arizonensis supports the notion of respiratory regulation as an evolved mechanism for conserving scorpion body water stores under stressful conditions.     

The effects of intertidal air exposure on the respiratory physiology and the killing activity of hemocytes in the pacific oyster, Crassostrea gigas (Thunberg)

The occurrence of summer mortalities of the commercially important Pacific oyster, Crassostrea gigas, has increased in recent years. These mortality events occur during the late summer when water temperatures are at their highest. Many theories have been proposed concerning the causes including reproductive stress, environmental stress, disease, or synergistic interactions of these factors. C. gigas are grown intertidally and are exposed to the air (emersed) for hours at a time. These organisms can experience extreme changes in temperature during the course of a day. An oyster closed during emersion depletes the oxygen stores to near zero within the shell and builds up CO₂ causing a decrease in tissue pH. The focus of this study is to determine the respiratory (pH, Po₂, Pco₂ and total CO₂) and immune responses of oysters exposed to air at normal seasonal temperatures, and to determine whether these stresses associated with emersion inhibit the immune system of the oyster and contribute to the summer mortalities. The respiratory variables of the hemolymph of oysters submerged at 18 °C (pH = 7.52 ± 0.04 S.E.M., Po₂ = 7.09 ± 0.53 S.E.M. kPa and Pco₂ = 0.20 ± 0.03 S.E.M. kPa) varied significantly from oysters emersed for four hours at 22°C (pH = 7.11 ± 0.03 S.E.M., Po₂ = 3.83 ± 0.15 S.E.M. kPa, Pco₂ = 0.36 ± 0.03 S.E.M. kPa) and those emersed for four hours at 30 °C (pH = 6.84 ± 0.02 S.E.M., Po₂ = 3.10 ± 0.12 S.E.M. kPa, Pco₂ = 1.31 ± 0.06 S.E.M. kPa). The ability of hemocytes to kill the bacterium Vibrio campbellii was assessed using an in vitro assay to generate a killing index. There was no significant difference in the killing index between pH treatment groups (p = 0.856): at pH 7.6 killing index = 50.2% ± 2.33 S.E.M., at pH 6.6 killing index = 52.3% ± 3.67 S.E.M.. Temperature was the only factor to significantly affect the killing indices among temperature and oxygen treatment groups. The killing index was lowest (29.3% ± 3.25 S.E.M.) at 30 °C and 7% oxygen, simulating in vivo oxygen pressure in well-aerated conditions and 30 °C and 3% oxygen, simulating in vivo oxygen pressure in hypoxia (30.5% ± 3.25 S.E.M.), compared with the index in 7% oxygen at low temperature (18 °C) (44.4% ± 4.50 S.E.M.) or compared with low oxygen (3%) at low temperature (18 °C) (39.7% ± 2.51 S.E.M.). The seasonal and diurnal rise in temperature may, therefore, be an important factor contributing to summer mortalities of C. gigas.     

Effects of ether vs. ester linkage on lipid bilayer structure and water permeability

The structure and water permeability of bilayers composed of the ether-linked lipid, dihexadecylphosphatidylcholine (DHPC), were studied and compared with the ester-linked lipid, dipalmitoylphosphaditdylcholine (DPPC). Wide angle X-ray scattering on oriented bilayers in the fluid phase indicate that the area per lipid A is slightly larger for DHPC than for DPPC. Low angle X-ray scattering yields A = 65.1 Å² for DHPC at 48 °C. LAXS data provide the bending modulus, K_C = 4.2 × 10⁻¹³ erg, and the Hamaker parameter H = 7.2 × 10⁻¹⁴ erg for the van der Waals attractive interaction between neighboring bilayers. For the low temperature phases with ordered hydrocarbon chains, we confirm the transition from a tilted L_β′ gel phase to an untilted, interdigitated L_βI phase as the sample hydrates at 20 °C. Our measurement of water permeability, P_f = 0.022 cm/s at 48 °C for fluid phase DHPC is slightly smaller than that of DPPC (P_f = 0.027 cm/s) at 50 °C, consistent with our triple slab theory of permeability.