Durian fruit pulp extract enhances intracellular glutathione levels, mitigating oxidative stress and inflammation for neuroprotection

Durian (Durio zibethinus L.) fruit pulp is a rich source of γ-glutamylcysteine (γ-EC), a direct precursor to the antioxidant glutathione (GSH). This study elucidated the in vitro neuroprotective potential of unripe durian fruit pulp extract (UDE) against H2O2-induced neurotoxicity in SH-SY5Y cells and neuroinflammation in lipopolysaccharide (LPS)-stimulated BV-2 cells. Treatments with γ-EC, GSH standards, or UDE exhibited no cytotoxicity in SH-SY5Y and BV-2 cells, except at high concentrations. A 4-h pretreatment with 100 µM γ-EC or UDE containing 100 µM γ-EC significantly increased SH-SY5Y cell viability post H2O2 induction. Moreover, a similar pretreatment reduced LPS-stimulated production of proinflammatory cytokines in BV-2 cells. The neuroprotective effect of UDE is primarily attributed to γ-EC provision and the promotion of GSH synthesis, which in turn elevates intracellular GSH levels and reduces proinflammatory cytokines. This study identifies γ-EC in UDE as a potential neuroprotective biomarker boosting intracellular GSH levels, providing insights into UDE's therapeutic potential.

Low Antioxidant Glutathione Levels Lead to Longer Telomeres: A Sex-Specific Link to Longevity?

Telomeres are repetitive DNA sequences at the end of chromosomes that protect them from degradation. They have been the focus of intense research because short telomeres would predict accelerated ageing and reduced longevity in vertebrates. Oxidative stress is considered a physiological driver of the telomere shortening and, consequently, short lifespan. Among molecules fighting against oxidative stress, glutathione is involved in many antioxidant pathways. Literature supports that oxidative stress may trigger a compensatory "hormetic" response increasing glutathione levels and telomere length. Here, we tested the link between total glutathione concentration and telomere length in captive birds (zebra finches; Taeniopygia guttata). Total glutathione levels were experimentally decreased during birds' growth using a specific inhibitor of glutathione synthesis (buthionine sulfoximine; BSO). We monitored the birds' reproductive performance in an outdoor aviary during the first month of life, and their longevity for almost 9 years. Among control individuals, erythrocyte glutathione levels during development positively predicted erythrocyte telomere length in adulthood. However, BSO-treated females, but not males, showed longer telomeres than control females in adulthood. This counterintuitive finding suggests that females mounted a compensatory response. Such compensation agrees with precedent findings in the same population where the BSO treatment increased growth and adult body mass in females but not males. BSO did not influence longevity or reproductive output in any sex. However, early glutathione levels and adult telomere length interactively predicted longevity only among control females. Those females with "naturally" low (non-manipulated) glutathione levels at the nestling age but capable of producing longer telomeres in adulthood seem to live longer. The results suggest that the capability to mount a hormetic response triggered by low early glutathione levels can improve fitness via telomere length. Overall, the results may indicate a sex-specific link between glutathione and telomere values. Telomerase activity and sexual steroids (estrogens) are good candidates to explain the sex-biased mechanism underlying the early-life impact of oxidative stress on adult telomere length.

Mitochondrial superoxide dismutase overexpression and low oxygen conditioning hormesis improve the performance of irradiated sterile males

The Sterile Insect Technique (SIT) is a successful autocidal control method that uses ionizing radiation to sterilize insects. However, irradiation in normal atmospheric conditions can be damaging for males, because irradiation generates substantial biological oxidative stress that, combined with domestication and mass-rearing conditions, may reduce sterile male sexual competitiveness and quality. In this study, biological oxidative stress and antioxidant capacity were experimentally manipulated in Anastrepha suspensa using a combination of low-oxygen conditions and transgenic overexpression of mitochondrial superoxide dismutase (SOD2) to evaluate their role in the sexual behavior and quality of irradiated males. Our results showed that SOD2 overexpression enhances irradiated insect quality and improves male competitiveness in leks. However, the improvements in mating performance were modest, as normoxia-irradiated SOD2 males exhibited only a 22% improvement in mating success compared to normoxia-irradiated wild type males. Additionally, SOD2 overexpression did not synergistically improve the mating success of males irradiated in either hypoxia or severe hypoxia. Short-term hypoxic and severe-hypoxic conditioning hormesis, per se, increased antioxidant capacity and enhanced sexual competitiveness of irradiated males relative to non-irradiated males in leks. Our study provides valuable new information that antioxidant enzymes, particularly SOD2, have potential to improve the quality and lekking performance of sterile males used in SIT programs.

Multicomponent Training Prevents Memory Deficit Related to Amyloid-β Protein-Induced Neurotoxicity

BACKGROUND

Alzheimer's disease (AD) is characterized by the accumulation of the amyloid-β peptide in the brain, leading to early oxidative stress and neurotoxicity. It has been suggested that physical exercise could be beneficial in preventing AD, but studies with multicomponent training are scanty.

OBJECTIVE

Verify the effects of multicomponent exercise training to prevent deficits in recognition memory related to Aβ neurotoxicity.

METHODS

We subjected Wistar rats to multicomponent training (including aerobic and anaerobic physical exercise and cognitive exercise) and then infused amyloid-β peptide into their hippocampus.

RESULTS

We show that long-term multicomponent training prevents the amyloid-β-associated neurotoxicity in the hippocampus. It reduces hippocampal lipid peroxidation, restores antioxidant capacity, and increases glutathione levels, finally preventing recognition memory deficits.

CONCLUSION

Multicomponent training avoids memory deficits related to amyloid-β neurotoxicity on an animal model.

Supplementation with γ-glutamylcysteine (γ-GC) lessens oxidative stress, brain inflammation and amyloid pathology and improves spatial memory in a murine model of AD

INTRODUCTION

The accumulation of oxidative stress, neuroinflammation and abnormal aggregation of amyloid β-peptide (Aβ) have been shown to induce synaptic dysfunction and memory deficits in Alzheimer's disease (AD). Cellular depletion of the major endogenous antioxidant Glutathione (GSH) has been linked to cognitive decline and the development of AD pathology. Supplementation with γ-glutamylcysteine (γ-GC), the immediate precursor and the limiting substrate for GSH biosynthesis, can transiently augment cellular GSH levels by bypassing the regulation of GSH homeostasis.

METHODS

In the present study, we investigated the effect of dietary supplementation of γ-GC on oxidative stress and Aβ pathology in the brains of APP/PS1 mice. The APP/PS1 mice were fed γ-GC from 3 months of age with biomarkers of apoptosis and cell death, oxidative stress, neuroinflammation and Aβ load being assessed at 6 months of age.

RESULTS

Our data showed that supplementation with γ-GC lowered the levels of brain lipid peroxidation, protein carbonyls and apoptosis, increased both total GSH and the glutathione/glutathione disulphide (GSH/GSSG) ratio and replenished ATP and the activities of the antioxidant enzymes (superoxide dismutase (SOD), catalase, glutamine synthetase and glutathione peroxidase (GPX)), the latter being a key regulator of ferroptosis. Brain Aβ load was lower and acetylcholinesterase (AChE) activity was markedly improved compared to APP/PS1 mice fed a standard chow diet. Alteration in brain cytokine levels and matrix metalloproteinase enzymes MMP-2 and MMP-9 suggested that γ-GC may lower inflammation and enhance Aβ plaque clearance in vivo. Spatial memory was also improved by γ-GC as determined using the Morris water maze.

CONCLUSION

Our data collectively suggested that supplementation with γ-GC may represent a novel strategy for the treatment and/or prevention of cognitive impairment and neurodegeneration.

Urban ecophysiology: beyond costs, stress and biomarkers

Natural habitats are rapidly declining due to urbanisation, with a concomitant decline in biodiversity in highly urbanised areas. Yet thousands of different species have colonised urban environments. These organisms are exposed to novel urban conditions, which are sometimes beneficial, but most often challenging, such as increased ambient temperature, chemicals, noise and light pollution, dietary alterations and disturbance by humans. Given the fundamental role of physiological responses in coping with such conditions, certain physiological systems such as the redox system, metabolism and hormones are thought to specifically influence organisms' ability to persist and cope with urbanisation. However, these physiological systems often show mixed responses to urbanisation. Does this mean that some individuals, populations or species are resilient to the urban environmental challenges? Or is something missing from our analyses, leading us to erroneous conclusions regarding the impact of urbanisation? To understand the impact of urbanisation, I argue that a more integrated mechanistic and ecological approach is needed, along with experiments, in order to fully understand the physiological responses; without knowledge of their ecological and evolutionary context, physiological measures alone can be misinterpreted. Furthermore, we need to further investigate the causes of and capacity for individual plasticity in order to understand not only the impact of urbanisation, but also species resilience. I argue that abiotic and biotic urban factors can interact (e.g. pollution with micro- and macronutrients) to either constrain or relax individual physiological responses - and, thereby, plasticity - on a temporal and/or spatial scale, which can lead to erroneous conclusions regarding the impact of urbanisation.

Oxidative Stress Experienced during Early Development Influences the Offspring Phenotype

AbstractOxidative stress (OS) experienced early in life can affect an individual's phenotype. However, its consequences for the next generation remain largely unexplored. We manipulated the OS level endured by zebra finches (Taeniopygia guttata) during their development by transitorily inhibiting the synthesis of the key antioxidant glutathione ("early-high-OS"). The offspring of these birds and control parents were cross fostered at hatching to enlarge or reduce its brood size. Independent of parents' early-life OS levels, the chicks raised in enlarged broods showed lower erythrocyte glutathione levels, revealing glutathione sensitivity to environmental conditions. Control biological mothers produced females, not males, that attained a higher body mass when raised in a benign environment (i.e., the reduced brood). In contrast, biological mothers exposed to early-life OS produced heavier males, not females, when allocated in reduced broods. Early-life OS also affected the parental rearing capacity because 12-day-old nestlings raised by a foster pair with both early-high-OS members grew shorter legs (tarsus) than chicks from other groups. The results indicate that environmental conditions during development can affect early glutathione levels, which may in turn influence the next generation through both pre- and postnatal parental effects. The results also demonstrate that early-life OS can constrain the offspring phenotype.

The Precursor to Glutathione (GSH), γ-Glutamylcysteine (GGC), Can Ameliorate Oxidative Damage and Neuroinflammation Induced by Aβ40 Oligomers in Human Astrocytes

Glutathione (GSH) is one of the most abundant thiol antioxidants in cells. Many chronic and age-related diseases are associated with a decline in cellular GSH levels or impairment in the catalytic activity of the GSH biosynthetic enzyme glutamate cysteine ligase (GCL). γ-glutamylcysteine (GGC), a precursor to glutathione (GSH), can replenish depleted GSH levels under oxidative stress conditions, by circumventing the regulation of GSH biosynthesis and providing the limiting substrate. Soluble amyloid-β (Aβ) oligomers have been shown to induce oxidative stress, synaptic dysfunction and memory deficits which have been reported in Alzheimer’s disease (AD). Calcium ions, which are increased with age and in AD, have been previously reported to enhance the formation of Aβ₄₀ oligomers, which have been casually associated with the pathogenesis of the underlying neurodegenerative condition. In this study, we examined the potential beneficial effects of GGC against exogenous Aβ₄₀ oligomers on biomarkers of apoptosis and cell death, oxidative stress, and neuroinflammation, in human astrocytes. Treatment with Aβ₄₀ oligomers significantly reduced the cell viability and apoptosis of astrocyte brain cultures and increased oxidative modifications of DNA, lipids, and protein, enhanced pro-inflammatory cytokine release and increased the activity of the proteolytic matrix metalloproteinase enzyme, matric metalloproteinase (MMP)-2 and reduced the activity of MMP-9 after 24 h. Co-treatment of Aβ₄₀ oligomers with GGC at 200 μM increased the activity of the antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx) and led to significant increases in the levels of the total antioxidant capacity (TAC) and GSH and reduced the GSSG/GSH ratio. GGC also upregulated the level of the anti-inflammatory cytokine IL-10 and reduced the levels of the pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) and attenuated the changes in metalloproteinase activity in oligomeric Aβ₄₀-treated astrocytes. Our data provides renewed insight on the beneficial effects of increased GSH levels by GGC in human astrocytes, and identifies yet another potential therapeutic strategy to attenuate the cytotoxic effects of Aβ oligomers in AD.

Exposure to a competitive social environment activates an epigenetic mechanism that limits pheomelanin synthesis in zebra finches

Competitive environments promote high testosterone levels, produce oxidative stress and, consequently, impair cellular homeostasis. The regulation of genes involved in the synthesis of the pigment pheomelanin in melanocytes seems to help to maintain homeostasis against environmental oxidative stress. Here, we experimentally increased social interactions in some zebra finch (Taeniopygia guttata) males by keeping them in groups of six birds during feather growth, while others were kept alone, to test if melanocytes show epigenetic lability under a competitive social environment. As these changes may depend on the oxidative status, we administrated buthionine sulfoximine (BSO) to decrease the antioxidant capacity of some birds. The competitive environment downregulated a gene involved in pheomelanin synthesis (Slc7a11) by changing the level of DNA methylation in feather melanocytes. In other genes involved in pheomelanin synthesis (Slc45a2, MC1R and AGRP), DNA methylation was also affected, but no changes in expression were detected. Exposure to the competitive environment did not affect systemic oxidative stress and damage, indicating that a protective epigenetic mechanism that changes the expression of Slc7a11 may have been activated. However, no changes to the pigmentation phenotype of birds were found, probably due to the short duration or low intensity of the competitive environment. BSO treatment did not affect the epigenetic mechanism, suggesting that the antioxidant capacity of birds was high enough to deal with the competitive environment. An epigenetic mechanism limiting pheomelanin synthesis therefore becomes activated under exposure to a competitive environment in male zebra finches, which may help to avoid damage caused by competitive interactions.

Sex-Specific Associations between Telomere Dynamics and Oxidative Status in Adult and Nestling Pied Flycatchers

Oxidative stress can contribute to an acceleration of telomere erosion, leading to cellular senescence and aging. Increased investment in reproduction is known to accelerate senescence, generally resulting in reduced future reproductive potential and survival. To better understand the role played by oxidative status and telomere dynamics in the conflict between maintenance and reproduction, it is important to determine how these factors are related in parents and their offspring. We investigated the relationship between oxidative status and telomere measurements in pied flycatchers (Ficedula hypoleuca). Total antioxidant status (TAS) in plasma, total levels of glutathione in red blood cells (RBCs), and oxidative damage in plasma lipids (malondialdehyde [MDA]) were assessed in both parents and nestlings. Telomeres were measured in RBCs in adults. Our results showed sex differences in oxidative variables in adults that are likely to be mediated by sex steroids, with testosterone and estrogens increasing and reducing, respectively, the production of reactive oxygen and nitrogen species. We found a negative association between telomere length (TL) and MDA in adults in the previous season. Moreover, TL was positively associated with TAS in females, while telomere shortening (ΔTL) correlated positively with MDA in males in the current year. These associations could be reflecting differences between sexes in reproductive physiology. We found a positive correlation between parental ΔTL and nestling MDA, an example of how parental physiological aging could affect offspring quality in terms of oxidative stress that highlights the constraints imposed by higher rates of ΔTL during reproduction and rearing.

Age and infection history are revealed by different ornaments in a warbler

Female preference for older or more disease-resistant males are both possible outcomes of parasite-mediated sexual selection, but the extent to which infection alters the development of ornaments to yield signals of male age and health has rarely been explored. In a longitudinal study of 61 male common yellowthroats (Geothlypis trichas), age-related increases in the size of the melanin-based mask and carotenoid-based bib were not correlated among young males, likely owing to differences in how blood parasites affect ornament development. Infection with trypanosomes and hemosporidians in a male's first breeding season was associated with slower growth of the mask; uninfected males attained large masks in their second breeding season, while infected males attained large masks in their third breeding season. In contrast, the bib size of males increased every year regardless of infection. As a consequence, different populations of males are identified by the largest ornaments-older males in the case of bib and a combination of older males and young, uninfected males in the case of mask. Although mask is thus the more informative trait with respect to male health, females prefer large bibs in our population. If infection is opportunistic, young, uninfected males may not possess good genes for parasite resistance but simply good luck, and it may benefit females to prefer older males who are more likely to have withstood prior episodes of selection. A "pure" signal of age may be a more reliable signal of resistance to parasites than an ornament whose expression is modulated by infection.

Condition-dependence of pheomelanin-based coloration in nuthatches Sitta europaea suggests a detoxifying function: implications for the evolution of juvenile plumage patterns

Adult-like juvenile plumage patterns often signal genotypic quality to parents. During adulthood, the same patterns often signal quality to mates. This has led to assume that adult-like juvenile plumage is a developmental consequence of sexual selection operating in adults. Many of these patterns are produced by the pigment pheomelanin, whose synthesis may help remove toxic excess cysteine. Excess cysteine is likely to arise under conditions of relatively low stress, such as those experienced by nestling birds. Thus, adult-like plumage may be advantageous for juveniles if produced by pheomelanin. In the Eurasian nuthatch Sitta europaea, juveniles are sexually dichromatic and identical to adults. Nestling nuthatches in poorer condition develop more intense pheomelanin-based feathers, indicating greater pigment production. The same is not observed in adults. This is contrary to a function related to signaling quality and instead suggests that, at least in the Eurasian nuthatch, adult-like juvenile plumage has evolved because of the detoxifying function of pheomelanin-based pigmentation. Given the prevalence of colors typically conferred by pheomelanin in juvenile plumage patterns, the detoxifying capacity of pheomelanin under low stress levels should be considered as an explanation for the evolution of both adult-like and distinctively juvenile plumage patterns.

Interacting effects of early dietary conditions and reproductive effort on the oxidative costs of reproduction

The hypothesis that oxidative damage accumulation can mediate the trade-off between reproduction and lifespan has recently been questioned. However, in captive conditions, studies reporting no evidence in support of this hypothesis have usually provided easy access to food which may have mitigated the cost of reproduction. Here, I test the hypothesis that greater investment in reproduction should lead to oxidative damage accumulation and telomere loss in domestic zebra finches Taeniopygia guttata. Moreover, since the change or fluctuation in diet composition between early and late postnatal period can impair the ability to produce antioxidant defences in zebra finches, I also tested if early nutritional conditions (constant vs fluctuating early diet) influenced the magnitude of any subsequent costs of reproduction (e.g., oxidative damage and/or telomere shortening). In comparison to pairs with reduced broods, the birds that had to feed enlarged broods showed a higher level of oxidative DNA damage (8-OHdG), but brood size had no effect on telomeres. Fluctuating early diet composition reduced the capacity to maintain the activity of endogenous antioxidants (GPx), particularly when reproductive costs were increased (enlarged brood). The decline in GPx in birds feeding enlarged broods was accompanied by a change in bill colouration. This suggests that birds with lower endogenous antioxidant defences might have strategically increased the mobilization of antioxidants previously stored in other tissues (i.e., bill and liver) and thus, preventing an excessive accumulation of damage during reproduction.

Adaptive downregulation of pheomelanin-related Slc7a11 gene expression by environmentally induced oxidative stress

Pheomelanin is a sulphur-containing yellow-to-reddish pigment whose synthesis consumes the main intracellular antioxidant (glutathione; GSH) and its precursor cysteine. Cysteine used for pheomelanogenesis cannot be used for antioxidant protection. We tested whether the expression of Slc7a11, the gene regulating the transport of cysteine to melanocytes for pheomelanogenesis, is environmentally influenced when cysteine/GSH are most required for antioxidant protection. We found that zebra finches Taeniopygia guttata developing pheomelanin-pigmented feathers during a 12-day exposure to the pro-oxidant diquat dibromide downregulated the expression of Slc7a11 in feather melanocytes, but not the expression of other genes that affect pheomelanogenesis by mechanisms different from cysteine transport such as MC1R and Slc45a2. Accordingly, diquat-treated birds did not suffer increased oxidative stress. This indicates that some animals have evolved an adaptive epigenetic lability that avoids damage derived from pheomelanogenesis. This mechanism should be explored in human Slc7a11 to help combat some cancer types related to cysteine consumption.

The effect of food quality during growth on spatial memory consolidation in adult pigeons

Poor environmental conditions experienced during early development can have negative long-term consequences on fitness. Animals can compensate for negative developmental effects through phenotypic plasticity by diverting resources from non-vital to vital traits such as spatial memory to enhance foraging efficiency. We tested in young feral pigeons (Columba livia) how diets of different nutritional value during development affect the capacity to retrieve food hidden in a spatially complex environment, a process we refer to as 'spatial memory'. Parents were fed with either high- or low-quality food from egg laying until young fledged, after which all young pigeons received the same high-quality diet until memory performance was tested at 6 months of age. The pigeons were trained to learn a food location out of 18 possible locations in one session, and then their memory of this location was tested 24 h later. Birds reared with the low-quality diet made fewer errors in the memory test. These results demonstrate that food quality during development has long-lasting effects on memory, with a moderate nutritional deficit improving spatial memory performance in a foraging context. It might be that under poor feeding conditions resources are redirected from non-vital to vital traits, or pigeons raised with low-quality food might be better in using environmental cues such as the position of the sun to find where food was hidden.

Specific carotenoid pigments in the diet and a bit of oxidative stress in the recipe for producing red carotenoid-based signals

Colorful ornaments have been the focus of sexual selection studies since the work of Darwin. Yellow to red coloration is often produced by carotenoid pigments. Different hypotheses have been formulated to explain the evolution of these traits as signals of individual quality. Many of these hypotheses involve the existence of a signal production cost. The carotenoids necessary for signaling can only be obtained from food. In this line, carotenoid-based signals could reveal an individual’s capacity to find sufficient dietary pigments. However, the ingested carotenoids are often yellow and became transformed by the organism to produce pigments of more intense color (red ketocarotenoids). Biotransformation should involve oxidation reactions, although the exact mechanism is poorly known. We tested the hypothesis that carotenoid biotransformation could be costly because a certain level of oxidative stress is required to correctly perform the conversion. The carotenoid-based signals could thus reveal the efficiency of the owner in successfully managing this challenge. In a bird with ketocarotenoid-based ornaments (the red-legged partridge; Alectoris rufa), the availability of different carotenoids in the diet (i.e. astaxanthin, zeaxanthin and lutein) and oxidative stress were manipulated. The carotenoid composition was analyzed and quantified in the ornaments, blood, liver and fat. A number of oxidative stress biomarkers were also measured in the same tissues. First, we found that color and pigment levels in the ornaments depended on food levels of those carotenoids used as substrates in biotransformation. Second, we found that birds exposed to mild levels of a free radical generator (diquat) developed redder bills and deposited higher amounts of ketocarotenoids (astaxanthin) in ornaments. Moreover, the same diquat-exposed birds also showed a weaker resistance to hemolysis when their erythrocytes were exposed to free radicals, with females also enduring higher oxidative damage in plasma lipids. Thus, higher color production would be linked to higher oxidative stress, supporting the biotransformation hypothesis. The recent discovery of an avian oxygenase enzyme involved in converting yellow to red carotenoids may support our results. Nonetheless, the effect could also depend on the abundance of specific substrate carotenoids in the diet. Birds fed with proportionally higher levels of zeaxanthin showed the reddest ornaments with the highest astaxanthin concentrations. Moreover, these birds tended to show the strongest diquat-mediated effect. Therefore, in the evolution of carotenoid-based sexual signals, a biotransformation cost derived from maintaining a well-adjusted redox machinery could coexist with a cost linked to carotenoid acquisition and allocation (i.e. a resource allocation trade-off).

The oxidative cost of reproduction depends on early development oxidative stress and sex in a bird species

In the early 2000s, a new component of the cost of reproduction was proposed: oxidative stress. Since then the oxidative cost of reproduction hypothesis has, however, received mixed support. Different arguments have been provided to explain this. Among them, the lack of a life-history perspective on most experimental tests was suggested. We manipulated the levels of a key intracellular antioxidant (glutathione) in captive zebra finches (Taeniopygia guttata) during a short period of early life and subsequently tested the oxidative cost of reproduction. Birds were allowed to mate freely in an outdoor aviary for several months. We repeatedly enlarged or reduced their broods to increase or reduce, respectively, breeding effort. Birds whose glutathione levels were reduced during growth showed higher erythrocyte resistance to free radical-induced haemolysis when forced to rear enlarged broods. This supports the hypothesis predicting the occurrence of developing programmes matching early and adult environmental conditions to improve fitness. Moreover, adult males rearing enlarged broods endured higher plasma levels of lipid oxidative damage than control males, whereas adult females showed the opposite trend. As most previous studies reporting non-significant or opposite results used females only, we also discuss some sex-related particularities that may contribute to explain unexpected results.

Oxidative Stress in Early Life: Associations with Sex, Rearing Conditions, and Parental Physiological Traits in Nestling Pied Flycatchers

Conditions experienced during juvenile development can affect the fitness of an organism. During early life, oxidative stress levels can be particularly high as a result of the increased metabolism and the relatively immature antioxidant system of the individual, and this may have medium- and long-term fitness consequences. Here we explore variation in levels of oxidative stress measured during early life in relation to sex, rearing conditions (hatching date and brood size), and parental condition and levels of oxidative markers in a wild population of the pied flycatcher (Ficedula hypoleuca) followed for 2 yr. A marker of total antioxidant status (TAS) in plasma and total levels of glutathione (GSH) in red blood cells, as well as a marker of oxidative damage in plasma lipids (malondialdehyde [MDA]), were assessed simultaneously. Our results show that nestling total GSH levels were associated with parental oxidative status, correlating negatively with maternal MDA and positively with total GSH levels of both parents, with a high estimated heritability. This suggests that parental physiology and genes could be determinants for endogenous components of the antioxidant system of the offspring. Moreover, we found that total GSH levels were higher in female than in male nestlings and that hatching date was positively associated with antioxidant defenses (higher TAS and total GSH levels). These results suggest that different components of oxidative balance are related to a variety of environmental and intrinsic--including parental--influencing factors. Future experimental studies must disentangle the relative contribution of each of these on nestling oxidative status and how the resulting oxidative stress at early phases shape adult phenotype and fitness.

Temperature experienced during incubation affects antioxidant capacity but not oxidative damage in hatchling red-eared slider turtles (Trachemys scripta elegans)

Our understanding of how oxidative stress resistance phenotypes are affected by the developmental environment is limited. One component of the developmental environment, which is likely central to early life oxidative stress among ectothermic and oviparous species, is that of temperature. We investigated how incubation temperature manipulations affect oxidative damage and total antioxidant capacity (TAC) in red-eared slider turtle (Trachemys scripta elegans) hatchlings. First, to determine if temperature fluctuations elicit oxidative stress, eggs from clutches were randomly assigned to either a constant (29.5°C) or daily fluctuating temperature incubation (28.7±3°C) treatment. Second, to assess the effect of temperature fluctuation frequency on oxidative stress, eggs were incubated in one of three fluctuating incubation regimes; 28.7±3°C fluctuations every 12 (Hyper), 24 (Normal), or 48 hours (Hypo). Third, we tested the influence of average incubation temperature by incubating eggs in a daily fluctuating incubation temperature regime with a mean temperature of 26.5°C (Low), 27.1°C (Medium), or 27.7°C (High). Although the accumulation of oxidative damage in hatchlings was unaffected by any thermal manipulation, TAC was affected by both temperature fluctuation frequency and average incubation temperature. Individuals incubated with a low frequency of temperature fluctuations had reduced TAC, while incubation at a lower average temperature was associated with enhanced TAC. These results indicate that while sufficient to prevent oxidative damage, TAC is influenced by developmental thermal environments, potentially due to temperature mediated changes in metabolic rate. The observed differences in TAC may have important future consequences for hatchling fitness and overwinter survival.