Mass-specific Basis Research Articles

CO2 methanation on Ni/Y2O3 Catalysts: The effects of preparation procedure and cerium oxide promotion

Present paper reports on the CO2 methanation (CME) performance of novel Ni catalysts supported on yttria, ceria, and ceria-doped yttria carriers. Catalysts were synthesized using incipient wetness impregnation and precursor nitrate co-decomposition. These systems outperformed on a mass-specific basis an industrial Ni/alumina benchmark catalyst. In addition, this work examines in details the impact of both the preparation procedure and the Ni-content on the CME activity both in terms of the reaction rate and the apparent activation energy. Our research demonstrates that Y2O3 is an effective catalytic support promoting stability and activity of the catalysts. CeO2–doping further improves activity, remarkably with little to no penalty to the thermal stability of the catalysts. Comparison of the performance of a conventional IWI-synthesized Ni-catalyst with a counterpart obtained via a co-decomposition route, demonstrated an advantage of the latter. Our findings suggest Ni-CeO2/Y2O3 prepared via co-decomposition may be advised as the active and stable catalysts for CME applications.

Species-specific traits predict whole-assemblage detritus processing by pond invertebrates.

Functional trait diversity determines if ecosystem processes are sensitive to shifts in species abundances or composition. For example, trait variation suggests detritivores process detritus at different rates and make different contributions to whole-assemblage processing, which could be sensitive to compositional shifts. Here, we used a series of microcosm experiments to quantify species-specific coarse and fine particulate organic matter (CPOM and FPOM) processing for ten larval caddisfly species and three non-caddisfly species in high-elevation wetlands. We then compared trait-based models including life history, dietary, and extrinsic traits to determine which traits explained interspecific variation in detritus processing. Finally, we compared processing by mixed caddisfly assemblages in microcosms and natural ponds to additive predictions based on species-specific processing to determine if single-species effects are additive in multi-species assemblages. We found considerable interspecific variation in biomass-specific CPOM (13-fold differences) and FPOM (8-fold differences) processing. Furthermore, on a mass-specific basis, amphipods, chironomids, and caddisflies processed similar amounts of detritus, suggesting non-shredder taxa could process more than previously recognized. Trait models including dietary percent detritus, development rate, body size, and wetland hydroperiod explained 81 and 57% of interspecific variation in CPOM and FPOM processing, respectively. Finally, species-specific additive predictions were strikingly similar to mixed-assemblage processing in microcosms and natural ponds, with the largest difference being a 15% overestimate. Thus, additivity of species-specific processing suggests single-species rates may be useful for understanding functional consequences of shifting assemblages, and a trait-based approach to predicting species-specific processing could support generating additive predictions of whole-assemblage processing.

Ocean Warming Leads to Increases in Aerobic Demand and Changes to Gene Expression in the Pinfish (Lagodon rhomboides)

Anthropogenic climate change is causing increases in the frequency, intensity, and duration of marine heatwaves (MHWs). These short-term warming events can last for days to weeks and can produce severe disruptions in marine ecosystems, as many aquatic species are poikilotherms that depend on the conditions of the environment for physiological processes. It is crucial to investigate the effects of these thermal fluctuations on species that play a disproportionate ecological role in marine ecosystems, such as the pinfish (Lagodon rhomboides) in the Gulf of Mexico and western Atlantic. In this study, we exposed pinfish to a simulated MHW in aquaria and examined the impacts of acute warming on two life stages (juvenile and adult), measuring oxygen consumption and gene expression in two relevant tissue types (liver and muscle). We saw significant increases in routine metabolic rate with increasing temperature in both juveniles (24.58 mgO2/kg/h increase per 1°C of warming) and adults (10.01 mgO2/kg/h increase per 1°C of warming). These results indicate that exposure to increased temperatures was more metabolically costly for juveniles than for adults, on a mass-specific basis. This was also observed in the molecular analyses, where the largest number of differentially expressed genes were observed in the juvenile pinfish. The analyses of gene expression suggest warming produces changes to immune function, cell proliferation, muscle contraction, nervous system function, and oxygen transport. These results indicate that this ecologically relevant species will be significantly impacted by projected increases in frequency and magnitude of MHWs, particularly in the juvenile stage.

Thermodynamic properties of microorganisms: determination and analysis of enthalpy, entropy, and Gibbs free energy of biomass, cells and colonies of 32 microorganism species

Thermodynamic analysis is an important part of chemical engineering. However, its application in biotechnology has been hampered by lack of data on thermodynamic properties of microorganism biomass. In this paper, a review was made of methods for estimation of thermodynamic properties of biomass, including standard enthalpy of combustion hC⁰, enthalpy of formation hf⁰, entropy s⁰, and Gibbs free energy of formation gf⁰. These parameters were calculated on molar and mass specific basis for 32 microorganism species, including 14 bacteria, 7 yeast and 11 algae species. It was found that hf⁰, s⁰, gf⁰ are, respectively, similar for all the analyzed species, due to the fact that all living organisms have a common ancestor and thus a similar chemical composition. Furthermore, all the analyzed microorganisms have negative hf⁰, originating from partial oxidation of all other elements by oxygen and nitrogen. A brief review was given of microorganism endogenous and growth metabolic rates. Finally, based on the determined thermodynamic properties, entropy of individual E. coli and Pseudomonas cells were determined and entropy of a Pseudomonas colony during its lifespan was calculated and analyzed. Three periods can be distinguished in the existence of a microorganism colony: (a) accumulation period when cell number, mass and entropy increase, (b) steady state period when they are approximately constant, and (c) decumulation period when they decrease.

Oxygen consumption of desert pupfish at ecologically relevant temperatures suggests a significant role for anaerobic metabolism.

Oxygen consumption is oftentimes used as a proxy for metabolic rate. However, pupfish acclimated to ecologically relevant temperatures may employ extended periods of anaerobism despite the availability of oxygen-a process we called paradoxical anaerobism. In this study, we evaluated data from pupfish exhibiting stable oxygen consumption. Routine oxygen consumption ([Formula: see text]) of a refuge population derived from Cyprinodon spp. acclimated to 28 and 33°C was evaluated at the ecologically relevant assay temperatures of between 25 and 38°C. Different interpretations of the data are available depending on normalization. For instance, [Formula: see text] of smaller fish, measured per fish, was remarkably stable over a wide range of assay temperatures and was not different between acclimation groups. However, when measured on a mass-specific basis, [Formula: see text] in these same smaller fish increases more predictably as temperature increased. [Formula: see text] of refuge fish and the closely related pupfish, C. nevadensis mionectes, measured near their respective acclimation temperatures, were essentially identical. However, [Formula: see text] of 28°C acclimated fish of both species, when measured at 34°C, was greater than that of the 33°C acclimated fish measured at 28°C. We suggest that this observed 'efficiency' may result from significant anaerobic metabolism use. Experiments investigating factorial aerobic scope ([Formula: see text]/[Formula: see text]) yielded values less than 1 in 21-36% of the 33°C acclimated fish. These values indicate a substantial contribution of anaerobic metabolism to energy utilization by these fish. However, muscle lactate levels are not elevated in exercising fish-a result that is consistent with paradoxical anaerobism use.

Can⿿t take the heat: Temperature-enhanced toxicity in the mayfly Isonychia bicolor exposed to the neonicotinoid insecticide imidacloprid

Neonicotinoid insecticide usage has increased globally in recent decades. Neonicotinoids, such as imidacloprid, are potent insect neurotoxicants that may pose a threat to non-target aquatic organisms, such as aquatic insects. In nature, insects typically live in thermally fluctuating conditions, which may significantly alter both contaminant exposures and affects. Here we investigate the relationship between temperature and time-to-effect for imidacloprid toxicity with the aquatic insect Isonychia bicolor, a lotic mayfly. Additionally, we examined the mechanisms driving temperature-enhanced toxicity including metabolic rate, imidacloprid uptake rate, and tissue bioconcentration. Experiments included acute toxicity tests utilizing sublethal endpoints and mortality, as well as respirometry and radiotracer assays with [14C] imidacloprid. Further, we conducted additional uptake experiments with a suite of aquatic invertebrates (including I. bicolor, Neocloeon triangulifer, Macaffertium modestum, Pteronarcys proteus, Acroneuria carolinensis, and Pleuroceridae sp) to confirm and contextualize our findings from initial experiments. The 96h EC50 (immobility) for I. bicolor at 15°C was 5.81μg/L which was approximately 3.2 fold lower than concentrations associated with 50% mortality. Assays examining the impact of temperature were conducted at 15, 18, 21, and 24°C and demonstrated that time-to-effect for sublethal impairment and immobility was significantly decreased with increasing temperature. Uptake experiments with [14C] imidacloprid revealed that initial uptake rates were significantly increased with increasing temperature for I. bicolor, as were oxygen consumption rates. Further, in the separate experiment with multiple species across temperatures 15, 20, and 25°C, we found that all the aquatic insects tested had significantly increased imidacloprid uptake with increasing temperatures, with N. triangulifer accumulating the most imidacloprid on a mass-specific basis. Our acute toxicity results highlight the importance of evaluating sublethal endpoints, as profound impairments of motor function were evident far before mortality. Further, we demonstrate that temperature is a powerful modulator of sublethal toxicity within a range of environmentally relevant temperatures, impacting both uptake rates and metabolic rates of I. bicolor. Finally, we show that temperature alters imidacloprid uptake across a range of species, highlighting the physiological variation present within aquatic invertebrate communities and the challenge associated with relying solely on surrogate species. Taken together, this research points to the need to consider the role of temperature in toxicity assessments.

Methanol oxidation at platinized copper particles prepared by galvanic replacement

Bimetallic Pt-Cu particles have been prepared by galvanic replacement of Cu precursor nanoparticles, upon the treatment of the latter with a chloro-platinate acidic solution. The resulting particles, typically a few tens of nm large, were supported on high surface area carbon ( Vulcan ® XC–72R, Cabot) and tested as electrodes. Surface electrochemistry in deaerated acid solutions was similar to that of pure Pt, indicating the existence of a Pt shell (hence the particles are denoted as Pt(Cu)). Pt(Cu)/C supported catalysts exhibit superior carbon monoxide and methanol oxidation activity with respect to their Pt/C analogues when compared on a per electroactive surface area basis, due to the modification of Pt activity by Cu residing in the particle core. However, as a result of large particle size and agglomeration phenomena, Pt(Cu)/C are still inferior to Pt/C when compared on a mass specific activity basis.

In situ target strength measurements of the scyphomedusa Chrysaora melanaster

Large medusae can dominate the pelagic biomass in marine environments, but their contribution to acoustic scattering remains poorly characterized. Here we report on in situ target strength (TS) measurements of Chrysaora melanaster, a dominant species of scyphomedusa in the North Pacific and Arctic, made with 38 and 120kHz split-beam echosounders in the Chukchi Sea. The average TS of a ∼25cm bell diameter C. melanaster is estimated to be −60.1dB re 1m2 at 38kHz and −60.5dB re 1m2 at 120kHz. There was no evident relationship between mean jellyfish size and TS, which is likely attributable to a combination of a small range in average jellyfish size at the sampling sites and geographic variability in TS corresponding to factors other than size and/or errors in determining the size of the jellyfish. The TS of C. melanaster is similar to that of a small swimbladdered fish, but on a mass-specific basis, the TS of these jellyfish is substantially lower. These measurements will aid in acoustic estimates of jellyfish abundance and in partitioning the relative contribution of jellyfish to acoustic backscatter in mixed species assemblages.

A study of the sodium‐glucose co‐transports of the avian kidney

Given animals of similar body mass, birds have been shown to have much higher plasma glucose concentrations than that of mammals. However, birds appear not to show the pathological symptoms associated with high plasma glucose levels as seen in mammals. As the glomerular filtration rates (on a mass specific basis) of birds and mammals are not significantly different and with higher plasma glucose levels, birds must have a larger filtered load of glucose. Despite this there is little or no detectable glucose in the ureteral urine of birds. This suggests that the mechanisms for glucose reabsorption by the bird kidney must be significantly up-regulated. In mammals glucose reabsorption is achieved through the sodium-glucose co-transport proteins (SGLTs) located in the apical cell membrane of the proximal renal tubule. The putative SGLTs within the avian kidney have not been isolated or characterized. Using SDS-PAGE and Western blots, we have been able to demonstrate the present of an immuno-reactive protein in the kidneys from mourning doves albeit not at the same intensity as that the rat kidney used as control.

Magnetic signature of different vegetation species in polluted environment

Detailed magnetic study on vegetation samples from several strongly polluted and clean sites in Bulgaria is carried out in order to evaluate suitability of different species as passive dust collectors in magnetometry. From each location, available species among lichens, mosses, poplar leaves, dandelion, needles have been sampled. Magnetic susceptibility calculated on mass-specific basis shows wide variability between diamagnetic signal up to 846 × 10−8 m3/kg. Lichens and mosses are found to be the species, showing magnetic signals with the strongest contrast between clean and polluted environment. The main magnetic phase is magnetite-like according to the results from thermomagnetic analysis of susceptibility on magnetic extracts. Scanning electron microscopy (SEM) microphotographs reveal the presence of abundant particulate matter on vegetation surface both with anthropogenic (spherules) and lithogenic origin. Magnetic grain size deduced by the ratio of saturation remanent magnetization (SIRM) and mass-specific magnetic susceptibility (χ) and coercivities (Bc and Bcr) suggest that different species accumulate preferentially small SD-like grains from pollution emissions. Contrasting relationship of the ratio of anhysteretic remanent magnetization (ARM) and χ for polluted vs clean sites deduced by needles and lichens may be related to transformation of the accumulated dust particles within lichens’ tissue. This finding indicates that the exact species used as biological dust collector is of importance when studying spatial grain size distribution of magnetic dust particles. Pilot study on polycyclic aromatic hydrocarbons (PAH) content and its relation to magnetic parameters shows good correspondence between high levels of PAHs and high SIRM values for locations affected by non-ferrous industrial production.

Responses of alkaline phosphatase activity to phosphorus stress in Daphnia magna

We examined how alkaline phosphatase (AP) activity within the bodies and in the materials released by the crustacean Daphnia magna responds to variable algal food phosphorus (P)-content. We found that Daphnia eating P-poor food (C:P approximately 700) had significantly higher AP activity in their bodies on a mass-specific basis compared with individuals eating P-rich food (C:P approximately 100). This dietary P effect on AP activity was not altered by Daphnia starvation but was partially related to differences in the P concentration of animal body homogenates. By contrast, poor P-nutrition of Daphnia lowered AP activity in released materials compared with that measured from their P-sufficient conspecifics. Moreover, AP activity in Daphnia release was lowest in animals consuming P-poor food for longer time periods. Our results support the hypothesis that AP activity increases inside P-limited Daphnia as a mechanism to increase P-acquisition and retention from ingested algae in these nutritionally stressed animals. The lower level of AP activity present in the water of P-deprived animals could reflect a change from largely free to membrane-bound AP isotypes in the digestive tracts of P-starved animals or a decrease in the shedding of membrane-anchored AP from their intestinal lining. These results supplement accumulating evidence that P-poor algal food reduces the dietary mineral P available to Daphnia. In addition, animal body AP activity measurements, with some refinement, may prove useful as an in situ indicator of P-stress in aquatic consumers.

Comparison of total tract digestibility, development of visceral organs and digestive tract of Mong cai and Yorkshire × Landrace piglets fed diets with different fibre sources

The aim of the study was to evaluate the effects of piglet age and dietary fibre source on the development of visceral organs and the gastrointestinal tract (GIT), and on growth performance and total tract apparent digestibility (TTAD) in local [pure-breed Mong cai (MC)] and exotic [Landrace x Yorkshire (LY)] piglets. The experimental diets contained different fibre sources: C (basal diet), RB (basal diet + rice bran), SPVM (basal diet + sweet potato vine meal) and CReM (basal diet + cassava residue meal). The neutral detergent fibre (NDF) content in diet C and the fibrous diets was 8.8% and 17.1%-17.7% respectively (dry matter basis). Collection of faecal samples to determine TTAD was carried out for five consecutive days before the experiment was finished (63 days). The piglets were killed at the age of 10 days (before being given the same solid feed), 30 days (weaning, 20 days after solid feed introduced) and 63 days (33 days after being given the different fibrous diets) when the length of intestinal segments, weight of organs (liver, heart, kidneys) and empty weight of the GIT (stomach, small intestine, caecum and colon + rectum) were measured. As the age of animals increased, the relative weight of organs and the length of intestines (expressed on a mass-specific basis) decreased (p < 0.05), and the weight of GIT increased (p < 0.001). The piglets fed fibrous diets had heavier GIT than those fed diet C with the highest values in CReM (p < 0.05). The colon + rectum length was not significantly different among C, RB and SPVM, but was shorter than in CReM (p < 0.05). Coefficient of total tract apparent digestibility (CTTAD) of nutrients in the fibrous diets was lower than in C (p < 0.01). Average daily gain (ADG) and feed conversion ratio (FCR) in C, RB and CReM were not different and were better than in SPVM (p < 0.01). There were no significant differences in the weights of organs between the two breeds at day 10, 30 and 63 (p > 0.05). The weight and length of GIT were not significantly different between the two breeds at day 10 and day 30, but were greater for MC at day 63. The caecum and colon + rectum at 10 and 30 days were longer in MC than in LY (p < 0.001). The relative development of GIT post-weaning was higher than pre-weaning, the difference being most apparent in MC. As a result at 63 days, MC had heavier visceral organs and GIT, and longer intestines on fibrous diets than LY (p < 0.05). The MC at 63 days had higher CTTAD of organic matter, gross energy, crude fibre and NDF (p < 0.001) and ether extract and crude protein (p < 0.05), but lower ADG and poorer FCR than LY (p < 0.001). It can be concluded that the GIT of the MC piglets developed more rapidly than LY when they were introduced to solid feed, and that the difference was more marked on the fibrous diets and after weaning, which resulted in higher total tract digestibility of nutrients in MC compared with LY. Cassava residue meal was better digested than RB and SPVM, and supported higher live weight gains.

Sodium uptake in different life stages of crustaceans: the water fleaDaphnia magnaStrauss

The concentration-dependent kinetics and main mechanisms of whole-body Na+ uptake were assessed in neonate and adult water flea Daphnia magna Strauss acclimated to moderately hard water (0.6 mmol l(-1) NaCl, 1.0 mmol l(-1) CaCO3 and 0.15 mmol l(-1) MgSO4.7H2O; pH 8.2). Whole-body Na+ uptake is independent of the presence of Cl(-) in the external medium and kinetic parameters are dependent on the life stage. Adults have a lower maximum capacity of Na+ transport on a mass-specific basis but a higher affinity for Na+ when compared to neonates. Based on pharmacological analyses, mechanisms involved in whole-body Na+ uptake differ according to the life stage considered. In neonates, a proton pump-coupled Na+ channel appears to play an important role in the whole-body Na+ uptake at the apical membrane. However, they do not appear to contribute to whole-body Na+ uptake in adults, where only the Na+ channel seems to be present, associated with the Na+/H+ exchanger. In both cases, carbonic anhydrase contributes by providing H+ for the transporters. At the basolateral membrane of the salt-transporting epithelia of neonates, Na+ is pumped from the cells to the extracellular fluid by a Na+, K+-ATPase and a Na+/Cl(-) exchanger whereas K+ and Cl(-) move through specific channels. In adults, a Na+/K+/2Cl(-) cotransporter replaces the Na+/Cl(-) exchanger. Differential sensitivity of neonates and adults to iono- and osmoregulatory toxicants, such as metals, are discussed with respect to differences in whole-body Na+ uptake kinetics, as well as in the mechanisms of Na+ transport involved in the whole-body Na+ uptake in the two life stages.

Modulation of proximal muscle function during level versusincline hopping in tammar wallabies (Macropus eugenii)

We examined the functional role of two major proximal leg extensor muscles of tammar wallabies during level and inclined hopping (12 degrees, 21.3% grade). Previous in vivo studies of hopping wallabies have revealed that, unlike certain avian bipeds, distal hindlimb muscles do not alter their force-length behavior to contribute positive work during incline hopping. This suggests that proximal muscles produce the increased mechanical work associated with moving up an incline. Based on relative size and architectural anatomy, we hypothesized that the biceps femoris (BF), primarily a hip extensor, and the vastus lateralis (VL), the main knee extensor, would exhibit changes in muscle strain and activation patterns consistent with increased work production during incline versus level hopping. Our results clearly support this hypothesis. The BF experienced similar activation patterns during level and incline hopping but net fascicle shortening increased (-0.5% for level hopping versus -4.2% for incline hopping) during stance when the muscle likely generated force. Unlike the BF, the VL experienced active net lengthening during stance, indicating that it absorbs energy during both level and incline hopping. However, during incline hopping, net lengthening was reduced (8.3% for level hopping versus 3.9% for incline hopping), suggesting that the amount of energy absorbed by the VL was reduced. Consequently, the changes in contractile behavior of these two muscles are consistent with a net production of work by the whole limb. A subsidiary aim of our study was to explore possible regional variation within the VL. Although there was slightly higher fascicle strain in the proximal VL compared with the distal VL, regional differences in strain were not significant, suggesting that the overall pattern of in vivo strain is fairly uniform throughout the muscle. Estimates of muscle work based on inverse dynamics calculations support the conclusion that both the BF and VL contribute to the additional work required for incline hopping. However, on a muscle mass-specific basis, these two muscles appear to contribute less than their share. This indicates that other hindlimb muscles, or possibly trunk and back muscles, must contribute substantial work during incline hopping.

Reproduction and embryonic diapause in a marsupial: Insights from captive female Honey possums, Tarsipes rostratus (Tarsipedidae)

The reproductive physiology of the polyoestrous Honey possum ( Tarsipes rostratus) is virtually unknown except that it shares with the kangaroos and wallabies the phenomenon of embryonic diapause. Its tiny size necessitates an alternate approach to study their reproductive cycle. We have accordingly utilised faecal steroid analysis. Baseline faecal cortisol levels in the Honey possum, at 4.1 ± 0.3 μg g −1, are approximately 100-fold those of other mammals and are associated with adrenal glands that, on a mass-specific basis, are almost 10 times larger than the adrenals of other mammalian, including marsupial, species. Histological examination of the adrenal glands revealed no abnormalities, however, but their hypertrophy and the peaks recorded in faecal levels following disturbance suggest that the Honey possum is vulnerable to chronic stressors in the captive situation. Mean faecal progestagens (124.4 ± 107.3 ng g −1) and oestradiol-17β (4.1 ± 1.1 ng g −1) in 4 non-pregnant females maintained long term were not different from those of 5 pregnant females (101.4 ± 61.0 ng g −1 and 4.3 ± 1.5 ng g −1, respectively) and, on analysis, revealed a cyclicity of 24 ± 1.2 days. We would predict from this evidence that the gestation period, in the absence of lactation, is approximately 23 days. Four of the pregnant females, monitored from July to November under conditions of 10:14 L:D photoperiod, showed a fall in levels of progestagens from 175.9 ± 10.8 ng g −1 in July and August to 30.9 ± 9.4 ng g −1 in October, while mean faecal levels of oestradiol-17β increased from 3.8 ± 0.4 ng g −1 in July to 5.7 ± 0.3 ng g −1 in October. September and October are months of peak reproductive activity in the wild and we suggest that these hormonal modulations may represent an entrained reproductive rhythm. Blastocysts appear to develop at varying rates, both within the one uterus, and between the two uteri of a single female. In addition, the time taken to reach the blastocyst stage may be longer than in any other marsupial studied to date. An association of the age of the pouch young with the stage reached by the developing blastocyst does not support the conclusion that blastocysts, once formed, grow slowly during lactation or diapause. Contrary to previous reports, we have documented what appears to be a lactational inhibition on blastocysts in diapause and have estimated the length of the ‘delayed’ reproductive cycle in two females as less than 2 weeks. Reactivation of blastocysts in Tarsipes has been shown to be stimulated by shortening day lengths after the summer solstice, a response similar to the annual breeding period of macropodid marsupials. Results from studying Honey possums in captive conditions suggest that the control of diapause in Tarsipes appears to be three-fold; lactational, photoperiodic and an entrained rhythm.

Life-history evolution under a production constraint

The recently formulated metabolic theory of ecology has profound implications for the evolution of life histories. Metabolic rate constrains the scaling of production with body mass, so that larger organisms have lower rates of production on a mass-specific basis than smaller ones. Here, we explore the implications of this constraint for life-history evolution. We show that for a range of very simple life histories, Darwinian fitness is equal to birth rate minus death rate. So, natural selection maximizes birth and production rates and minimizes death rates. This implies that decreased body size will generally be favored because it increases production, so long as mortality is unaffected. Alternatively, increased body size will be favored only if it decreases mortality or enhances reproductive success sufficiently to override the preexisting production constraint. Adaptations that may favor evolution of larger size include niche shifts that decrease mortality by escaping predation or that increase fecundity by exploiting new abundant food sources. These principles can be generalized to better understand the intimate relationship between the genetic currency of evolution and the metabolic currency of ecology.

Precombustion Chamber NOx Emission Contribution to an Industrial Natural Gas Engine

This work expands the knowledge base concerning the formation of oxides of nitrogen (NO x) in the precombustion chamber (PCC) of a four-stroke lean burn (4SLB) industrial gas engine. Two analysis methods were used to characterize specific exhaust constituent concentrations formed in the PCC. The first method extracted gas from the PCC and the overall engine exhaust to be analysed by the industry standard five gas rack (THC, NO x, O 2, CO 2, and CO) and a Fourier transform infrared spectrometer (FTIR) to quantify formaldehyde (CH2O), nitric oxide (NO), and nitrogen dioxide (NO2) concentrations. This paper focuses only on NO x. The engine was operated at the manufacturer's recommended conditions and at the engine's lean limit. A PCC air-fuel ratio (A/F) map was performed at each engine operating condition by varying the fuel supply pressure to the PCC. An analytical model was developed to estimate the mass flow between the PCC and main cylinder, and mass flow out of the PCC through a sample extraction apparatus. The model was applied at specific instances during the engine cycle to clarify raw emissions data obtained directly from a cylinde's PCC. The model was developed to determine the origin of the mass sampled from the PCC which, in turn, was used to correct the measured pollutant concentrations. The corrected concentrations allowed for a comparison between NO x, emissions formed in the PCC and the overall engine exhaust on a mass specific basis. PCC-formed NO x, were found to constitute ε10 per cent while operating at the manufacture's recommended conditions and upwards of ε75 per cent when at the lean limit. The second test method utilized the high-speed chemiluminescence capabilities of a Cambustion fNOX400 analyser to measure NO concentration in gas extracted from the PCC on a half crank angle basis. The intra-cycle NO data were recorded simultaneously with pressure traces from the PCC and main cylinder by a Hi-Techniques combustion analysis system. The high-speed data acquisition system provided qualitative information on both intra-cycle NO concentrations and cycle-to-cycle variations.

Digestibility and digestive organ development in indigenous and improved chickens and ducks fed diets with increasing inclusion levels of cassava leaf meal

Growing indigenous Cambodian chickens and ducks, and broiler chickens and White Pekin ducks were fed diets containing 0%, 7%, 14% and 20% of cassava leaf meal (CLM) to study the effects of CLM level on diet digestibility and gastrointestinal tract (GIT) and organ development. The coefficient of total tract apparent digestibility (CTTAD) of dry matter (DM) and intake of digestible DM decreased with increased dietary CLM. DM and digestible DM intake was higher for local breeds than for the corresponding exotic breeds, and higher for ducks than for chickens (p < 0.001), although there were no species or breed effects on CTTAD of DM (p > 0.05). Weight of small intestine, caeca, gizzard and pancreas, expressed as per kg body weight, increased with increased CLM in the diet (p < 0.001). There was no consistent diet effect on liver weight. Length of small intestine and caeca, expressed on a mass-specific basis, increased with dietary CLM content (p < 0.001). When expressed as per kg body weight small intestine, proventriculus, gizzard, pancreas and liver weights, and small intestine length, were higher in ducks than in chickens (p < 0.001), and were higher in the indigenous than in the improved breeds (p < 0.01), except for small intestine weights, which were similar. However chickens had higher weight of caeca (p < 0.001) and colon (p < 0.01) in absolute units and per kg body weight.

PYTHON'S HEARTY MEAL

Carnivorous reptiles exhibit a massive increase in oxygen demand following a meal to meet the increased metabolic demands associated with digestion. Inherently, this increase in oxygen demand places an extra demand on the cardiovascular system; the heart needs to work harder to transport more oxygen to the metabolically active digestive organs. Pythons appear to deal with this increased cardiac demand by substantially increasing the mass of their heart(cardiac hypertrophy) within two days of feeding. But just how do these snakes manage to pump up their heart's mass?Andersen and colleagues at the University of California, Irvine, were interested in determining the cause of the cardiac hypertrophy following feeding in the python (Python molurus). They wanted to know if the increase in heart mass was due to increased protein synthesis (i.e. formation of new heart muscle) or a water shift between extracellular and intracellular compartments, leading to increased fluid content of the heart tissues. In order to investigate this, Andersen and colleagues obtained ventricles from three groups of pythons: (1) fasting (these snakes had been fasted for 28 days); (2) digesting (these animals had digested a large meal 2 days earlier);and (3) post-digestive (these pythons had digested a large meal 28 days earlier). For each of these groups, the team measured ventricular dry/wet mass ratio, the ventricle's total protein, RNA and myofibrillar protein concentrations on a mass-specific basis, and the expression of messenger RNA for heavy-chain cardiac myosin, a contractile element of the heart.As they expected, the team observed a 40% increase in pythons' ventricular mass during digestion. They identified several clues that this hypertrophy was due to de novo protein synthesis and not increased fluid content of the heart. Primarily, the team found that the expression of messenger RNA for heavy-chain cardiac myosin increased significantly 2 days after feeding,indicating that digesting snakes synthesise myosin. Further, they discovered that the hearts' mass-specific total protein, RNA and myofibrillar protein concentrations did not change during digestion. In other words, as the pythons' hearts increased in mass after feeding, the ratio of protein to heart mass remained the same, indicating that new protein was being formed as the hearts expanded. This finding also ruled out increased water content as an explanation for the cardiac hypertrophy; if the increased heart mass was due to an increase in fluid content, these mass-specific protein concentrations would have decreased. Finally, they found that ventricular dry/wet mass ratio did not differ between fasted and fed snakes, providing further evidence that the larger hearts were not due to increased water content. The team concluded that the cardiac hypertrophy observed in digesting pythons is due to the synthesis of new contractile protein.Additionally, the team showed that the increase in heart mass during digestion was a fully reversible process. The mass of post-digestive snakes'hearts was similar to the mass of fasted snakes' hearts. Thus, following a meal, a python can rapidly increase its heart size by 40% and then decrease it again within 28 days. In comparison with mammalian species, in which comparable increments in ventricular size take weeks to develop, this cardiac remodelling occurs very rapidly. As such, Andersen and colleagues stress that this natural, rapidly occurring and fully reversible cardiac hypertrophy could provide a useful model for investigating the mechanisms that lead to cardiac remodelling and growth in other animals.

Milk intake and energy expenditure of free-ranging northern fur seal, Callorhinus ursinus, pups.

Milk ingested by mammalian offspring, coupled with offspring's utilization of this energetic investment, influences survival and growth. A number of studies have examined milk intake in otariids, but few have examined milk intake over the entire lactation period, and none has independently measured energy expenditure concurrent with milk intake. We concurrently examined milk intake, field metabolic rate (FMR), and body composition of 41 pups over the entire lactation interval in 1995 and 1996 on St. Paul Island, Alaska. One hundred two metabolic measurements were obtained with isotope dilution methods. Mean milk intake did not differ annually but increased with age and mass, ranging from 3,400+/-239 to 6,780+/-449 (+/-SE) mL per suckling bout. Milk energy consumption did not vary with age on a mass-specific basis. No differences were detected in milk volume consumed by male and female pups, either absolutely or on a mass-specific basis. Mass-specific FMR peaked during molting, was lowest postmolt, and did not vary by sex. Pups in 1995 had lower FMR than pups in 1996 and were also fatter. Mean milk energy utilized for maintenance metabolism decreased over time from 77% to 43% in 1995 and remained at 71% in 1996. Pup body mass was negatively correlated with the percentage of total body water and positively correlated with the percentage of total body lipid (TBL). Pups increased the percentage of TBL from 16% to 37%. Northern fur seal pups increased energy intake over lactation, while concurrent changes in body composition and pelage condition resulted in mass-specific metabolic savings after the molt.