Showing papers in "Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology in 2008"

Negligible senescence in the longest living rodent, the naked mole-rat: insights from a successfully aging species

Abstract: Aging refers to a gradual deterioration in function that, over time, leads to increased mortality risk, and declining fertility. This pervasive process occurs in almost all organisms, although some long-lived trees and cold water inhabitants reportedly show insignificant aging. Negligible senescence is characterized by attenuated age-related change in reproductive and physiological functions, as well as no observable age-related gradual increase in mortality rate. It was questioned whether the longest living rodent, the naked mole-rat, met these three strict criteria. Naked mole-rats live in captivity for more than 28.3 years, approximately 9 times longer than similar-sized mice. They maintain body composition from 2 to 24 years, and show only slight age-related changes in all physiological and morphological characteristics studied to date. Surprisingly breeding females show no decline in fertility even when well into their third decade of life. Moreover, these animals have never been observed to develop any spontaneous neoplasm. As such they do not show the typical age-associated acceleration in mortality risk that characterizes every other known mammalian species and may therefore be the first reported mammal showing negligible senescence over the majority of their long lifespan. Clearly physiological and biochemical processes in this species have evolved to dramatically extend healthy lifespan. The challenge that lies ahead is to understand what these mechanisms are.

How insects survive the cold: molecular mechanisms—a review

Abstract: Insects vary considerably in their ability to survive low temperatures. The tractability of these organisms to experimentation has lead to considerable physiology-based work investigating both the variability between species and the actual mechanisms themselves. This has highlighted a range of strategies including freeze tolerance, freeze avoidance, protective dehydration and rapid cold hardening, which are often associated with the production of specific chemicals such as antifreezes and polyol cryoprotectants. But we are still far from identifying the critical elements behind over-wintering success and how some species can regularly survive temperatures below −20°C. Molecular biology is the most recent tool to be added to the insect physiologist’s armoury. With the public availability of the genome sequence of model insects such as Drosophila and the production of custom-made molecular resources, such as EST libraries and microarrays, we are now in a position to start dissecting the molecular mechanisms behind some of these well-characterised physiological responses. This review aims to provide a state-of-the-art snapshot of the molecular work currently being conducted into insect cold tolerance and the very interesting preliminary results from such studies, which provide great promise for the future.

Phenotypic flexibility in basal metabolic rate and the changing view of avian physiological diversity: a review

Abstract: Comparative analyses of avian energetics often involve the implicit assumption that basal metabolic rate (BMR) is a fixed, taxon-specific trait. However, in most species that have been investigated, BMR exhibits phenotypic flexibility and can be reversibly adjusted over short time scales. Many non-migrants adjust BMR seasonally, with the winter BMR usually higher than the summer BMR. The data that are currently available do not, however, support the idea that the magnitude and direction of these adjustments varies consistently with body mass. Long-distance migrants often exhibit large intra-annual changes in BMR, reflecting the physiological adjustments associated with different stages of their migratory cycles. Phenotypic flexibility in BMR also represents an important component of short-term thermal acclimation under laboratory conditions, with captive birds increasing BMR when acclimated to low air temperatures and vice versa. The emerging view of avian BMR is of a highly flexible physiological trait that is continually adjusted in response to environmental factors such as temperature. The within-individual variation observed in avian BMR demands a critical re-examination of approaches used for comparisons across taxa. Several key questions concerning the shapes and other properties of avian BMR reaction norms urgently need to be addressed, and hypotheses concerning metabolic adaptation should explicitly account for phenotypic flexibility.

Physical characteristics of digesta and their influence on flow and mixing in the mammalian intestine: a review

Abstract: The physical properties of digesta may influence mixing, efficiency of digestion, and absorption within the lumen of the intestine. We review how the physical properties of digesta change during transit through the various segments of the intestine, and how their influence on flow and mixing may be modulated by peristaltic activity. We examine how, in more fluid digesta, the solid and liquid phases interact to influence flow and mixing. Similarly, how in viscid digesta, shear strength, plasticity and elasticity of contained particulate material may influence the permeation of the fluid phase and secretions into and out of the digesta bolus. The manner in which the solid and liquid phases of digesta interact in a partly gaseous environment, such as the lower bowel, to influence bolus cohesion is also examined. Those mechanisms that promote the formation of a less viscous layer at the mucosal interface to promote plug flow are reviewed, and their effect on the efficiency of mixing and digestion discussed. It is recommended that in any future work investigating the character of mixing in the intestine, a wider range of appropriate digesta properties be measured and that, in investigations of intestinal movement, perfusates with similar characteristics to digesta be used.

Variation in stress and innate immunity in the tree lizard (Urosaurus ornatus) across an urban-rural gradient.

Abstract: The urban environment presents new and different challenges to wildlife, but also potential opportunities depending on the species. As urban encroachment onto native habitats continues, understanding the impact of this expansion on native species is vital to conservation. A key physiological indicator of environmental disturbance is the vertebrate stress response, involving increases in circulating glucocorticoids (i.e. corticosterone), which exert influence on numerous physiological parameters including energy storage, reproduction, and immunity. We examined how urbanization in Phoenix, Arizona influences corticosterone levels, blood parasitism, and innate immunity in populations of tree lizards (Urosaurus ornatus) to determine whether urbanization may be detrimental or beneficial to this species. Both baseline and stress-induced corticosterone concentrations were significantly lower in urban lizards relative to the rural ones, however, the magnitude of the increase in corticosterone with stress did not differ across populations. Urban lizards also had a lower ratio of heterophils to lymphocytes, but elevated overall leukocyte count, as compared to lizards from the natural site. Urban and rural lizards did not differ in their prevalence of the blood parasite, Plasmodium mexicanum. Taken together, these results suggest that urban tree lizards may have suppressed overall corticosterone concentrations possibly from down-regulation as a result of frequent exposure to stressors, or increased access to urban resources. Also, urban lizards may have bolstered immunocompetence possibly from increased immune challenges, such as wounding, in the urban environment, or from greater energetic reserves being available as a result of access to urban resources.

Invertebrate aquaporins: a review

Abstract: Aquaporins (AQPs) or water channels render the lipid bilayer of cell membranes permeable to water. The numerous AQP subtypes present in any given species, the transport properties of each subtype and the variety of methods of their regulation allows different cell types to be transiently or permanently permeable to water or other solutes that AQPs are capable of transporting (e.g. urea or glycerol). AQPs have been well characterized in all vertebrate classes, other than reptilia. Here we review the current state of knowledge of invertebrate AQPs set in the context of the much more thoroughly studied vertebrate AQPs. By phylogenetic analysis of the total AQP complement of several completed insect genomes, we propose a classification system of insect AQPs including three sub-families (DRIP, BIB and PRIP) that have one representative from all the complete insect genomes. The physiological role of AQPs in invertebrates (insects, ticks and nematodes) is discussed, including their function in common invertebrate phenomena such as high-volume liquid diets, cryoprotection and anhydrobiosis.

3-Iodothyronamine: a novel hormone controlling the balance between glucose and lipid utilisation

Abstract: 3-Iodothyronamine is considered as a derivate of thyroid hormone as a result of enzymatic deiodination and decarboxylation. The physiological role of thyronamine (T1AM) is not known. The aim of this study was to analyze the metabolic response to T1AM in the Djungarian hamster Phodopus sungorus. We measured the influence of T1AM (50 mg/kg) on metabolic rate (VO2), body temperature (T b) and respiratory quotient (RQ) in this species and in BL/6 mice. T1AM treated hamsters as well as the mice showed a rapid decrease in VO2 and T b, accompanied by a reduction of RQ from normal values of about ∼0.9 to ∼0.70 for several hours. This indicates that carbohydrate utilisation is blocked by the injection of T1AM and that metabolic pathways are rerouted from carbohydrate to lipid utilisation in response to T1AM. This assumption was further supported by the observation that the treatment of T1AM caused ketonuria and a significant loss of body fat. Our results indicate that T1AM has the potential to control the balance between glucose and lipid utilisation in vivo.

Invertebrate trypsins: a review.

Abstract: Food protein hydrolysis, a crucial step in digestion, is catalyzed by trypsin enzymes from the digestive apparatus of invertebrates. Trypsin appeared early in evolution and occurs in all phyla and, in the digestive systems of invertebrates, it became the most abundant proteinase. As in vertebrates, invertebrate trypsin is also present in several forms (isoenzymes). Its physiological importance in food protein digestion in several invertebrate species has emerged with compelling evidence; and several other physiological functions, such as regulation of digestive functions, are now settled. Recent advances in the knowledge of invertebrate trypsin synthesis, regulation, genetics, catalytic characteristics; structure, evolution, as well as inhibition, especially in non-Drosophilidae insects and in some crustaceans are reviewed. Most of the existing information is largely based on the use of several tools, including molecular techniques, to answer many still open questions and solve medical, agricultural, and food quality problems.

Transcriptome analysis of the response to chronic constant hypoxia in zebrafish hearts

Abstract: Insufficient blood supply during acute infarction and chronic ischemia leads to tissue hypoxia which can significantly alter gene expression patterns in the heart. In contrast to most mammals, some teleost fishes are able to adapt to extremely low oxygen levels. We describe here that chronic constant hypoxia (CCH) leads to a smaller ventricular outflow tract, reduced lacunae within the central ventricular cavity and around the trabeculae and an increase in the number of cardiac myocyte nuclei per area in the hearts of two teleost species, zebrafish (Danio rerio) and cichlids (Haplochromis piceatus). In order to identify the molecular basis for the adaptations to CCH, we profiled the gene expression changes in the hearts of adult zebrafish. We have analyzed over 15,000 different transcripts and found 376 differentially regulated genes, of which 260 genes showed increased and 116 genes decreased expression levels. Two notch receptors (notch-2 and notch-3) as well as regulatory genes linked to cell proliferation were transcriptionally upregulated in hypoxic hearts. We observed a simultaneous increase in expression of IGF-2 and IGFbp1 and upregulation of several genes important for the protection against reactive oxygen species (ROS). We have identified here many novel genes involved in the response to CCH in the heart, which may have potential clinical implications in the future.

Mitochondrial metabolism in hibernation and daily torpor: a review.

Abstract: Hibernation and daily torpor involve substantial decreases in body temperature and metabolic rate, allowing birds and mammals to cope with cold environments and/or limited food. Regulated suppression of mitochondrial metabolism probably contributes to energy savings: state 3 (phosphorylating) respiration is lower in liver mitochondria isolated from mammals in hibernation or daily torpor compared to normothermic controls, although data on state 4 (non-phosphorylating) respiration are equivocal. However, no suppression is seen in skeletal muscle, and there is little reliable data from other tissues. In both daily torpor and hibernation, liver state 3 substrate oxidation is suppressed, especially upstream of electron transport chain complex IV. In hibernation respiratory suppression is reversed quickly in arousal even when body temperature is very low, implying acute regulatory mechanisms, such as oxaloacetate inhibition of succinate dehydrogenase. Respiratory suppression depends on in vitro assay temperature (no suppression is evident below ~30°C) and (at least in hibernation) dietary polyunsaturated fats, suggesting effects on inner mitochondrial membrane phospholipids. Proton leakiness of the inner mitochondrial membrane does not change in hibernation, but this also depends on dietary polyunsaturates. In contrast proton leak increases in daily torpor, perhaps limiting reactive oxygen species production.

Hibernation by tree-roosting bats.

Abstract: In summer, long-eared bats (Nyctophilus spp.) roost under bark and in tree cavities, where they appear to benefit from diurnal heating of roosts. In contrast, hibernation is thought to require a cool stable temperature, suggesting they should prefer thermally insulated tree cavities during winter. To test this prediction, we quantified the winter thermoregulatory physiology and ecology of hibernating tree-roosting bats, Nyctophilus geoffroyi and N. gouldi in the field. Surprisingly, bats in winter continued to roost under exfoliating bark (65%) on the northern, sunny side of trees and in shallow tree cavities (35%). Despite passive re-warming of torpid bats by 10–20°C per day, torpor bouts lasted up to 15 days, although shorter bouts were also common. Arousals occurred more frequently and subsequent activity lasted longer on warmer nights, suggesting occasional winter foraging. We show that, because periodic arousals coincide with maximum roost temperatures, when costs of rewarming and normothermic thermoregulation are minimal, exposure to a daily temperature cycle could largely reduce energy expenditure during hibernation. Our study provides further evidence that models of torpor patterns and energy expenditure from hibernators in cold temperate climates are not directly applicable in milder climates, where prolonged torpor can be interspersed with more frequent arousals and occasional foraging.

Effects of corticosteroids on oxidative damage and circulating carotenoids in captive adult kestrels (Falco tinnunculus)

Abstract: Birds control body homeostasis through the secretion of corticosterone. This hormone is the end-product of the hypothalamic–pituitary–adrenal (HPA) axis response to stressors. High levels of corticosterone may be associated with low individual fitness and may affect balance between pro-oxidants and antioxidants. Given these points, chronic stress modulated by hormones could undermine individual fitness by increasing oxidative tissue damage. In this study, we administered corticosteroids by diet (20 mg/kg of diet) to captive adult kestrels (Falco tinnunculus) over a 14-day period to evaluate the effects of a simulated chronic stress modulated by corticosteroids. We found that dietary administration of corticosterone caused a 32% increase of reactive oxygen metabolites, but did not impair total serum antioxidant capacity, serum carotenoids or body mass. Oxidative stress had a 64% increase in treated birds compared to 30% in controls. The two groups did not differ in the total serum antioxidant capacity, which showed a significant decrease over the study period. In contrast, circulating carotenoids and body mass increased in both groups. These results suggest that stress hormones, such as corticosterone, may also act as modulators of oxidative stress in birds.

The cold but not hard fats in ectotherms: consequences of lipid restructuring on susceptibility of biological membranes to peroxidation, a review.

Abstract: The production of reactive oxygen species is a regular feature of life in the presence of oxygen. Some reactive oxygen species possess sufficient energy to initiate lipid peroxidation in biological membranes, self-propagating reactions with the potential to damage membranes by altering their physical properties and ultimately their function. Two of the most prominent patterns of lipid restructuring in membranes of ectotherms involve contents of polyunsaturated fatty acids and ratios of the abundant phospholipids, phosphatidylcholine and phosphatidylethanolamine. Since polyunsaturated fatty acids and phosphatidylethanolamine are particularly vulnerable to oxidation, it is likely that higher contents of these lipids at low body temperature elevate the inherent susceptibility of membranes to lipid peroxidation. Although membranes from animals living at low body temperatures may be more prone to oxidation, the generation of reactive oxygen species and lipid peroxidation are sensitive to temperature. These scenarios raise the possibility that membrane susceptibility to lipid peroxidation is conserved at physiological temperatures. Reduced levels of polyunsaturated fatty acids and phosphatidylethanolamine may protect membranes at warm temperatures from deleterious oxidations when rates of reactive oxygen species production and lipid peroxidation are relatively high. At low temperatures, enhanced susceptibility may ensure sufficient lipid peroxidation for cellular processes that require lipid oxidation products.

Torpor and hibernation in a basal placental mammal, the Lesser Hedgehog Tenrec Echinops telfairi

Abstract: The patterns of heterothermy were measured in Lesser Hedgehog Tenrecs, Echinops telfairi, under semi-natural conditions in an outdoor enclosure during the austral mid-winter in southwestern Madagascar. The animals were implanted with miniaturized body temperature (Tb) loggers (iButtons) that measured body temperature every 42 min for 2 months (May and June). The tenrecs entered daily torpor on all 60 consecutive days of measurement, that is, on 100% of animal days, with body temperature closely tracking ambient temperature (Ta) during the ambient heating phase. The mean minimum daily Tb of the tenrecs was 18.44 +/- 0.50 degrees C (n = 174, N = 3), and never exceeded 25 degrees C whereas, apart from a few hibernation bouts in one animal, the mean maximum daily Tb was 30.73 +/- 0.15 degrees C (n = 167, N = 3). Thus during winter, tenrecs display the lowest normothermic Tb of all placental mammals. E. telfairi showed afternoon and early evening arousals, but entered torpor before midnight and remained in torpor for 12-18 h each day. One animal hibernated on two occasions for periods of 2-4 days. We consider E. telfairi to be a protoendotherm, and discuss the relevance and potential of these data for testing models on the evolution of endothermy.

The role of hepatic, renal and intestinal gluconeogenic enzymes in glucose homeostasis of juvenile rainbow trout

Abstract: Rainbow trout is unable to utilize high levels of dietary carbohydrates and experiences hyperglycemia after consumption of carbohydrate-rich meals. Carbohydrates stimulate hepatic glycolytic activity, but gene expression of the rate-limiting gluconeogenic enzymes glucose-6-phosphatase (G6Pase), fructose-1,6-bisphosphatase (FBPase) and phosphoenolpyruvate carboxykinase (PEPCK) remains high. Although there is significant mRNA expression and activity of gluconeogenic enzymes in trout intestine and kidney, the regulation of these enzymes by diet is not known. We tested the hypothesis that dietary carbohydrate modulates intestinal and renal G6Pase, FBPase and PEPCK. Fish were either fasted or fed isocaloric carbohydrate-free (CF) or high carbohydrate (HC) diets for 14 days. As expected, fish fed HC exhibited postprandial hyperglycemia and enhanced levels of hepatic glucokinase mRNA and activity. Dietary carbohydrates had no significant effect on the expression and activity of PEPCK, FBPase and G6Pase in all three organs. In contrast, fasting enhanced the activity, but not the mRNA expression of both hepatic and intestinal PEPCK, as well as intestinal FBPase. Therefore, the activity of rate-limiting gluconeogenic enzymes in trout can be modified by fasting, but not by the carbohydrate content of the diet, potentially causing hyperglycemia when fed high levels of dietary carbohydrates. In this species consuming low carbohydrate diets at infrequent intervals in the wild, fasting-induced increases in hepatic and intestinal gluconeogenic enzyme activities may be a key adaptation to prevent perturbations in blood glucose during food deprivation.

Dietary fatty acid composition changes mitochondrial phospholipids and oxidative capacities in rainbow trout red muscle

Abstract: Dietary conditioning of juvenile trout changed the acyl chain composition of mitochondrial phospholipids and the oxidative capacities of muscle mitochondria. Trout were fed three diets differing only in fatty acid (FA) composition. The highly unsaturated 22:6 n-3 (DHA) accounted for 0.4, 14, and 30% of fatty acids in Diets 1, 2 and 3. After 10 weeks of growth, the dietary groups differed markedly in FA composition of mitochondrial phospholipids, with significant dietary effects for virtually all FA. Mean mitochondrial DHA levels were 19, 40 and 33% in trout fed Diets 1, 2 and 3. Mitochondrial oxidative capacities changed with diet, while mitochondrial concentrations of cytochromes and of the adenylate nucleotide translocase (nmol mg1 protein) did not. Mitochondria from fish fed Diet 1 had higher non-phosphorylating (state 4) rates at 5°C than those fed other diets. When phosphorylating (state 3) rates differed between dietary groups, rates at 5 and 15°C were higher for fish fed the more unsaturated diets. Stepwise multiple regressions indicated that FA composition could explain much (42–70%) of the variability of state 4 rates, particularly at 5°C. At 15°C, FA composition explained 16–42% of the variability of states 3 and 4 rates. Similar conclusions were obtained for the complete data set (trout fed diets 1, 2 and 3) and for the data from trout achieving similar growth rates (e.g. those fed Diets 1 and 2). Neither general characteristics of membrane FA, such as % saturates, unsaturation index, n-3, n-6 or n-3/n-6 nor levels of abundant unsaturated FA such as DHA or 18:1(n-9 + n-7), were systematically correlated with mitochondrial capacities even though they differed considerably between trout fed the different diets. Relatively minor FA (20:5n-3, 20:0, 18:2n-6, 18:3n-3, 18:0 and 15:0) showed better correlations with mitochondrial oxidative capacities. This supports the concept that acyl chain composition modulates mitochondrial capacities via interactions between membrane proteins and specific FA of particular phospholipid classes in their microenvironment.

High-definition spatiotemporal mapping of contractile activity in the isolated proximal colon of the rabbit.

Abstract: Four types of contractile activity were identified and characterised in the isolated triple haustrated proximal colon of the rabbit using high-definition spatiotemporal mapping techniques. Mass peristalses were hexamethonium-sensitive deep circular contractions with associated taenial longitudinal contractile activity that occurred irregularly and propagated rapidly aborad, preceded by a zone of local lumen distension. They were sufficiently sustained for each event to occupy the length of the isolated colonic segment and the contraction persisted longer orally than aborally, the difference being more pronounced when lumen contents were viscous. Haustra were bounded by deep even-spaced ring contractions that progressed slowly aborad (haustral progression). Haustral formation and progression were hexamethonium-sensitive and coordinated across intertaenial domains. Ripples were hexamethonium-resistant phasic circular contractions that propagated predominantly orad at varying rates. In the presence of haustra, they were uncoordinated across intertaenial domains but were more coordinated when haustra were absent. Fast phasic contractions were relatively shallow hexamethonium-resistant contractions that propagated rapidly in a predominantly aborad direction. Fast phasic circular contractions were accompanied by taenial longitudinal muscle contractions which increased in amplitude prior to a mass peristaltic event and following the administration of hexamethonium. On the basis of the concurrence and interaction of these contractile activities, we hypothesise that dual pacemakers are present with fast phasic contractions being modulated by the interstitial cells of Cajal in the Auerbach's plexus (ICC-MY) while ripples are due to the submucosal ICC (ICC-SM). Further, that ICC-SM mediate the enteric motor neurons that generate haustral progression, while the intramuscular ICC (ICC-IM) mediate mass peristalsis. The orad movement of watery fluid was possibly due to ripples in the absence of haustra.

Northern grass lizards ( Takydromus septentrionalis ) from different populations do not differ in thermal preference and thermal tolerance when acclimated under identical thermal conditions

Abstract: We acclimated adults of Takydromus septentrionalis (northern grass lizard) from four localities (populations) under identical thermal conditions to examine whether local thermal conditions have a fixed influence on thermal preference and thermal tolerance in the species. Selected body temperature (Tsel), critical thermal minimum (CTMin), and critical thermal maximum (CTMax) did not differ between sexes and among localities in lizards kept under identical laboratory conditions for ∼5 months, and the interaction effects between sex and locality on these measures were not significant. Lizards acclimated to the three constant temperatures (20, 25, and 35°C) differed in Tsel, CTMin, and CTMax. Tsel, CTMin, and CTMax all shifted upward as acclimation temperature increased, with Tsel shifting from 32.0 to 34.1°C, CTMin from 4.9 to 8.0°C, and CTMax from 42.0 to 44.5°C at the change-over of acclimation temperature from 20 to 35°C. Lizards acclimated to the three constant temperatures also differed in the range of viable body temperatures; the range was widest in the 25°C treatment (38.1°C) and narrowest in the 35°C treatment (36.5°C), with the 20°C treatment in between (37.2°C). The results of this study show that local thermal conditions do not have a fixed influence on thermal preference and thermal tolerance in T. septentrionalis.

Molecular cloning and characterization of two novel cellulase genes from the mollusc Ampullaria crossean.

Abstract: Cellulase genes have been reported not only from fungi, bacteria and plant, but also from some invertebrate animals. Here, two cellulase (endo-β-1,4-glucanase, EC 3.2.1.4) genes, eg27I and eg27II, were cloned from the freshwater snail Ampullaria crossean cDNA using degenerate primers. The nucleotide sequences of the two genes shared 94.5% identity. The open reading frames of both genes consisted of 588 bp, encoding 195 amino acids. Both EG27I and EG27II belong to the glycoside hydrolase family 45, and each lacks a carbohydrate-binding module. The presence of introns demonstrated a eukaryotic origin of the EG27 gene, and, in addition, successful cloning of EG27 cDNA supported endogenous production of EG27 cellulase by Ampullaria crossean. Investigation of the EG27 cDNA from A. crossean will provide further information on GHF45 cellulases.

A critical analysis of transepithelial potential in intact killifish (Fundulus heteroclitus) subjected to acute and chronic changes in salinity

Abstract: We investigated the in vivo salinity-dependent behavior of transepithelial potential (TEP) in Fundulus heteroclitus (3–9 g) using indwelling coelomic catheters, a technique which was validated against blood catheter measurements in a larger species (Opsanus beta; 35–70 g). In seawater (SW)-acclimated killifish, TEP was +23 mV (inside positive), but changed to −39 mV immediately after transfer to freshwater (FW). Acute transfer to dilute salinities produced a TEP profile, which rapidly attenuated as salinity increased (0, 2.5, 5 and 10% SW), with cross-over to positive values between 20 and 40% SW, and a linear increase thereafter (60, 80 and 100% SW). TEP response profiles were also recorded after acute transfer to comparable dilutions of 500 mmol L−1 NaCl, NaNO3, Na gluconate, choline chloride, N-methyl-d-glutamate (NMDG) chloride, or 1,100 mosmol kg−1 mannitol. These indicated high non-specific cation permeability and low non-specific anion permeability without influence of osmolality in SW-acclimated killifish. While there was a small electrogenic component in high salinity, a Na+ diffusion potential predominated at all salinities due to the low PCl/PNa (0.23) of the gills. The very negative TEP in FW was attenuated in a linear fashion by log elevations in [Ca2+] such that PCl/PNa increased to 0.73 at 10 mmol L−1. SW levels of [K+] or [Mg2+] also increased the TEP, but none of these cations alone restored the positive TEP of SW-acclimated killifish. The very negative TEP in FW attenuated over the first 12 h of exposure and by 24–30 h reached +3 mV, representative of long-term FW-acclimated animals; this reflected a progressive increase in PCl/PNa from 0.23 to 1.30, probably associated with closing of the paracellular shunt pathway. Thereafter, the TEP in FW-acclimated killifish was unresponsive to [Ca2+] (also to [K+], [Mg2+], or chloride salts of choline and NMDG), but became more positive at SW levels of [Na+]. Killifish live in a variable salinity environment and are incapable of gill Cl− uptake in FW. We conclude that the adaptive significance of the TEP patterns is that changeover to a very negative TEP in FW will immediately limit Na+ loss while not interfering with active Cl− uptake because there is none. Keeping the shunt permeability high for a few hours means that killifish can return to SW and instantaneously re-activate their NaCl excretion mechanism.

Cold tolerance of an Antarctic nematode that survives intracellular freezing: comparisons with other nematode species.

Abstract: Panagrolaimus davidi is an Antarctic nematode with very high levels of cold tolerance. Its survival was compared with that of some other nematodes (P. rigidus, Rhabditophanes sp., Steinernema carpocapsae, Panagrellus redivivus and Ditylenchus dipsaci) in both unacclimated samples and those acclimated at 5 degrees C. Levels of recrystallization inhibition in homogenates were also compared, using the splat-cooling assay. The survival of P. davidi after the freezing of samples was notably higher than that of the other species tested, suggesting that its survival ability is atypical compared to other nematodes. In general, acclimation improved survival. Levels of recrystallization inhibition were not associated with survival but such a relationship may exist for those species that are freezing tolerant.

Boom and bust: a review of the physiology of the marsupial genus Antechinus.

Abstract: The marsupial genus Antechinus is a group of small carnivorous marsupials from the order Dasyuromorphia (Family Dasyuridae) and is found in eastern Australia. The life history of all species in the genus is characterized by a complex, but highly synchronized life cycle in both sexes, culminating in a short mating period followed by total male mortality (semelparity). The breeding season is defined by a specific rate of increase in photoperiod, which is different for each species. In Antechinus spp., male mortality is due to the effects of high free testosterone and cortisol levels on many organ systems. Unusually, spermatogenesis is complete before testosterone levels begin to rise at the winter solstice. In males, low sperm counts have been compensated for by high proportions of sperm reaching the isthmus of the female reproductive tract and long-term storage in the crypts. The females survive to rear their young and may mate again in their second year. Gestation lasts from 26 to 34 days, depending on the species. However, developmental arrest can occur at several stages during embryogenesis, elongating the apparent gestation duration by several days. Several species have strong female sex biases in their litters. The high degree of life history synchrony and the cascade of endocrine-driven physiological events that result in male death are unusual physiological characteristics for mammals. Suggestions why semelparity may have evolved in Antechinus are discussed.

Antioxidants in eggs of great tits Parus major from Chernobyl and hatching success

Abstract: Antioxidants are powerful protectors against the damaging effects of free radicals that constitute the inevitable by-products of aerobic metabolism. Growing embryos are particularly susceptible to the damaging effects of free radicals produced during rapid growth, and mothers of many species provide protection against such damage by allocating antioxidants to their eggs. Birds living in radioactively contaminated areas use dietary antioxidants to cope with the damaging effects of radiation, but females also allocate dietary antioxidants to eggs, potentially enforcing a physiological trade-off between self-maintenance and reproductive investment. Here we tested whether female great tits Parus major breeding in radioactively contaminated study areas near Chernobyl allocated less dietary antioxidants to eggs, and whether such reduced allocation of dietary antioxidants to eggs had fitness consequences. Concentrations of total yolk carotenoids and vitamins A and E were depressed near Chernobyl compared to concentrations in a less contaminated Ukrainian study area and a French control study area, and all antioxidants showed dose-dependent relationships with all three dietary antioxidants decreasing with increasing level of radiation at nest boxes. These effects held even when controlling statistically for potentially confounding habitat variables and covariation among antioxidants. Laying date was advanced and clutch size increased at nest boxes with high dose rates. Hatching success increased with increasing concentration of vitamin E, implying that hatching success decreased at boxes with high levels of radiation, eventually eliminating and even reversing the higher potential reproductive output associated with early reproduction and large clutch size. These findings are consistent with the hypothesis that radioactive contamination reduced levels of dietary antioxidants in yolks, with negative consequences for hatching success and reproductive success.

The swimming performance of brown trout and whitefish: the effects of exercise on Ca2+ handling and oxidative capacity of swimming muscles.

Abstract: The swimming performance of two fish species, the brown trout and whitefish, having initially different swimming strategies, was measured after nine different training programs in order to relate the effects of exercise on Ca(2+) handling and oxidative capacity of swimming muscles. The time to 50% fatigue was measured during the training period, and compared with the density of dihydropyridine (DHP) and ryanodine (Ry) receptors and succinate dehydrogenase (SDH) and phosphorylase activity determined by histochemical analysis of the swimming muscles. Overall, both trained brown trout and whitefish had superior swimming performance as compared to control ones. Interestingly, the training programs had different effect on the two species studied since brown trout achieved the highest swimming performance, swimming against the water flow velocity of 2 BL s(-1) while among whitefish the best efficiency was seen after training with lower swimming velocities. Training also induced a significant increase in DHP and Ry receptor density in both species. Generally, in brown trout the most notable increase in the receptor densities was observed in red muscle sections from the fish swimming for 6 weeks against water currents of 1 BL s(-1) (DHPR 176.5 +/- 7.7% and RyR 231.4 +/- 11.8%) and white muscle sections against 2 BL s(-1) (DHPR 129.6 +/- 12.4% and RyR 161.9 +/- 15.5%). In whitefish the most prominent alterations were noted in samples from both muscle types after 6 weeks of training against water current of 1.5 BL s(-1) (DHPR 167.1 +/- 16.9% and RyR 190.4 +/- 19.4%). Finally, after all the training regimens the activity of SDH increased but the phosphorylase activity decreased significantly in both the species. To conclude, our findings demonstrate an improved swimming performance and enhanced Ca(2+) regulation and oxidative capacity after training. Moreover, there seems to be a connection between the swimming performance and receptor levels, especially in white swimming muscles of different fish species, regardless of their initially deviant swimming behaviours. However, depending on the training regimen the divergent swimming behaviours do cause a different response, resulting in the most prominent adaptational changes in the receptor levels of red muscle samples with lower swimming velocities in brown trout and with higher ones in whitefish.

Salinity-dependent changes in Na(+)/K (+)-ATPase content of mitochondria-rich cells contribute to differences in thermal tolerance of Mozambique tilapia.

Abstract: The Mozambique tilapia (Oreochromis mossambicus) is prone to osmoregulatory disturbances when faced with fluctuating ambient temperatures. To investigate the underlying causes of this phenomenon, freshwater (FW)- and seawater (SW)-acclimated tilapia were transferred to 15, 25, or 35°C for 2 weeks, and along with typically used indicators of osmoregulatory status [plasma osmolality and branchial and intestinal specific Na+, K+-ATPase (NKA) activity], we used tissue microarrays (TMA) and laser-scanning cytometry (LSC) to characterize the effects of temperature acclimation. Tissue microarrays were stained with fluorescently labeled anti-Na+, K+-ATPase antibodies that allowed for the quantification of NKA abundance per unit area within individual branchial mitochondria-rich cells (MRCs) as well as sections of renal tissue. Mitochondria-rich cell counts and estimates of size were carried out for each treatment by the detection of DASPMI fluorescence. The combined analyses showed that SW fish have larger but fewer MRCs that contain more NKA per unit area. After a 2-week acclimation to 15°C tilapia experienced osmotic imbalances in both FW and SW that were likely due to low NKA activity. SW-acclimated fish compensated for the low activity by increasing MRC size and subsequently the concentration of NKA within MRCs. Although there were no signs of osmotic stress in FW-acclimated tilapia at 25°C, there was an increased NKA capacity that was most likely mediated by a higher MRC count. We conclude on the basis of the different responses to temperature acclimation that salinity-induced changes in the NKA concentration of MRCs alter thermal tolerance limits of tilapia.

Energy expenditure during flight in relation to body mass: effects of natural increases in mass and artificial load in Rose Coloured Starlings

Abstract: Rose Coloured Starlings (Sturnus roseus) flew repeatedly for several hours in a wind tunnel while undergoing spontaneous variation in body mass. The treatments were as follows: flying unrestrained (U), with a control harness of 1.2% of their body mass (C), or with a harness of 7.4% of their body mass, which was either applied immediately before the flight (LS) or at least 9 days in advance (LL). Energy expenditure during flight (ef in W) was measured with the Doubly Labelled Water method. Flight costs in LS and LL were not significantly different and therefore were pooled (L). The harness itself did not affect ef, i.e. U and C flights were not different. ef was allometrically related with body mass m (in g). The slopes were not significantly different between the treatments, but ef was increased by 5.4% in L compared to C flights (log10(ef) = 0.050 + 0.47 × log10(m) for C, and log10(ef) = 0.073 + 0.47 × log10(m) for L). The difference in ef between C, LS and LL was best explained by taking the transported mass mtransp (in g) instead of m into account (log10(ef) = −0.08 + 0.54 × log10(mtransp)). Flight costs increased to a lesser extent than expected from interspecific allometric comparison or aerodynamic theory, regardless of whether the increase in mass occurred naturally or artificially. We did not observe an effect of treatment on breast muscle size and wingbeat frequency. We propose that the relatively low costs at a high mass are rather a consequence of immediate adjustments in physiology and/or flight behaviour than of long-term adaptations.

Seasonal patterns of heat loss in wild bottlenose dolphins (Tursiops truncatus)

Abstract: This study investigated patterns of heat loss in bottlenose dolphins (Tursiops truncatus) resident to Sarasota Bay, FL, USA, where water temperatures vary seasonally from 11 to 33°C. Simultaneous measurements of heat flux (HF) and skin surface temperature were collected at the body wall and appendages of dolphins during health-monitoring events in summer (June 2002–2004) and winter (February 2003–2005). Integument thickness was measured and whole body conductance (W/m2 °C) was estimated using HF and colonic temperature measurements. Across seasons, HF values were similar at the appendages, but their distribution differed significantly at the flipper and fluke. In summer, these appendages displayed uniformly high values, while in winter they most frequently displayed very low HF values with a few high HF values. In winter, blubber thickness was significantly greater and estimated conductance significantly lower, than in summer. These results suggest that dolphins attempt to conserve heat in winter. In winter, though, HF values across the body wall were similar to (flank) or greater than (caudal keel) summer values. It is likely that higher winter HF values are due to the steep temperature gradient between the body core and colder winter water, which may limit the dolphin’s ability to decrease heat loss across the body wall.

Increased urea synthesis and/or suppressed ammonia production in the African lungfish, Protopterus annectens, during aestivation in air or mud.

Abstract: The objective of this study was to elucidate how the African lungfish, Protopterus annectens, ameliorated ammonia toxicity during 12 or 46 days of aestivation in air or in mud. Twelve days of aestivation in air led to significant increases in contents of urea, but not ammonia, in tissues of P. annectens. The estimated rate of urea synthesis increased 2.7-fold despite the lack of changes in the activities of hepatic ornithine–urea cycle enzymes, but there was only a minor change in the estimated rate of ammonia production. After 46 days of aestivation in air, the ammonia content in the liver decreased significantly and contents of urea in all tissues studied increased significantly, indicating that the fish shifted to a combination of increased urea synthesis (1.4-fold of the day 0 value) and decreased ammonia production (56% of the day 0 value) to defend against ammonia toxicity. By contrast, 12 days of aestivation in mud produced only minor increases in tissue urea contents, with ammonia contents remained unchanged. This was apparently achieved through decreases in urea synthesis and ammonia production (40 and 15%, respectively, of the corresponding day 0 value). Surprisingly, 46 days of aestivation in mud resulted in no changes in tissue urea contents, indicating that profound suppressions of urea synthesis and ammonia production (2.6 and 1.2%, respectively, of the corresponding day 0 value) had occurred. This is the first report on such a phenomenon, and the reduction in ammonia production was so profound that it could be the greatest reduction known among animals. Since fish aestivated in mud had relatively low blood pO2 and muscle ATP content, they could have been exposed to hypoxia, which induced reductions in metabolic rate and ammonia production. Consequently, fish aestivating in mud had a lower dependency on increased urea synthesis to detoxify ammonia, which is energy intensive, than fish aestivating in air.

Physiological response in the European flounder (Platichthys flesus) to variable salinity and oxygen conditions.

Abstract: Physiological mechanisms involved in acclimation to variable salinity and oxygen levels and their interaction were studied in European flounder. The fish were acclimated for 2 weeks to freshwater (1‰ salinity), brackish water (11‰) or full strength seawater (35‰) under normoxic conditions (water Po2 = 158 mmHg) and then subjected to 48 h of continued normoxia or hypoxia at a level (Po2 = 54 mmHg) close to but above the critical Po2. Plasma osmolality, [Na+] and [Cl−] increased with increasing salinity, but the rises were limited, reflecting an effective extracellular osmoregulation. Muscle water content was the same at all three salinities, indicating complete cell volume regulation. Gill Na+/K+-ATPase activity did not change with salinity, but hypoxia caused a 25% decrease in branchial Na+/K+-ATPase activity at all three salinities. Furthermore, hypoxia induced a significant decrease in mRNA levels of the Na+/K+-ATPase α1-subunit, signifying a reduced expression of the transporter gene. The reduced ATPase activity did not influence extracellular ionic concentrations. Blood [Hb] was stable with salinity, and it was not increased by hypoxia. Instead, hypoxia decreased the erythrocytic nucleoside triphosphate content, a common mechanism for increasing blood O2 affinity. It is concluded that moderate hypoxia induced an energy saving decrease in branchial Na+/K+-ATPase activity, which did not compromise extracellular osmoregulation.

Is the strategy for cold hardiness in insects determined by their water balance? A study on two closely related families of beetles: Cerambycidae and Chrysomelidae

Abstract: The strategy for cold-hardiness and water balance features of two closely related families of Coleoptera, Cerambycidae and Chrysomelidae, were investigated. Cerambycids were freeze-avoiding with low supercooling points, whereas chrysomelids froze at high temperatures and were tolerant to freezing. Hence, the two families have adopted different strategies for cold-hardiness. Due to their low trans-cuticular water permeability, the cerambycids have low rates of evaporative water loss. Chrysomelids have much higher trans-cuticular water permeability, but freezing brings their body fluids in vapour pressure equilibrium with ice and prevents evaporative water loss. The differences in cold-hardiness strategies and rates of water loss are likely to reflect the water content of the diets of the two families. Cerambycids feed on dry wood with low water content, causing a restrictive water balance. Chrysomelids feed on leaves with high water content and may use evaporation through the cuticle as a route of water excretion. Haemolymph ice nucleators help chrysomelids to freeze at a high temperature and thus to maximize the period they spend in the water saving frozen state. The diet-related differences in water balance may be the reason why the two families have developed different strategies for cold-hardiness.