Nutritional homeostasis in carnivorous southern catfish (Silurus meridionalis): is there a mechanism for increased energy expenditure during carbohydrate overfeeding?

In previous growth experiments with carnivorous southern catfish (Silurus meridionalis), the non-fecal energy lose was positively related to dietary carbohydrate level. To test whether metabolic energy expenditure accounts for such energy loss, an experiment was performed with southern catfish juveniles (33.2-71.9 g) to study the effect of dietary carbohydrate level on fasting metabolic rate and specific dynamic action (SDA) at 27.5 degrees C. The fasting metabolic rate in this catfish was increased with dietary carbohydrate level, and the specific dynamic action (SDA) coefficient (energy expended on SDA as percent of assimilated energy) was not affected by dietary carbohydrate level. The results suggest that in southern catfish, carbohydrate overfeeding increases metabolic rate to oxidize unwanted assimilated carbohydrate. A discussion on the poor capacity of intermediate metabolism for adapting dietary carbohydrate in carnivorous fish and its possible relationship with facultative component of SDA was also documented in this paper.     

Moult-related reduction of aerobic scope in passerine birds

It is well established that the nutrient and energy requirements of birds increase substantially during moult, but it is not known if these increased demands affect their aerobic capacity. We quantified the absolute aerobic scope of house and Spanish sparrows, Passer domesticus and P. hispaniolensis, respectively, before and during sequential stages of their moult period. The absolute aerobic scope (AAS) is the difference between maximum metabolic rate (MMR) during peak locomotor activities and minimum resting metabolic rate (RMR_min), thus representing the amount of aerobic power above that committed to maintenance needs available for other activities. As expected, RMR_min increased over the moult period by up to 40 and 63% in house and Spanish sparrows, respectively. Surprisingly, the maximum metabolic rates also decreased during moult in both species, declining as much as 25 and 38% compared with pre-moult values of house and Spanish sparrows, respectively. The concurrent changes in RMR_min and MMR during moult resulted in significant decreases in AAS, being up to 32 and 47% lower than pre-moult levels of house and Spanish sparrows, respectively, during moult stages having substantial feather replacement. We argue that the combination of reduced flight efficiency due to loss of wing feathers and reduced aerobic capacity places moulting birds at greater risk of predation. Such performance constraints likely contribute to most birds temporally separating moult from annual events requiring peak physiological capacity such as breeding and migration.

     

Effect of fasting in the digestive system: Histological study of the small intestine in house sparrows

In birds and mammals the metabolic response to fasting has been studied and can be characterized by three consecutive phases reflecting metabolic and physiological adjustments. An effective way to minimize energy expenditure during food scarcity is to decrease the mass of the organs. As the digestive system is metabolically expensive to maintain, the small intestine and the liver are the most affected organs. We evaluated the effects of phase III starvation on the mass of the different organs and histological parameters on house sparrows, a small non-migrant bird. In a short period of time (34 h) we observed a larger reduction in the digestive organ mass when compared to the mass of the body and non-alimentary tissues. Furthermore, the intestinal mass was proportionally more reduced than its length and nominal surface area. A reduction on the intestinal mucosal layer also resulted in a shortening of villus (length and thickness) and crypt depth. Moreover, the morphology of the enterocytes changed from cylindrical to cubical, suggesting that the surface exposed to the lumen was conserved. This may indicate an adaptive response to the moment of refeeding. The nominal surface area/body mass remained constant in both groups and several histological parameters were reduced, suggesting that starving induces the atrophy of the small intestine. However, the goblet cells were conserved after fasting indicating a protective tendency.     

Validation of the doubly labeled water technique for measuring energy metabolism in starlings and sparrows

I have tested the idea that doubly labeled water (DLW) can accurately predict CO2 production in savannah sparrows, song sparrows, white-throated sparrows, starlings, and a single house sparrow by comparing DLW estimates with those obtained simultaneously by capturing expired CO2 in Ascarite. In addition I used the energy balance method to see if metabolic rates generated from DLW measurements accurately reflected the actual metabolic rates of these birds. I found close agreement in DLW and the gravimetric and energy balance methods, with DLW underestimating CO2 production on average by -3.5% in sparrows, and -7.1% in starlings. Similarly, the energy balance method indicated a -3.1% underestimate by DLW for sparrows and a -5.1% for starlings. The DLW method can yield reasonable estimates of CO2 production in a variety of passerine birds.     

Responding to inflammatory challenges is less costly for a successful avian invader, the house sparrow (Passer domesticus), than its less-invasive congener

When introduced into new regions, invading organisms leave many native pathogens behind and also encounter evolutionarily novel disease threats. In the presence of predominantly novel pathogens that have not co-evolved to avoid inducing a strong host immune response, costly and potentially dangerous defenses such as the systemic inflammatory response could become more harmful than protective to the host. We therefore hypothesized that introduced populations exhibiting dampened inflammatory responses will tend to be more invasive. To provide initial data to assess this hypothesis, we measured metabolic, locomotor, and reproductive responses to inflammatory challenges in North American populations of the highly invasive house sparrow (Passer domesticus) and its less-invasive relative, the tree sparrow (Passer montanus). In the house sparrow, there was no effect of phytohemagglutinin (PHA) challenge on metabolic rate, and there were no detectable differences in locomotor activity between lipopolysaccharide (LPS)-injected birds and saline-injected controls. In contrast, tree sparrows injected with PHA had metabolic rates 20-25% lower than controls, and LPS injection resulted in a 35% drop in locomotor activity. In a common garden captive breeding experiment, there was no effect of killed-bacteria injections on reproduction in the house sparrow, while tree sparrows challenged with bacteria decreased egg production by 40% compared to saline-injected controls. These results provide some of the first data correlating variation in immune defenses with invasion success in introduced-vertebrate populations.     

GC/MS-based metabolomic studies reveal key roles of glycine in regulating silk synthesis in silkworm,Bombyx mori

Metabolic profiling of silkworm, especially the factors that affect silk synthesis at the metabolic level, is little known. Herein, metabolomic method based on gas chromatography-mass spectrometry was applied to identify key metabolic changes in silk synthesis deficient silkworms. Forty-six differential metabolites were identified in Nd group with the defect of silk synthesis. Significant changes in the levels of glycine and uric acid (up-regulation), carbohydrates and free fatty acids (down-regulation) were observed. The further metabolomics of silk synthesis deficient silkworms by decreasing silk proteins synthesis using knocking out fibroin heavy chain gene or extirpating silk glands operation showed that the changes of the metabolites were almost consistent with those of the Nd group. Furthermore, the increased silk yields by supplying more glycine or its related metabolite confirmed that glycine is a key metabolite to regulate silk synthesis. These findings provide important insights into the regulation between metabolic profiling and silk synthesis.     

House sparrows (Passer domesticus) increase protein catabolism in response to water restriction

Birds primarily rely on fat for energy during fasting and to fuel energetically demanding activities. Proteins are catabolized supplemental to fat, the function of which in birds remains poorly understood. It has been proposed that birds may increase the catabolism of body protein under dehydrating conditions as a means to maintain water balance, because catabolism of wet protein yields more total metabolic and bound water (0.155·H(2)O(-1)·kJ(-1)) than wet lipids (0.029 g·H(2)O(-1)·kJ(-1)). On the other hand, protein sparing should be important to maintain function of muscles and organs. We used quantitative magnetic resonance body composition analysis and hygrometry to investigate the effect of water restriction on fat and lean mass catabolism during short-term fasting at rest and in response to a metabolic challenge (4-h shivering) in house sparrows (Passer domesticus). Water loss at rest and during shivering was compared with water gains from the catabolism of tissue. At rest, water-restricted birds had significantly greater lean mass loss, higher plasma uric acid concentration, and plasma osmolality than control birds. Endogenous water gains from lean mass catabolism offset losses over the resting period. Water restriction had no effect on lean mass catabolism during shivering, as water gains from fat oxidation appeared sufficient to maintain water balance. These data provide direct evidence supporting the hypothesis that water stress can increase protein catabolism at rest, possibly as a metabolic strategy to offset high rates of evaporative water loss.     

Behavioural responses during feather replacement in house sparrows

Birds lose feathers, whether during molt or by accident, and replace them by processes that are energetically demanding. We hypothesized that house sparrows Passer domesticus biblicus use behavioral means to save energy when feathers are lost, and tested the general prediction that house sparrows growing new feathers adjust their behavior to minimize the energy costs of foraging and to increase net energy gain from their food. To test these predictions we divided 18 house sparrows into three groups: 1) plucked – house sparrows from which we plucked 15 flight feathers; 2) cut – house sparrows in which the same 15 feathers were cut off at the calamus below the barbs; and 3) control – unmanipulated house sparrows with plumage intact. We recorded both the quantity of seeds the house sparrows ate and the time they spent foraging from assay food patches. We found that ‘plucked’ sparrows growing new feathers adjust their foraging behavior by reducing their feeding time and the number of visits to a food patch. This allowed them to increase their patch harvest rate while maintaining a steady body mass.     

Variation in inflammation as a correlate of range expansion in Kenyan house sparrows

Many introduced animals harbor fewer parasites than native ones. This “enemy release” can select for individuals that bias resources away from parasite resistance traits, including immune functions, and towards traits that enhance success in new areas. One vertebrate example that supports this hypothesis involves house sparrows (Passer domesticus) and Eurasian tree sparrows (Passer montanus) introduced to St. Louis, MO, USA, over 150 years ago. Since ca. 1850, house sparrows have colonized most of North America whereas tree sparrows have expanded little from the area of introduction. The more successful house sparrows now exhibit weaker inflammatory responses than the less successful tree sparrows, which supports the possibility that diminished investments in immune defense may have been conducive to the initial colonization by the more successful species. The goal of the present study was to determine whether damped inflammation generally facilitates invasion by comparing inflammatory markers between house sparrows invading Kenya and a native congener. House sparrows arrived in Mombasa, Kenya, about 50 years ago whereas rufous sparrows (Passer ruficinctus) are native but ecologically similar. We predicted that if inflammation mediated invasion success, Kenyan house sparrows would mount weaker inflammatory responses than the native species. Complete Freund’s adjuvant (CFA), a strong inflammatory stimulus, increased body mass in house sparrows, a result unprecedented in any other vertebrate. Haptoglobin (Hp), a multi-functional acute phase protein, was elevated by CFA in both species but rufous sparrows maintained more Hp than house sparrows irrespective of treatment. Lysozyme, a broadly effective antimicrobial enzyme, was reduced by CFA in both species, but not differentially so. Corticosterone was unaffected by CFA in either species, but elevated in both relative to free-living individuals.     

Responding to inflammatory challenges is less costly for a successful avian invader,the house sparrow (<Emphasis Type="Italic">Passer domesticus</Emphasis>), than its less-invasive congener

When introduced into new regions, invading organisms leave many native pathogens behind and also encounter evolutionarily novel disease threats. In the presence of predominantly novel pathogens that have not co-evolved to avoid inducing a strong host immune response, costly and potentially dangerous defenses such as the systemic inflammatory response could become more harmful than protective to the host. We therefore hypothesized that introduced populations exhibiting dampened inflammatory responses will tend to be more invasive. To provide initial data to assess this hypothesis, we measured metabolic, locomotor, and reproductive responses to inflammatory challenges in North American populations of the highly invasive house sparrow (Passer domesticus) and its less-invasive relative, the tree sparrow (Passer montanus). In the house sparrow, there was no effect of phytohemagglutinin (PHA) challenge on metabolic rate, and there were no detectable differences in locomotor activity between lipopolysaccharide (LPS)-injected birds and saline-injected controls. In contrast, tree sparrows injected with PHA had metabolic rates 20–25% lower than controls, and LPS injection resulted in a 35% drop in locomotor activity. In a common garden captive breeding experiment, there was no effect of killed-bacteria injections on reproduction in the house sparrow, while tree sparrows challenged with bacteria decreased egg production by 40% compared to saline-injected controls. These results provide some of the first data correlating variation in immune defenses with invasion success in introduced-vertebrate populations.     

Metabolic profiling by 13C-NMR spectroscopy: [1,2-13C2]glucose reveals a heterogeneous metabolism in human leukemia T cells

Metabolic profiling is defined as the simultaneous assessment of substrate fluxes within and among the different pathways of metabolite synthesis and energy production under various physiological conditions. The use of stable-isotope tracers and the analysis of the distribution of labeled carbons in various intermediates, by both mass spectrometry and NMR spectroscopy, allow the role of several metabolic processes in cell growth and death to be defined. In the present paper we describe the metabolic profiling of Jurkat cells by isotopomer analysis using (13)C-NMR spectroscopy and [1,2-(13)C(2)]glucose as the stable-isotope tracer. The isotopomer analysis of the lactate, alanine, glutamate, proline, serine, glycine, malate and ribose-5-phosphate moiety of nucleotides has allowed original integrated information regarding the pentose phosphate pathway, TCA cycle, and amino acid metabolism in proliferating human leukemia T cells to be obtained. In particular, the contribution of the glucose-6-phosphate dehydrogenase and transketolase activities to phosphoribosyl-pyrophosphate synthesis was evaluated directly by the determination of isotopomers of the [1'-(13)C], [4',5'-(13)C(2)]ribosyl moiety of nucleotides. Furthermore, the relative contribution of the glycolysis and pentose cycle to lactate production was estimated via analysis of lactate isotopomers. Interestingly, pyruvate carboxylase and pyruvate dehydrogenase flux ratios measured by glutamate isotopomers and the production of isotopomers of several metabolites showed that the metabolic processes described could not take place simultaneously in the same macrocompartments (cells). Results revealed a heterogeneous metabolism in an asynchronous cell population that may be interpreted on the basis of different metabolic phenotypes of subpopulations in relation to different cell cycle phases.     

Testosterone effects on avian basal metabolic rate and aerobic performance: facts and artefacts

We examined the effects of cage size and testosterone (T) levels on basal and peak metabolic rates (BMR and PMR, respectively) and on pectoral and leg muscle masses of male house sparrows (Passer domesticus). Birds were housed either in small birdcages or in flight aviaries for at least 2 weeks prior to the initial metabolic evaluations. They were then implanted with either empty or T-filled silastic capsules and remeasured 5-6 weeks later. Birds treated with single T implants achieved breeding levels (4-6 ng/mL) and one group given double implants reached 10 ng/mL. There was no effect of T on BMR or PMR in any group studied, but there was an effect of caging. Caged birds showed significant reductions in PMR over the course of captivity, whereas PMR in aviary-housed birds were indistinguishable from their free-living counterparts. Testosterone treatment significantly increased leg muscle mass in caged birds, but had no effect on muscle mass in aviary-housed sparrows. We conclude that testosterone has no direct effect on sparrow metabolic rate or muscle mass, but may interact with cage conditions to produce indirect changes to these variables.     

Testosterone effects on avian basal metabolic rate and aerobic performance: facts and artefacts.

We examined the effects of cage size and testosterone (T) levels on basal and peak metabolic rates (BMR and PMR, respectively) and on pectoral and leg muscle masses of male house sparrows (Passer domesticus). Birds were housed either in small birdcages or in flight aviaries for at least 2 weeks prior to the initial metabolic evaluations. They were then implanted with either empty or T-filled silastic capsules and remeasured 5-6 weeks later. Birds treated with single T implants achieved breeding levels (4-6 ng/mL) and one group given double implants reached 10 ng/mL. There was no effect of T on BMR or PMR in any group studied, but there was an effect of caging. Caged birds showed significant reductions in PMR over the course of captivity, whereas PMR in aviary-housed birds were indistinguishable from their free-living counterparts. Testosterone treatment significantly increased leg muscle mass in caged birds, but had no effect on muscle mass in aviary-housed sparrows. We conclude that testosterone has no direct effect on sparrow metabolic rate or muscle mass, but may interact with cage conditions to produce indirect changes to these variables.     

Ontogeny and nutritional status influence oxidative kinetics of nutrients and whole-animal bioenergetics in zebra finches, Taeniopygia guttata: new applications for (13)C breath testing

Rapidly growing animals or those that are recovering from nutritional stress may use exogenous nutrients differently from well fed adults. To test this possibility, we compared the rates of exogenous nutrient oxidation among fledgling, fasted adult, and refed adult zebra finches using a technique called breath testing, where animals are fed (13)C-labeled nutrients and (13)C in the exhaled breath is collected and quantified. In order to identify the possible mechanisms responsible for differences in oxidative kinetics of ingested nutrients, we also compared body mass (m(b)), organ mass, core body temperature (T(b)), and metabolic rate (MR). We found that fasted birds had lower T(b), relative liver and intestine masses, MR, and respiratory exchange ratios (RERs) than fed adults. Adult birds recovering from nutritional stress had much lower rates of exogenous nutrient oxidation than fed birds; this difference was particularly evident for fatty acids. Differences in oxidative kinetics were correlated with reduced RER, m(b), and liver mass, suggesting that previously fasted birds were using recently assimilated nutrients to replenish exhausted fuel stores. Rapidly growing fledglings oxidized exogenous nutrients as quickly as fed adults, despite their significantly lower m(b) and T(b). We suggest that fledglings had higher mass-specific rates of exogenous nutrient oxidation because they must compensate for the relatively low conversion efficiency of feather production and other lean tissue growth, which was not taking place in the adults. Although this study demonstrates that ontogeny and nutritional status influence the way that birds oxidize exogenous nutrients, it also underscores the likelihood that environmental and endogenous factors shape how other types of animals spend the nutrients they ingest.     

Assessment of age-related glucose oxidation rates of broiler chickens by using stable isotopes

During their relatively short commercial lifespan of six weeks, broiler chickens undergo very pronounced age- or body weight-related changes in metabolic rate and body composition. The present study was aimed to assess the age-related changes in glucose oxidation rate of broiler chickens by using 13C-labeled glucose. The methodology for this breath test needed to be established first. Broiler chickens aged from two to six weeks were placed in open-circuit respiration cells and received a single intubation of U-13C6-glucose, followed by breath sampling for 4 hours and mass spectrometric analysis of 13C: 12C ratio in the exhaled air. Simultaneously, CO2 concentration in the respiration cell air was continuously monitored in order to calculate the cumulative percentage dose recovery (CPDR). With respect to the methodology, an oral dose of 2 mg U-13C6-glucose per kg body weight while maintaining a CO2 in the concentration of 0.4 to 0.5% was considered to be optimal. The three-parameter Gompertz curve fitted the CPDR values very well. Pronounced age-related changes in exogenous glucose oxidation rates in rapidly growing meat-type chickens were assessed. Young broiler chickens spend only a relatively low percentage of ingested glucose for immediate oxidation. In contrast, broiler chickens approaching the age of maximal absolute growth rate oxidize a greater proportion of the recently ingested glucose relative to the non-oxidative disposal pathways. This shift in the exogenous partitioning is discussed in relation to age-dependent changes in glucose turnover, lipid oxidation and deposition and metabolic heat production.     

Phenotypic flexibility in passerine birds: Seasonal variation of aerobic enzyme activities in skeletal muscle

Improved winter cold tolerance is widespread among small passerines resident in cold climates and is generally associated with elevated summit metabolic rate (M_sum=maximum thermoregulatory metabolic rate) and improved shivering endurance with increased reliance on lipids as fuel. Elevated M_sum and improved cold tolerance may result from greater metabolic intensity, due to mass-specific increase in oxidative enzyme capacity, or increase in the masses of thermogenic tissues. To examine the mechanisms underlying winter increases in M_sum, we investigated seasonal changes in mass-specific and total activities of the key aerobic enzymes citrate synthase (CS) and β-hydroxyacyl CoA-dehydrogenase (HOAD) in pectoralis, supracoracoideus and mixed leg muscles of three resident passerine species, black-capped chickadee (Poecile atricapillus), house sparrow (Passer domesticus), and white-breasted nuthatch (Sitta carolinensis). Activities of CS were generally higher in winter than in summer muscles for chickadees and house sparrows, but not nuthatches. Mass-specific HOAD activity was significantly elevated in winter relative to summer in all muscles for chickadees, but did not vary significantly with season for sparrows or nuthatches, except for sparrow leg muscle. These results suggest that modulation of substrate flux and cellular aerobic capacity in muscle contribute to seasonal metabolic flexibility in some species and tissues, but such changes play varying roles among small passerines resident in cold climates.     

Traffic noise decreases nestlings’ metabolic rates in an urban exploiter

High levels of anthropogenic noise produced in urban areas are known to negatively affect wildlife. Although most research has been focused on the disturbances of communication systems, chronic noise exposure can also lead to physiological and behavioural changes that have strong consequences for fitness. For instance, behavioural changes mediated by anthropogenic noise (e.g. quality of parental care) may alter development and could influence nestling phenotype. We tested if nestling metabolism was influence by traffic noise in an urban exploiter, the house sparrow Passer domesticus. We experimentally exposed breeding house sparrows from a rural area to a playback of traffic noise and we examined the impacts of this experimental procedure on metabolic rates and morphology of nestlings. We did not find an effect of traffic noise on the morphology of nestlings. Surprisingly, we found that disturbed nestlings had overall lower metabolic rates and mass‐adjusted metabolic rates than undisturbed birds. Our results suggest a specific effect of noise exposure per se, rather than an indirect effect of anthropogenic noise through the quality of parental care. Both the proximate mechanisms and the ultimate consequences of such metabolic changes on nestlings remain unknown and deserve future experimental studies.     

Metabolic and ventilatory acclimatization to cold stress in house sparrows (Passer domesticus)

Passerines that overwinter in temperate climates undergo seasonal acclimatization that is characterized by metabolic adjustments that may include increased basal metabolic rate (BMR) and cold-induced summit metabolism (M(sum)) in winter relative to summer. Metabolic changes must be supported by equivalent changes in oxygen transport. While much is known about the morphology of the avian respiratory system, little is known about respiratory function under extreme cold stress. We examined seasonal variation in BMR, M(sum), and ventilation in seasonally acclimatized house sparrows from Wisconsin. BMR and M(sum) increased significantly in winter compared with summer. In winter, BMR increased 64%, and M(sum) increased 29% over summer values. The 64% increase in winter BMR is the highest recorded for birds. Metabolic expansibility (M(sum)/BMR) was 9.0 in summer and 6.9 in winter birds. The metabolic expansibility of 9.0 in summer is the highest yet recorded for birds. Ventilatory accommodation under helox cold stress was due to changes in breathing frequency (f), tidal volume, and oxygen extraction efficiency in both seasons. However, the only significant difference between summer and winter ventilation measures in helox cold stress was f. Mean f in helox cold stress for winter birds was 1.23 times summer values.     

An enzootic vector-borne virus is amplified at epizootic levels by an invasive avian host

Determining the effect of an invasive species on enzootic pathogen dynamics is critical for understanding both human epidemics and wildlife epizootics. Theoretical models suggest that when a naive species enters an established host–parasite system, the new host may either reduce (‘dilute’) or increase (‘spillback’) pathogen transmission to native hosts. There are few empirical data to evaluate these possibilities, especially for animal pathogens. Buggy Creek virus (BCRV) is an arthropod-borne alphavirus that is enzootically transmitted by the swallow bug (Oeciacus vicarius) to colonially nesting cliff swallows (Petrochelidon pyrrhonota). In western Nebraska, introduced house sparrows (Passer domesticus) invaded cliff swallow colonies approximately 40 years ago and were exposed to BCRV. We evaluated how the addition of house sparrows to this host–parasite system affected the prevalence and amplification of a bird-associated BCRV lineage. The infection prevalence in house sparrows was eight times that of cliff swallows. Nestling house sparrows in mixed-species colonies were significantly less likely to be infected than sparrows in single-species colonies. Infected house sparrows circulated BCRV at higher viraemia titres than cliff swallows. BCRV detected in bug vectors at a site was positively associated with virus prevalence in house sparrows but not with virus prevalence in cliff swallows. The addition of a highly susceptible invasive host species has led to perennial BCRV epizootics at cliff swallow colony sites. The native cliff swallow host confers a dilution advantage to invasive sparrow hosts in mixed colonies, while at the same sites house sparrows may increase the likelihood that swallows become infected.