Metabolic Water Production Research Articles

Fat storage and drought tolerance in a seasonally‐adapted primate: Implications for modeling the effects of animal responses to global climate change

AbstractGlobal warming is changing habitats and affecting biodiversity, and is expected to exacerbate aridification in many regions. Animals and plants in seasonally dry tropical forests often exhibit adaptations to cope with seasonal resource limitation. However, whether these adaptations will facilitate drought tolerance or increase drought vulnerability is unclear. Here, we combine long‐term individual‐based data on phenology, morphometrics, and demographics to investigate how drought impacts the food resources, health, reproduction, and behavior of a population of Verreaux's sifaka (Propithecus verreauxi), a critically endangered lemur inhabiting dry deciduous forests in Madagascar. Between December 2010 and May 2023, the population experienced 3 years of severe drought (2016, 2017, 2022). During green periods in severe drought, the availability of high‐quality sifaka foods (young leaves, fruit) was significantly reduced and fruit tree mortality increased. This reduced availability of fruit persisted in the year after a drought, despite typical rainfall. Yet surprisingly, we found no negative effects on body condition or commonly‐used metrics for reproductive success during drought years or years following a drought. Instead, sifaka exhibited significantly higher levels of subcutaneous body fat during severe droughts. We observed little change in sifaka behavior between drought and non‐drought periods. However, they were more likely to lick dew during severe drought, and spent significantly less time feeding on young and mature leaves. They also significantly increased their time feeding on flowers and fruits, despite the reduced abundance of fruit in the habitat. Together, our results suggest that increased consumption of water‐rich fruit and flowers during severe droughts could facilitate physiological mechanisms that help sifaka cope with water scarcity, including fructose‐mediated fat storage, metabolic water production, and water conservation. These results provide new insights into how critically endangered animals may respond to climate change, suggesting that behavioral and physiological adaptations to seasonal resource limitation may buffer some mammals from the effects of severe drought or other extreme weather events.

Long-term health outcomes associated with hydration status.

Body water balance is determined by fundamental homeostatic mechanisms that maintain stable volume, osmolality and the composition of extracellular and intracellular fluids. Water balance is maintained by multiple mechanisms that continuously match water losses through urine, the skin, the gastrointestinal tract and respiration with water gains achieved through drinking, eating and metabolic water production. Hydration status is determined by the state of the water balance. Underhydration occurs when a decrease in body water availability, due to high losses or low gains, stimulates adaptive responses within the water balance network that are aimed at decreasing losses and increasing gains. This stimulation is also accompanied by cardiovascular adjustments. Epidemiological and experimental studies have linked markers of low fluid intake and underhydration - such as increased plasma concentration of vasopressin and sodium, as well as elevated urine osmolality - with an increased risk of new-onset chronic diseases, accelerated aging and premature mortality, suggesting that persistent activation of adaptive responses may be detrimental to long-term health outcomes. The causative nature of these associations is currently being tested in interventional trials. Understanding of the physiological responses to underhydration may help to identify possible mechanisms that underlie potential adverse, long-term effects of underhydration and inform future research to develop preventative and treatment approaches to the optimization of hydration status.

Metabolic Water As a Route for Water Acquisition in Vertebrates Inhabiting Dehydrating Environments.

Vertebrates have expanded their habitats during evolution, which accompanies diversified routes for water acquisition. Water is acquired by oral intake and subsequent absorption by the intestine in terrestrial and marine animals which are subjected to constant dehydration, whereas most water is gained osmotically across body surfaces in freshwater animals. In addition, a significant amount of water, called metabolic water, is produced within the body by the oxidation of hydrogen in organic substrates. The importance of metabolic water production as a strategy for water acquisition has been well documented in desert animals, but its role has attracted little attention in marine animals which also live in a dehydrating environment. In this article, the author has attempted to reevaluate the role of metabolic water production in body fluid regulation in animals inhabiting desiccating environments. Because of the exceptional ability of their kidney, marine mammals are thought to typically gain water by drinking environmental seawater and excreting excess NaCl in the urine. On the other hand, it is established that marine teleosts drink seawater to enable intestinal water and ion absorption, and the excess NaCl is excreted by branchial ionocytes. In addition to the oral route, we suggest through experiments using eels that water production by lipid metabolism is an additional route for water acquisition when they encounter seawater. It seems that metabolic water production contributes to counteract dehydration before mechanisms for water regulation are reversed from excretion in freshwater to acquisition in seawater.

Sweat Production During Continuous and Interval Aerobic Exercise

INTRODUCTION:Aerobic exercise within the habitable volume of small spacecraft needed for space exploration beyond low Earth orbit is expected to challenge the capacity of environmental control systems. Moisture control is a primary concern. Crewmembers will contribute moisture to the cabin environment in the form of sweat while exercising. The effects of continuous aerobic exercise for improving and maintaining aerobic capacity is well characterized. Likewise, evidence suggests that high intensity interval exercise for shorter durations is also effective in building and maintaining aerobic capacity. METHODS: On separate days, measures of sweat and respiratory responses were made for continuous (30 min of steady state exercise at ∼75% of aerobic capacity) and two interval (4 × 4 min, 8 × 30 s) exercise protocols. RESULTS: We observed that the 4-min and 30-s interval protocols produce 16% and 66% less metabolic water loss vs. the continuous exercise protocol, respectively. These responses were highly correlated with the amount of work performed (R2 = 0.81) and the amount of energy expenditure (R2 = 0.83) during exercise. DISCUSSION: These results suggest that interval exercise may be a useful alternative to continuous aerobic exercise when metabolic water production is an environmental concern. The results may inform the choices of aerobic exercise countermeasure protocols for use in deep space exploration. Ryder JW, Crowell JB, Song HJ, Ewert M. Sweat production during continuous and interval aerobic exercise. Aerosp Med Hum Perform. 2023; 94(8):623–628.

A multi-isotope approach reveals seasonal variation in the reliance on marine resources, production of metabolic water, and ingestion of seawater by two species of coastal passerine to maintain water balance

Tracing how free-ranging organisms interact with their environment to maintain water balance is a difficult topic to study for logistical and methodological reasons. We use a novel combination of triple-oxygen stable isotope analyses of water extracted from plasma (δ16O, δ17O, δ18O) and bulk tissue carbon (δ13C) and nitrogen (δ15N) isotopes of feathers and blood to estimate the proportional contribution of marine resources, seawater, and metabolic water used by two species of unique songbirds (genus Cinclodes) to maintain their water balance in a seasonal coastal environment. We also assessed the physiological adjustments that these birds use to maintain their water balance. In agreement with previous work on these species, δ13C and δ15N data show that the coastal resident and invertivore C. nigrofumosus consumes a diet rich in marine resources, while the diet of migratory C. oustaleti shifts seasonally between marine (winter) to freshwater aquatic resources (summer). Triple-oxygen isotope analysis (Δ17O) of blood plasma, basal metabolic rate (BMR), and total evaporative water loss (TEWL) revealed that ~25% of the body water pool of both species originated from metabolic water, while the rest originated from a mix of seawater and fresh water. Δ17O measurements suggest that the contribution of metabolic water tends to increase in summer in C. nigrofumosus, which is coupled with a significant increase in BMR and TEWL. The two species had similar BMR and TEWL during the austral winter when they occur sympatrically in coastal environments. We also found a positive and significant association between the use of marine resources as measured by δ13C and δ15N values and the estimated δ18O values of ingested (pre-formed) water in both species, which indicates that Cinclodes do not directly drink seawater but rather passively ingest when consuming marine invertebrates. Finally, results obtained from physiological parameters and the isotope-based estimates of marine (food and water) resource use are consistent, supporting the use of the triple-oxygen isotopes to quantify the contribution of water sources to the total water balance of free-ranging birds.

Comparison of water balance among healthy young and old adults and handicapped adults.

The body's water balance is changed by food and beverage intake, metabolism, and excretion. In this study, we performed a cross-sectional study that investigated the changes of water intake and water output in healthy Japanese young and elderly people and handicapped adults. Water balance was assessed by water intake from foods and beverages, metabolic water production, non-renal water losses (NRWL), and urine volume. Most of the parameters did not change with aging in healthy adults. Estimated total water intake (ml/kg/day) increased with aging. In the healthy men, healthy women, and handicapped adults, daily water intake (median [interquartile range]) accounted for 49.4 (41.4-59.9) ml/kg, 42.9 (38.7-51.8) ml/kg, and 50.9 (43.8-74.0) ml/kg, respectively. Water loss from the kidney accounted for 19.2 (16.2-29.2) ml/kg, 22.0 (16.2-26.6) ml/kg, and 27.5 (22.7-47.2) ml/kg, respectively. NRWL accounted for 26.6 (18.5-35.2) ml/kg, 22.4 (16.2-28.8) ml/kg, and 23.5 (19.8-28.5) ml/kg, respectively. Our findings suggest that a daily total water intake of more than 50-55 ml/kg is required to prevent dehydration in healthy and handicapped adults. J. Med. Invest. 70 : 195-199, February, 2023.

Fluid Overload and Tissue Sodium Accumulation as Main Drivers of Protein Energy Malnutrition in Dialysis Patients.

Protein energy malnutrition is recognized as a leading cause of morbidity and mortality in dialysis patients. Protein-energy-wasting process is observed in about 45% of the dialysis population using common biomarkers worldwide. Although several factors are implicated in protein energy wasting, inflammation and oxidative stress mechanisms play a central role in this pathogenic process. In this in-depth review, we analyzed the implication of sodium and water accumulation, as well as the role of fluid overload and fluid management, as major contributors to protein-energy-wasting process. Fluid overload and fluid depletion mimic a tide up and down phenomenon that contributes to inducing hypercatabolism and stimulates oxidation phosphorylation mechanisms at the cellular level in particular muscles. This endogenous metabolic water production may contribute to hyponatremia. In addition, salt tissue accumulation likely contributes to hypercatabolic state through locally inflammatory and immune-mediated mechanisms but also contributes to the perturbation of hormone receptors (i.e., insulin or growth hormone resistance). It is time to act more precisely on sodium and fluid imbalance to mitigate both nutritional and cardiovascular risks. Personalized management of sodium and fluid, using available tools including sodium management tool, has the potential to more adequately restore sodium and water homeostasis and to improve nutritional status and outcomes of dialysis patients.

High-fat diet changes the behavioural and hormonal responses to water deprivation in male Wistar rats.

What is the central question of this study? What is the effect of an obesogenic diet on the control of hydromineral balance in rats? What is the main finding and its importance? The results showed that, when dehydrated, rats fed a high-fat diet drink less water than their control-diet-fed counterparts. Changes in aquaporin-7 and peroxisome proliferator-activated receptor α expression in the white adipose tissue might be involved. High-fat diet (HFD) increases fat accumulation, glycaemia and blood triglycerides and is used as a model to study obesity. Besides the metabolic changes, obesity likely affects water intake. We assessed the effects of HFD on behavioural and hormonal responses to water deprivation. Additionally, we measured if the adipose tissue is differentially affected by water deprivation in control and HFD-fed rats. HFD rats showed a decreased basal water intake when compared to control-fed rats. When subjected to 48h of water deprivation, as expected, both control and HFD rats drank more water than the hydrated rats. However, the increase in water intake was lessened in HFD dehydrated rats. Similarly, the increase in haematocrit in dehydrated rats was less pronounced in HFD dehydrated rats. These results suggest that HFD diminishes drinking behaviour. White adipose tissue weight, glycaemia and plasma glycerol concentration were increased in HFD rats; however, after 48h of water deprivation, these parameters were significantly decreased in dehydrated HFD rats, when compared to controls. The increase in adipose tissue caused by HFD may mitigate the effects of dehydration, possibly through the increased production of metabolic water caused by lipolysis in the adipocytes. Oxytocin possibly mediates the lipolytic response, since both its secretion and receptor expression are affected by dehydration in both control and HFD rats, which suggests that oxytocin signalling is maintained in these conditions. Changes in mediators of lipolysis, such as aquaporin-7 and peroxisome proliferator-activated receptor α, might contribute to the different effects observed in control and HFD rats.

Sex And Habitual Water Intake Are Related To Dimensions Of Mood

Water intake has previously been linked to dimensions of mood and other cognitive performance. However, it is yet to be determined if the relationships are solely because of changes in water intake (i.e., moving from high to low-volume consumption) or if they can be linked to habitual intake. Furthermore, sex differences related to the effect of water on mood have yet to be outlined. PURPOSE: To assess for differences in mood-dimensions across fluid volume demarcations and biological sex using objective measures of habitual water intake. METHODS: 51 women (42 ± 14y, 164 ± 6 cm, 72.0 ± 16.6 kg) and 49 men (40 ± 13 y, 177 ± 7 cm, 81.5 ± 16.0 kg) took part in the current study over 8 days. Participants consumed 0.05 g⸱kgLBM-1 of deuterium oxide (2H2O) at baseline. Then, 2H2O urine enrichment was measured 1 and 7 days after to determine total body water turnover (WTO) by dilution method. Participants simultaneously completed food diaries which were used to calculate metabolic water production given participant weight stability. Total water intake (TWI) was calculated as WTO-metabolic water production. The profile of mood state survey (POMS) and a visual analog scale to measure alertness were completed on the second day of observation. Data were dichotomized by sex and divided into HIGH (4.5 ± 1.4, 4.7 ± 1.1 L⸱d-1), MOD (2.9 ± 0.2, 3.3 ± 0.2 L⸱d-1), and LOW (2.2 ± 0.2, 2.7 ± 0.3 L⸱d-1) TWI tertiles, for women and men, respectively. RESULTS: Alertness and Vigor were significantly greater within women in HIGH versus MOD and LOW (all P ≤ 0.027), while Depression was lower in HIGH compared to LOW (P = 0.015). There were no significant differences in any mood-dimensions between any male TWI groups (all P ≥ 0.124). After controlling for macronutrient intake and physical activity, follow-up regression modeling in women, identified that the addition of TWI produced a significant change in the F score of the models for Depression, Anxiety, Vigor, and Total Mood Disturbance (all P ≤ 0.043). CONCLUSION: Within this sample, increased habitual water consumption was related to more favorable dimensions of mood in women, but not men. The conflicting results between sexes may be because of a larger TWI range in women relative to lean body mass and/or differences in fluid handling as evidenced by prior reporting on the divergence of urine concentrations between sexes.

Total water intake guidelines are sufficient for optimal hydration in United States adults.

Recent studies suggest that 24-h urine osmolality (UOsm) for optimal water intake should be maintained < 500mmol·kg-1. The purpose of this study was to determine the total water intake (TWI) requirement for healthy adults to maintain optimal hydration as indicated by 24-h urine osmolality < 500mmol·kg-1. Twenty-four-hour UOsm was assessed in 49 men and 50 women residing in the United States (age: 41 ± 14 y, body mass index: 26.3 ± 5.2kg·m-2). TWI was assessed from 7-day water turnover, using a dilution of deuterium oxide, corrected for metabolic water production. The diagnostic accuracy of TWI to identify UOsm < 500mmol·kg-1 was evaluated using receiver operating characteristic (ROC) analysis in men and women separately. Twenty-four-hour UOsm was 482 ± 229 and 346 ± 182mmol·kg-1 and TWI was 3.57 ± 1.10L·d-1 and 3.20 ± 1.27L·d-1 in men and women, respectively. ROC analysis for TWI detecting 24-h UOsm < 500mmol·kg-1 in men yielded an area under the curve (AUC) of 77.4% with sensitivity, specificity, and threshold values of 83.3%, 64.5%, and 3.39L·d-1, respectively. The AUC was 82.4% in women with sensitivity, specificity, and threshold values of 85.7%, 72.1%, and 2.61L·d-1. Considering threshold values in men and women of 3.4L·d-1 and 2.6L·d-1, respectively, maintaining TWI in line with National Academy of Medicine guidelines of 3.7L·d-1 in men and 2.7L·d-1 in women should be sufficient for most individuals in the United States to maintain 24-h UOsm < 500mmol·kg-1.

Relative Water Economy Is a Useful Index of Aridity Tolerance for Australian Poephiline Finches

We evaluate if the iconic Australian Zebra Finch (Taeniopygia guttata) has a unique physiology or if its metabolic, thermal and hygric physiology are similar to other Australian poephiline finches, by comparing it with three other species, the arid-habitat Painted Finch (Emblema pictum) and the mesic-habitat Double-barred (Taeniopygia bichenovii) and Red-browed (Neochmia temporalis) Finches. All physiological variables responded to ambient temperature as expected. There were no species differences for any of the standard physiological variables, consistent with the hypotheses that birds are pre-adapted to arid habitats, the recent development of Australian deserts has limited opportunity for physiological adaptation, and all four species share similar behavioural and ecological traits. Nevertheless, the ambient temperature where metabolic water production equals evaporative water loss (point of relative water economy) was highest for the Zebra (19.1 °C), lower for Double-barred (16.4 °C) and Painted (15.2 °C) and lowest for Red-Browed (4.1 °C) Finches, corresponding with their general patterns of habitat aridity. The point of relative water economy may be a sensitive index for assessing a species’ tolerance of aridity because it integrates individual physiological variables. We conclude that the Zebra Finch is not a physiological outlier amongst Australian finches, but is at the end of a continuum of aridity tolerance for the four study species.

Lean Mass Dynamics in Hibernating Bats and Implications for Energy and Water Budgets.

AbstractHibernation requires balancing energy and water demands over several months. Many studies have noted the importance of fat for hibernation energy budgets, but protein catabolism in hibernation has received less attention, and whole-animal changes in lean mass have not previously been considered. We used quantitative magnetic resonance body composition analysis to measure deposition of fat and lean mass of cave myotis (Myotis velifer) during the prehibernation period and decreases in fat and lean mass of Townsend's big-eared bats (Corynorhinus townsendii) during hibernation. For cave myotis, lean mass represented 25% and 38% (female and male, respectively) of prehibernation mass gain. In hibernating Townsend's big-eared bats, lean mass decrease was similar for females and males. We used values for Townsend's big-eared bats to explore the functional implications of lean mass change for water and energy budgets. Lean mass accounted for a substantial proportion of mass change during hibernation (female: 18%, male: 35%), and although not accounting for a large proportion of the energy budget (female: 3%, male: 7%), lean mass catabolism represented an important contribution to water production (female: 14%, male: 29%). Although most mammals cannot rely on protein catabolism for metabolic water production because of the water cost of excreting urea, we propose a variation of the protein-for-water strategy whereby hibernators could temporally compartmentalize the benefits of protein catabolism to periods of torpor and the water cost to periodic arousals when free drinking water is typically available. Combined, our analyses demonstrate the importance of considering changes in lean mass during hibernation.

Integrative Physiological Responses to Acute Dehydration in the Rufous-Collared Sparrow: Metabolic, Enzymatic, and Oxidative Traits

Predictions indicate that birds worldwide will be affected by global warming and extreme climatic events which is especially relevant for passerines because the diurnal habits, small body size, and high mass-adjusted metabolic rates of this group make it particularly susceptible to increases in temperature and aridity. Some bird species respond to conditions that stress osmoregulation by increasing their rates of energy expenditure, nevertheless, the effect of dehydration on metabolic rates in birds has produced contrasting results. It also remains unknown whether hydration state may cause shifts in tissue-specific metabolic rates or modify tissue oxidative status. We used the rufous-collared sparrow (Zonotrichia capensis), to experimentally test the effect of dehydration on metabolic enzymes in erythrocytes, tissue oxidative status, basal metabolic rate (BMR), and total evaporative water loss. We found a significant increase in mass-adjusted BMR in water restricted (WR) birds compared to control birds (CT). Activity of cytochrome-c-oxidase (COX) in red blood cells (RBCs) was also significantly higher in the WR group relative to the CT group and this activity was positively correlated with mass-adjusted BMR. We found a moderate effect of water restriction on membrane damage of skeletal muscle. In a second set of individuals subjected to the same experimental conditions, lean mass and total water were tightly correlated and decreased by 10 and 12%, respectively, in birds in the WR group relative to the CT group. Decreases in total water and lean mass leads to an increase in mass-adjusted BMR in WR Z. capensis, suggesting that birds may simultaneously increase protein catabolism and production of metabolic water through oxidation. The significant positive relationship between BMR and COX in RBCs is a finding that requires additional research to determine whether erythrocyte metabolism is affected by dehydration per se and or it more generally reflects rates of energy expenditure in birds.

Multiple energy sources and metabolic strategies sustain microbial diversity in Antarctic desert soils

Numerous diverse microorganisms reside in the cold desert soils of continental Antarctica, though we lack a holistic understanding of the metabolic processes that sustain them. Here, we profile the composition, capabilities, and activities of the microbial communities in 16 physicochemically diverse mountainous and glacial soils. We assembled 451 metagenome-assembled genomes from 18 microbial phyla and inferred through Bayesian divergence analysis that the dominant lineages present are likely native to Antarctica. In support of earlier findings, metagenomic analysis revealed that the most abundant and prevalent microorganisms are metabolically versatile aerobes that use atmospheric hydrogen to support aerobic respiration and sometimes carbon fixation. Surprisingly, however, hydrogen oxidation in this region was catalyzed primarily by a phylogenetically and structurally distinct enzyme, the group 1l [NiFe]-hydrogenase, encoded by nine bacterial phyla. Through gas chromatography, we provide evidence that both Antarctic soil communities and an axenic Bacteroidota isolate (Hymenobacter roseosalivarius) oxidize atmospheric hydrogen using this enzyme. Based on ex situ rates at environmentally representative temperatures, hydrogen oxidation is theoretically sufficient for soil communities to meet energy requirements and, through metabolic water production, sustain hydration. Diverse carbon monoxide oxidizers and abundant methanotrophs were also active in the soils. We also recovered genomes of microorganisms capable of oxidizing edaphic inorganic nitrogen, sulfur, and iron compounds and harvesting solar energy via microbial rhodopsins and conventional photosystems. Obligately symbiotic bacteria, including Patescibacteria, Chlamydiae, and predatory Bdellovibrionota, were also present. We conclude that microbial diversity in Antarctic soils reflects the coexistence of metabolically flexible mixotrophs with metabolically constrained specialists.

Validity and Reliability of a Water Frequency Questionnaire to Estimate Daily Total Water Intake in Adults.

The purpose of this investigation was to assess the validity and reliability of a seven-day water frequency questionnaire (TWI-FQ) to estimate daily total water intake (TWI) in comparison to a water turnover objective reference value via deuterium oxide (D2O). Data collection occurred over 3 weeks, with a wash-out period during week two. Healthy adults (n = 98; 52% female; 41 ± 14 y; BMI, 26.4 ± 5.5 kg·m−2) retrospectively self-reported consumption frequencies of 17 liquids and 35 foods with specified volumes/amounts for weeks one and three via TWI-FQ. Standard water content values were utilized to determine the volume of water consumed from each liquid and food for calculation of mean daily TWI for each week. Diet records were completed daily during week two to estimate metabolic water production. To assess validity of the TWI-FQ, participants consumed D2O at the start of each week and provided urine samples immediately before ingestion, the following day, and at the end of the week to calculate water turnover. Metabolic water was subtracted from water turnover to estimate TWI. TWI-FQ validity was assessed via Bland-Altman plot for multiple observations. Reliability was assessed via intraclass correlation and Pearson's correlation between weeks. TWI-FQ significantly underestimated D2O TWI by −350 ± 1,431 mL·d−1 (95% confidence interval (CI): −551, −149 mL·d−1). TWI-FQ TWI was significantly correlated (r = 0.707, P <0.01) and not different (198 ± 1,180 mL·d−1, 95% CI: −38, 435 mL·d−1) between weeks. TWI-FQ intraclass correlation = 0.706 was significant [95% CI: 0.591, 0.793; F(97, 98) = 5.799], indicating moderate test-retest reliability. While this tool would not be suitable for individual TWI assessment, the magnitude of bias may be acceptable for assessment at the sample-level.

Thermoregulatory Tactics and Water Balance of Centris caesalpiniae Males in Flight

It is advantageous for flying insects to be functional across a range of temperatures when competing for mates; breadth of performance can arise from broad tolerance or thermoregulation. Tactics of flying insects typically include moving hot hemolymph from the thorax to cooler body segments, evaporative water loss, and changes in metabolic heat production. For dimorphic Centris caesalpiniae male bees, the large morphs dig for females at ground-level, flying infrequently, whereas the small morph hovers and flies. At a mate-aggregation site, air temperature varied from 17 ºC to 37 ºC across and within days; operative temperatures of metanders reached 50 ºC on the ground when mating activity ceased, suggesting that high temperatures and radiation constrain the mating period, and that C. caesalpiniae's upper thermal tolerance is high, but not exceptional. These bees exhibited modest thermoregulation of thorax and head temperatures, with segment temperatures increasing 0.5-0.6 ºC per ºC air temperature both on the ground and in flight. During flight, evaporative water loss and heat movement to the abdomen contributed to thermoregulation. On the ground, bees moved hemolymph to the head. These results suggest bees thermoregulate the thorax to improve flight performance. Metabolic water production was about half of water loss rates and metanders lose about 17% of their body water per hour during flight. No one has observed metanders feeding or drinking, and several hours of flight would presumably cause a lethal loss of body water. While we currently lack information on the duration of activity of individuals, it is possible that thermoregulatory water loss may constrain the activity of metanders.

PSVI-10 Effects of lipid and starch supplementation on total water intake of Holstein bull-calves

Abstract Water intake of dairy calves is often overlooked by most nutrition models which can be associated with the misconception that dairy calves meet their water requirements with milk or milk replacer (MR) alone. The goals herein were to investigate the effect of two isoenergetic supplements fed in a MR diet on total water intake (TWI) and fresh water intake (FWI). Twenty-three Holstein bull-calves (94.67 ± 12.07 kg) were distributed in a completely randomized design and received one of three supplements for 68 days: control (CON; n = 7), carbohydrates (CHO; n = 8), and lipid (FAT; n = 8); on top of a MR-based diet. The CON was composed of ad libitum MR alone. The FAT was composed of a supplementation of menhaden fish oil on CON (3%); and CHO was composed of corn starch supplementation on CON. All animals were provided free access to mineral mix, 200 g daily dried brewer’s spent grains, and clean water. Data were analyzed with orthogonal contrasts for pre-specified treatment comparisons using R statistical software [R Core Team (2019)]. No significant differences were observed for MR intake, 3.13, 3.05, and 3.14 kg, final bodyweight, 208.75, 200.94, 202.64 kg, and average daily gain, 1.74, 1.60, 1.64 kg, for FAT, CHO, and CON, respectively. TWI in a metabolic bodyweight (MBW) basis was different (P &amp;lt; 0.05) amongst treatments; lower TWI intake was seen for FAT than CHO than CON (0.363 and 0.388 vs 0.423 L/kg0.75, respectively). TWI without MBW resulted in similar results (P &amp;lt; .05) with average TWI of 15.69, 16.08, and 18.00 L; FWI differences (P &amp;lt; .05) were seen alone 1.51, 2.59, and 3.77 L, as well as in MBW basis 0.033, 0.060, and 0.088 L/kg.75 for FAT, CHO, and CON. These data could potentially show that metabolic water production in early ruminant animals can significantly decrease water intake.

The physiological and molecular mechanisms to maintain water and salt homeostasis in response to high salt intake in Mongolian gerbils (Meriones unguiculatus).

Desert rodents are faced with many challenges such as high dietary salt in their natural habitats and they have evolved abilities to conserve water and tolerate salt. However, the physiological and molecular mechanisms involved in water and salt balances in desert rodents are unknown. We hypothesized that desert rodents regulated water and salt balances by altering the expression of AQP2 and α-ENaC in the kidney. Mongolian gerbils (Meriones unguiculatus), a desert species, were acclimated to drinking water with different salt contents: (0, control; 4% NaCl, moderate salt, MS; 8% NaCl, high salt, HS) for 4weeks. The gerbils drinking salty water had lower body mass, food intake, water intake, metabolic water production and urine volume. The HS gerbils increased the expression of arginine vasopressin (AVP) in the hypothalamus, and also enhanced the expression of AQP2 and cAMP/PKA/CREB signaling pathway in the kidney. In addition, these gerbils reduced serum aldosterone levels and α-ENaC expression in the kidney. Creatinine clearance was lower in the HS group than that in the control group, but serum and urine creatinine levels did not change. These data indicate that desert rodents rely on AVP-dependent upregulation of AQP2 and aldosterone-dependent downregulation of α-ENaC in the kidney to promote water reabsorption and sodium excretion under high salt intake.

Fog and fauna of the Namib Desert: past and future

AbstractThe future of fog‐dependent habitats under climate change is unknown but likely precarious; many have experienced recent declines in fog. Fog‐dependent deserts particularly will be threatened, because, there, fog can be the main water source for biota. We review the interactions between fog and fauna of the Namib Desert, about which there is 50 yr of research. We resynthesize the data, seeking patterns and mechanisms that could provide a framework for predicting outcomes of changes in fog regime in other fog‐dependent deserts. In the Namib, fog constitutes the most‐predictable form of free water. At least 48 Namib animal species consume free water from fog, or are likely to do so, employing both liquid and vapor phase. Fog also sustains plants that form the base for metabolic water production and wets the diet to provide pre‐formed water. So fog provides or underpins all the water intake of Namib fauna. Only a few species are active fog‐harvesters, though. Among Namib beetles, two species are unique in that they fog‐bask; they assume stereotyped postures in wind‐driven fog and droplets deposit on their carapaces. Some Namib beetle species construct surface ridges that trap fog water, which they consume. Some arthropods emerge from their subsurface habitats, or occupy its wet top layers, to access fog water, at times and in conditions outside their usual surface activity. Many more taxa, including vertebrates, use fog water opportunistically. They do not actively seek it out but use it when available. Acquiring fog water from droplets requires overcoming spherical surface tension so is possible only for animals heavier than ~100 mg. Smaller animals extract water from films or acquire it in the vapor phase. Some Namib animals use hygroscopic surfaces to extract vapor from unsaturated air, at ambient humidities attained in fog or sometimes between fogs. Rapid acquisition of water during episodic fog events creates problems for storage and osmoregulation, which some Namib animals have solved in enterprising ways, including long‐term internal storage of water and sequestering of osmolytes. Although not yet comprehensive, the body of research reviewed, and the principles that we have elucidated underlying fog usage, should inform future research on fauna throughout fog‐dependent deserts.

Suboptimal hydration remodels metabolism, promotes degenerative diseases, and shortens life.

With increased life expectancy worldwide, there is an urgent need for improving preventive measures that delay the development of age-related degenerative diseases. Here, we report evidence from mouse and human studies that this goal can be achieved by maintaining optimal hydration throughout life. We demonstrate that restricting the amount of drinking water shortens mouse lifespan with no major warning signs up to 14 months of life, followed by sharp deterioration. Mechanistically, water restriction yields stable metabolism remodeling toward metabolic water production with greater food intake and energy expenditure, an elevation of markers of inflammation and coagulation, accelerated decline of neuromuscular coordination, renal glomerular injury, and the development of cardiac fibrosis. In humans, analysis of data from the Atherosclerosis Risk in Communities (ARIC) study revealed that hydration level, assessed at middle age by serum sodium concentration, is associated with markers of coagulation and inflammation and predicts the development of many age-related degenerative diseases 24 years later. The analysis estimates that improving hydration throughout life may greatly decrease the prevalence of degenerative diseases, with the most profound effect on dementia, heart failure (HF), and chronic lung disease (CLD), translating to the development of these diseases in 3 million fewer people in the United States alone.