The finite element implementation of a K.P.P. equation for the simulation of tsetse control measures in the vicinity of a game reserve

An equation, strongly reminiscent of Fisher’s equation, is used to model the response of tsetse populations to proposed control measures in the vicinity of a game reserve. The model assumes movement is by diffusion and that growth is logistic. This logistic growth is dependent on an historical population, in contrast to Fisher’s equation which bases it on the present population. The model therefore takes into account the fact that new additions to the adult fly population are, in actual fact, the descendents of a population which existed one puparial duration ago, furthermore, that this puparial duration is temperature dependent. Artificially imposed mortality is modelled as a proportion at a constant rate. Fisher’s equation is also solved as a formality.The temporary imposition of a 2 % day⁻¹ mortality everywhere outside the reserve for a period of 2 years will have no lasting effect on the influence of the reserve on either the Glossina austeni or the G. brevipalpis populations, although it certainly will eradicate tsetse from poor habitat, outside the reserve. A 5 km-wide barrier with a minimum mortality of 4 % day⁻¹, throughout, will succeed in isolating a worst-case, G. austeni population and its associated trypanosomiasis from the surrounding areas. A more optimistic estimate of its mobility suggests a mortality of 2 % day⁻¹ will suffice. For a given target-related mortality, more mobile species are found to be more vulnerable to eradication than more sedentary species, while the opposite is true for containment.     

Some effects of low oxygen partial pressures on the development of Calliphora vomitoria;

The influence of wet conditions and low pO₂ on the survival and development of non-feeding final instar larvae and puparia of Calliphora vomitoria has been investigated. The larvae delay the formation of the puparium in wet conditions in air and in dry or wet conditions in 10 and 5% oxygen. This may be related to the susceptibility of the newly formed puparia to oxygen shortage. The pupal respiratory horns play an important part in maintaining O₂ uptake when the puparia are surrounded by particles covered with a film of water but are not involved in aiding survival in low pO₂. Zero age puparia are killed by a 2 day exposure to 10% O₂ but later stages can continue to develop in this gas. Fifty per cent of the 0, 1 and 9 day old puparia are killed by about a 12 hr exposure to 1% O₂ whereas 50 per cent of the 2 to 8 day old puparia can survive over 1·5 days exposure to this gas. Development, as measured by respiration rates and the timing of the emergence of the adults, is delayed by 1% O₂ by the amount of time that the insects spend in that gas. However, the first phase of elongation of the pharate adult longitudinal flight muscle, occurring between the third and fourth day of puparial life, is only slightly slowed down in 1% O₂. The variations in susceptibility to 1% O₂ and the growth of the muscles are discussed in relation to published accounts of protein synthesis in the puparium.     

Physiological responses to flooding and light in two tree species native to the Amazonian floodplains

In Amazonian floodplains, plant survival is determined by adaptations and growth strategies to effectively capture sunlight and endure extended periods of waterlogging. By measuring gas exchange, quantum efficiency of photosystem 2 (PSII), and growth parameters, we investigated the combined effects of flooding gradients and light on two common evergreen floodplain tree species, the light-tolerant Cecropia latiloba and the shade-tolerant Pouteria glomerata. Individual plants were subjected to different combinations of light and flooding intensity in short-term and long-term experiments. Plants of C. latiloba lost all their leaves under total submersion treatments (plants flooded to apex and with reduced irradiance) and showed highest maximum assimilation rates (A_max) in not flooded, high light treatments (6.1 μmol CO₂ m⁻² s⁻¹). Individuals of P. glomerata showed similar patterns, with A_max increasing from 1.9 μmol CO₂ m⁻² s⁻¹ under total flooding to 7.1 μmol CO₂ m⁻² s⁻¹ in not flooded, high light treatments. During the long-term flooding experiment, quantum efficiency of PSII (F_v/F_m) of C. latiloba was not affected by partial flooding. In contrast, in P. glomerata F_v/F_m decreased to values below 0.73 after 120 days of total flooding. Moreover, total submergence led P. glomerata to reduce significantly light saturation point (LSP), as compared to C. latiloba. For both species morphological adjustments to long-term flooding, such as the production of adventitious roots, resulted in reduced total biomass, relative growth rate (RGR) and leaf mass ratio (LMR). Growth increase in C. latiloba seemed to be more limited by low-light than by flooding. Therefore, the predominant occurrence of this species is in open areas with high light intensities and high levels of inundation. In P. glomerata flooding induced high reductions of growth and photosynthesis, whereas light was not limiting. This species is more abundant in positions where irradiance is reduced and periods of submergence are slightly modest. We could show that the physiological requirements are directly responsible for the flooding (C. latiloba) and shade (P. glomerata) tolerance of the two species, which explains their local distribution in Amazonian floodplain forests.     

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.     

Thermal preference,tolerance and oxygen consumption of adult white shrimp Litopenaeus vannamei (Boone) exposed to different acclimation temperatures

Final temperature preferendum of white shrimp adults were determined with acute and gravitation methods. The final preferendum was similar, independent of method (26.2–25.6 °C). A direct relationship was determined between the critical thermal maxima values and the acclimation temperatures (P<0.05). The end point of Critical Thermal Maxima (CTMax) for adults was defined as the loss of righting response (LRR). The acclimation response ratio (ARR) for adults of white shrimp had an interval of 0.36–0.76, values that agreed with others obtained for crustaceans from tropical and subtropical climates. The oxygen consumption rates increased significantly (P<0.05) from 39.6 up to 90.0 mg O₂ kg⁻¹ h⁻¹ wet weight (w.w.) as the acclimation temperature increased from 20 to 32 °C. The range of temperature coefficient (Q₁₀) of the white shrimp between 23 and 26 °C was the lower 1.60. The results obtained in this work are discussed in relation to the species importance in the reproductive scope and maintenance of breeders.     

Estimation of rates of predation on tsetse

The levels of natural predation of puparial and adult tsetse flies, Glossina pallidipes Austen, were investigated at Nguruman, Kenya, during January 1989. Puparial experiments involved the production, by individually tubed female flies, of naturally deposited, unhandled puparia in soil cores; handled puparia were obtained from groups of caged flies kept in the normal way. Equal numbers of handled and unhandled puparia were planted out at different densities (1, 2, 4 or 8 per linear metre) in fifty-one natural puparial sites in four major vegetation types. After 10 days puparia were recovered using a soil corer and sieving system. Average predation rates (adjusted for the displacement of puparia by vertebrate activity at the puparial sites) were 9.4% and 7.8% for the two types of puparia during the experiment, equivalent to an average loss of 23.7% of all puparia during a normal 30-day developmental period. Maximum potential predation rates of adult flies were investigated by pinning freshly killed adults at densities of 1, 2, 4 or 8 per m3 to natural vegetation and scoring the results after 24 h. 70% of flies were attacked during this time, by a variety of predators, thought to include both vertebrates and invertebrates. No density dependence was detected in the experiments, either because natural puparial densities were too low for it to occur at this stage of the life cycle or because adult predation levels were too high for it to be detected. Present results are compared and contrasted with previous results for this and another species of tsetse. Calculations of the life-time fertilities of female tsetse suggest that the levels of puparial predation revealed by the present experiments are entirely realistic. Behaviour of the adult flies allows them to escape most of the considerable predation pressure under which they live. How they do so remains a mystery.     

Short term effects of hypoxia and bioturbation on solute fluxes, denitrification and buffering capacity in a shallow dystrophic pond

The effects of short term hypoxia on bioturbation activity and inherent solute fluxes are scarcely investigated even if increasing number of coastal areas are subjected to transient oxygen deficits. In this work dark fluxes of oxygen (O₂), dissolved inorganic carbon (TCO₂) and nutrients across the sediment-water interface, as well as rates of denitrification (isotope pairing), were measured in intact sediment cores collected from the dystrophic pond of Sali e Pauli (Sardinia, Italy). Sediments were incubated at 100, 70, 40 and 10% of O₂ saturation in the overlying water, with both natural benthic communities, dominated by the polychaete Polydora ciliata (11.100 ± 2.500  ind. m^− 2), and after the addition of individuals of the deep-burrower polychaete Hediste diversicolor. Below an uppermost oxic layer of ~ 1 mm, sediments were highly reduced, with up to 6 mM of S²⁻ in the 5 mm layer. Flux of S²⁻ and O₂ calculated from pore water gradients were 8.61 ± 1.12 and − 2.27 ± 0.56 mmol m^− 2 h^− 1, respectively. However, sediment oxygen demand (SOD) calculated from core incubation was − 10.52 ± 0.33 mmol m^− 2 h^− 1, suggesting a major contribution of P. ciliata to O₂-mediated sulphide oxidation. P. ciliata also strongly stimulated NH₄⁺ and PO₄³⁻ fluxes, with rates ~ 15 and ~ 30 folds higher, respectively, than those estimated from pore water gradients. P. ciliata activity was significantly reduced at 10% O₂ saturation, coupled to decreased rates of solutes transfer. The addition of H. diversicolor further stimulated SOD, NH₄⁺ efflux and SiO₂ mobilisation. Similarly to P. ciliata, the degree of stimulation of SOD and NH₄⁺ flux by H. diversicolor depended on the level of oxygen saturation. TCO₂ regeneration, respiratory quotients, PO₄³⁻ fluxes and denitrification of added ¹⁵NO₃⁻ were not affected by the addition of H. diversicolor, but depended upon the O₂ levels in the water column. Denitrification rates supported by water column ¹⁴NO₃⁻ and sedimentary nitrification were both negligible (< 0.5 µmol m^− 2 h^− 1). They were not significantly affected by oxygen saturation nor by bioturbation, probably due to the limited availability of NO₃⁻ in the water column (< 3 µM) and O₂ in the sediments. This study demonstrates for the first time the integrated short term effect of transient hypoxia and bioturbation on solute fluxes across the sediment-water interface within a simplified lagoonal benthic community.     

Effects of water-level fluctuations on the arbuscular mycorrhizal colonization of Typha latifolia L.

Flooding has been described as one of the primary factors affecting arbuscular mycorrhizal (AM) colonization in wetlands. We investigated the effect of water-level fluctuations on AM colonization of Typha latifolia L. using an experimental wetland in southeastern Idaho, USA that received intermittent flows. Unlike previous research that has examined the effect of flooding on AM fungi using topographic gradients, we replicated flooding in time by sampling across multiple flooding events. AM colonization of T. latifolia occurred during flooded and unflooded periods, but was markedly reduced at drawdown. Both hyphal (R = 0.74, P = 0.015) and arbuscular (R = 0.67, P = 0.033) colonization were positively correlated with the length of the unflooded period. Taken together, the length of the unflooded period and soil moisture explained 83% of the variation in mean hyphal colonization (R² = 0.83, P = 0.001). Overall, the results of this investigation show that drawdown represents a period of reduced AM colonization in T. latifolia.     

Metabolic tolerance of the cold-water coral Lophelia pertusa (Scleractinia) to temperature and dissolved oxygen change

Lophelia pertusa is the world's most common and widespread framework-forming cold-water coral. It forms deep-water coral reefs and carbonate mounds supporting diverse animal communities on the continental shelf and on seamounts. These recently discovered ecosystems have been damaged by deep-sea fishing and are threatened by predicted shallowing of the aragonite saturation horizon. Despite this, very little is known about the ecophysiology of L. pertusa and its likely response to environmental changes. Here we describe the first study of the respiratory physiology of L. pertusa and the effects of altered temperature and oxygen level. This study shows that L. pertusa can maintain respiratory independence over a range of PO₂ illustrated by a high regulation value (R = 78%). The critical PO₂ value of 9-10 kPa is very similar to the lower values of oxygen concentration recorded in the field. This suggests that oxygen level may be a limiting factor in the distribution of this cold-water coral. L. pertusa survived periods of anoxia (1 h), hypoxia (up to 96 h), but high Q₁₀ values revealed sensitivity to short-term temperature changes (6.5-11 °C). For the first time vital data have been gathered on the physiology of this species that is essential to understand distribution and underpin future climate change studies.     

Environmental factors regulating the radial oxygen loss from roots of Myriophyllum spicatum and Potamogeton crispus

Myriophyllum spicatum and Potamogeton crispus are common species of shallow eutrophic lakes in north-eastern Germany, where a slow recovery of the submersed aquatic vegetation was observed. Thus, the characterisation of the root oxygen release (ROL) as well as its implication for geochemical processes in the sediment are of particular interest. A combination of microelectrode measurements, methylene blue agar and a titanium(III) redox buffer was used to investigate the influence of the oxygen content in the water column on ROL, diel ROL dynamics as well as the impact of sediment milieu. Oxygen gradients around the roots revealed a maximum oxygen diffusion zone of up to 250 μm. During a sequence with a light/dark cycle as well as alternating aeration of the water column, maximum ROL with up to 35% oxygen saturation at the root surface occurred under light/O₂-saturated conditions. A decrease to about 30% was observed under dark/O₂-saturated conditions, no ROL was detected at dark/O₂-depleted conditions and only a weak ROL with 5–10% oxygen saturation at the root surface was measured under light but O₂-depleted water column. These results indicate, that during darkness, ROL is supplied by oxygen from the water column and even during illumination and active photosynthesis production, ROL is modified by the oxygen content in the water column. Visualisation of ROL patterns revealed an enhanced ROL for plants which were grown in sulfidic littoral sediment in comparison to plants grown in pure quartz sand. For both plant species grown in sulfidic littoral sediment, a ROL rate of 3–4 μmol O₂ h⁻¹ plant⁻¹ was determined with the Ti(III) redox buffer. For plants grown in pure quartz sand, the ROL rate decreased to 1–2 μmol O₂ h⁻¹ plant⁻¹. Hence, aside from the oxygen content in the water column, the redox conditions and microbial oxygen demand in the sediment has to be considered as a further major determinant of ROL.     

Time-resolved single-turnover of ba3 oxidase from Thermus thermophilus

The kinetics of the oxidation of fully-reduced ba₃ cytochrome c oxidase from Thermus thermophilus by oxygen were followed by time-resolved optical spectroscopy and electrometry. Four catalytic intermediates were resolved during this reaction. The chemical nature and the spectral properties of three intermediates (compounds A, P and O) reproduce the general features of aa₃-type oxidases. However the F intermediate in ba₃ oxidase has a spectrum identical to the P state. This indicates that the proton taken up during the P → F transition does not reside in the binuclear site but is rather transferred to the covalently cross-linked tyrosine near that site. The total charge translocation associated with the F → O transition in ba₃ oxidase is close to that observed during the F → O transition in the aa₃ oxidases. However, the P_R → F transition is characterized by significantly lower charge translocation, which probably reflects the overall lower measured pumping efficiency during multiple turnovers.     

Effects of temperature and salinity on the standard metabolic rate (SMR) of the caridean shrimp Palaemon peringueyi

The standard metabolic rate (SMR) of the caridean shrimp Palaemon peringueyi to changes in temperature (15-30 °C), salinity (0-45‰) and a combination thereof was investigated. The rate of oxygen consumption of the shrimp was determined using a YSI oxygen meter. At a constant salinity of 35‰ the respiration rate of P. peringueyi increased with an increase in temperature and ranged between 0.260 and 0.982 μl O₂ mg wwt^− 1 h^− 1. The Q₁₀ value over the temperature range 15-25 °C was estimated at 3.13. At a constant temperature of 15 °C the respiration rate of P. peringueyi also increased with an increase in salinity and ranged between 0.231 and 0.860 μl O₂ mg wwt^− 1 h^− 1. For combination experiments the absence of any significant difference in the respiration rate of P. peringueyi at the four temperatures over the salinity range 15-35‰ suggests that the shrimp is well adapted to inhabiting environments characterised by variations in salinity and temperature such as those encountered within the middle and lower reaches of permanently open estuaries with substantial freshwater inflow. On the other hand, the total mortality of the shrimp recorded at salinities < 5‰ at all four temperatures suggests that the upper distribution of the shrimp may reflect physiological constraints. Similarly, the increase in the respiration rate of the shrimp at the four temperatures at salinities > 35‰ suggests that the shrimp may experience osmotic stress in freshwater deprived permanently open and intermittently open estuaries where hypersaline conditions may develop.     

Experimentally calibrated computational chemistry of tryptophan hydroxylase: Trans influence, hydrogen-bonding, and 18-electron rule govern O2-activation

Insight into the nature of oxygen activation in tryptophan hydroxylase has been obtained from density functional computations. Conformations of O₂-bound intermediates have been studied with oxygen trans to glutamate and histidine, respectively. An O₂-adduct with O₂trans to histidine (O_his) and a peroxo intermediate with peroxide trans to glutamate (P_glu) were found to be consistent (0.57-0.59 mm/s) with experimental Mössbauer isomer shifts (0.55 mm/s) and had low computed free energies. The weaker trans influence of histidine is shown to give rise to a bent O₂ coordination mode with O₂ pointing towards the cofactor and a more activated O-O bond (1.33 Å) than in O_glu (1.30 Å). It is shown that the cofactor can hydrogen bond to O₂ and activate the O-O bond further (from 1.33 to 1.38 Å). The O_his intermediate leads to a ferryl intermediate (F_his) with an isomer shift of 0.34 mm/s, also consistent with the experimental value (0.25 mm/s) which we propose as the structure of the hydroxylating intermediate, with the tryptophan substrate well located for further reaction 3.5 Å from the ferryl group. Based on the optimized transition states, the activation barriers for the two paths (glu and his) are similar, so a two-state scenario involving O_his and P_glu is possible. A structure of the activated deoxy state which is high-spin implies that the valence electron count has been lowered from 18 to 16 (glutamate becomes bidentate), giving a “green light” that invites O₂-binding. Our mechanism of oxygen activation in tryptophan hydroxylase does not require inversion of spin, which may be an important observation.     

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.     

Hemoglobin attenuates the effects of inspired oxygen on plasma isofurans in humans during upper-limb surgery

Reperfusion injury is characterized by significant oxidative stress. F₂-isoprostanes (F₂-IsoP's) and isofurans (IsoF's), the latter preferentially produced during increased oxygen tension, are recognized markers of in vivo oxidative stress. We aimed to determine whether increasing oxygen tension during reperfusion modified levels of plasma total IsoF's and F₂-IsoP's. Forty-five patients undergoing upper-limb surgery were randomized to receive inspired oxygen concentrations of 30, 50, or 80% during the last 15 min of surgery. Venous blood samples were taken before the change in inspired oxygen, after 10 min (before reperfusion), and after 15 min (5 min after reperfusion). IsoF's and F₂-IsoP's were measured by gas chromatography-mass spectrometry. Venous oxygen tension and hemoglobin concentrations were also measured. Plasma IsoF and F₂-IsoP levels in the 50 and 80% O₂ groups were not significantly different from those of the 30% O₂ group. In secondary analyses, using data combining all groups, levels of IsoF's, but not F₂-IsoP's, associated with higher venous oxygen tension (P = 0.038). Hemoglobin negatively modified the influence of oxygen tension on levels of IsoF's (P = 0.014). This study has shown, for the first time, that plasma IsoF levels associate with higher oxygen tension in a human model of reperfusion, and this effect is significantly attenuated by hemoglobin.     

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.     

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.     

Respiration rate and oxy-regulatory capacity in cold stenothermal chironomids

The effects of temperature and oxygen saturation on the respiration rate of two cold stenothermal chironomids, Diamesa insignipes and Pseudodiamesa branickii were investigated. Fourth instar larvae were collected in winter in a glacio-rhithral stream (1300 m a.s.l., Alps, NE-Italy) and their respiration rate was measured with a Clark's electrode in the range 0-14 °C. The respiration rate was significantly higher in D. insignipes than in P. branickii at low temperatures (≤4 °C), higher in P. branickii between 8 and 12 °C and comparable at 14 °C. Higher values of R (regulation value), R_25% (respiration rate at 25% oxygen saturation) and b₁/b₂ (slope ratio in piecewise linear regression), and lower values of P_c (critical pressure) and I (initial decrease) were recorded in P. branickii than in D. insignipes. These values are compatible with oxy-regulatory behaviour in P. branickii, whereas D. insignipes appeared to be almost an oxy-conformer. On the basis of this autoecological information, new implications regarding survival of species from cold, high altitude habitats under changing climatic conditions are made.     

Structure and phase behavior of O-stearoylethanolamine: A combined calorimetric, spectroscopic and X-ray diffraction study

Recent studies show that O-acylethanolamines (OAEs), structural isomers of the putative stress-fighting lipids, namely N-acylethanolamines (NAEs), can be derived from NAEs and are present in biological membranes under physiological conditions. In view of this, we have synthesized O-stearoylethanolamine (OSEA) as a representative OAE and investigated its phase behavior and crystal structure. The thermotropic phase transitions of OSEA dispersed in water and in 150 mM NaCl were characterized using calorimetric, spectroscopic, turbidimetric and X-ray diffraction studies. These studies have revealed that when dispersed in water OSEA undergoes a cooperative phase transition centered at 53.8 °C from an ordered gel phase to a micellar structure whereas in presence of 150 mM NaCl the transition temperature increases to 55.8 °C and most likely the bilayer structure is retained above the phase transition. O-Stearoylethanolamine crystallized in the orthorhombic space group P2₁2₁2₁ with four symmetry-related molecules in the unit cell. Single-crystal X-ray diffraction studies show that OSEA molecules adopt a linear structure with all-trans conformation in the acyl chain region. The molecules are organized in a tail-to-tail fashion, similar to the arrangement in a bilayer membrane. These studies are relevant to understanding the role of salt on the phase properties of this new class of lipids.     

Blood oxygenation and cardiorespiratory function in steelhead trout (Oncorhynchus mykiss) challenged with an acute temperature increase and zatebradine-induced bradycardia

To explore whether temperature-dependent increases in cardiac output (Q) are mediated solely through heart rate (f_H) in fish to ensure adequate/efficient blood oxygenation, we injected steelhead trout with saline (control) or zatebradine hydrochloride (1.0 mg kg⁻¹), and measured blood oxygen status, cardiorespiratory variables and cardiorespiratory synchrony during a critical thermal maximum (CT_Max) test. The increasing temperature regimen itself (from 12 °C to CT_Max) resulted in large decreases in arterial oxygen partial pressure (P_aO₂) and content (C_aO₂) (by ∼35% and 25%, respectively). Further, there was little evidence of cardiorespiratory synchrony at 12 °C, and the number of fish that showed synchrony at high temperatures only increased marginally (to 3 out of 7) despite the large decrease in P_aO₂. These results: (1) indicate that in some situations (e.g. when ventilation is exclusively/predominantly dependent on buccal–opercular pumping) the upper thermal tolerance of fish may be constrained by both cardiovascular and ventilatory performance; and (2) question the importance of cardiorespiratory synchrony (ventilation–perfusion matching) for gas exchange in salmonids, and fishes, in general.