Water Striders： The Biomechanics of Water Locomotion and Functional Morphology of the Hydrophobic Surface （Insecta： Hemiptera-Heteroptera）

Water striders are insects living on the water surface, over which they can move very quickly and rarely get wetted. We measured the force of free walking in water striders, using a hair attached to their backs and a 3D strain gauge. The error was calculated by comparing force and data derived from geometry and was estimated as 13%. Females on average were stronger （1.32 mN） than males （0.87 mN）, however, the ratio of force to weight was not significantly different. Compared with other lighter species, Aquarius paludum seems stronger, but the ratio of force to weight is actually lower. A. paludum applies about 0.3 mN.cm^-1 to 0.4 mN.cm 1 with its mid-legs, thus avoiding penetrating the surface tension layer while propelling itself rapidly over the water surface. We also investigated the external morphology with SEM. The body is covered by effectively two layers of macro-and micro-hairs, which renders them hydrophobic. The setae are long （40 μm-60μm） and stiff, being responsible for waterproofing, and the microtrichia are much smaller （〈10μm）, slender, and flexible, holding a bubble over the body when submerged.     

RETRACTED ARTICLE: An accurate method to directly measure water strider’s stroke force on the water (Aquarius paludum: Heteroptera: Gerridae)

We measured the force of free pulling water striders, using a hair attached to their backs and a 3D strain gauge force sensor. We showed the repeatability and accuracy of this method. The error of the method was estimated by comparing the projected angles of the force vector on each plane derived from the force data, with those angles derived from video recordings, and was estimated as 12.4%. Females on average were stronger (1.32 mN) than males (0.87 mN), however the ratio of force/weight was not significantly different. Compared with other lighter species, A. paludum seems to be stronger, but the force/weight ratio is actually lower as expected. A. paludum applies about 0.30–0.40 mN/cm with its mid-legs, thus avoiding penetrating the surface tension while propelling itself rapidly over the water. The corresponding author, Dr Pablo Perez Goodwyn, submitted this article [1] to Central European Journal of Biology (CEJB) shortly after submitting the article [2] to Journal of Bionic Engineering (JBE). JBE published it as a research article in June 2008, and in July 2008 the article was published as a communication in CEJB. Since there are significant unacknowledged similarities between the two papers, it has been brought to the attention of the authors that duplicate submission and publication have taken place. The editors of CEJB consider this an infringement of professional ethics and therefore the decision has been made to retract the article published in Central European Journal of Biology. [1] An accurate method to directly measure water strider’s stroke force on the water (Aquarius paludum: Heteroptera: Gerridae), Central European Journal of Biology, Vol. 3, No. 3, 2008, pp. 299–306 [2] Water striders: the biomechanics of water locomotion and functional morphology of the hydrophobic surface (Insecta: Hemiptera-Heteroptera), Journal of Bionic Engineering, Vol. 5, No. 2, 2008, pp. 121-126     

Sexual conflicts, loss of flight, and fitness gains in locomotion of polymorphic water striders

In insect wing polymorphism, morphs with fully developed, intermediate, and without wings are recognized. The morphs are interpreted as a trade‐off between flight and flightlessness; the benefits of flight are counterbalanced by the costs of development and the maintenance of wings and flight muscles. Such a trade‐off has been widely shown for reproductive and developmental parameters, and wing reduction is associated with species of stable habitats. However, in this context, the role of water locomotion performance has not been well explored. We chose seven water striders (Heteroptera: Gerridae) as a model to study this trade‐off and its relation to sexual conflicts, namely, Aquarius elongatus (Uhler), Aquarius paludum (Fabr.), Gerris insularis (Motschulsky), Gerris nepalensis Distant, Gerris latiabdominis Miyamoto, Metrocoris histrio (White), and Rhagadotarsus kraepelini Breddin. We estimated the locomotion performance as the legs’ stroke force, measured on tethered specimens placed on water with a force transducer attached to their backs. By dividing force by body weight, we made performance comparisons. We found a positive relationship between weight and force, and a negative one between weight and the force‐to‐weight ratio among species. The trade‐off between water and flight locomotion was manifested as differences in performance in terms of the force/weight ratio. However, the bias toward winged or wing‐reduced morphs was species dependent, and presumably related to habitat preference. Water strider species favouring a permanent habitat (G. nepalensis) showed higher performance in the apterous morph, but in those favouring temporary habitats (A. paludum and R. kraepelini) morphs’ performance did not differ significantly. Males had higher performance than females in all but three species studied (namely, A. elongatus, G. nepalensis, and R. kraepelini); these three have a type II mating strategy with minimized mating struggle. We hypothesized that in type I mating system, in which males must struggle strongly to subdue the female, males should outperform females to copulate successfully. This was not necessarily true among males of species with type II mating.     

Overwinter survival depends on immune defence and body length in male Aquarius najas water striders

Winter survival of organisms has a crucial effect on their fitness in a seasonal environment. We tested whether overwinter survival of male water striders, Aquarius najas (De Geer) (Heteroptera: Gerridae), is associated with the time of season they leave the water for winter diapause. This was performed by comparing parameters of males leaving the water at the beginning of autumn and 1 month later. The results show significantly higher overwinter survival in males of the early diapausing group. They were found to be larger than late diapausing individuals. Overall, overwinter survival was found to be associated with body length. The strength of immune defence measured as encapsulation response against nylon monofilament appeared to be stronger in the early than in the late dia‐pausing group. Body length had an effect on the encapsulation rates of water striders, with larger males having a stronger encapsulation response. The amount of lipids was larger in males of the early diapausing group, and the relationship between body length and absolute lipid reserves was positive in both groups. However, a correlation between body reserves and body length was not found when lipid content was expressed as a proportion of total body weight. The results suggest that body length is the main variable linking overwinter survival and resistance against pathogens and parasitoids. This study shows that differences in resistance can explain differential winter survival of larger and smaller A. najas water striders.     

Predation of frog eggs by the water strider Gerris latiabdominis Miyamoto (Hemiptera: Gerridae)

Water striders (Hemiptera: Gerridae) are predators found on the water surface that prey mainly on arthropods. The feeding on other organisms (dead vertebrates, fishes and tadpoles) is a rare event. To our knowledge, predation of frog eggs by water striders has not yet been reported. We observed that adult water striders, Gerris latiabdominis Miyamoto, 1958 (Hemiptera: Gerridae), preyed on the eggs of three frog species, Pelophylax nigromaculata Hallowell, 1861 (Anura: Ranidae), Rana japonica Boulenger, 1879 (Anura: Ranidae), and Rhacophorus schlegelii Günther, 1858 (Anura: Rhacophoridae). We found predation by the water striders affects the survival rate of frog eggs floating on the water surface. We suggest that this hunting event would occur in water bodies in which water striders and frogs coexist, especially the region where their phenology overlaps.     

Asymmetric competition between distant taxa: poecilid fishes and water striders

Summary Competition for water surface prey between fish (Priapichtus annectens: Poeciliidae) and water striders (Potamobates unidentatus: Gerridae) was studied in the laboratory and in pools in a small tropical stream. Laboratory experiments showed that fish depressed activity and foraging success of water striders. Large fish (4–5 cm) had a greater effect than small fish (2–3 cm). The field experiment showed that competition was highly asymmetric. Presence of fish decreased water strider foraging success while the reverse interaction was insignificant. It is suggested that the higher individual foraging success of the fish, harassment of water striders by fish and the use of an exclusive resource, benthic invertebrates, by the fish, contribute to this pattern. Habitat use differed between the two species. Fish used the deeper parts of stream pools and water striders used the shallower parts of the pools. Asymmetric interference and exploitation competition may force water striders to use shallow edge habitats.     

To fly or not to fly: response of water striders to drying out of habitat

Abstract .1. Adults of Aquarius paludum inhabit both temporary and permanent water surfaces; Gerris latiabdominis lives only in temporary habitats. To clarify whether adults of both species stay in position or fly when habitats dry up, overwintered adults of A. paludum and G. latiabdominis collected in spring were reared under one of the following four conditions: (A) on water with sufficient food, (B) on water, starved, (C) on wet paper with sufficient food, (D) on wet paper, starved. All rearings were at LD 15.5:8.5 h, 20 ± 2 °C, resembling natural conditions for April to June.
2. Females of A. paludum in group C had lower fecundity than the control group A and some stopped laying eggs. When a water surface was restored, females that had entered reproductive diapause began to lay eggs again. In contrast, females of G. latiabdominis continued to lay eggs even when reared on damp paper.
3. Adults of A. paludum lived longer and adopted diapause posture with high frequency when starved and reared without a water surface. There were, however, no significant differences in the longevity or in the number of adults showing diapause posture between groups A and D of G. latiabdominis.
4. Females of A. paludum collected in the middle of May had more mature oocytes (mean: 20.8) than females of G. latiabdominis (mean: 8.0), and most had histolysed their indirect flight muscles; most females of G. latiabdominis had retained their flight muscles and flew readily.
5. When water surfaces dry, with food shortage, adults of A. paludum may survive in place for a relatively long time until the water surface returns. Adults of G. latiabdominis may fly to other water surfaces and reproduce without delay.     

Costs and benefits for water strider (Aquarius paludum) females of carrying guarding, reproductive males

We describe the mating system of Aquarius paludum insularis based on field observations and test hypotheses about the effects of body size, hunger level and post-copulatory guarding on reproductive performance. The mating sequence of this species was typical for temperate water striders, except that most oviposition was carried out by tandem pairs, most of which were submerged. Mate guarding continued until the end of oviposition, lasting up to 18.2h, which was much longer than that recorded for other species of water striders. Pair partners changed after oviposition. Extended contact guarding reduced female mobility. In the case of females that carried long-winged males, there was a significant reduction in speed and stride between tandem as opposed to single females. However, when short-winged males were carried, there was not a significant difference. Short-term foraging efficiency did not differ significantly between tandem and single females, and thus did not reflect the difference in mobility. Hunger level did not significantly affect female mating receptivity. Although the number of harassment bouts by unpaired males did not differ between single and tandem females, single females suffered significantly more harassment. Females were able to lay fertilized eggs for about 15 days after a single copulation, but they accepted long guarding and multiple mating during this period as well. The cost of resisting male mating attempts appears to be greater than the cost of carrying males.     

Megafauna associations with deepwater corals (Primnoa spp.) in the Gulf of Alaska

Our study showed that one species of water strider (Aquarius najas) dominated the insect fauna (>90% of the biomass) on and near the surface of a small stream in southern Sweden, but the diet of Daubenton's bats (Myotis daubentonii), regularly feeding over the same stream, contained <1% of these insects. To explain why the bats did not eat water striders in proportion to the apparent abundance of these insects, we tested three hypotheses, with the following results: (1) The water striders did not respond to artificial bat calls and therefore their defence against bats is not based on ultrasonic hearing. (2) Water striders hand-fed to the bats were eaten with similar frequency as palatable controls (caddis flies), so there is no evidence that water striders are unpalatable to bats. (3) Attempted prey-captures by the bats occurred less often than expected within 1 m of the bank of the stream (the bank consisted of a stone wall), indicating that the bats' flight or, alternatively, their detection or capture of insects, was difficult within that area, possibly constrained by clutter. At dusk and just before the bats emerged to feed, the water striders moved away from the open water. They remained motionless close to the bank for as long as the bats were active.     

Conflict between sexes in the water strider, Gerris lacustris: a test of two hypotheses for male guarding behavior

We studied the effect of operational sex ratio on female reluctanceand male persistence to mate as well as on the length of copulationand postcopulatory guarding in Gerris lacustris by adding fivesurplus males or females to the basin with a pair in tandem.In the control treatment, a pair alone was tested. Accordingto the copulatory guarding hypothesis (CGH), males should prolongmating and guard females in the presence of surplus males. Accordingto the convenience polyandry hypothesis (CPH), females shouldshow lower levels of resistance to prolonged mating in the presenceof surplus males because the mating male protects the femaleagainst harassment from other males. As expected on the basisof both the CGH and CPH, mating (copulation + guarding) averagedlonger in the male-biased treatment. The behavior of males andfemales during mating suggested that both hypotheses hold true:females showed less resistance to prolonged mating (as predictedfrom CPH), and male behavior suggested stronger efforts to stayon the female when surplus males were present (as predictedfrom CGH). Comparisons of the treatment with surplus femaleswith the results from the mating pair without surplus individualssuggested that the capabilities of water striders in tandemto assess the sex of nearby nonmating striders are limited.     

Advanced Electro-active Dry Adhesive Actuated by an Artificial Muscle Constructed from an Ionic Polymer Metal Composite Reinforced with Nitrogen-doped Carbon Nanocages

An advanced electro-active dry adhesive,which was composed of a mushroom-shaped fibrillar dry adhesive array actuated by an Ionic Polymer Metal Composite (IPMC) artificial muscle reinforced with nitrogen-doped carbon nanocages (NCNCs),was developed to imitate the actuation of a gecko's toe.The properties of the NCNC-reinforced Nafion membrane,the electromechanical properties of the NCNC-reinforced IPMC,and the related electro-active adhesion ability were investigated.The NCNCs were uniformly dispersed in the 0.1 wt％ NCNC/Nafion membrane,and there was a seamless connection with no clear interface between the dry adhesive and the IPMC.Our 0.1 wt％ NCNC/Nafion-IPMC actuator shows a displacement and force that are 1.6-2 times higher than those of the recast Nafion-IPMC.This is due to the increased water uptake (25.39％) and tensile strength (24.5 MPa) of the specific 3D hollow NCNC-reinforced Nafion membrane,as well as interactions between the NCNCs and the sulfonated groups of the Nafion.The NCNC/Nafion-IPMC was used to effectively actuate the mushroom-shaped dry adhesive.The normal adhesion forces were 7.85 mN,12.1 mN,and 51.7 mN at sinusoidal voltages of 1.5 V,2.5 V,and 3.5 V,respectively,at 0.1 Hz.Under the bionic leg trail,the normal and shear forces were approximately 713.5 mN (159 mN·cm-2) and 1256.6 mN (279 mN·cm-2),respectively,which satisfy the required adhesion.This new electro-active dry adhesive can be applied for active,distributed actuation and flexible grip in robots.     

The evolution of marine insects: phylogenetic, ecological and geographical aspects of species diversity in marine water striders

No other group of insects have been more successful in colonizing marine habitats than water striders and their allies (Heteroptera, Gerromorpha). More than 10% of the 1700 species of gerromorphan bugs are marine. Water striders have colonized the marine environment at least 14 times. The fossil records suggest that marine habitats were invaded by members of the families Veliidae and Gerridae earlier than 20-30 and 45 million years before present, respectively. Estuaries and mangrove swamps are undoubtedly the ancestral type of habitat, but water striders have diversified further in marine habitats including the surface of the open ocean (sea skaters. Halobates). Except for being obligatorily flightless, marine water striders are structurally very similar to their non-marine relatives. Physiological and behavioral rather than morphological specializations are likely to have been key innovations in the transition from limnic to marine habitats. The oldest and most species-rich clades originated in the Indo-West Pacific region. There are 3.5 times as many species of marine water striders in the Indo-West Pacific region than in the Atlantic/Caribbean/East Pacific region. This "diversity anomaly" is explained historically by region-specific differences in the origin and proliferation of clades, in paleoclimate and paleogeography, and in the propensity for dispersal between regions.     

Influence of gut parasites on growth performance in the water strider Gerris buenoi (Hemiptera: Gerridae)

Water striders harbor a diverse assemblage of symbionts in their digestive tract We used a field experiment, in which water striders were reared in enclosures in their natural pond habitat, to assess the effects of gut symbionts on growth Trypanosomatid flagellates had significant adverse effects on both development time and adult size, and therefore are clearly parasitic Yet because of their low prevalences (2% or less), trypanosomatids cannot be a major factor in the dynamics of our study population Gregannes occurred in 36% of the water striders, often in high numbers, and filling the entire midgut of some bugs Nevertheless, infected and uninfected gerrids did not differ in their growth, and gregarine loads were uncorrelated with development time and adult size attained We also did not find effects of gregarines in a second experiment with different rearing conditions, including a treatment with food stress We used a quantitative genetic approach to test if resistance against gregarines has a heritable component There was no evidence for any genetic variation, suggesting that variability in gregarine loads is the result of environmental heterogeneity Comparison with published reports from water striders shows that there is a great variability in the diversity and prevalence of symbionts among different populations and species, of gerrids     

Fishing spiders, green sunfish, and a stream-dwelling water strider: male-female conflict and prey responses to single versus multiple predator environments

Many studies have experimentally addressed the effects of a particular predator species on prey behavior. In nature, however, prey frequently face multiple species of predators that often vary in their predatory mode and in their level of predation risk. Relatively few studies have considered prey responses under these complex conditions. In Kentucky, the stream-dwelling water strider (Aquariusremigis) coexists with many potentially dangerous predators, two of which are the green sunfish (Lepomiscyanellus) and the fishing spider (Dolomedesvittatus). Green sunfish occupy stream pools and attack water striders from below. In contrast, fishing spiders hunt along stream shorelines where they perch on overhanging vegetation or rocks and attack water striders near shore. We compared how A. remigis individuals respond to these two very different predators in pools with one or both predators. The presence of sunfish in pools had strong effects on male water strider behavior, including increased use of three types of refuge from sunfish (riffles, climbing out of the water, sitting on the water but at the edges of pools), decreased activity and a decreased number of aggressive males on the water. Spiders also influenced water strider behavior; male water striders avoided spiders by shifting away from the edges of pools. Comparisons of the effects of the two predator species showed that in general, antipredator responses by male water striders were stronger in pools with fish alone than in those with spiders alone. In the presence of both predators, male water strider behavior (microhabitat use and activity) was generally similar to behavior in the presence of fish alone. In contrast, female water striders showed no significant response to the presence of sunfish, and little response to the presence of spiders. This lack of response could be because females spent much of their time in refuges even in the absence of predators (apparently hiding from harassment by males). Both spiders and fish caused decreases in water strider mating activity. The presence of fish reduced both the number of matings per pool (mating frequency), and mean mating durations. Spiders induced a decrease in mean mating duration, but not in mating frequency. The largest reductions in mating activity occurred in pools with both predators present. Pools with either spiders or fish alone suffered 15–20% water strider mortality during our experiment (versus no mortality in predator-free pools). Extant theory suggests that when prey face conflicting microhabitat responses to two predators (as in this study), the predators should have facilitative effects on predation rates (i.e., prey that avoid one predator are often killed by the other and vice versa). Mortality rates in pools with both predators present, however, were not significantly different from that predicted by a null model of multiple predator effects. The lack of predator facilitation can be explained by the compensatory reductions in water strider activity and mating activity in the presence of both predators. Received: 26 August 1996 / Accepted: 12 June 1998     

Is bigger better? Water balance in the polymorphic desert harvester ant Messor pergandei

Abstract. Foraging activity of ants in xeric areas may be limited by desiccation stresses. To assess the extent of such stresses on a polymorphic ant species [Messor pergandei (Mayr), body mass range 1-12mg], we measured body water reserves, absolute rates of water loss, and cuticular permeability over the species' foraging temperature range (15–45C). Cuticular permeability of M. pergandei was typical of xeric arthropods (17μgcm^-2h^-1mmHg^-1). However, the effect of polymorphism on both absolute and relative rates of water loss was unexpected. Large workers lost water more slowly than small workers, even after adjusting for cuticular surface area. In addition, the body water reserves of large workers were larger, even after adjusting for body mass. Small workers of this ant species are therefore disproportionately prone to dehydration, yet, in spite of this, constitute a large and important component of the foraging force. To assess the practical relevance of desiccation to polymorphic ants, we developed a 'worst-case' model of desiccation-limited foraging parameters (time to complete loss of locomotor coordination in 5% of the foraging force). In this model, average actual foraging duration was substantially less than would be required to incapacitate the ants by dehydration. We discuss direct and indirect evidence suggesting that desiccation may, nevertheless, impose limitations on the foraging activity of ants.     

Fabrication of Biomimetic Water Strider Legs Covered with Setae

Water striders have remarkable water-repellent legs that enable them to stand effortlessly and move quickly on water.Fluidphysics indicates this feature is due to a surface-tension effect caused by the special hierarchical structure of the legs,which arecovered with a large number of inclined setae with fine nanogrooves inducing water resistance.This inspires us to fabricatespecial water-repellent structure on functional surfaces through the cooperation between the surface treatment and the surfacemicro-and nanostructures,which may bring great advantages in a wide variety of applications.In this paper we present aprocedure for fabricating biomimetic water strider legs covered with setae using Polycarbonate Track-Etched(PCTE)membranesas templates.By choosing appropriate membrane lengths,diameters,pitches and densities of the setae,the biomimeticlegs can be fabricated conveniently and at a low cost.Furthermore we investigated the relationship between stiffness of themolding materials,high aspect ratio and density,which affect the fidelity of fabrication and self adhesion,to optimize thestability of setae.The knowledge we gained from this study will offer important insights into the biomimetic design and fabricationof water strider setae.     

表面压与紫膜含量对紫膜LB膜质量的影响

本文报导了用表面轮廓测量仪测量了不同表面压和不同紫膜含量下制备的紫膜LB膜中紫膜碎片的厚度。实验结果表明:单个紫膜碎片在紫脂LB膜中的厚度为50左右,相当数量的紫膜碎片之间有重叠。当表面压为30mN/m或紫膜碎片与大豆磷脂之重量比为20:1时,紫膜碎片容易进入到水相或碎片之间相互重叠变得更加严重。     

Comparison of Antipredator Responses of Two Related Water Striders to a Common Predator

This study compares the antipredator responses of two congeneric water striders that live in different habitats yet share a common predator. Aquarius nebularis and A. remigis are stream-dwelling species of water striders found in close association in central Kentucky. Aquarius nebularis typically inhabit third- and fourth-order streams that support diverse and complex fish communities; A. remigis inhabit adjacent first- and second-order tributaries that tend to have either no fish or relatively few fish patchily distributed. The ecological conditions for these two species are distinctly different, yet the green sunfish (Lepomis cyanellus) is a surface-feeding predator and a potential risk to both species. In experimental pools with sunfish, an initial fish strike caused A. remigis to move to the edge of the pool and become inactive. For the rest of the observation period, A. remigis reduced behaviour patterns that attract predators such as skating on open water, mating and male–male aggression. The proportion of A. remigis missing from sunfish pools was 5 times higher than in pools lacking fish, suggesting that 20% of water striders were killed by predation. In contrast, an initial fish strike caused A. nebularis to exhibit a burst of activity as individuals erratically skated over the open water. They then resumed the less active pre-attack behaviours a short time later. Aquarius nebularis showed none of the antipredator behaviours typical for A. remigis. Furthermore, the proportion of A. nebularis missing from sunfish pools did not differ from that in pools without fish. Although antipredator behaviour has been examined for relatively few species of water striders, this study suggests that the behaviour of the most commonly studied species, A. remigis, may not be indicative for water striders in general., Corresponding author: James J. Krupa, School of Biological Sciences, University of Kentucky, Lexington, KY 40506-0225, U.S.A. E-mail: bio149@pop.uky.edu bio149@pop.uky.edu     

Puroindoline-b mutations control the lipid binding interactions in mixed puroindoline-a:puroindoline-b systems

The interactions have been investigated of puroindoline-a (Pin-a) and mixed protein systems of Pin-a and wild-type puroindoline-b (Pin-b+) or puroindoline-b mutants (G46S mutation (Pin-bH) or W44R mutation (Pin-bS)) with condensed phase monolayers of an anionic phospholipid (L-alpha-dipalmitoylphosphatidyl-dl-glycerol (DPPG)) at the air/water interface. The interactions of the mixed systems were studied at three different concentration ratios of Pin-a:Pin-b, namely 3:1, 1:1 and 1:3 in order to establish any synergism in relation to lipid binding properties. Surface pressure measurements revealed that Pin-a interaction with DPPG monolayers led to an equilibrium surface pressure increase of 8.7 +/- 0.6 mN m-1. This was less than was measured for Pin-a:Pin-b+ (9.6 to 13.4 mN m-1), but was significantly more than was measured for Pin-a:Pin-bH (4.0 to 6.2 mN m-1) or Pin-a:Pin-bS (3.8 to 6.3 mN m-1) over the complete range of concentration ratio. Consequently, surface pressure increases were shown to correlate to endosperm hardness phenotype, with puroindolines present in hard-textured wheat varieties yielding lower equilibrium surface pressure changes. Integrated amide I peak areas from corresponding external reflectance Fourier-transform infrared (ER-FTIR) spectra, used to indicate levels of protein adsorption to the lipid monolayers, showed that differences in adsorbed amount were less significant. The data therefore suggest that Pin-b mutants having single residue substitutions within their tryptophan-rich loop that are expressed in some hard-textured wheat varieties influence the degree of penetration of Pin-a and Pin-b into anionic phospholipid films. These findings highlight the key role of the tryptophan-rich loop in puroindoline-lipid interactions.     

Water turnover assessment in overweight adolescents

Adequate intake (AI) standards for water in adolescents range between 2.4-3.3 l/day for males and 2.1-2.3 l/day for females, independent of obesity status. Water intakes and excretions of this population are not well documented. The purposes of this study were to assess water turnover, inputs, and outputs in overweight adolescents, compare these parameters between males and females, and evaluate the reproducibility of water turnover. Eighteen girls (BMI 31.7 ± 4 kg/m(2); mean ± s.d.) and nine boys (BMI 26.3 ± 3 kg/m(2)) aged 12-15 years completed two 3-week metabolic balance trials. Rate of water turnover (rH(2)O) was measured by tracking the decline of deuterated water from the body over 14 days. Water inputs (diet*, ad libitum(#), metabolic(#)) and outputs (urine*, feces*, insensible(#)) were assessed (*measured, #estimated). rH(2)O was lower (P = 0.002) in girls vs. boys (3,742 ± 536 vs. 4,537 ± 623 g/day). Per kg body weight, rH(2)O was 28% lower in girls vs. boys (46 ± 7 vs. 64 ± 9 g·kg(-1)·day(-1)). Water input from food and beverages provided and metabolic production were 44 and 28% lower, respectively, in girls vs. boys. Urine and insensible water losses were 21 and 17% lower in girls vs. boys. BMI was positively associated with water turnover in both sexes (girls P = 0.037; boys P = 0.014). The intraclass correlation of rH(2)O between trials was 0.981 (P < 0.001). In conclusion, these overweight adolescents consumed water well in excess of sex-specific AI standards. The lower rH(2)O in girls compared to boys is consistent with adult females and males.