Social life results in social stress protection: a novel concept to explain individual life-history patterns in social insects

Resistance to and avoidance of stress slow aging and confer increased longevity in numerous organisms. Honey bees and other superorganismal social insects have two main advantages over solitary species to avoid or resist stress: individuals can directly help each other by resource or information transfer, and they can cooperatively control their environment. These benefits have been recognised in the context of pathogen and parasite stress as the concept of social immunity, which has been extensively studied. However, we argue that social immunity is only a special case of a general concept that we define here as social stress protection to include group-level defences against all biotic and abiotic stressors. We reason that social stress protection may have allowed the evolution of reduced individual-level defences and individual life-history optimization, including the exceptional aging plasticity of many social insects. We describe major categories of stress and how a colonial lifestyle may protect social insects, particularly against temporary peaks of extreme stress. We use the honey bee (Apis mellifera L.) to illustrate how patterns of life expectancy may be explained by social stress protection and how modern beekeeping practices can disrupt social stress protection. We conclude that the broad concept of social stress protection requires rigorous empirical testing because it may have implications for our general understanding of social evolution and specifically for improving honey bee health.

The Pupa Stage Is the Most Sensitive to Hypoxia in Drosophila melanogaster

Hypoxia not only plays a critical role in multiple disease conditions; it also influences the growth and development of cells, tissues and organs. To identify novel hypoxia-related mechanisms involved in cell and tissue growth, studying a precise hypoxia-sensitive time window can be an effective approach. Drosophila melanogaster has been a useful model organism for studying a variety of conditions, and we focused in this study on the life cycle stages of Drosophila to investigate their hypoxia sensitivity. When normoxia-grown flies were treated with 4% O2 at the pupa stage for 3, 2 and 1 day/s, the eclosion rates were 6.1%, 66.7% and 96.4%, respectively, and, when 4% O2 was kept for the whole pupa stage, this regimen was lethal. Surprisingly, when our hypoxia-adapted flies who normally live in 4% O2 were treated with 4% O2 at the pupa stage, no fly eclosed. Within the pupa stage, the pupae at 2 and 3 days after pupae formation (APF), when treated for 2 days, demonstrated 12.5 ± 8.5% and 23.6 ± 1.6% eclosion, respectively, but this was completely lethal when treated for 3 days. We conclude that pupae, at 2 days APF and for a duration of a minimum of 2 days, were the most sensitive to hypoxia. Our data from our hypoxia-adapted flies clearly indicate that epigenetic factors play a critical role in pupa-stage hypoxia sensitivity.

Hypoxia extends lifespan and neurological function in a mouse model of aging

There is widespread interest in identifying interventions that extend healthy lifespan. Chronic continuous hypoxia delays the onset of replicative senescence in cultured cells and extends lifespan in yeast, nematodes, and fruit flies. Here, we asked whether chronic continuous hypoxia is beneficial in mammalian aging. We utilized the Ercc1 Δ/- mouse model of accelerated aging given that these mice are born developmentally normal but exhibit anatomic, physiological, and biochemical features of aging across multiple organs. Importantly, they exhibit a shortened lifespan that is extended by dietary restriction, the most potent aging intervention across many organisms. We report that chronic continuous 11% oxygen commenced at 4 weeks of age extends lifespan by 50% and delays the onset of neurological debility in Ercc1 Δ/- mice. Chronic continuous hypoxia did not impact food intake and did not significantly affect markers of DNA damage or senescence, suggesting that hypoxia did not simply alleviate the proximal effects of the Ercc1 mutation, but rather acted downstream via unknown mechanisms. To the best of our knowledge, this is the first study to demonstrate that "oxygen restriction" can extend lifespan in a mammalian model of aging.

Hyperbaric oxygen therapy for healthy aging: From mechanisms to therapeutics

Hyperbaric oxygen therapy (HBOT), a technique through which 100% oxygen is provided at a pressure higher than 1 atm absolute (ATA), has become a well-established treatment modality for multiple conditions. The noninvasive nature, favorable safety profile, and common clinical application of HBOT make it a competitive candidate for several new indications, one of them being aging and age-related diseases. In fact, despite the conventional wisdom that excessive oxygen accelerates aging, appropriate HBOT protocols without exceeding the toxicity threshold have shown great promise in therapies against aging. For one thing, an extensive body of basic research has expanded our mechanistic understanding of HBOT. Interestingly, the therapeutic targets of HBOT overlap considerably with those of aging and age-related diseases. For another, pre-clinical and small-scale clinical investigations have provided validated information on the efficacy of HBOT against aging from various aspects. However, a generally applicable protocol for HBOT to be utilized in therapies against aging needs to be defined as a subsequent step. It is high time to look back and summarize the recent advances concerning biological mechanisms and therapeutic implications of HBOT in promoting healthy aging and shed light on prospective directions. Here we provide the first comprehensive overview of HBOT in the field of aging and geriatric research, which allows the scientific community to be aware of the emerging tendency and move beyond conventional wisdom to scientific findings of translational value.

Lifespan and ROS levels in different Drosophila melanogaster strains after 24 h hypoxia exposure

During recent decades, model organisms such as Drosophila melanogaster have made it possible to study the effects of different environmental oxygen conditions on lifespan and oxidative stress. However, many studies have often yielded controversial results usually assigned to variations in Drosophila genetic background and differences in study design. In this study, we compared longevity and ROS levels in young, unmated males of three laboratory wild-type lines (Canton-S, Oregon-R and Berlin-K) and one mutant line (Sod1ⁿ¹) as a positive control of redox imbalance, under both normoxic and hypoxic (2% oxygen for 24 h) conditions. Lifespan was used to detect the effects of hypoxic treatment and differences were analysed by means of Kaplan–Meier survival curves and log-rank tests. Electron paramagnetic resonance spectroscopy was used to measure ROS levels and analysis of variance was used to estimate the effects of hypoxic treatment and to assess ROS differences between strains. We observed that the genetic background is a relevant factor involved in D. melanogaster longevity and ROS levels. Indeed, as expected, in normoxia Sod1ⁿ¹ are the shortest-lived, while the wild-type strains, despite a longer lifespan, show some differences, with the Canton-S line displaying the lowest mortality rate. After hypoxic stress these variances are amplified, with Berlin-K flies showing the highest mortality rate and most evident reduction of lifespan. Moreover, our analysis highlighted differential effects of hypoxia on redox balance/unbalance. Canton-S flies had the lowest increase of ROS level compared to all the other strains, confirming it to be the less sensitive to hypoxic stress. Sod1ⁿ¹ flies displayed the highest ROS levels in normoxia and after hypoxia. These results should be used to further standardize future Drosophila research models designed to investigate genes and pathways that may be involved in lifespan and/or ROS, as well as comparative studies on specific mutant strains.

Summary: In our study Drosophila melanogaster was used to evaluate the effects of different environmental oxygen conditions on survival and ROS levels in three wild-type and one mutant strain.

Made for Each Other: Vector-Pathogen Interfaces in the Huanglongbing Pathosystem

Citrus greening, or huanglongbing (HLB), currently is the most destructive disease of citrus. HLB disease is putatively caused by the phloem-restricted α-proteobacterium 'Candidatus Liberibacter asiaticus'. This bacterium is transmitted primarily by the Asian citrus psyllid Diaphorina citri (Hemiptera: Liviidae). Most animal pathogens are considered pathogenic to their insect vectors, whereas the relationships between plant pathogens and their insect vectors are variable. Lately, the relationship of 'Ca. L. asiaticus' with its insect vector, D. citri, has been well investigated at the molecular, biochemical, and biological levels in many studies. Herein, the findings concerning this relationship are discussed and molecular features of the acquisition of 'Ca. L. asiaticus' from the plant host and its growth and circulation within D. citri, as well as its transmission to plants, are presented. In addition, the effects of 'Ca. L. asiaticus' on the energy metabolism (respiration, tricarboxylic acid cycle, and adenosine triphosphate production), metabolic pathways, immune system, endosymbionts, and detoxification enzymes of D. citri are discussed together with other impacts such as shorter lifespan, altered feeding behavior, and higher fecundity. Overall, although 'Ca. L. asiaticus' has significant negative effects on its insect vector, it increases its vector fitness, indicating that it develops a mutualistic relationship with its vector. This review will help in understanding the specific interactions between 'Ca. L. asiaticus' and its psyllid vector in order to design innovative management strategies.

Lifespan Extension in Long-Lived Vertebrates Rooted in Ecological Adaptation

Contemporary studies on aging and longevity have largely overlooked the role that adaptation plays in lifespan variation across species. Emerging evidence indicates that the genetic signals of extended lifespan may be maintained by natural selection, suggesting that longevity could be a product of organismal adaptation. The mechanisms of adaptation in long-lived animals are believed to account for the modification of physiological function. Here, we first review recent progress in comparative biology of long-lived animals, together with the emergence of adaptive genetic factors that control longevity and disease resistance. We then propose that hitchhiking of adaptive genetic changes is the basis for lifespan changes and suggest ways to test this evolutionary model. As individual adaptive or adaptation-linked mutations/substitutions generate specific forms of longevity effects, the cumulative beneficial effect is largely nonrandom and is indirectly favored by natural selection. We consider this concept in light of other proposed theories of aging and integrate these disparate ideas into an adaptive evolutionary model, highlighting strategies in decoding genetic factors of lifespan control.

Neonatal hyperoxia impairs adipogenesis of bone marrow-derived mesenchymal stem cells and fat accumulation in adult mice

Preterm birth is a risk factor for growth failure and development of respiratory disease in children and young adults. Their early exposure to oxygen may contribute to lung disease because adult mice exposed to hyperoxia as neonates display reduced lung function, changes in the host response to respiratory viral infections, and develop pulmonary hypertension and heart failure that shortens their lifespan. Here, we provide new evidence that neonatal hyperoxia also impairs growth by inhibiting fat accumulation. Failure to accumulate fat may reflect a systemic defect in adipogenic potential of stem cells because bone marrow-derived mesenchymal cells (BMSCs) isolated from the mice grew slower and were more oxidized compared to controls. They also displayed reduced capacity to accumulate lipid and differentiate into adipocytes. BMSCs from adult mice exposed to neonatal hyperoxia express lower levels of peroxisome proliferator-activated receptor gamma (PPARγ), a transcription factor that drives adipocyte differentiation. The defect in adipogenesis was rescued by expressing PPARγ in these cells. These findings reveal early life exposure to high levels of oxygen may suppresses fat accumulation and impair adipogenic differentiation upstream of PPARγ signaling, thus potentially contributing to growth failure seen in people born preterm.

To breathe or not to breathe: Understanding how oxygen sensing contributes to age-related phenotypes

Aging is characterized by a progressive loss of tissue integrity and functionality due to disrupted homeostasis. Molecular oxygen is pivotal to maintain tissue functions, and aerobic species have evolved a sophisticated sensing system to ensure proper oxygen supply and demand. It is not surprising that aberrations in oxygen and oxygen-associated pathways subvert health and promote different aspects of aging. In this review, we discuss emerging findings on how oxygen-sensing mechanisms regulate different cellular and molecular processes during normal physiology, and how dysregulation of oxygen availability lead to disease and aging. We describe various clinical manifestations associated with deregulation of oxygen balance, and how oxygen-modulating therapies and natural oxygen oscillations influence longevity. We conclude by discussing how a better understanding of oxygen-related mechanisms that orchestrate aging processes may lead to the development of new therapeutic strategies to extend healthy aging.

Rejuvenation Through Oxygen, More or Less

Modest modulation of oxygen intake, either by inducing mild intermittent hypoxia or hyperoxia appears to induce modest rejuvenative changes in mammals, in part, by activating key regulator hypoxia-induced factor 1a (HIF-1a). Interestingly both lower oxygen and transient higher oxygen levels induce this hypoxia regulator. Hyperbaric oxygen induces HIF-1a by the hyperoxic-hypoxic paradox that results from an overinduction of protective factors under intermittent hyperoxic conditions, leading to a state somewhat similar to that induced by hypoxia. A key difference being that SIRT1 is induced by hyperoxia, whereas it is reduced during hypoxia by the activity of HIF-1a. In a recent report, a small clinical trial employing 60 sessions of intermittent hyperbaric oxygen therapy (HBOT) studying old humans resulted in increased mean telomere length of immune cells including B cells, natural killer cells, T helper, and cytotoxic T lymphocytes. Moreover, there was a reduction in CD28^null senescent T helper and cytotoxic T cells. In a parallel report, HBOT has been reported to enhance cognition in older adults, especially attention and information processing speed through increased cerebral blood flow (CBF) in brain regions where CBF tends to decline with age. The durability of these beneficial changes is yet to be determined. These preliminary results require follow-up, including more extensive characterization of changes in aging-associated biomarkers. An interesting avenue of potential work is to elucidate potential connections between hypoxia and epigenetics, especially the induction of the master pluripotent regulatory factors, which when expressed transiently have been reported to ameliorate some aging biomarkers and pathologies.

Responses to Alteration of Atmospheric Oxygen and Social Environment Suggest Trade-Offs among Growth Rate, Life Span, and Stress Susceptibility in Giant Mealworms (Zophobas morio)

Growth rate, development time, and response to environmental stressors vary tremendously across organisms, suggesting trade-offs that are affected by evolutionary or ecological factors, but such trade-offs are poorly understood. Prior studies using artificially selected lines of Manduca sexta suggest that insects with high growth rates, long development time, and large body size are more sensitive to hypoxic or hyperoxic stresses, such as reactive oxygen species (ROS) production, but the mechanisms and specific life-history associations remain unclear. Here, we manipulated the social environment to differentiate the effects of size, growth rate, and development time on oxygen sensitivity of the giant mealworm, Zophobas morio. Crowding reduced growth rates but yielded larger adults as a result of supernumerary molts and longer development times. The juvenile performance (growth rate, development time, adult mass) of crowd-reared mealworms was less sensitive to variation in atmospheric oxygen than it was for individually reared animals, consistent with the hypothesis that high growth rates are associated with increased sensitivity to ROS. Life span in normoxia was extended by crowd rearing, perhaps due to the larger size and/or increased resources of the larger adults. Life spans of crowd-reared animals were more negatively affected by hypoxia or hyperoxia than life spans of individually reared animals, possibly due to the longer total stress exposure of crowd-reared animals. These data suggest that animals with high growth rates experience a negative trade-off of performance with greater sensitivity to stress during the juvenile phase, while animals with long development times or life spans experience a negative trade-off of greater susceptibility of life span to environmental stress.

Early-life hypoxia alters adult physiology and reduces stress resistance and lifespan in Drosophila

In many animals, short-term fluctuations in environmental conditions in early life often exert long-term effects on adult physiology. In Drosophila, one ecologically relevant environmental variable is hypoxia. Drosophila larvae live on rotting, fermenting food rich in microorganisms, an environment characterized by low ambient oxygen. They have therefore evolved to tolerate hypoxia. Although the acute effects of hypoxia in larvae have been well studied, whether early-life hypoxia affects adult physiology and fitness is less clear. Here, we show that Drosophila exposed to hypoxia during their larval period subsequently show reduced starvation stress resistance and shorter lifespan as adults, with these effects being stronger in males. We find that these effects are associated with reduced whole-body insulin signaling but elevated TOR kinase activity, a manipulation known to reduce lifespan. We also identify a sexually dimorphic effect of larval hypoxia on adult nutrient storage and mobilization. Thus, we find that males, but not females, show elevated levels of lipids and glycogen. Moreover, we see that both males and females exposed to hypoxia as larvae show defective lipid mobilization upon starvation stress as adults. These data demonstrate how early-life hypoxia can exert persistent, sexually dimorphic, long-term effects on Drosophila adult physiology and lifespan.

Oxygen supply limits the chronic heat tolerance of locusts during the first instar only

Although scientists know that overheating kills many organisms, they do not agree on the mechanism. According to one theory, referred to as oxygen- and capacity-limitation of thermal tolerance, overheating occurs when a warming organism's demand for oxygen exceeds its supply, reducing the organism's supply of ATP. This model predicts that an organism's heat tolerance should decrease under hypoxia, yet most terrestrial organisms tolerate the same amount of warming across a wide range of oxygen concentrations. This point is especially true for adult insects, who deliver oxygen through highly efficient respiratory systems. However, oxygen limitation at high temperatures may be more common during immature life stages, which have less developed respiratory systems. To test this hypothesis, we measured the effects of heat and hypoxia on the survival of South American locusts (Schistocerca cancellata) throughout development and during specific instars. We demonstrate that the heat tolerance of locusts depends on oxygen supply during the first instar but not during later instars. This finding provides further support for the idea that oxygen limitation of thermal tolerance depends on respiratory performance, especially during immature life stages.

Intragenic repeat expansion in the cell wall protein gene HPF1 controls yeast chronological aging

Aging varies among individuals due to both genetics and environment, but the underlying molecular mechanisms remain largely unknown. Using a highly recombined Saccharomyces cerevisiae population, we found 30 distinct quantitative trait loci (QTLs) that control chronological life span (CLS) in calorie-rich and calorie-restricted environments and under rapamycin exposure. Calorie restriction and rapamycin extended life span in virtually all genotypes but through different genetic variants. We tracked the two major QTLs to the cell wall glycoprotein genes FLO11 and HPF1 We found that massive expansion of intragenic tandem repeats within the N-terminal domain of HPF1 was sufficient to cause pronounced life span shortening. Life span impairment by HPF1 was buffered by rapamycin but not by calorie restriction. The HPF1 repeat expansion shifted yeast cells from a sedentary to a buoyant state, thereby increasing their exposure to surrounding oxygen. The higher oxygenation altered methionine, lipid, and purine metabolism, and inhibited quiescence, which explains the life span shortening. We conclude that fast-evolving intragenic repeat expansions can fundamentally change the relationship between cells and their environment with profound effects on cellular lifestyle and longevity.

Developmental plasticity and stability in the tracheal networks supplying Drosophila flight muscle in response to rearing oxygen level

While it is clear that the insect tracheal system can respond in a compensatory manner to both hypoxia and hyperoxia, there is substantial variation in how different parts of the system respond. However, the response of tracheal structures, from the tracheoles to the largest tracheal trunks, have not been studied within one species. In this study, we examined the effect of larval/pupal rearing in hypoxia, normoxia, and hyperoxia (10, 21 or 40kPa oxygen) on body size and the tracheal supply to the flight muscles of Drosophila melanogaster, using synchrotron radiation micro-computed tomography (SR-µCT) to assess flight muscle volumes and the major tracheal trunks, and confocal microscopy to assess the tracheoles. Hypoxic rearing decreased thorax length whereas hyperoxic-rearing decreased flight muscle volumes, suggestive of negative effects of both extremes. Tomography at the broad organismal scale revealed no evidence for enlargement of the major tracheae in response to lower rearing oxygen levels, although tracheal size scaled with muscle volume. However, using confocal imaging, we found a strong inverse relationship between tracheole density within the flight muscles and rearing oxygen level, and shorter tracheolar branch lengths in hypoxic-reared animals. Although prior studies of larger tracheae in other insects indicate that axial diffusing capacity should be constant with sequential generations of branching, this pattern was not found in the fine tracheolar networks, perhaps due to the increasing importance of radial diffusion in this regime. Overall, D. melanogaster responded to rearing oxygen level with compensatory morphological changes in the small tracheae and tracheoles, but retained stability in most of the other structural components of the tracheal supply to the flight muscles.

Supply and demand: How does variation in atmospheric oxygen during development affect insect tracheal and mitochondrial networks?

Atmospheric oxygen is one of the most important atmospheric component for all terrestrial organisms. Variation in atmospheric oxygen has wide ranging effects on animal physiology, development, and evolution. This variation in oxygen has the potential to affect both respiratory systems (the supply side) and mitochondrial networks (the demand side) in animals. Insect respiratory systems supplying oxygen to tissues in the gas phase through blind ended tracheal systems are particularly susceptible to this variation. While the large conducting tracheae have previously been shown to respond developmentally to changes in rearing oxygen, the effect of oxygen on the tracheolar network has been relatively unexplored, especially in adult insects. Similarly, mitochondrial networks that meet energy demand in insects and other animals are dynamic and their enzyme activities have been shown to vary in the presence of oxygen. These two systems together should be under selective pressure to meet the aerobic metabolic requirements of insects. To test this hypothesis, we reared Mito-YFP Drosophila under three different oxygen concentrations hypoxia (12%), normoxia (21%), and hyperoxia (31%) and imaged their tracheolar and mitochondrial networks within their flight muscle using confocal microscopy. In terms of oxygen supply, hypoxia increased mean (mid-length) tracheolar diameters, tracheolar tip diameters, the number of tracheoles per main branch and affected tracheal branching patterns, while the opposite was observed in hyperoxia. In terms of oxygen demand, hypoxia increased mitochondrial investment and mitochondrial to tracheolar volume ratios; while the opposite was observed in hyperoxia. Generally, hypoxia had a stronger effect on both systems than hyperoxia. These results show that insects are capable of developmentally changing investment in both their supply and demand networks to increase overall fitness.

Functional Hypoxia in Insects: Definition, Assessment, and Consequences for Physiology, Ecology, and Evolution

Insects can experience functional hypoxia, a situation in which O₂ supply is inadequate to meet oxygen demand. Assessing when functional hypoxia occurs is complex, because responses are graded, age and tissue dependent, and compensatory. Here, we compare information gained from metabolomics and transcriptional approaches and by manipulation of the partial pressure of oxygen. Functional hypoxia produces graded damage, including damaged macromolecules and inflammation. Insects respond by compensatory physiological and morphological changes in the tracheal system, metabolic reorganization, and suppression of activity, feeding, and growth. There is evidence for functional hypoxia in eggs, near the end of juvenile instars, and during molting. Functional hypoxia is more likely in species with lower O₂ availability or transport capacities and when O₂ need is great. Functional hypoxia occurs normally during insect development and is a factor in mediating life-history trade-offs.

A plant pathogenic bacterium exploits the tricarboxylic acid cycle metabolic pathway of its insect vector

Huanglongbing in citrus is caused by a phloem-limited, uncultivable, gram-negative α-proteobacterium, Candidatus Liberibacter asiaticus (CLas). CLas is transmitted by the phloem-sucking insect, Diaphorina citri (Hemiptera: Liviidae), in a persistent, circulative, and propagative manner. In this study, we investigated the metabolomic and respiration rates changes in D. citri upon infection with CLas using gas chromatography-mass spectrometry (GC-MS) and gas exchange analysis. The level of glycine, _L-serine, _L-threonine, and gamma-amino butyric acid were higher in CLas-infected D. citri, while _L-proline, _L-aspartic acid, and _L-pyroglutamic acid were lower in CLas-infected D. citri compared with the control. Citric acid was increased in CLas-infected D. citri, whereas malic and succinic acids were reduced. Interestingly, most of the reduced metabolites such as malate, succinate, aspartate, and _L-proline are required for the growth of CLas. The increase in citric acid, serine, and glycine indicated that CLas induced glycolysis and the tricarboxylic acid cycle (TCA) in its vector. In agreement with the GC-MS results, the gene expression results also indicated that glycolysis and TCA were induced in CLas-infected D. citri and this was accompanied with an increases in respiration rate. Phosphoric acid and most of the sugar alcohols were higher in CLas-infected D. citri, indicating a response to the biotic stress or cell damage. Only slight increases in the levels of few sugars were observed in CLas-infected D. citri, which indicated that sugars are tightly regulated by D. citri. Our results indicated that CLas induces nutrient and energetic stress in its host insect. This study may provide some insights into the mechanism of colonization of CLas in its vector.

More oxygen during development enhanced flight performance but not thermal tolerance of Drosophila melanogaster

High temperatures can stress animals by raising the oxygen demand above the oxygen supply. Consequently, animals under hypoxia could be more sensitive to heating than those exposed to normoxia. Although support for this model has been limited to aquatic animals, oxygen supply might limit the heat tolerance of terrestrial animals during energetically demanding activities. We evaluated this model by studying the flight performance and heat tolerance of flies (Drosophila melanogaster) acclimated and tested at different concentrations of oxygen (12%, 21%, and 31%). We expected that flies raised at hypoxia would develop into adults that were more likely to fly under hypoxia than would flies raised at normoxia or hyperoxia. We also expected flies to benefit from greater oxygen supply during testing. These effects should have been most pronounced at high temperatures, which impair locomotor performance. Contrary to our expectations, we found little evidence that flies raised at hypoxia flew better when tested at hypoxia or tolerated extreme heat better than did flies raised at normoxia or hyperoxia. Instead, flies raised at higher oxygen levels performed better at all body temperatures and oxygen concentrations. Moreover, oxygen supply during testing had the greatest effect on flight performance at low temperature, rather than high temperature. Our results poorly support the hypothesis that oxygen supply limits performance at high temperatures, but do support the idea that hyperoxia during development improves performance of flies later in life.

Supplementation of Spirulina (Arthrospira platensis) Improves Lifespan and Locomotor Activity in Paraquat-Sensitive DJ-1βΔ93 Flies, a Parkinson's Disease Model in Drosophila melanogaster

Spirulina (Arthrospira platensis) is a cyanobacterium (blue-green alga) consumed by humans and other animals because of its nutritional values and pharmacological properties. Apart from high protein contents, it also contains high levels of antioxidant and anti-inflammatory compounds, such as carotenoids, β-carotene, phycocyanin, and phycocyanobilin, indicating its possible pharmaco-therapeutic utility. In the present study using DJ-1β^Δ93 flies, a Parkinson's disease model in Drosophila, we have demonstrated the therapeutic effect of spirulina and its active component C-phycocyanin (C-PC) in the improvement of lifespan and locomotor behavior. Our findings indicate that dietary supplementation of spirulina significantly improves the lifespan and locomotor activity of paraquat-fed DJ-1β^Δ93 flies. Furthermore, supplementation of spirulina and C-PC individually and independently reduced the cellular stress marked by deregulating the expression of heat shock protein 70 and Jun-N-terminal kinase signaling in DJ-1β^Δ93 flies. A significant decrease in superoxide dismutase and catalase activities in spirulina-fed DJ-1β^Δ93 flies tends to indicate the involvement of antioxidant properties associated with spirulina in the modulation of stress-induced signaling and improvement in lifespan and locomotor activity in Drosophila DJ-1β^Δ93 flies. Our results suggest that antioxidant boosting properties of spirulina can be used as a nutritional supplement for improving the lifespan and locomotor behavior in Parkinson's disease.

Knockdown of Drosophila hemoglobin suggests a role in O2 homeostasis

Almost all insects are equipped with a tracheal system, which appears to be sufficient for O2 supply even in phases of high metabolic activity. Therefore, with the exception of a few species dwelling in hypoxic habitats, specialized respiratory proteins had been considered unnecessary in insects. The recent discovery and apparently universal presence of intracellular hemoglobins in insects has remained functionally unexplained. The fruitfly Drosophila melanogaster harbors three different globin genes (referred to as glob1-3). Glob1 is the most highly expressed globin and essentially occurs in the tracheal system and the fat body. To better understand the functions of insect globins, the levels of glob1 were modulated in Drosophila larvae and adults by RNAi-mediated knockdown and transgenic over-expression. No effects on the development were observed in flies with manipulated glob1 levels. However, the knockdown of glob1 led to a significantly reduced survival rate of adult flies under hypoxia (5% and 1.5% O2). Surprisingly, the glob1 knockdown flies also displayed increased resistance towards the reactive oxygen species-forming agent paraquat, which may be explained by a restricted availability of O2 resulting in decreased formation of harmful O2(-). In summary, our results suggest an important functional role of glob1 in O2 homeostasis, possibly by enhancing O2 supply.

The Oxygen Environment at Birth Specifies the Population of Alveolar Epithelial Stem Cells in the Adult Lung

Alveolar epithelial type II cells (AEC2) maintain pulmonary homeostasis by producing surfactant, expressing innate immune molecules, and functioning as adult progenitor cells for themselves and alveolar epithelial type I cells (AEC1). How the proper number of alveolar epithelial cells is determined in the adult lung is not well understood. Here, BrdU labeling, genetic lineage tracing, and targeted expression of the anti-oxidant extracellular superoxide dismutase in AEC2s are used to show how the oxygen environment at birth influences postnatal expansion of AEC2s and AEC1s in mice. Birth into low (12%) or high (≥60%) oxygen stimulated expansion of AEC2s through self-renewal and differentiation of the airway Scgb1a1 + lineage. This non-linear or hormesis response to oxygen was specific for the alveolar epithelium because low oxygen stimulated and high oxygen inhibited angiogenesis as defined by changes in V-cadherin and PECAM (CD31). Although genetic lineage tracing studies confirmed adult AEC2s are stem cells for AEC1s, we found no evidence that postnatal growth of AEC1s were derived from self-renewing Sftpc + or the Scbg1a1 + lineage of AEC2s. Taken together, our results show how a non-linear response to oxygen at birth promotes expansion of AEC2s through two distinct lineages. Since neither lineage contributes to the postnatal expansion of AEC1s, the ability of AEC2s to function as stem cells for AEC1s appears to be restricted to the adult lung. Stem Cells 2016;34:1396-1406.

NPGPx modulates CPEB2-controlled HIF-1α RNA translation in response to oxidative stress

Non-selenocysteine-containing phospholipid hydroperoxide glutathione peroxidase (NPGPx or GPx7) is an oxidative stress sensor that modulates the antioxidative activity of its target proteins through intermolecular disulfide bond formation. Given NPGPx's role in protecting cells from oxidative damage, identification of the oxidative stress-induced protein complexes, which forms with key stress factors, may offer novel insight into intracellular reactive oxygen species homeostasis. Here, we show that NPGPx forms a disulfide bond with the translational regulator cytoplasmic polyadenylation element-binding protein 2 (CPEB2) that results in negative regulation of hypoxia-inducible factor 1-alpha (HIF-1α) RNA translation. In NPGPx-proficient cells, high oxidative stress that disrupts this bonding compromises the association of CPEB2 with HIF-1α RNA, leading to elevated HIF-1α RNA translation. NPGPx-deficient cells, in contrast, demonstrate increased HIF-1α RNA translation under normoxia with both impaired induction of HIF-1α synthesis and blunted HIF-1α-programmed transcription following oxidative stress. Together, these results reveal a molecular mechanism for how NPGPx mediates CPEB2-controlled HIF-1α RNA translation in a redox-sensitive manner.

Why is aging conserved and what can we do about it?

The field of aging research has progressed rapidly over the past few decades. Genetic modulators of aging rate that are conserved over a broad evolutionary distance have now been identified. Several physiological and environmental interventions have also been shown to influence the rate of aging in organisms ranging from yeast to mammals. Here we briefly review these conserved pathways and interventions and highlight some key unsolved challenges that remain. Although the molecular mechanisms by which these modifiers of aging act are only partially understood, interventions to slow aging are nearing clinical application, and it is likely that we will begin to reap the benefits of aging research prior to solving all of the mysteries that the biology of aging has to offer.

Old age is the single greatest risk factor for the leading causes of death in the developed world. Advances in aging research promise to alleviate the diseases of aging by targeting aging itself.

Effects of oxygen concentration and pressure on Drosophila melanogaster: oxidative stress, mitochondrial activity, and survivorship

Organisms are known to be equipped with an adaptive plasticity as the phenotype of traits in response to the imposed environmental challenges as they grow and develop. In this study, the effects of extreme changes in oxygen availability and atmospheric pressure on physiological phenotypes of Drosophila melanogaster were investigated to explore adaptation mechanisms. The changes in citrate synthase activity (CSA), lifespan, and behavioral function in different atmospheric conditions were evaluated. In the CAS test, hyperoxia significantly increased CSA; both hypoxia and hyperbaric conditions caused a significant decrease in CSA. In the survivorship test, all changed atmospheric conditions caused a significant reduction in lifespan. The lifespan reduced more after hypoxia exposure than after hyperbaria exposure. In behavioral function test, when mechanical agitation was conducted, bang-sensitive flies showed a stereotypical sequence of initial muscle spasm, paralysis, and recovery. The percentage of individuals that displayed paralysis or seizure was measured on the following day and after 2 weeks from each exposure. The majority of flies showed seizure behavior 15 days after exposure, especially after 3 h of exposure. The percentage of individuals that did not undergo paralysis or seizure and was able to move in the vial, was also tested. The number of flies that moved and raised the higher level of the vial decreased after exposure. Animal's speed decreased significantly 15 days after exposure to extreme environmental conditions. In summary, the alteration of oxygen availability and atmospheric pressure may lead to significant changes in mitochondria mass, lifespan, and behavioral function in D. melanogaster.

Pushing the limit: examining factors that affect anoxia tolerance in a single genotype of adult D. melanogaster

Drosophila melanogaster is a promiscuous species that inhabits a large range of harsh environments including flooded habitats and varying temperature changes. To survive these environments, fruit flies have adapted mechanisms of tolerance that allow them to thrive. During exposure to anoxic stress, fruit flies and other poikilotherms enter into a reversible, protective coma. This coma can be manipulated based on controlled environmental conditions inside the laboratory. Here we utilize a common laboratory raised strain of D. melanogaster to characterize adaptation abilities to better understand coma recovery and survival limitations. Our goal is to mimic the fly's natural environments (wet anoxia) and relate findings to a typical gas induced environment (dry anoxia) that is commonly used in a laboratory. Despite the abundance of research regarding acute and chronic anoxic exposure and cold stress, the literature is lacking evidence linking anoxic stress with variable environmental conditions such as animal age and stress duration. We present novel ways to assess coma recovery and survival using readily available laboratory tools. Our findings suggest that younger age, exposure to colder temperatures and wet environments increase resistance to anoxic stress.

Hypoxia disrupts proteostasis in Caenorhabditis elegans

Oxygen is fundamentally important for cell metabolism, and as a consequence, O₂ deprivation (hypoxia) can impair many essential physiological processes. Here, we show that an active response to hypoxia disrupts cellular proteostasis – the coordination of protein synthesis, quality control, and degradation that maintains the functionality of the proteome. We have discovered that specific hypoxic conditions enhance the aggregation and toxicity of aggregation-prone proteins that are associated with neurodegenerative diseases. Our data indicate this is an active response to hypoxia, rather than a passive consequence of energy limitation. This response to hypoxia is partially antagonized by the conserved hypoxia-inducible transcription factor, hif-1. We further demonstrate that exposure to hydrogen sulfide (H₂S) protects animals from hypoxia-induced disruption of proteostasis. H₂S has been shown to protect against hypoxic damage in mammals and extends lifespan in nematodes. Remarkably, our data also show that H₂S can reverse detrimental effects of hypoxia on proteostasis. Our data indicate that the protective effects of H₂S in hypoxia are mechanistically distinct from the effect of H₂S to increase lifespan and thermotolerance, suggesting that control of proteostasis and aging can be dissociated. Together, our studies reveal a novel effect of the hypoxia response in animals and provide a foundation to understand how the integrated proteostasis network is integrated with this stress response pathway.

Plasticity of insect body size in response to oxygen: integrating molecular and physiological mechanisms

The hypoxia-induced reduction of body size in Drosophila and Manduca is ideal for understanding the mechanisms of body size plasticity. The mechanisms of size regulation are well-studied in these species, and the molecular mechanisms of oxygen sensing are also well-characterized. What is missing is the connection between oxygen sensing and the mechanisms that regulate body size in standard conditions. Oxygen functions both as a substrate for metabolism to produce energy and as a signaling molecule that activates specific cellular signaling networks. Hypoxia affects metabolism in a passive, generalized manner. Hypoxia also induces the activation of targeted signaling pathways, which may mediate the reduction in body size, or alternatively, compensate for the metabolic perturbations and attenuate the reduction in size. These alternative hypotheses await testing. Both perspectives-metabolism and information-are necessary to understand how oxygen affects body size.

Extended hypoxia in the alfalfa leafcutting bee, Megachile rotundata, increases survival but causes sub-lethal effects

Many insects are tolerant of hypoxic conditions, but survival may come at a cost to long-term health. The alfalfa leaf-cutting bee, Megachile rotundata, develops in brood cells inside natural cavities, and may be exposed to hypoxic conditions for extended periods of time. Whether M. rotundata is tolerant of hypoxia, and whether exposure results in sub-lethal effects, has never been investigated. Overwintering M. rotundata prepupae were exposed to 10%, 13%, 17%, 21% and 24% O2 for 11 months. Once adults emerged, five indicators of quality - emergence weight, body size, feeding activity, flight performance, and adult longevity, - were measured to determine whether adult bees that survived past exposure to hypoxia were competent pollinators. M. rotundata prepupae are tolerant of hypoxic condition and have higher survival rates in hypoxia, than in normoxia. Under hypoxia, adult emergence rates did not decrease over the 11 months of the experiment. In contrast, bees reared in normoxia had decreased emergence rates by 8 months, and were dead by 11 months. M. rotundata prepupae exposed to extended hypoxic conditions had similar emergence weight, head width, and cross-thorax distance compared to bees reared in standard 21% oxygen. Despite no significant morphological differences, hypoxia-exposed bees had lower feeding rates and shorter adult lifespans. Hypoxia may play a role in post-diapause physiology of M. rotundata, with prepupae showing better survival under hypoxic conditions. Extended exposure to hypoxia, while not fatal, causes sub-lethal effects in feeding rates and longevity in the adults, indicating that hypoxia tolerance comes at a cost.

Oxygen, gastrin-releasing Peptide, and pediatric lung disease: life in the balance

Excessive oxygen (O2) can cause tissue injury, scarring, aging, and even death. Our laboratory is studying O2-sensing pulmonary neuroendocrine cells (PNECs) and the PNEC-derived product gastrin-releasing peptide (GRP). Reactive oxygen species (ROS) generated from exposure to hyperoxia, ozone, or ionizing radiation (RT) can induce PNEC degranulation and GRP secretion. PNEC degranulation is also induced by hypoxia, and effects of hypoxia are mediated by free radicals. We have determined that excessive GRP leads to lung injury with acute and chronic inflammation, leading to pulmonary fibrosis (PF), triggered via ROS exposure or by directly treating mice with exogenous GRP. In animal models, GRP-blockade abrogates lung injury, inflammation, and fibrosis. The optimal time frame for GRP-blockade and the key target cell types remain to be determined. The concept of GRP as a mediator of ROS-induced tissue damage represents a paradigm shift about how O2 can cause injury, inflammation, and fibrosis. The host PNEC response in vivo may depend on individual ROS sensing mechanisms and subsequent GRP secretion. Ongoing scientific and clinical investigations promise to further clarify the molecular pathways and clinical relevance of GRP in the pathogenesis of diverse pediatric lung diseases.

Nature's inordinate fondness for metabolic enzymes: why metabolic enzyme loci are so frequently targets of selection

Metabolic enzyme loci were some of the first genes accessible for molecular evolution and ecology research. New technologies now make the whole genome, transcriptome or proteome readily accessible, allowing unbiased scans for loci exhibiting significant differences in allele frequency or expression level and associated with phenotypes and/or responses to natural selection. With surprising frequency and in many cases in proportions greater than chance relative to other genes, glycolysis and TCA cycle enzyme loci appear among the genes with significant associations in these studies. Hence, there is an ongoing need to understand the basis for fitness effects of metabolic enzyme polymorphisms. Allele-specific effects on the binding affinity and catalytic rate of individual enzymes are well known, but often of uncertain significance because metabolic control theory and in vivo studies indicate that many individual metabolic enzymes do not affect pathway flux rate. I review research, so far little used in evolutionary biology, showing that metabolic enzyme substrates affect signalling pathways that regulate cell and organismal biology, and that these enzymes have moonlighting functions. To date there is little knowledge of how alleles in natural populations affect these phenotypes. I discuss an example in which alleles of a TCA enzyme locus associate with differences in a signalling pathway and development, organismal performance, and ecological dynamics. Ultimately, understanding how metabolic enzyme polymorphisms map to phenotypes and fitness remains a compelling and ongoing need for gaining robust knowledge of ecological and evolutionary processes.

Caterpillars selected for large body size and short development time are more susceptible to oxygen-related stress

Recent studies suggest that higher growth rates may be associated with reduced capacities for stress tolerance and increased accumulated damage due to reactive oxygen species. We tested the response of Manduca sexta (Sphingidae) lines selected for large or small body size and short development time to hypoxia (10 kPa) and hyperoxia (25, 33, and 40 kPa); both hypoxia and hyperoxia reduce reproduction and oxygen levels over 33 kPa have been shown to increase oxidative damage in insects. Under normoxic (21 kPa) conditions, individuals from the large-selected (big-fast) line were larger and had faster growth rates, slightly longer developmental times, and reduced survival rates compared to individuals from a line selected for small size (small-fast) or an unselected control line. Individuals from the big-fast line exhibited greater negative responses to hyperoxia with greater reductions in juvenile and adult mass, growth rate, and survival than the other two lines. Hypoxia generally negatively affected survival and growth/size, but the lines responded similarly. These results are mostly consistent with the hypothesis that simultaneous acquisition of large body sizes and short development times leads to reduced capacities for coping with stressful conditions including oxidative damage. This result is of particular importance in that natural selection tends to decrease development time and increase body size.

The lifespan extension effects of resveratrol are conserved in the honey bee and may be driven by a mechanism related to caloric restriction

Our interest in healthy aging and in evolutionarily conserved mechanisms of lifespan extension prompted us to investigate whether features of age-related decline in the honey bee could be attenuated with resveratrol. Resveratrol is regarded as a caloric restriction mimetic known to extend lifespan in some but not all model species. The current, prevailing view is that resveratrol works largely by activating signaling pathways. It has also been suggested that resveratrol may act as an antioxidant and confer protection against nervous system impairment and oxidative stress. To test whether honey bee lifespan, learning performance, and food perception could be altered by resveratrol, we supplemented the diets of honey bees and measured lifespan, olfactory learning, and gustatory responsiveness to sucrose. Furthermore, to test the effects of resveratrol under metabolic challenge, we used hyperoxic environments to generate oxidative stress. Under normal oxygen conditions, two resveratrol treatments-30 and 130 μM-lengthened average lifespan in wild-type honey bees by 38% and 33%, respectively. Both resveratrol treatments also lengthened maximum and median lifespan. In contrast, hyperoxic stress abolished the resveratrol life-extension response. Furthermore, resveratrol did not affect learning performance, but did alter gustation. Honey bees that were not fed resveratrol exhibited greater responsiveness to sugar, while those supplemented with resveratrol were less responsive to sugar. We also discovered that individuals fed a high dose of resveratrol-compared to controls-ingested fewer quantities of food under ad libitum feeding conditions.

Interactions between oxygen homeostasis, food availability, and hydrogen sulfide signaling

The ability to sense and respond to stressful conditions is essential to maintain organismal homeostasis. It has long been recognized that stress response factors that improve survival in changing conditions can also influence longevity. In this review, we discuss different strategies used by animals in response to decreased O(2) (hypoxia) to maintain O(2) homeostasis, and consider interactions between hypoxia responses, nutritional status, and H(2)S signaling. O(2) is an essential environmental nutrient for almost all metazoans as it plays a fundamental role in development and cellular metabolism. However, the physiological response(s) to hypoxia depend greatly on the amount of O(2) available. Animals must sense declining O(2) availability to coordinate fundamental metabolic and signaling pathways. It is not surprising that factors involved in the response to hypoxia are also involved in responding to other key environmental signals, particularly food availability. Recent studies in mammals have also shown that the small gaseous signaling molecule hydrogen sulfide (H(2)S) protects against cellular damage and death in hypoxia. These results suggest that H(2)S signaling also integrates with hypoxia response(s). Many of the signaling pathways that mediate the effects of hypoxia, food deprivation, and H(2)S signaling have also been implicated in the control of lifespan. Understanding how these pathways are coordinated therefore has the potential to reveal new cellular and organismal homeostatic mechanisms that contribute to longevity assurance in animals.

Loss of the oxidative stress sensor NPGPx compromises GRP78 chaperone activity and induces systemic disease

NPGPx is a member of the glutathione peroxidase (GPx) family; however, it lacks GPx enzymatic activity due to the absence of a critical selenocysteine residue, rendering its function an enigma. Here, we show that NPGPx is a newly identified stress sensor that transmits oxidative stress signals by forming the disulfide bond between its Cys57 and Cys86 residues. This oxidized form of NPGPx binds to glucose-regulated protein (GRP)78 and forms covalent bonding intermediates between Cys86 of NPGPx and Cys41/Cys420 of GRP78. Subsequently, the formation of the disulfide bond between Cys41 and Cys420 of GRP78 enhances its chaperone activity. NPGPx-deficient cells display increased reactive oxygen species, accumulated misfolded proteins, and impaired GRP78 chaperone activity. Complete loss of NPGPx in animals causes systemic oxidative stress, increases carcinogenesis, and shortens life span. These results suggest that NPGPx is essential for releasing excessive ER stress by enhancing GRP78 chaperone activity to maintain physiological homeostasis.

Fast molecular evolution associated with high active metabolic rates in poison frogs

Molecular evolution is simultaneously paced by mutation rate, genetic drift, and natural selection. Life history traits also affect the speed of accumulation of nucleotide changes. For instance, small body size, rapid generation time, production of reactive oxygen species (ROS), and high resting metabolic rate (RMR) are suggested to be associated with faster rates of molecular evolution. However, phylogenetic correlation analyses failed to support a relationship between RMR and molecular evolution in ectotherms. In addition, RMR might underestimate the metabolic budget (e.g., digestion, reproduction, or escaping predation). An alternative is to test other metabolic rates, such as active metabolic rate (AMR), and their association with molecular evolution. Here, I present comparative analyses of the associations between life history traits (i.e., AMR, RMR, body mass, and fecundity) with rates of molecular evolution of and mitochondrial loci from a large ectotherm clade, the poison frogs (Dendrobatidae). My results support a strong positive association between mass-specific AMR and rates of molecular evolution for both mitochondrial and nuclear loci. In addition, I found weaker and genome-specific covariates such as body mass and fecundity for mitochondrial and nuclear loci, respectively. No direct association was found between mass-specific RMR and rates of molecular evolution. Thus, I provide a mechanistic hypothesis of the link between AMRs and the rate of molecular evolution based on an increase in ROS within germ line cells during periodic bouts of hypoxia/hyperoxia related to aerobic exercise. Finally, I propose a multifactorial model that includes AMR as a predictor of the rate of molecular evolution in ectothermic lineages.

Evolutionary consequences of altered atmospheric oxygen in Drosophila melanogaster

Twelve replicate populations of Drosophila melanogaster, all derived from a common ancestor, were independently evolved for 34+ generations in one of three treatment environments of varying PO(2): hypoxia (5.0-10.1 kPa), normoxia (21.3 kPa), and hyperoxia (40.5 kPa). Several traits related to whole animal performance and metabolism were assayed at various stages via "common garden" and reciprocal transplant assays to directly compare evolved and acclimatory differences among treatments. Results clearly demonstrate the evolution of a greater tolerance to acute hypoxia in the hypoxia-evolved populations, consistent with adaptation to this environment. Greater hypoxia tolerance was associated with an increase in citrate synthase activity in fly homogenate when compared to normoxic (control) populations, suggesting an increase in mitochondrial volume density in these populations. In contrast, no direct evidence of increased performance of the hyperoxia-evolved populations was detected, although a significant decrease in the tolerance of these populations to acute hypoxia suggests a cost to adaptation to hyperoxia. Hyperoxia-evolved populations had lower productivity overall (i.e., across treatment environments) and there was no evidence that hypoxia or hyperoxia-evolved populations had greatest productivity or longevity in their respective treatment environments, suggesting that these assays failed to capture the components of fitness relevant to adaptation.

The effect of developmental stage on the sensitivity of cell and body size to hypoxia in Drosophila melanogaster

Animals reared in hypoxic environments frequently exhibit smaller body sizes than when reared under normal atmospheric oxygen concentrations. The mechanisms responsible for this widely documented pattern of body size plasticity are poorly known. We studied the ontogeny of responses of Drosophila melanogaster adult body size to hypoxic exposure. We hypothesized that there may be critical oxygen-sensitive periods during D. melanogaster development that are primarily responsive to body size regulation. Instead, our results showed that exposure to hypoxia (an atmospheric partial pressure of oxygen of 10 kPa) during any developmental stage (embryo, larvae and pupae) leads to smaller adult size. However, short hypoxic exposures during the late larval and early pupal stages had the greatest effects on adult size. We then investigated whether the observed reductions in size induced by hypoxia at various developmental stages were the result of a decrease in cell size or cell number. Abdominal epithelial cells of flies reared continuously in hypoxia were smaller in mean diameter and were size-limited compared with cells of flies reared in normoxia. Flies reared in hypoxia during the embryonic, larval or pupal stage, or during their entire development, had smaller wing areas than flies reared in normoxia. Flies reared during the pupal stage, or throughout development in hypoxia had smaller wing cells, even after controlling for the effect of wing size. These results suggest that hypoxia effects on the body size of D. melanogaster probably occur by multiple mechanisms operating at various developmental stages.

Responses of Drosophila melanogaster to atypical oxygen atmospheres

We examined physiological phenotypes of Drosophila melanogaster in hypoxic to hyperoxic atmospheres. We performed measurements on life span or behavioural function in 5, 21, 40, 60, and 80% O(2), and combined this with literature data for 2% and 100% O(2). O(2) incubation resulted in a concentration-dependent reduction of life span in both hypoxia and hyperoxia, though different measures of life span were affected differently. We also examined how behavioural and metabolic functions were affected by exposure to hyperoxia (up to 60% O(2)). Climbing behaviour was measured as a fast (4 s) and slow (55 s) response in a negative geotaxis assay. In normoxia, both measures of climbing response declined exponentially until disappearing completely. Interestingly, survivorship was very high until the loss of climbing ability, after which it dropped rapidly. This pattern appeared accelerated in 40% O(2). However, while flies in 60% O(2) also apparently lost their fast climbing ability immediately prior to the drop in survivorship, they maintained considerable climbing ability over the longer trial. Metabolism, measured by CO(2) release, did not change with age in normoxic flies, but was significantly lower in flies exposed to hyperoxia, particularly as the flies aged. There was, however, a slight increase in water loss rate with age in normoxia, while in hyperoxia, water loss was reduced. Uniquely, the water loss rates of flies in 60% O(2) doubled immediately prior to the end of their life span. Because ageing results in generally irreversible functional declines, we examined if functional declines in hyperoxia (60% O(2)) were also irreversible, or whether some functioning could recover after a return to normoxia. After 7 days of recovery, water loss rates decreased, CO(2) exhalation slightly increased, and climbing ability was partially recovered. Therefore, the effect of O(2) on D. melanogaster function is non-linear, may be reversible, and may include unique phenotypes that arise at some O(2) concentrations, and not others.