Net Intake Research Articles

Use of Bioimpedance Spectroscopy for Postoperative Fluid Management in Patients Undergoing Cardiac Surgery with Cardiopulmonary Bypass

ObjectiveTo assess whether bioimpedance spectroscopy analysis (BIA) can be used as a potential tool to guide postoperative fluid management in patients who undergo cardiac surgery. DesignAn observational study. SettingA single, tertiary hospital. ParticipantsPatients who underwent cardiac surgery with cardiopulmonary bypass between June to November 2023 who were able to undergo BIA measurements. InterventionsNone. Measurements and Main ResultsCorrelations between BIA measurements of extracellular fluid (ECF) and total body water (TBW) volumes and daily changes in weight and 24-hour net intake and output (I/O) of fluids were assessed. Correlations between pre-discharge ECF volume as a percentage of TBW volume (ECF%TBW) and pre-discharge Pro-BNP (Pro-BNP) levels and readmissions were analyzed. Changes in daily ECF volume significantly correlated with daily weight changes (p<0.01) and 24-hr I/O (p<0.01). TBW volume significantly correlated with daily weight changes (p<0.01) and with 24-hr I/O (p=0.04). Daily weight changes did not correlate with 24-hr I/O (p=0.06). The patients with pre-discharge ECF%TBW(%) greater than or equal to 51 had significantly higher pre-discharge Pro-BNP than those with ECF%TBW(%) less than 51 (p<0.01). Patients who had heart failure revisits or admissions after discharge had a higher pre-discharge ECF%TBW(%) on index admission compared to patients that did not have heart failure readmissions (p=0.01). ConclusionsUtilization of BIA measurements in postoperative cardiac surgery patients may be a valuable tool to quantitatively determine fluid status to help guide fluid management in this patient population. Further studies validating the use of BIA for postoperative care in this population are warranted.

Sugar consumption induces the consummatory suppression of sugary ethanol: Differential effects of sugar restriction according to sex and age

Sweet foods activate the reward system that is essential in processing natural reinforcers. Maturation changes in this system during adolescence are linked to heightened impulsivity and risk-seeking behavior, including the use of drugs like ethanol. This usually starts with the consumption of sugary mixtures. However, the influence of sugar exposure on ethanol consumption remains inconclusive. The present research examines the effect of long-term sugar exposure on sugary ethanol (S-EtOH) preference and net intake, exploring the implications of sex, age, accessor restriction of sugar, and its effect during the transition into adulthood. Wistar rats of both sexes were given 24-hour access to a sugar solution for 21 days during adolescence or adulthood. Subsequently, four preference tests of S-EtOH vs. water were carried out every other day, with or without sugar access between each preference test. Our results demonstrate that continuous acute and long-term sugar access induces a consummatory suppression effect on S-EtOH intake, particularly in adult rats, irrespective of sex. This effect becomes more pronounced with more extended periods of exposure to sugar, leading to a higher prevalence of low consumers. Notably, when sugar access was restricted after high familiarization, the suppression effect in adolescent male rats was reduced. Under these conditions, the rats appeared to be more susceptible to developing a preference for S-EtOH consumption. Furthermore, our longitudinal observations reveal that sugar access or restriction conditions during the transition from adolescence to adulthood play a crucial role in shaping S-EtOH consumption patterns in adulthood.

Intake of corn stover botanical parts by growing and finishing beef steers.

Single-pass corn stover harvest is a method whereby combine harvester tailings consisting of cob, stalk, leaf, husk, and tassel fractions are collected and baled without coming into contact with soil. The objective was to feed beef steers diets that included a roughage component consisting of harvested corn residue in chopped form from conventional corn stover bales (CST) or single-pass bales (SPB) to assess intake selectivity of corn stover fractions and estimate net energy values of these corn stovers. Whole plant corn silage served as the control roughage in the control diet (CSIL). Steers (n = 90, 5 pens per treatment) were fed during Grow (84 d) and Finish (66 d) trials. Steers sorted through corn stover during both trials and consumed 52.5% of corn stover offered and 40% of cob offered. Intake of SPB cob was 2.6-fold and 3.3-fold greater than CST cob intake (P < 0.01) in Grow and Finish trials, respectively, indicating that when more cob was available, cattle consumed more. During the Grow trial, stover intake tended (P = 0.07) to be lower for SPB and diet dry matter intake (DMI) was less (P ≤ 0.05) for SPB, which may be due to the elevated cob intake by SPB steers. Across treatments, stover DMI was similar in the Grow (1.10 kg per steer per d) and Finish (1.11 kg per steer per d) trials. The proportion (65%) of Fines (<8 mm) consumed from the Grow diet (40% neutral detergent fiber, aNDF) was greater than the Finish diet (25% aNDF; 18% to 31%) and gleaning of concentrate feeds from orts seemed to be more extensive in the Grow diet. Steers consuming Finish diets containing SPB and CST had DMI that were 17% and 18%, respectively, greater (P ≤ 0.05) than CSIL, an indication of compensatory intake. The physical effectiveness factors for stovers fed in the Grow and Finish diets were 0.85 and 0.95, respectively. Estimates for net energy maintenance and net energy gain (NEg), respectively, using National Research Council methods from 2001 were as follows for consumed stovers: SPB (1.09 and 0.54 Mcal/kg) and CST (0.98 and 0.44 Mcal/kg) in the Grow trial, and SPB (0.96 and 0.42 Mcal/kg) and CST (0.95 and 0.40 Mcal/kg) in the Finish trial. Although SPB and CST differ in botanical fraction composition and net intakes of botanical fractions, their energetic contributions to steer performance were very similar. Steers fed the Finish diet (1.25 Mcal performance-adjusted NEg per kg) selected stover botanical components to achieve a diet composition of 25% aNDF.

Association of Fluid Overload with Escalation of Respiratory Support and Endotracheal Intubation in Acute Bronchiolitis Patients.

Fluid overload has been associated with increased oxygen requirement, prolonged duration of mechanical ventilation, and longer length of hospital stay in children hospitalized with pulmonary diseases. Critically ill infants with bronchiolitis admitted to the pediatric intensive care unit (PICU) also tend to develop fluid overload and there is limited information of its role on noninvasive respiratory support. Thus, our primary objective was to study the association of fluid overload in patients with bronchiolitis admitted to the PICU with respiratory support escalation (RSE) and need for endotracheal intubation (ETI). Infants ≤24 months of age with bronchiolitis and admitted to the PICU between 9/2009 and 6/2015 were retrospectively studied. Demographic variables, clinical characteristics including type of respiratory support and need for ETI were evaluated. Fluid overload as assessed by net fluid intake and output (net fluid balance), cumulative fluid balance (CFB) (mL/kg), and percentage fluid overload (FO%), was compared between patients requiring and not requiring RSE and among patients requiring ETI and not requiring ETI at 0 (PICU admission), 12, 24, 36, 48, 72, 96, and 120 hours. One-hundred sixty four of 283 patients with bronchiolitis admitted to the PICU qualified for our study. Thirty-four of 164 (21%) patients required escalation of respiratory support within 5 days of PICU admission and of these 34 patients, 11 patients required ETI. Univariate analysis by Kruskal-Wallis test of fluid overload as assessed by net fluid balance, CFB, and FO% between 34 patients requiring and 130 patients not requiring RSE and among 11 patients requiring ETI and 153 patients not requiring ETI, at 0, 12, 24, 36, 48, 72, 96 and 120 hours did not reveal any significant difference ( p >0.05) at any time interval. Multivariable logistic regression analysis revealed higher PRISM score (odds ratio [OR]: 4.95, 95% confidence interval [95% CI]: 1.79-13.66; p = 0.002), longer hours on high flow nasal cannula (OR: 4.86, 95% CI: 1.68-14.03; p = 0.003) and longer hours on noninvasive ventilation (OR: 11.16, 95% CI: 3.36-36.98; p < 0.001) were associated with RSE. Fluid overload as assessed by net fluid balance, CFB, and FO% was not associated with RSE or need for ETI in critically ill bronchiolitis patients admitted to the PICU. Further prospective studies involving larger number of patients with bronchiolitis are needed to corroborate our findings.

Strategic evaluation of limiting factors affecting algal growth – An approach to waste mitigation and carbon dioxide sequestration

This work outlines major critical physico-chemical parameters that play a key role in increasing the fixation of CO2 from coal-fired flue gas CO2 into green microalgae biomass. Nitrogen concentration, gas flow rate, initial medium pH, and incident light intensity were determined to be the most important process variables with significant impact on CO2 fixation. Therefore, NaNO3 (500–3000 mg L−1), pH (6.8–8.0), light (50–200 mol m−2 s−1) and aeration (0.1–1.0 vvm) were varied to assess the biological assimilation potential of CO2 from the flue gas. The parameters that resulted in maximal CO2 fixation from raw flue gas, resulting in a maximum biomass density of 3.1 g L−1, were NaNO3 = 1500 mg L−1, pH =7.2–7.5, incident light intensity = 133.33 mol m−2 s−1, and 0.5–0.75 vvm aeration without any cost-incurring flue gas pre-treatment step. The inductively coupled plasma-mass spectrometer (ICP-MS) was used to investigate heavy metals uptake from raw flue gas, and it was discovered that no net intake of trace metals had a significant influence on biomass production. The research lays the path for efficient large-scale microalgal cultivations for industrial uses, as well as bolstering the circular economy concept.

Nutritional Profiles of U.S. Adults With Suboptimal Dietary Creatine Intake

ObjectivesWe determined the prevalence of inadequate dietary intake of creatine and described nutritional profiles of individuals with low creatine intake in U.S. adults using data from the 2017–2018 National Health and Nutrition Examination Survey (NHANES) round. MethodsData for this study were obtained from the latest round of NHANES 2017–2018. Detailed dietary intake information from adult NHANES participants was obtained by dietary interview component through two 24-hour dietary recall interviews. To calculate creatine intake, we first identified meat-based protein foods using 8-digit USDA food codes organized in five database subgroups using dietary interview entry for individual foods. Next, we recorded the gram weight of each food/individual component containing meat-based protein, and calculated the net intake of meat-based protein for each respondent by merging all relevant food items on daily basis. Individual values for total grams of creatine consumed per day for each respondent were computed using the average amount of creatine (3.88 g/kg) across all sources of meat-based protein. A threshold for dietary intake of creatine was set at 1.00 gram per day, with respondents were classified into two subpopulations with the suboptimal intake of creatine (<1.00 g/day) or recommended intake (dietary creatine 3 1.00 g/day). ResultsAmong 4,004 NHANES adult participants that reported detailed dietary intake information, 2,611 (65.2%) were calculated to have dietary creatine intake below recommended levels of 1.00 g/day. The average daily creatine intake in this subpopulation was 0.52 ± 0.26 g (95% confidence interval, from 0.51 to 0.53). This was accompanied by a significantly lower dietary intake of meat-based protein, as compared to participants whose dietary creatine intake was equal to or above recommended levels (20.1 ± 10.2 g/day vs. 67.1 ± 30.4 g/day; P < 0.001). ConclusionsThe large-scale rate of suboptimal dietary creatine intake found in this cross-sectional study warrants additional research, and calls for immediate public health measures fostering creatine-rich foods in human nutrition. Funding SourcesNone.

Is dietary phosphatidylcholine essential for juvenile slipper lobster (Thenus australiensis)?

Phospholipids, especially phosphatidylcholine (PC), are considered essential nutrients for larval and juvenile stages of many decapod crustacean species due to low rates of endogenous biosynthesis and potential nutritional benefits in assisting lipid digestion and transport. This study was conducted to test the hypothesis that dietary PC is essential and would subsequently have beneficial effects on lipid utilisation and digestibility of fish oil triacylglycerol (TAG) in the slipper lobster, Thenus australiensis. Juvenile slipper lobsters were supplied six formulated experimental feeds with actual PC contents of 0.05, 0.48, 0.65, 0.98, 1.15 and 1.43% (dry matter) for 12 weeks. Manipulating dietary PC content had no effects on survival, growth, chemical composition, whole body or tissue lipid distribution, or apparent digestibility (AD) of gross energy (GE), total lipid (TL) or PC. Juvenile slipper lobsters appeared to possess fully developed and efficient mechanisms for GE, TAG and PC digestion (>95% AD). In vivo lipid class mass balance calculations demonstrated net intake of TL and TAG was considerably greater than was accumulated in the whole-body during growth. Thus, a significant proportion of dietary TL and TAG was utilised for energy and other metabolic processes. In contrast, particularly for low PL dietary treatments (≤ 0.5%), net gain of PC was greater than net intake, indicating a reliance on biosynthesis of PC. Thus, it is concluded that there is no or a very low requirement for dietary PC and thus may not be essential for the examined size class of juvenile T. australiensis when supplied adequate dietary PC biosynthetic precursors and other potentially related dietary nutrients. Further targeted research is recommended to verify if these findings are applicable to larval and early juvenile stages, and to enhance overall understanding of lipid nutritional requirements for T. australiensis.

Rationale to reduce calcium intake in adult patients with chronic kidney disease.

Calcium is an essential ion for the maintenance of normal bone health and physiologic functions. The extracellular and intracellular levels of calcium are maintained through hormonal regulation called homeostasis. Balance, the net intake minus excretion of calcium, is maintained by hormonal regulation of intestinal absorption and fecal/urinary excretion. Homeostasis and balance are disconnected in patients with chronic kidney disease (CKD). The purpose of this review is to understand how calcium homeostasis and balance are impaired in CKD. Two formal calcium balance studies have found that an oral intake of 800-1000 mg of calcium in adults with CKD leads to neutral calcium balance, whereas amounts greater than that lead to positive calcium balance. In patients with CKD, the main determinant of positive calcium balance is the intake and the lack of urinary calcium excretion. Calcium balance is different in patients with advanced CKD compared with patients without CKD. Thus, the oral intake of calcium in the form of diet and binders should not exceed 800-1000 mg/day to achieve neutral calcium balance in adult patients with CKD stages 3b/4.

Short-term prey field lability constrains individual specialisation in resource selection and foraging site fidelity in a marine predator.

Spatio-temporally stable prey distributions coupled with individual foraging site fidelity are predicted to favour individual resource specialisation. Conversely, predators coping with dynamic prey distributions should diversify their individual diet and/or shift foraging areas to increase net intake. We studied individual specialisation in Scopoli's shearwaters (Calonectris diomedea) from the highly dynamic Western Mediterranean, using daily prey distributions together with resource selection, site fidelity and trophic-level analyses. As hypothesised, we found dietary diversification, low foraging site fidelity and almost no individual specialisation in resource selection. Crucially, shearwaters switched daily foraging tactics, selecting areas with contrasting prey of varying trophic levels. Overall, information use and plastic resource selection of individuals with reduced short-term foraging site fidelity allow predators to overcome prey field lability. Our study is an essential step towards a better understanding of individual responses to enhanced environmental stochasticity driven by global changes, and of pathways favouring population persistence.

Effects of dietary fat on the saturated and monounsaturated fatty acid metabolism in growing pigs

ABSTRACTThe effect of dietary fats differing in fatty acid (FA) composition on the metabolism of saturated FA (SFA) and monounsaturated FA (MUFA) in growing pigs was investigated. The deposition of FA in the body and the fate of individual dietary FA were assessed after slaughter. Gilts with an initial body weight (BW) of 60 kg were used as experimental animals. Six pigs were slaughtered at 60 kg BW, while further 18 pigs received three isoenergetic and isonitrogen experimental diets containing linseed oil, rapeseed oil or beef tallow at 50 g/kg diet until they reached 105 kg (six pigs per group). The chemical composition and the content of FA in the whole body were determined and compared across groups. Regardless of dietary treatment, the whole body contained similar amounts of protein, fat and total FA. The total accumulation (percentage of net intake and de novo production) of SFA and MUFA was similar in all groups, but the processes of elongation and desaturation of SFA and MUFA depended upon the type of FA added to the diet. A high dietary content and intake of MUFA inhibits desaturation compared to SFA- and PUFA-rich diets, whereas a high SFA content and intake lowers elongation rate. The increasing net intake of total SFA and MUFA was associated with a lower total de novo production of these FA in the whole body of pigs.

Honeybee economics: optimisation of foraging in a variable world.

In honeybees fast and efficient exploitation of nectar and pollen sources is achieved by persistent endothermy throughout the foraging cycle, which means extremely high energy costs. The need for food promotes maximisation of the intake rate, and the high costs call for energetic optimisation. Experiments on how honeybees resolve this conflict have to consider that foraging takes place in a variable environment concerning microclimate and food quality and availability. Here we report, in simultaneous measurements of energy costs, gains, and intake rate and efficiency, how honeybee foragers manage this challenge in their highly variable environment. If possible, during unlimited sucrose flow, they follow an ‘investment-guided’ (‘time is honey’) economic strategy promising increased returns. They maximise net intake rate by investing both own heat production and solar heat to increase body temperature to a level which guarantees a high suction velocity. They switch to an ‘economizing’ (‘save the honey’) optimisation of energetic efficiency if the intake rate is restricted by the food source when an increased body temperature would not guarantee a high intake rate. With this flexible and graded change between economic strategies honeybees can do both maximise colony intake rate and optimise foraging efficiency in reaction to environmental variation.

Quantifying rapid spatial and temporal variations of CO2 fluxes from small, lowland freshwater ponds

Small ponds comprise a substantial portion of the total area of the Earth’s inland waters. They can be powerful carbon sinks or sources, potentially significant processors of organic carbon. Our understanding of their role is constrained by the absence of information regarding their CO2 fluxes (F CO2) and how these change with wet or dry phases and across distinct pond plant communities. We monitored the F CO2 from 26 neighbouring small ponds over a 2-week drying period in late summer in 2014. The mean F CO2 on day 1 (−641 ± 1490 mg m−2 day−1) represented a net intake across the site. As ponds dried they switched to becoming CO2 sources resulting in a net site emission of CO2 by day 12 (3792 ± 2755 mg m−2 day−1) although flux rates did not vary systematically between plant communities. Significant variability in the F CO2 was observed amongst adjacent ponds on individual sampling days, resulting in marked spatial heterogeneity in CO2 processing. This large degree of temporal and spatial heterogeneity across short time periods and small distances highlights the variability in the F CO2 from temporary systems, making it hard to generalize their role in carbon cycle models.

Site-specific flight speeds of nonbreeding Pacific dunlins as a measure of the quality of a foraging habitat

Many studies have investigated how foraging behavior such as prey choice varies with factors such as prey size or density. Models of such relationships can be applied reverse to translate easily observed foraging behaviors into assays of habitat attributes that cannot (easily) be measured directly. One such model analyzes the speed of a forager flying between patches, where it captures prey. Faster flight shortens the travel time and hence elevates the intake rate, but is increasingly expensive. The model shows that the net intake rate is maximized at the point at which the energetic cost of flight is equivalent to the net rate of intake. Easy-to-measure flight speeds can thus be translated into hard-to-measure foraging intake rates using established flight power relationships. We studied nonbreeding Pacific dunlins (Calidris alpina pacifica) at 4 intertidal sites on the Fraser River estuary, British Columbia, Canada. These sites differed sufficiently that we expected food availability and hence the attainable foraging rate to differ. We measured interpatch flight speeds of dunlins foraging along the tideline within each site. The measured ground speed, calculated airspeed, and the statistically derived zero-wind effect airspeed all differed significantly between sites, matching in rank order our expectation of habitat quality based on their physical differences. Intake rate estimates ranged from 4.10 W (best mudflat) to 3.48 W (poorest). We think it unlikely that we would have been able to find such small differences using direct measures of foraging intake.

Arachidonic Acid and Eicosapentaenoic Acid Metabolism in Juvenile Atlantic Salmon as Affected by Water Temperature.

Salmons raised in aquaculture farms around the world are increasingly subjected to sub-optimal environmental conditions, such as high water temperatures during summer seasons. Aerobic scope increases and lipid metabolism changes are known plasticity responses of fish for a better acclimation to high water temperature. The present study aimed at investigating the effect of high water temperature on the regulation of fatty acid metabolism in juvenile Atlantic salmon fed different dietary ARA/EPA ratios (arachidonic acid, 20:4n-6/ eicosapentaenoic acid, 20:5n-3), with particular focus on apparent in vivo enzyme activities and gene expression of lipid metabolism pathways. Three experimental diets were formulated to be identical, except for the ratio EPA/ARA, and fed to triplicate groups of Atlantic salmon (Salmo salar) kept either at 10°C or 20°C. Results showed that fatty acid metabolic utilisation, and likely also their dietary requirements for optimal performance, can be affected by changes in their relative levels and by environmental temperature in Atlantic salmon. Thus, the increase in temperature, independently from dietary treatment, had a significant effect on the β-oxidation of a fatty acid including EPA, as observed by the apparent in vivo enzyme activity and mRNA expression of pparα -transcription factor in lipid metabolism, including β-oxidation genes- and cpt1 -key enzyme responsible for the movement of LC-PUFA from the cytosol into the mitochondria for β-oxidation-, were both increased at the higher water temperature. An interesting interaction was observed in the transcription and in vivo enzyme activity of Δ5fad–time-limiting enzyme in the biosynthesis pathway of EPA and ARA. Such, at lower temperature, the highest mRNA expression and enzyme activity was recorded in fish with limited supply of dietary EPA, whereas at higher temperature these were recorded in fish with limited ARA supply. In consideration that fish at higher water temperature recorded a significantly increased feed intake, these results clearly suggested that at high, sub-optimal water temperature, fish metabolism attempted to increment its overall ARA status -the most bioactive LC-PUFA participating in the inflammatory response- by modulating the metabolic fate of dietary ARA (expressed as % of net intake), reducing its β-oxidation and favouring synthesis and deposition. This correlates also with results from other recent studies showing that both immune- and stress- responses in fish are up regulated in fish held at high temperatures. This is a novel and fundamental information that warrants industry and scientific attention, in consideration of the imminent increase in water temperatures, continuous expansion of aquaculture operations, resources utilisation in aquafeed and much needed seasonal/adaptive nutritional strategies.

SUN-PP009: Reduced Trypsin I (Prss1) Gene Expression Following Roux-En-Y Gastric Bypass Surgery: Potential Contribution to Reduced Net Protein Intake

SUN-PP009: Reduced Trypsin I (Prss1) Gene Expression Following Roux-En-Y Gastric Bypass Surgery: Potential Contribution to Reduced Net Protein Intake

Passive partner choice through exploitation barriers

Floral features that affect the efficiency with which pollinators can harvest their resources, or the profitability they obtain from them, affect the foraging decisions of pollinators. Foraging choices of pollinators, in turn, affect pollen flow: increases in flower constancy lead to more efficient pollen transport. It follows that exploitation barriers—flower traits that differentially affect net intake rates of potential visitors—will promote resource partitioning and enhance pollen export. In this paper we first generalise foraging models to show that exploitation barriers can lead to partial resource partitioning even when flowers are randomly distributed in space. Then we develop a model to study how the foraging rules of pollinators, pollen removal and pollen deposition, affect pollen flow. The model shows that resource partitioning, even incomplete, can substantially increase the efficiency of pollen flow. Finally, we use computer simulations to demonstrate that exploitation barriers promoting partial resource partitioning can evolve. Many of the flower traits associated with pollination syndromes have small but consistent effects on the efficiency with which different taxonomic groups exploit flowers, and can be considered exploitation barriers. Even if these barriers are not strong enough to promote strict specialisation, and may have little effect on the female component of fitness when pollinators are not a limiting resource, they are likely to be selected because they enhance the male component of fitness.

Renal control of calcium, phosphate, and magnesium homeostasis.

Calcium, phosphate, and magnesium are multivalent cations that are important for many biologic and cellular functions. The kidneys play a central role in the homeostasis of these ions. Gastrointestinal absorption is balanced by renal excretion. When body stores of these ions decline significantly, gastrointestinal absorption, bone resorption, and renal tubular reabsorption increase to normalize their levels. Renal regulation of these ions occurs through glomerular filtration and tubular reabsorption and/or secretion and is therefore an important determinant of plasma ion concentration. Under physiologic conditions, the whole body balance of calcium, phosphate, and magnesium is maintained by fine adjustments of urinary excretion to equal the net intake. This review discusses how calcium, phosphate, and magnesium are handled by the kidneys.

Phosphorus limitation and excess carbon in zooplankton

Organisms rely on a series of chemical reactions, which are constrained by the availability of key chemical elements, such as carbon (C), nitrogen (N), and phosphorus (P). Ecological stoichiometry provides a tool for analyzing how the balance of elements required by organisms affects food-web dynamics. Ecological stoichiometric theory suggests that the balance between supply and demand of elements is determined by the conversion efficiency from resources to organisms.Autotrophs and heterotrophs commonly face unequal access to and uptake of elements. The stoichiometric variability of autotrophs is based on their ability to maintain the balance of elements required for growth. This creates a challenge for their grazers. Phytoplankton can adjust their P content to ambient nutrient concentrations, while zooplankton cannot store excess nutrients. Ecological stoichiometric theory thus suggests that zooplankton have relatively fixed stoichiometry compared with phytoplankton.Nutrient limitation is common in aquatic systems. Stoichiometric imbalances between phytoplankton and zooplankton mean that zooplankton rarely find optimal food sources, and phytoplankton production is in excess. P availability potentially limits zooplankton growth, because of the high C:P ratio in phytoplankton relative to zooplankton demand. Based on the Liebig minimum principle, organisms are normally limited by a single nutrient, while everything else is in excess. Under P deficiency, excess C cannot be allocated to zooplankton somatic growth, and the net intake of C must balance the C:P ratio of zooplankton. Thus, when zooplankton encounter nutritionally imbalanced foods the elements in excess are released in order to maintain homeostasis. Excess C, released by zooplankton results in two biochemical challenges: (1) to sequester the limiting element and (2) to either store or dispose of the element in surplus.Zooplankton must resort to various physiological solutions to cope with these challenges. As a first option, zooplankton can reduce their C assimilation efficiency but maintain their P assimilation efficiency. Alternatively, after assimilation, excess C may be stored in C-rich compounds. Finally, assimilated excess C could also be disposed of through respiration or extracellular release. Excess C released by zooplankton reduces C transfer efficiency and sequestration in aquatic ecosystems.In aquatic ecosystems, C sequestration largely depends on the balance between uptake and demand for key nutrient elements. These feedback mechanisms have arisen only because organisms must obey stoichiometric rules at the cell and body levels, which greatly constrain the range of element values in ecosystems. Thus, the fate of C in ecosystems is determined by the absolute and relative demands for N and P of each organism. Limiting elements are utilized for growth and transferred in food chains with high efficiency, while non-limiting elements must be disposed of. Therefore, low C:P phytoplankton communities subject to high turnover rates and high productivity are selectively channeled into zooplankton. When zooplankton face high C:P foods, excess C is returned to the environment. Hence, nutrient-deficient phytoplankton constitute poor food, influencing the entire food web and adversely affecting secondary production at all levels.Excess C processed by zooplankton has far-reaching implications for ecosystem food-web functioning and C sequestration. Studies of the fate of excess C in zooplankton would increase the understanding of energy flow and material cycling in aquatic ecosystems. This paper reviews the reasons for P limitation and excess C in zooplankton, principal routes for the disposal of excess C, and the ecological effects of this. In addition, the paper aims to provide insight and a theoretical foundation for related studies in China.

Interspecific kleptoparasitism by Brown-headed Gulls (Chroicocephalus maculipennis) on two hosts with different foraging strategies: a comparative approach

Kleptoparasitism is a well known foraging strategy used opportunistically by many seabirds. Our study compares the strategies performed by a facultative kleptoparasite species, the Brown-hooded Gull (Chroicocephalus maculipennis), associated with two hosts with different foraging strategies, the American Oystercatcher (Haematopus palliatus) and Red-gartered Coot (Fulica armillata). In total, 97% of the prey items stolen from Oystercatchers were the clam Tagelus plebeius, and all prey items stolen from Coots were the crab Cyrtograpsus angulatus. The attack rate by Gulls (number of kleptoparasitic attacks per unit time) did not differ significantly between Oystercatchers and Coots, but the success rate of attacks (successful kleptoparasitic attacks as a proportion of total attacks) was greater for attacks on Coots than on Oystercatchers. The mean rate of feeding (number of stolen items ingested per minute) by Brown-hooded Gulls did not differ with host. Gulls strongly selected large prey when stealing food. The comparison of net intake (cost—benefit balance) for each kleptoparasite—host system showed that profitability was 3.5 times higher when kelptoparsitising Coots than when stealing from Oystercatchers. We suggest future work should study in more detail the costs and benefits for kleptoparasites with multiple hosts in similar systems elsewhere.

Gustatory, Trigeminal, and Olfactory Aspects of Nicotine Intake in Three Mouse Strains

Studies of nicotine consumption in rodents often intend to investigate nicotine's post-absorptive effects, yet little is known about the pre-absorptive sensory experience of nicotine drinking, including gustatory, trigeminal, and olfactory influences. We conditioned taste aversion (CTA) to nicotine in males of 3 inbred mouse strains: C57BL/6J, DBA/2J, and 129X1/SvJ by repeatedly pairing 150 μg/ml nicotine drinking with lithium chloride injections. Generalization to a variety of bitter, sour, sweet, salty, and irritant solutions and to nicotine odor was then examined. Nicotine CTA generalized to the bitter stimulus quinine hydrochloride and the chemosensory irritant spilanthol in all strains. It also showed strain specificity, generalizing to hydrogen peroxide (an activator of TRPA1) in C57BL/6J mice and to the olfactory cue of nicotine in DBA/2J mice. These behavioral assays demonstrate that the sensory properties of nicotine are complex and include multiple gustatory, irritant, and olfactory components. How these qualities combine at the level of perception remains to be assessed, but sensory factors clearly exert an important influence on nicotine ingestion and their contribution to net intake of nicotine should not be neglected in animal or human studies.