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Flight training and dietary antioxidants have mixed effects on the oxidative status of multiple tissues in a female migratory songbird
Abstract
Birds, like other vertebrates, rely on a robust antioxidant system to protect themselves against oxidative imbalance caused by energy-intensive activities such as flying. Such oxidative challenges may be especially acute for females during spring migration, since they must pay the oxidative costs of flight while preparing for reproduction; however, little previous work has examined how the antioxidant system of female spring migrants responds to dietary antioxidants and the oxidative challenges of regular flying. We fed two diets to female European starlings, one supplemented with a dietary antioxidant and one without, and then flew them daily in a windtunnel for two weeks during the fall and spring migration periods. We measured the activity of enzymatic antioxidants (GPx, SOD, CAT), non-enzymatic antioxidant capacity (ORAC), and markers of oxidative damage (protein carbonyls and lipid hydroperoxides) in four tissues: pectoralis, leg, liver, and heart. Dietary antioxidants affected enzymatic antioxidant activity and lipid damage in the heart, non-enzymatic antioxidant capacity in the pectoralis, and protein damage in leg muscle. In general, birds fed less antioxidants appear to incur increased oxidative damage while upregulating non-enzymatic and enzymatic antioxidant activity, though these effects were strongly tissue-specific. We also found trends for diet x training interactions for enzymatic antioxidant activity in the heart and leg. Flight-training may condition the antioxidant system of females to dynamically respond to oxidative challenges, and females during spring migration may shift antioxidant allocation to reduce oxidative damage.
... These studies together demonstrate that migratory bats and birds respond to such oxidative challenges by increasing antioxidant enzyme activities, depleting or augmenting non-enzymatic antioxidant capacity, and in these cases increasing oxidative damage. They also reveal that too little is known about tissue-specific oxidative status of migratory birds (Dick and Guglielmo 2019) and the extent to which an individual's circulating oxidative status reflects the oxidative state of muscles and organs at a given time (Costantini 2019, Frawley et al. 2021a). Additionally, measurements reflecting different levels of the Central Dogma (e.g. ...
... For example, in a companion study the enzyme activities of CAT in the liver and pectoralis and GPx in the liver were higher in European starlings Sturnus vulgaris after recovering from flight training compared to birds that were not flight trained, yet these activities did not correlate with the higher gene expression levels of these enzymes in trained birds compared to untrained birds (DeMoranville et al. 2022). Consistent with these results, Frawley et al. (2021a) employed a similar experimental design and observed lower GPx activity in the heart and SOD activity in the liver of trained European starlings compared to starlings not trained in a wind tunnel during recovery, indicating that research on how antioxidant capacity recovers after flight should be mechanistically studied (McWilliams et al. 2021). What remains to be determined for migratory songbirds, and is the focus of this study, is how the oxidative status of the flightmuscle, liver, and primarily plasma responds to both flight training and ecologically relevant differences in diet quality (i.e. ...
... We also found evidence in the liver and pectoralis that flight training activated the antioxidant system so that after several weeks of daily flying the non-enzymatic antioxidant capacity was maintained at levels similar to those of untrained birds, and oxidative damage was prevented in all tissues, although this is contrary to our predictions that antioxidant capacity would be greater and oxidative damage levels would be lower in trained versus untrained birds (H1c). Repeated bouts of flight apparently protected birds against lipid damage in the liver and the pectoralis (Frawley et al. 2021a), as lipid hydroperoxide concentration was lower or similar in the liver and pectoralis, respectively, of flighttrained birds compared to untrained birds. In our companion study, DeMoranville et al. (2022), the gene expression of CAT, SOD2, and GPX1 were upregulated in the liver of Page 13 of 17 flight-trained birds, while only SOD2 was upregulated in the pectoralis, which likely explains how lower liver damage levels in flight-trained birds was achieved. ...
Ecologically relevant factors such as exercise and diet quality can directly influence how multifaceted physiological systems work; however, little is known about how such factors directly and interactively affect key components of the antioxidant system in multiple tissues of migratory songbirds. We tested 3 main hypotheses across three tissues in European starlings fed diets with more or less antioxidants (anthocyanins) and long‐chain omega‐6 polyunsaturated fats (18:2n6) while being flight‐trained in a wind tunnel. Stimulatory effect of flight: flight‐training stimulated the antioxidant system in that 1) plasma oxidative damage (dROMs) was reduced during a given acute flight, and contrary to our predictions, 2) antioxidant capacity (OXY or ORAC) and oxidative damage in plasma (dROMs), flight‐muscle, and liver (LPO) of flight‐trained birds were similar to that of untrained birds (i.e. not flown in a wind tunnel). Flight‐trained birds that expended more energy per unit time (kJ min⁻¹) during their longest, final flight decreased antioxidant capacity (OXY) the most during the final flight. Dietary fat quality effect: contrary to our predictions, dietary 18:2n‐6 did not influence oxidative status even after flight training. Dietary antioxidant effect: flight‐trained birds supplemented with dietary anthocyanins did not have higher antioxidant capacity in plasma (OXY), or liver and flight‐muscle (ORAC) compared to untrained birds. Counterintuitively, oxidative damage (dROMs) was higher in flight‐trained supplemented birds compared to unsupplemented birds after an acute flight. In sum, the antioxidant system of songbirds flexibly responded to changes in availability of dietary antioxidants as well as increased flight time and effort, and such condition‐dependent, individual‐level, tissue‐specific responses to the oxidative costs of long‐duration flights apparently requires recovery periods for maintaining oxidative balance during migration.
... Es importante considerar que los efectos en un tejido pueden correlacionar o no con otros (p.ej. Oldakowski y Taylor 2018; Frawley et al., 2021). Además, las implicaciones del estrés oxidativo pueden ser más o menos grandes dependiendo del tejido concreto Mendonca et al., 2020). ...
... Así, en murciélagos y aves, el vuelo migratorio se ha asociado a un mayor estrés oxidativo (Jenni-Eiermann et al., 2014, Costantini et al., 2019. Sin embargo, periodos intermitentes de ejercicio, con oportunidad de recuperación, permiten una adaptación ("hormesis"; véase más abajo) y menores niveles de estrés oxidativo post-esfuerzo (Radak et al., 2008;Frawley et al., 2021). Finalmente, a medida que el individuo alcanza la madurez sexual, nuevos compromisos emergen: los asociados a la reproducción. ...
El estrés oxidativo es un fenómeno complejo que ha sido el foco de intensa investigación desde diferentes campos del conocimiento. Desde hace más de veinte años ha atraído también la atención de los ecólogos del comportamiento. En este artículo pretendemos describir (1) los métodos más simples y útiles para su medición, (2) los procedimientos más viables para su manipulación y (3) las preguntas más interesantes que pueden ser respondidas mediante la aplicación de las aproximaciones que describimos. Con este texto, pretendemos animar al desarrollo de éste campo entre los estudiosos del comportamiento, sirviendo de instrumento y estímulo para futuras líneas de trabajo.
Flight can be highly energy demanding, but its efficiency depends largely on flight style, wing shape and wing loading, and a range of morphological and lifestyle adaptations that can modify the cost of sustained flight. Such behavioural and morphological adaptations can also influence the physiological costs associated with migration. For instance, during intense flight and catabolism of reserves, lipid damage induced by pro‐oxidants increases, and to keep oxidative physiological homeostasis under control, the antioxidant machinery can be upregulated. Studies on the oxidative physiology of endurance flight have produced contradictory results, making generalization difficult, especially because multispecies studies are missing. Therefore, to explore the oxidative cost of flight and migration, we used samples collected during the breeding season from 113 European bird species and explored the associations of measures of antioxidant capacity (total antioxidant status, uric acid and glutathione concentration) and oxidative damage of lipids (malondialdehyde) with variables reflecting flight energetics (year‐round or specifically during migration) using a phylogenetic framework. We found that none of the traits predicting year‐round flight energy expenditure (flight style, wing morphology and flight muscle morphology) explained any measures of oxidative state. Our results suggest that birds endure their everyday flight exercise without or with low oxidative cost. However, oxidative damage to lipids and one component of the endogenous antioxidant system (uric acid), measured after the end of spring migration on breeding adult birds, increased with migration distance. Our results suggest that migration could have oxidative consequences that might be carried over to subsequent life‐history stages (breeding).
Physical effort requires a number of energetic, metabolic, hormonal, and cardiovascular responses that can be highly costly for the organism to sustain. Even physical inactivity, typical of animals during hibernation or aestivation, requires several physiological adjustments of the metabolic machinery, which have also to prepare the organism for the reoxygenation and increased metabolic activity that will characterise the phase of arousal. A number of studies described the many ways in which animals regulate their oxidative status during different phases of physical (in)activity, such as strenuous migratory flight, dormancy, or arousal. Many authors also pointed to a role of exercise-induced reactive oxygen species in mediating hormetic responses to physical effort. In this chapter, I have examined the role of oxidative stress induced by physical effort as cost of and constraint on migration strategies and sibling competition. I have also analysed the oxidative challenges that animals face during periods of inactivity, and the transition from dormancy to arousal due to tissue reoxygenation and consequent burst of reactive oxygen species generation in body tissues.
Flight can be highly-energy demanding, but its efficiency depends largely on flight style, wing shape and loading, and a range of morphological and lifestyle adaptations that can modify the cost of sustained flight. Such behavioural and morphological adaptations can also influence the physiological costs associated with migration. For instance, during intense flight and catabolism of reserves, lipid damage induced by pro-oxidants increases, and to keep oxidative physiological homeostasis under control, the antioxidant machinery is upregulated. Studies on the oxidative physiology of endurance flight have produced contradictory results, making generalization difficult, especially because multispecies studies are missing. Therefore, to explore the oxidative cost of flight and migration, we explored the association between three measures of the antioxidant capacity (total antioxidant status, uric acid and glutathione concentration) and one measure of oxidative damage of lipids (malondialdehyde) with variables reflecting flight energetics (year-round or specifically during migration) across 113 European bird species using a phylogenetic framework. We found that none of the traits predicting year-round flight energy expenditure, including flight style, wing morphology and flight muscle morphology explained any measures of oxidative state measured during the energy demanding breeding period, suggesting that birds endure their everyday exercise without or low oxidative cost. However, oxidative damage to lipids and one component of the endogenous antioxidant system (uric acid), measured after the end of spring migration on breeding adult birds, increased with migration distance. Our results suggest that migration might have oxidative consequences that are carried over to subsequent life history stages (breeding).
Ecologically-relevant factors such as exercise and diet quality can directly influence how physiological systems work including those involved in maintaining oxidative balance; however, to our knowledge, no studies to date have focused on how such factors directly affect expression of key components of the endogenous antioxidant system (i.e., transcription factors, select antioxidant genes, and corresponding antioxidant enzymes) in several metabolically active tissues of a migratory songbird. We conducted a 3-factor experiment that tested the following hypotheses: (H1) Daily flying over several weeks increases the expression of transcription factors NRF2 and PPARs as well as endogenous antioxidant genes (i.e., CAT, SOD1, SOD2, GPX1, GPX4), and upregulates endogenous antioxidant enzyme activities (i.e., CAT, SOD, GPx). (H2) Songbirds fed diets composed of more 18:2n-6 PUFA are more susceptible to oxidative damage and thus upregulate their endogenous antioxidant system compared to when fed diets with less PUFA. (H3) Songbirds fed dietary anthocyanins gain additional antioxidant protection and thus upregulate their endogenous antioxidant system less compared to songbirds not fed anthocyanins. Flight training increased the expression of 3 of the 6 antioxidant genes and transcription factors measured in the liver, consistent with H1, but for only one gene (SOD2) in the pectoralis. Dietary fat quality had no effect on antioxidant pathways (H2) whereas dietary anthocyanins increased the expression of select antioxidant enzymes in the pectoralis, but not in the liver (H3). These tissue-specific differences in response to flying and dietary antioxidants are likely explained by functional differences between tissues as well as fundamental differences in their turnover rates. The consumption of dietary antioxidants along with regular flying enables birds during migration to stimulate the expression of genes involved in antioxidant protection likely through increasing the transcriptional activity of NRF2 and PPARs, and thereby demonstrates for the first time that these relevant ecological factors affect the regulation of key antioxidant pathways in wild birds. What remains to be demonstrated is how the extent of these ecological factors (i.e., intensity or duration of flight, amounts of dietary antioxidants) influences the regulation of these antioxidant pathways and thus oxidative balance.
Elite human and animal athletes must acquire the fuels necessary for extreme feats, but also contend with the oxidative damage associated with peak metabolic performance. Here, we show that a migratory bird with fuel stores composed of more omega-6 polyunsaturated fats (PUFA) expended 11% less energy during long-duration (6 hr) flights with no change in oxidative costs; however, this short-term energy savings came at the long-term cost of higher oxidative damage in the omega-6 PUFA-fed birds. Given that fatty acids are primary fuels, key signaling molecules, the building blocks of cell membranes, and that oxidative damage has long-term consequences for health and ageing, the energy savings-oxidative cost trade-off demonstrated here may be fundamentally important for a wide diversity of organisms on earth.
Glucocorticoids (GCs) are metabolic hormones that promote catabolic processes, which release stored energy and support high metabolic demands such as during prolonged flights of migrating birds. Dietary antioxidants (e.g. anthocyanins) support metabolism by quenching excess reactive oxygen species produced during aerobic metabolism and also by activating specific metabolic pathways. For example, similar to GCs' function, anthocyanins promote the release of stored energy, although the extent of complementarity between GCs and dietary antioxidants is not well known. If anthocyanins complement GCs functions, birds consuming anthocyanin-rich food can be expected to limit the secretion of GCs when coping with a metabolically challenging activity, avoiding the exposure to potential hormonal detrimental effects. We tested this hypothesis in European starlings (Sturnus vulgaris) flying in a wind tunnel. We compared levels of corticosterone, the main avian GC, immediately after a sustained flight and at rest for birds that were fed diets with or without an anthocyanin supplement. As predicted, we found (i) higher corticosterone after flight than at rest in both diet groups and (ii) anthocyanin-supplemented birds had less elevated corticos-terone after flight than unsupplemented control birds. This provides novel evidence that dietary antioxidants attenuate the activation of the HPA axis (i.e. increased secretion of corticosterone) during long-duration flight.
Most migrating birds need to stopover in between flights in order to refuel. Lately, additional purposes of stopover have been suggested, including physiological recovery from metabolically demanding migratory flight. One apparently unavoidable, but harmful physiological effect of migratory flight is increased oxidative damage to lipids and proteins.
We here, for the first time, tested whether migrating birds are able to reduce their oxidative damage during stopover. To be able to collect longitudinal data on a large number of individual birds, we temporarily caged wild northern wheatears, a long‐distance migrant which does not suffer stress when caged during migration. Around noon on the first and third day at stopover, the birds were blood‐sampled to determine malondialdehyde (MDA) concentration, a commonly used marker of oxidative damage to lipids.
We found that MDA concentrations significantly decreased during stopover, a result unchanged when correcting for the peroxidizability of the substrate. The extent of the decrease was unrelated to the amounts of food consumed or of fuel accumulated.
Our findings support the hypothesis that stopovers serve reduction of oxidative damage, warranting re‐thinking of how birds accomplish their migrations. They also highlight the need to include physiological recovery as a driver of the (temporal) organization of migration.
A free Plain Language Summary can be found within the Supporting Information of this article.
Abstract Dietary micronutrients have the ability to strongly influence animal physiology and ecology. For songbirds, dietary polyunsaturated fatty acids (PUFAs) and antioxidants are hypothesized to be particularly important micronutrients because of their influence on an individual's capacity for aerobic metabolism and recovery from extended bouts of exercise. However, the influence of specific fatty acids and hydrophilic antioxidants on whole‐animal performance remains largely untested. We used diet manipulations to directly test the effects of dietary PUFA, specifically linoleic acid (18:2n6), and anthocyanins, a hydrophilic antioxidant, on basal metabolic rate (BMR), peak metabolic rate (PMR), and rates of fat catabolism, lean catabolism, and energy expenditure during sustained flight in a wind tunnel in European starlings (Sturnus vulgaris). BMR, PMR, energy expenditure, and fat metabolism decreased and lean catabolism increased over the course of the experiment in birds fed a high (32%) 18:2n6 diet, while birds fed a low (13%) 18:2n6 diet exhibited the reverse pattern. Additionally, energy expenditure, fat catabolism, and flight duration were all subject to diet‐specific effects of whole‐body fat content. Dietary antioxidants and diet‐related differences in tissue fatty acid composition were not directly related to any measure of whole‐animal performance. Together, these results suggest that the effect of dietary 18:2n6 on performance was most likely the result of the signaling properties of 18:2n6. This implies that dietary PUFA influence the energetic capabilities of songbirds and could strongly influence songbird ecology, given their availability in terrestrial systems.
The acute effects of an energy-intensive activity such as exercise may alter an animal's redox homeostasis, although these short-term effects may be ameliorated by chronic exposure to that activity, or training, over time. Although well documented in mammals, how energy-intensive training affects the antioxidant system and damage by reactive species has not been investigated fully in flight-trained birds. We examined changes to redox homeostasis in zebra finches exposed to energy-intensive activity (60 min of perch-to-perch flights twice a day), and how exercise training over many weeks affected this response. We measured multiple components of the antioxidant system: an enzymatic antioxidant (glutathione peroxidase, GPx) and non-enzymatic antioxidants (measured by the OXY-adsorbent test) as well as a measure of oxidative damage (d-ROMs). At no point during the experiment did oxidative damage change. We discovered that exposure to energy-intensive exercise training did not alter baseline levels of GPx, but induced exercise-trained birds to maintain a higher non-enzymatic antioxidant status as compared with untrained birds. GPx activity was elevated above baseline in trained birds immediately after completion of the second 1 h flight on each of the three sampling days, and non-enzymatic antioxidants were acutely depleted during flight after 13 and 44 days of training. The primary effect of exercise training on the acute response of the antioxidant system to 2 h flights was increased coordination between the enzymatic (GPx) and non-enzymatic components of the antioxidant system of birds that reduced oxidative damage associated with exercise.
In birds, many physiological parameters appear to remain constant with increasing age, showing no deterioration until ‘catastrophic’ mortality sets in. Given their high whole-organism metabolic rate and the importance of flight in foraging and predator avoidance, flight muscle deterioration and accumulated oxidative stress and tissue deterioration may be an important contributor to physiological senescence in wild birds. As a by-product of aerobic respiration, reactive oxygen species are produced and can cause structural damage within cells. The anti-oxidant system deters oxidative damage to macromolecules. We examined oxidative stress and muscle ultrastructure in thick-billed murres aged 8 to 37 years (N = 50) in pectoralis muscle biopsies. When considered in general linear models with body mass, body size and sex, no oxidative stress parameter varied with age. In contrast, there was a decrease in myonuclear domain similar to that seen in human muscle aging. We conclude that for wild birds with very high flight activity levels, muscle ultrastructural changes may be an important contributor to demographic senescence. Such gradual, linear declines in muscle morphology may eventually contribute to ‘catastrophic’ failure in foraging or predator avoidance abilities, leading to demographic senescence.
During migration, birds substantially increase their metabolic rate and burn fats as fuel and yet somehow avoid succumbing to overwhelming oxidative damage. The physiological means by which vertebrates such as migrating birds can counteract an increased production of reactive species (RS) are rather limited: they can upregulate their endogenous antioxidant system and/or consume dietary antioxidants (prophylactically or therapeutically). Thus, birds can alter different components of their antioxidant system to respond to the demands of long-duration flights, but much remains to be discovered about the complexities of RS production and antioxidant protection throughout migration. Here, we use bird migration as an example to discuss how RS are produced during endurance exercise and how the complex antioxidant system can protect against cellular damage caused by RS. Understanding how a bird's antioxidant system responds during migration can lend insights into how antioxidants protect birds during other life-history stages when metabolic rate may be high, and how antioxidants protect other vertebrates from oxidative damage during endurance exercise.
Physiological challenges during one part of the annual cycle can carry over and affect performance at a subsequent phase, and antioxidants could be one mediator of trade-offs between phases.We performed a controlled experiment with zebra finches to examine how songbirds use nutrition to manage trade-offs in antioxidant allocation between endurance flight and subsequent reproduction. Our treatment groups included (1) a non-supplemented, non-exercised group (control group) fed a standard diet with no exercise beyond that experienced during normal activity in an aviary; (2) a supplemented non-exercised group fed a water- and lipid-soluble antioxidant supplemented diet with no exercise; (3) a non-supplemented exercised group fed a standard diet and trained to perform daily endurance flight for 6 weeks; and (4) a supplemented exercised group fed an antioxidant-supplemented diet and trained to perform daily flight for 6 weeks. After flight training, birds were paired within treatment groups for breeding. We analyzed eggs for lutein and vitamin E concentrations and the plasma of parents throughout the experiment for non-enzymatic antioxidant capacity and oxidative damage. Exercised birds had higher oxidative damage levels than non-exercised birds after flight training, despite supplementation with dietary antioxidants. Supplementation with water-soluble antioxidants decreased the deposition of lipid-soluble antioxidants into eggs and decreased yolk size. Flight exercise also lowered deposition of lutein, but not vitamin E, to eggs. These findings have important implications for future studies of wild birds during migration and other oxidative challenges.
All air-breathing organisms must face the challenge of oxidative damage, and understanding how animals cope can lend insight into their ecology. Unlike other vertebrates, birds rely primarily on fats to fuel endurance exercise such as migration, and therefore face a greater potential for damage from the reactive by-products of their own metabolism. We review the physiological ecology of migrating birds through the lens of oxidation-reduction chemistry, underscoring how oxidative balance in wild birds may affect their dietary choices and use of critical stopover habitats during migration. Recent studies reveal that migratory birds prepare for oxidative challenges either by up-regulating endogenous antioxidants or by consuming them in their diet, and they repair oxidative damage after long flights, although much remains to be discovered about how birds maintain oxidative balance over the course of migration. We conclude by describing some of the most used and useful measures of antioxidant status and oxidative damage that field ornithologists can include in their tool kit of techniques to probe the oxidative balance of wild birds.
Managing oxidative stress is an important physiological function for all aerobic organisms, particularly during periods of prolonged high metabolic activity, such as long-distance migration across ecological barriers. However, no previous study has investigated the oxidative status of birds at different stages of migration and whether that oxidative status depends on the condition of the birds. In this study, we compared (1) energy stores and circulating oxidative status measures in (a) two species of Neotropical migrants with differing migration strategies that were sampled at an autumn stopover site before an ecological barrier; and (b) a species of trans-Saharan migrant sampled at a spring stopover site after crossing an ecological barrier; and (2) circulating oxidative measures and indicators of fat metabolism in a trans-Saharan migrant after stopovers of varying duration (0–8 nights), based on recapture records. We found fat stores to be positively correlated with circulating antioxidant capacity in Blackpoll Warblers and Red-eyed Vireos preparing for fall migration on Block Island, USA, but uncorrelated in Garden Warblers on the island of Pon-za, Italy, after a spring crossing of the Sahara Desert and Mediterranean Sea. In all circumstances, fat stores were positively correlated with circulating lipid oxidation levels. Among Garden Warblers on the island of Ponza, fat anabolism increased with stopover duration while oxidative damage levels decreased. Our study provides evidence that birds build antioxidant capacity as they build fat stores at stopover sites before long flights, but does not support the idea that antioxidant stores remain elevated in birds with high fuel levels after an ecological barrier. Our results further suggest that lipid oxidation may be an inescapable hazard of using fats as the primary fuel for flight. Yet, we also show that birds on stopover are capable of recovering from the oxidative damage they have accrued during migration, as lipid oxidation levels decrease with time on stopover. Thus, the physiological strategy of migrating songbirds may be to build prophylactic antioxidant capacity in concert with fuel stores at stopover sites before a long-distance flight, and then repair oxidative damage while refueling at stopover sites after long-distance flight.
To learn some of the bases for consumption of temperate fleshy fruits by birds, we examined nutritional and morphological traits of temperate fleshy fruits and made laboratory observations on consumption of individual fruit species using 18 fruit species and 11 migrant frugivorous bird species in Illinois. The only seasonal trends in fruit traits were interspecific increases in absolute quantity of potassium and protein per fruit. Fruit energy content did not differ among species having bicolored vs. monochrome or small vs. large fruit displays. The fruit mass consumed was correlated best with dry pulp mass per fruit, providing significant positive correlations in 6 of 11 frugivorous species. Large fruit size relative to bill size did not appear to affect fruit consumption over the range of fruit sizes and bird species used. Because retained energy was correlated with mass consumed, the fruit pulp mass consumed was in most cases a good index of the energy obtained. Some significant differences occurred in digestive efficiency of a bird species eating different fruit species, and among different bird species eating a single fruit species, but no trends were apparent. Regurgitated seeds generally spent less time in a bird than did defecated seeds, facilitating more rapid disposal of seed ballast. Smaller birds defecated only small seeds and regurgitated some small seeds as wells as large ones, whereas larger birds defecated all smaller seeds may larger ones. Consequently, resultant seed shadows may depend upon both bird and seed size.
The early life period is characterized by fast growth and development, which can lead to high reactive oxygen species (ROS) production. Young animals thus have to balance their investment in growth versus ROS defence, and this balance is likely mediated by resource availability. Consequently resources transferred prenatally by the mother and nutritional conditions experienced shortly after birth may crucially determine the oxidative status of young animals. Here, we experimentally investigated the relative importance of pre- and early postnatal nutritional conditions on the oxidative status of great tit nestlings (Parus major). We show that resources transferred by the mother through the egg and nutritional conditions encountered after hatching affect the oxidative status of nestling in a sex-specific way. Daughters of non-supplemented mothers and daughters which did not receive extra food during the early postnatal period had higher oxidative damage than sons, while no differences between sons and daughters were found when extra food was provided pre- or postnatally. No effect of the food supplementations on growth, fledging mass or tarsus length was observed, indicating that female nestlings maintained their investment in growth at the expense of ROS defence mechanisms when resources were limited. The lower priority of the antioxidant defence system for female nestlings was also evidenced by lower levels of specific antioxidant components. These results highlight the important role of early parental effects in shaping oxidative stress in the offspring, and show that the sensitivity to these parental effects is sex-specific.
Avian mothers can influence offspring phenotype through the deposition of different compounds into eggs, such as antibodies, hormones and antioxidants. The concentration of carotenoids in yolk is larger than in maternal plasma, suggesting an important role of these compounds for offspring development. Since carotenoids have to be acquired from the diet, they may be available in limiting amounts to the mothers. Here, we investigated the role of egg carotenoids for offspring growth by experimentally increasing the concentration of yolk lutein, the main carotenoid in great tit (Parus major) yolk. We subsequently measured body condition, oxidative stress, immune response, plumage colouration and fledging success. Lutein increased body mass soon after hatching and fledging success, but did not affect tarsus length, oxidative stress, immune response and plumage colouration. The higher content of yolk lutein could have increased body mass by reducing oxidative stress caused by high metabolic rates of rapidly growing embryos or by promoting cell differentiation and proliferation. The positive effect of lutein on fledging success seems to be mediated by its influence on body mass 3 days post-hatch, since these two traits were correlated. The finding that our treatment did not affect traits measured later in the nestling period, except for fledging success, suggests that yolk lutein has short-term effects that are essential to increase survival until fledging. Our study shows the positive effect of yolk lutein on offspring survival in the great tit, and therefore suggests an important role of carotenoid-mediated maternal effects.
Recent nutrigenomic studies have shown that animal nutrition can have a major influence on tissue gene expression. Dietary antioxidant supplements can enhance the quality of meat through modification of tissue metabolic processes. This study investigated the influence of dietary antioxidants and quality of oil on the oxidative and enzymatic properties of chicken broiler breast meat stored in an oxygen-enriched package (HiOx: 80% O2/20% CO2) in comparison with air-permeable polyvinylchloride (PVC) or skin packaging systems during retail display at 2 to 4°C for up to 21 d. Broilers were fed either a diet with a low-oxidized (peroxide value 23 mEq of O2/kg) or high-oxidized (peroxide value 121 mEq of O2/kg) oil, supplemented with or without an algae-based Se yeast and organic mineral antioxidant pack for 42 d. Lipid and protein oxidation and tissue enzymatic activity were analyzed. In all packaging systems, lipid oxidation (TBA reactive substances) was inhibited by up to 32.5% (P < 0.05) with an antioxidant-supplemented diet when compared with diets without antioxidants, particularly in the HiOx and PVC systems. Protein sulfhydryls were significantly protected by antioxidant diets (e.g., by 14.6 and 17.8% for low-and high-oxidized dietary groups, respectively, in PVC d 7 samples). Glutathione peroxidase, catalase, and superoxide dismutase activities were significantly higher (P < 0.05) in antioxidant-supplemented diets compared with the basal diet, regardless of oil quality. Also, serum carbonyls were lower in broilers fed a low-oxidized antioxidant-supplemented treatment. The results demonstrate that dietary antioxidants can minimize the oxidative instability of proteins and lipids, and the protection may be linked to improved cellular antioxidant enzymatic activity.
Migrating birds perform extraordinary endurance flights, up to 200 h non-stop, at a very high metabolic rate and while fasting. Such an intense and prolonged physical activity is normally associated with an increased production of reactive oxygen and nitrogen species (RONS) and thus increased risk of oxidative stress. However, up to now it was unknown whether endurance flight evokes oxidative stress. We measured a marker of oxidative damage (protein carbonyls, PCs) and a marker of enzymatic antioxidant capacity (glutathione peroxidase, GPx) in the European robin (Erithacus rubecula), a nocturnal migrant, on its way to the non-breeding grounds. Both markers were significantly higher in European robins caught out of their nocturnal flight than in conspecifics caught during the day while resting. Independently of time of day, both markers showed higher concentrations in individuals with reduced flight muscles. Adults had higher GPx concentrations than first-year birds on their first migration. These results show for the first time that free-flying migrants experience oxidative stress during endurance flight and up-regulate one component of antioxidant capacity. We discuss that avoiding oxidative stress may be an overlooked factor shaping bird migration strategies, e.g. by disfavouring long non-stop flights and an extensive catabolism of the flight muscles.
Consuming food rich in antioxidants may help organisms to increase their antioxidant defences and avoid oxidative damage. Under the hypothesis that organisms actively consume food for its antioxidant properties, they would need to do so in view of other physiological requirements, such as energy requirements. Here, we observed that Gouldian finches (Erythrura gouldiae) consumed most seeds rich in antioxidants in the middle of the day, while their consumption of staple seeds more profitable in energy intake (and poor in antioxidants) was maximal in the morning and the evening. This consumption of seeds rich in antioxidants in the middle of the day may be explicable (1) because birds took advantage of a time window associated with relaxed energy requirements to ingest antioxidant resources, or (2) because birds consumed antioxidant resources as a response to highest antioxidant requirements in the middle of the day. If the latter hypothesis holds true, having the possibility to ingest antioxidants should be most beneficial in terms of oxidative balance in the middle of the day. Even though feeding on seeds rich in antioxidants improved Gouldian finches’ overall antioxidant capacity, we did not detect any diurnal effect of antioxidant intake on plasma oxidative markers (as measured by the d-ROM and the OXY-adsorbent tests). This indicates that the diurnal pattern of antioxidant intake that we observed was most likely constrained by the high consumption of staple food to replenish or build up body reserves in the morning and in the evening, and not primarily determined by elevated antioxidant requirements in the middle of the day. Consequently, animals appear to have the possibility to increase antioxidant defences by selecting food rich in antioxidants, only when energetic constraints are relaxed.
Egg yolks contain carotenoids that protect biological molecules against free‐radical damage and promote maturation of the immune system. Availability of carotenoids to birds is often limited. Trade‐offs can thus arise in the allocation of carotenoids to different physiological functions, and mothers may influence the immunocompetence of nestlings by modulating the transfer of carotenoid to the yolk.
In the great tit Parus major , we experimentally manipulated the dietary supply of carotenoid to mothers, and partially cross‐fostered hatchlings to investigate the effect of an increased availability of carotenoids during egg laying on immunocompetence of nestlings.
In addition, we infested half of the nests with hen fleas Ceratophyllus gallinae to investigate the relationship between carotenoid availability, resistance to ectoparasites and immunocompetence.
We found that the procedure of cross‐fostering can reduce the immune response of nestlings, but this effect can be compensated by the maternally transferred carotenoids. Cross‐fostered nestlings of carotenoid‐supplemented females show a similar immune response to non‐cross‐fostered nestlings, while cross‐fostered nestlings of control females mounted a weaker cell‐mediated immune response. This suggests that yolk carotenoids may help nestlings to cope with stress, for example the one generated by cross‐fostering and/or they may enhance nestling competitiveness.
There was no statistically significant interaction between parasite and carotenoid treatments, as would be expected if carotenoids helped nestlings to fight parasites. Under parasite pressure, however, lighter nestlings raised a lower immune response, while the immune response was only weakly correlated with body mass in uninfested nests.
Summary 1. The intake of antioxidants confers health benefits to consumers by reducing oxidative stress and improving immune functions. Therefore, several life-history traits such as growth, immunity, senescence and the expression of sexually selected traits might be affected by dietary antioxidants. 2. Flavonoids are strong antioxidants in vitro , and are among the commonest found in fruits, which are a primary source of antioxidants for many animals. It is therefore likely that flavonoids play a beneficial role as dietary antioxidants, but their potential has been ignored in evolutionary ecology. 3. We investigated the ecological importance of flavonoids, using wild-caught blackcaps ( Sylvia atricapilla ), a frugivorous European songbird. 4. We verified the assumption that flavonoids can be absorbed and circulated by blackcaps. 5. In a food selection experiment, we showed that, when given a choice between food with and without fruit flavonoids, blackcaps actively select food with flavonoids. 6. We found a positive effect of flavonoids on humoral immune response. Birds supplemented for 4 weeks with a modest quantity of flavonoids were more likely to mount a humoral immune response after an immune-challenge, compared with control birds. 7. To conclude, our study demonstrates that birds select food with flavonoids and that these antioxidants increase consumer humoral immune response. Since these effects occurred at a moderate dose that is obtainable also by many omnivorous consumers, we suggest that flavonoids may play a beneficial role in ecological immunology for several wild species.
Unlike exercising mammals, migratory birds fuel very high intensity exercise (e.g., flight) with fatty acids delivered from the adipose tissue to the working muscles by the circulatory system. Given the primary importance of fatty acids for fueling intense exercise, we discuss the likely limiting steps in lipid transport and oxidation for exercising birds and the ecological factors that affect the quality and quantity of fat stored in wild birds. Most stored lipids in migratory birds are comprised of three fatty acids (16:0, 18:1 and 18:2) even though migratory birds have diverse food habits. Diet selection and selective metabolism of lipids play important roles in determining the fatty acid composition of birds which, in turn, affects energetic performance during intense exercise. As such, migratory birds offer an intriguing model for studying the implications of lipid metabolism and obesity on exercise performance. We conclude with a discussion of the energetic costs of migratory flight and stopover in birds, and its implications for bird migration strategies.
During mate choice, individuals are predicted to assess traits that honestly signal the quality of potential partners. Locomotor
capacity may be such a trait, potentially signalling condition and ability to resist oxidative damage. In this study, we experimentally
manipulated nutritional status: Male wild-type budgerigars, imported from Australia, were provided with either an enhanced
(EQ) or reduced quality (RQ) diet varying in vitamin (particularly retinol and α-tocopherol) and mineral levels. Then, we
assessed whether this influenced locomotor capacity, i.e. escape flight performance, and sexual attractiveness in male budgerigars
Melopsittacus undulatus. Males in the EQ group showed significantly greater total antioxidant capacity and higher blood plasma concentrations of the
dietary antioxidants retinol and α-tocopherol, but not carotenoids, than the RQ group. Over 8weeks of flight training, males
on the EQ diet showed significantly greater improvement on the most strenuous flight test than RQ males. In mate choice trials,
females preferred EQ over RQ males. EQ males that were relatively fast in escape flight trials were more strongly preferred
in the mate preference arena than their RQ competitors. Interestingly, males with high plasma carotenoid levels flew slower
and were less attractive than males with low carotenoid levels. This might indicate that carotenoids are not effective antioxidants
in birds. Overall, our results show that dietary-derived antioxidants can influence sexual attractiveness and other fitness-related
traits through multiple pathways. Locomotor capacity appears to be an honest signal of male condition in birds.
KeywordsBudgerigars-ABTS-α-Tocopherol-Carotenoids-TAC-Mate choice-Takeoff flight
Progression of the vernal migratory life history stage to breeding presents a number of apparent behavioral and physiological
conflicts. Features that characterize the migratory stage include: high mobility, sociality, repetitive cycles of feeding
(hyperphagia and fattening) and migratory flight. Breeding comprises: sedentary, territorial and reproductive behaviors, an
initial decline in hyperphagia and reduction of fuel stores. Because morphology, physiology and behavior change, the transition
between stages cannot be instantaneous. In many species development of the reproductive system actually occurs during migration,
but in others gonadal development may not commence until later. This variation in degree of overlap of migration and reproductive
functions is not well understood, but may be related to migratory distance and length of the breeding season, which tends
to be shorter at higher latitudes and altitudes. In these habitats, migrants may arrive at their breeding sites to find unpredictable
conditions that cannot support breeding. At this juncture, migrants may retreat to refugia and prolong maintenance of facultative
migratory functions, termed arrival biology, until conditions improve sufficiently to initiate breeding. In this review, we
focus on the Pacific races of the white-crowned sparrow, Zonototrichia leucophyrs, in which the entire spectrum of migratory strategies are represented from resident to long distance migrants and about which
much is known. This species presents a unique view of the appearance and variations in arrival biology. Focusing on the juncture
between migration and breeding, we discuss the diversity of responses of congeners to a spectrum of environmental conditions
that favor survival and reproductive success.
Antioxidants have a large potential to coevolve with life-histories because of their capacity to counteract the negative effects of free radicals on fitness. However, only a few studies have explored the association between antioxidant levels and life-history strategies comparing a large number of species. Here we used an extensive dataset of 125 species of birds to investigate the association between concentrations of antioxidants (carotenoids and vitamin E) in the liver, which is the main storage organ for fat-soluble antioxidants, and life-history and morphology. We found that high liver antioxidant concentrations were associated with life-history strategies characterized by "live slow, die old", in clear contrast to previous studies reporting a relationship between high plasma antioxidants and life-histories characterized by "live fast, die young". Thus, high carotenoid concentrations were present in species with large body, brain and egg sizes, high absolute metabolic rate and a resident lifestyle, while high vitamin E concentrations were present in species with large brain size and long life span and incubation period. Our results indicate that antioxidants and life-histories coevolve, and that this may be mediated by positive fitness consequences of the accumulation of liver antioxidants, as species with higher antioxidant levels live longer.
The central aim of this review is to address the highly multidisciplinary topic of redox biology as related to exercise using an integrative and comparative approach rather than focusing on blood, skeletal muscle or humans. An attempt is also made to re-define 'oxidative stress' as well as to introduce the term 'alterations in redox homeostasis' to describe changes in redox homeostasis indicating oxidative stress, reductive stress or both. The literature analysis shows that the effects of non-muscle-damaging exercise and muscle-damaging exercise on redox homeostasis are completely different. Non-muscle-damaging exercise induces alterations in redox homeostasis that last a few hours post exercise, whereas muscle-damaging exercise causes alterations in redox homeostasis that may persist for and/or appear several days post exercise. Both exhaustive maximal exercise lasting only 30 s and isometric exercise lasting 1-3 min (the latter activating in addition a small muscle mass) induce systemic oxidative stress. With the necessary modifications, exercise is capable of inducing redox homeostasis alterations in all fluids, cells, tissues and organs studied so far, irrespective of strains and species. More importantly, 'exercise-induced oxidative stress' is not an 'oddity' associated with a particular type of exercise, tissue or species. Rather, oxidative stress constitutes a ubiquitous fundamental biological response to the alteration of redox homeostasis imposed by exercise. The hormesis concept could provide an interpretative framework to reconcile differences that emerge among studies in the field of exercise redox biology. Integrative and comparative approaches can help determine the interactions of key redox responses at multiple levels of biological organization.
Life-history theory predicts that animals face a trade-off in energy allocation between performing strenuous exercise, such as migratory flight, and mounting an immune response. We experimentally tested this prediction by studying immune function in European starlings, Sturnus vulgaris, flown in a wind tunnel. Specifically, we predicted that constitutive immune function decreases in response to training and, additionally, in response to immediate exercise. We compared constitutive immune function among three groups: (1) 'untrained' birds that were kept in cages and were not flown; (2) 'trained' birds that received flight training over a 15 day period and performed a 1-4 h continuous flight, after which they rested for 48 h before being sampled; and (3) 'post-flight' birds that differed from the 'trained' group only in being sampled immediately after the final flight. A bird in our trained group represents an individual during migration that has been resting between migratory flights for at least 2 days. A bird in our post-flight group represents an individual that has just completed a migratory flight and has not yet had time to recover. Three of our four indicators (haptoglobin, agglutination and lysis) showed the predicted decrease in immune function in the post-flight group, and two indicators (haptoglobin, agglutination) showed the predicted decreasing trend from the untrained to trained to post-flight group. Haptoglobin levels were negatively correlated with flight duration. No effect of training or flight was detected on leukocyte profiles. Our results suggest that in European starlings, constitutive immune function is decreased more as a result of immediate exercise than of exercise training. Because of the recent emergence of avian-borne diseases, understanding the trade-offs and challenges faced by long-distance migrants has gained a new level of relevance and urgency.
Despite observational evidence of carry-over effects (COEs, events occurring in one season that produce residual effects on individuals the following seasons), to our knowledge no experimental studies have been carried out to explore how COEs might affect reproductive output. We simulated an environmental perturbation affecting spring-staging migrants to investigate COEs in greater snow geese (Anser caerulescens atlanticus). During three consecutive years, 2037 females captured during spring staging (approx. 3000 km south of their Arctic breeding grounds) were maintained in captivity (with or without access to food) for 0-4 days. Duration of captivity (but not food treatment) negatively affected reproductive success, probably through stress response. Reproductive success was reduced by 45-71% in 2 years, but not in a third year with unusually favourable breeding conditions. This unprecedented manipulation indicates that COEs can have a strong effect on individual reproductive success in long-distance migrants, but that this effect can be partly compensated for by good environmental conditions on the breeding ground.
Numerous animals have successfully invaded urban habitats, although the factors associated with invasion success remain poorly understood. Urban areas are characterized by warmer microclimates, higher levels of primary productivity, longer breeding seasons and higher levels of pollutants. All these factors should cause oxidative stress, favoring invasion by species that have access to high levels of antioxidants. We analyzed concentrations of two categories of dietary, fat-soluble antioxidants (total carotenoids, total vitamin E) in the liver, the main storage organ in birds. Individuals killed by cats had lower levels of vitamin E than individuals that died for other reasons, showing natural selection on stored antioxidants. Bird species that had successfully colonized urban areas had significantly higher levels of vitamin E and total carotenoids than species that did not succeed, and rural populations had higher concentrations of vitamin E and total carotenoids than urban populations of the same species. Interspecific differences in concentrations of fat-soluble antioxidants, and differences between rural and urban populations of the same species, were accounted for by diet, but also by time since urbanization and number of generations since urbanization. These findings suggest that antioxidants, and by implication the ability to cope with oxidative stress, have contributed to successful invasion of urban areas by birds, and that the concentration of these antioxidants has changed in response to the urban environment.
Migratory birds engage in 2 periods of endurance flight annually as they travel between summer breeding and overwintering grounds, and such endurance flights likely incur oxidative costs. These costs may differ between fall and spring migration, especially for females who must prepare for breeding and egg laying in spring. The objective of this study of a migratory bird was to test proposed hypotheses about how key components of the female’s antioxidant system differ in response to flight training in the fall and spring and to dietary antioxidant supplementation. We hand raised female European Starlings (Sturnus vulgaris) and fed them either a diet supplemented with dietary anthocyanins or a diet without added anthocyanins. We flew females in a wind tunnel for 15 days during fall and spring migration seasons and measured over time oxidative lipid damage (d-ROMs) and 3 components of the antioxidant system: nonenzymatic antioxidant capacity (OXY), uric acid, and glutathione peroxidase (GPx) activity. Prior to flight training, OXY and oxidative damage were lower in females during spring compared with fall, and females fed a low-antioxidant diet had consistently higher circulating uric acid. GPx activity decreased more in spring immediately after a long-duration flight. Females fed a high-antioxidant diet had a greater decrease in OXY after the 15-day flight training. Flight-trained females had higher circulating uric acid than untrained females immediately after the longest-duration flight and decreased GPx activity after the 15-day flight training. In sum, females upregulated enzymatic and nonenzymatic endogenous antioxidants in spring, and females fed a diet with less antioxidants appear to compensate by increasing circulating uric acid. Our findings emphasize the important role of dietary antioxidants for birds during migration, and similar flights in fall and spring likely represent distinct oxidative challenges in the life history of female birds.
Training and diet are hypothesized to directly stimulate key molecular pathways that mediate animal performance, and flight-training, dietary fats, and dietary antioxidants are likely important in modulating molecular metabolism in migratory birds. This study experimentally investigated how long-distance flight-training as well as diet composition, affected the expression of key metabolic genes in the pectoralis muscle and the liver of European starlings (Sturnus vulgaris, N=95). Starlings were fed diets composed of either a high or low polyunsaturated fatty acid (PUFA; 18:2n-6) and supplemented with or without a water-soluble antioxidant, and half of these birds were flight-trained in a wind-tunnel while the rest were untrained. We measured the expression of 7 (liver) or 10 (pectoralis) key metabolic genes in flight-trained and untrained birds. Fifty percent of genes involved in mitochondrial metabolism and fat utilization were upregulated by flight-training in the pectoralis (P<0.05), whereas flight-training increased the expression of only one gene responsible for fatty acid hydrolysis (LPL) in the liver (P=0.04). Dietary PUFA influenced the gene expression of LPL and fat transporter CD36 in the pectoralis and one metabolic transcription factor (PPARα) in the liver, whereas dietary antioxidants had no effect on the metabolic genes measured in this study. Flight-training initiated a simpler causal network between PGC-1 coactivators, PPARs, and metabolic genes involved in mitochondrial metabolism and fat storage in the pectoralis. Molecular metabolism is modulated by flight-training and dietary fat quality in a migratory songbird indicating that these environmental factors will affect the migratory performance of birds in the wild.
Plasma metabolites provide information about the physiological state and fuel use of birds, and have been used for predicting refueling rates of birds during migratory stopovers. However, little is known about the effect of diet on metabolite concentrations in small songbirds. We investigated the effect of dietary macronutrient composition on lipid and protein metabolites in captive White-throated Sparrows (Zonotrichia albicollis). Birds fed a high-protein, low-carbohydrate insect diet had lower plasma triglyceride concentrations and higher plasma B-hydroxybutyrate concentrations than birds fed a high-carbohydrate, low-protein grain diet during feeding. The insect-fed birds also had higher plasma uric acid concentrations than grain-fed birds and birds fed a low-protein, high-fat, and high-carbohydrate fruit diet. Diet did not significantly influence plasma concentrations of glycerol or nonesterified fatty acids. After subsequent overnight fasting, birds in all three diet groups had similar concentrations of lipid metabolites, but uric acid was marginally elevated in insect-fed birds. Given that dietary macronutrient composition affected certain plasma metabolite concentrations in sparrows, investigators should consider such diet effects when using these metabolites to estimate refueling rates of free-living migratory songbirds, particularly in species that exhibit dietary plasticity during migration.
Migration poses many physiological challenges for birds, including sustaining high intensity aerobic exercise for hours or days. A consequence of endurance flight is the production of reactive oxygen species (ROS). ROS production may be influenced by dietary polyunsaturated fatty acids (PUFA), which, although prone to oxidative damage, may limit mitochondrial ROS production and increase antioxidant capacity. We examined how flight muscles manage oxidative stress during flight, and whether dietary long-chain PUFA influence ROS management or damage. Yellow-rumped warblers were fed diets low in PUFA, or high in long-chain n-3 or n-6 PUFA. Flight muscle was sampled from birds in each diet treatment at rest or immediately after flying for up to a maximum of 360 min in a wind tunnel. Flight increased flight muscle superoxide dismutase activity but had no effect on catalase activity. The ratio of glutathione to glutathione disulphide decreased during flight. Oxidative protein damage, indicated by protein carbonyls, increased with flight duration (Pearson r=0.4). Further examination of just individuals that flew for 360 min (N=15) indicates that oxidative damage was related more to total energy expenditure (Pearson r=0.86) than to flight duration itself. This suggests that high quality individuals with higher flight efficiency have not only lower energy costs but also potentially less oxidative damage to repair after arrival at the destination. No significant effects of dietary long-chain PUFA were observed on antioxidants or damage. Overall, flight results in oxidative stress and the degree of damage is likely driven more by energy costs than fatty acid nutrition.
Environmental cues, such as photoperiod, regulate the timing of major life-history events like breeding through direct neuroendocrine control. Less known is how supplementary environmental cues (e.g., nest sites, food availability) interact to influence key hormones and behaviors involved in reproduction, specifically in migratory species with gonadal recrudescence largely occurring at breeding sites. We investigated the behavioral and physiological responses of male European starlings to the sequential addition of nest boxes and nesting material, green herbs, and female conspecifics and how these responses depend on the availability of certain antioxidants (anthocyanins) in the diet. As expected, cloacal protuberance volume and plasma testosterone of males generally increased with photoperiod. More notably, testosterone levels peaked in males fed the high antioxidant diet when both nest box and herbal cues were present, while males fed the low antioxidant diet showed no or only a muted testosterone response to the sequential addition of these environmental cues; thus our results are in agreement with the oxidation handicap hypothesis. Males fed the high antioxidant diet maintained a constant frequency of breeding behaviors over time, whereas those fed the low antioxidant diet decreased breeding behaviors as environmental cues were sequentially added. Overall, sequential addition of the environmental cues modulated physiological and behavioral measures of reproductive condition, and dietary antioxidants were shown to be a key factor in affecting the degree of response to each of these cues. Our results highlight the importance of supplementary environmental cues and key resources such as dietary antioxidants in enhancing breeding condition of males, which conceivably aid in attraction of high quality females and reproductive success.
Migratory birds are physiologically specialized to accumulate massive fat stores (up to 50-60% of body mass), and to transport and oxidize fatty acids at very high rates to sustain flight for many hours or days. Target gene, protein and enzyme analyses and recent -omic studies of bird flight muscles confirm that high capacities for fatty acid uptake, cytosolic transport, and oxidation are consistent features that make fat-fueled migration possible. Augmented circulatory transport by lipoproteins is suggested by field data but has not been experimentally verified. Migratory bats have high aerobic capacity and fatty acid oxidation potential; however, endurance flight fueled by adipose-stored fat has not been demonstrated. Patterns of fattening and expression of muscle fatty acid transporters are inconsistent, and bats may partially fuel migratory flight with ingested nutrients. Changes in energy intake, digestive capacity, liver lipid metabolism and body temperature regulation may contribute to migratory fattening. Although control of appetite is similar in birds and mammals, neuroendocrine mechanisms regulating seasonal changes in fuel store set-points in migrants remain poorly understood. Triacylglycerol of birds and bats contains mostly 16 and 18 carbon fatty acids with variable amounts of 18:2n-6 and 18:3n-3 depending on diet. Unsaturation of fat converges near 70% during migration, and unsaturated fatty acids are preferentially mobilized and oxidized, making them good fuel. Twenty and 22 carbon n-3 and n-6 polyunsaturated fatty acids (PUFA) may affect membrane function and peroxisome proliferator-activated receptor signaling. However, evidence for dietary PUFA as doping agents in migratory birds is equivocal and requires further study.
Longitudinal studies often include multiple, repeated measurements of each patient’s status or outcome to assess differences in outcomes or in the rate of recovery or decline over time. Repeated measurements from a particular patient are likely to be more similar to each other than measurements from different patients, and this correlation needs to be considered in the analysis of the resulting data. Many common statistical methods, such as linear regression models, should not be used in this situation because those methods assume measurements to be independent of one another.
This book presents an up-to-date, detailed and thorough review of the most fascinating ecological findings of bird migration. It deals with all aspects of this absorbing subject, including the problems of navigation and vagrancy, the timing and physiological control of migration, the factors that limit their populations, and more. Author, Ian Newton, reveals the extraordinary adaptability of birds to the variable and changing conditions across the globe, including current climate change. This adventurous book places emphasis on ecological aspects, which have received only scant attention in previous publications. Overall, the book provides the most thorough and in-depth appraisal of current information available, with abundant tables, maps and diagrams, and many new insights. Written in a clear and readable style, this book appeals not only to migration researchers in the field and Ornithologists, but to anyone with an interest in this fascinating subject. * Hot ecological aspects include: various types of bird movements, including dispersal and nomadism, and how they relate to food supplies and other external conditions * Contains numerous tables, maps and diagrams, a glossary, and a bibliography of more than 2,700 references * Written by an active researcher with a distinguished career in avian ecology, including migration research.
Oxidative stress is suggested to be central to the ageing process, with endogenous antioxidant defence and repair mechanisms in place to minimize damage. Theoretically, supplementation with exogenous antioxidants might support the endogenous antioxidant system, thereby reducing oxidative damage, ageing-related functional decline and prolonging life- and health-span. Yet supplementation trials with antioxidants in animal models have had minimal success. Human epidemiological data are similarly unimpressive, leading some to question whether vitamin C, for example, might have pro-oxidant properties in vivo. We supplemented cold exposed (7±2°C) female C57BL/6 mice over their lifespan with vitamin C (ascorbyl-2-polyphosphate), widely advocated and self administered to reduce oxidative stress, retard ageing and increase healthy lifespan. No effect on mean or maximum lifespan following vitamin C treatment or any significant impact on body mass, or on parameters of energy metabolism was observed. Moreover, no differences in hepatocyte and lymphocyte DNA oxidative damage or hepatic lipid peroxidation was seen between supplemented and control mice. Using a DNA macroarray specific for oxidative stress-related genes, we found that after 18 months of supplementation, mice exhibited a significantly reduced expression of several genes in the liver linked to free-radical scavenging, including Mn-superoxide dismutase. We confirmed these effects by Northern blotting and found additional down-regulation of glutathione peroxidase (not present on macroarray) in the vitamin C treated group. We suggest that high dietary doses of vitamin C are ineffective at prolonging lifespan in mice because any positive benefits derived as an antioxidant are offset by compensatory reductions in endogenous protection mechanisms, leading to no net reduction in accumulated oxidative damage.
Publisher Summary Several methods have been developed to assess the total antioxidant capacities of various biological samples, particularly complex matrices such as plasma, serum, wine, fruits, vegetables, and animal tissues. This chapter presents a method called “oxygen radical absorbance capacity” (ORAC) assay based largely on the work reported by Glazer's laboratory, which depends on the unique properties of phycoerythrin (PE). The ORAC assay is the only method that takes reactive species (RS) reaction to completion and uses an “area under the curve” (AUC) technique for quantitation, thus combining both inhibition time and inhibition percentage of the RS action by antioxidants into a single quantity. The chapter discusses the general principles of ORAC assay for assessing antioxidant capacity against peroxyl radicals. By integrating inhibition percentages over the whole inhibition time period, the ORAC assay successfully overcomes all related problems in quantitation of the antioxidant capacity of a biological sample. Either B- or R-phycoerythrin (B-PE or R-PE) can be used in the ORAC assay. The sensitivity of B- or R-PE to hydroxyl radical damage may be different even for the same PE with different lot numbers. The concentrations of Cu 2+ and standard (Tro lox) can be adjusted, when it is necessary. The aforementioned procedures are based on using B- or R-PE that loses more than 90% of its fluorescence within 30 rains. The chapter concludes with a discussion of ORAC assay for assessing antioxidant capacity against transition metals.
European starlings add fresh green plants to their dry nest material. Male starlings of our 60-nest-box colony carried 68 different plant species into their nests. Some males were polygynous and had 3-6 clutches, others were monogynous and had 1-2 clutches per reproductive season. The 'nest protection hypothesis' proposes that insecticidal compounds in green plants reduce the parasite load of the nests. The 'courtship hypothesis' predicts that carrying nest greenery is a courtship activity to attract females. The aim of this study was to collect field data suitable for distinguishing these two hypotheses. 1. Some plant species occurred more often in the nest-boxes than expected from their frequency in the nest-box environment. A significant number of these preferred plants were rich in volatiles, some of which are said to be insecticidal. But volatiles could also attract females and/or influence their breeding activity and the chicks' development directly. 2. The males carried greenery into their nest boxes maximal around 5 days before the onset of laying, when pair formation took place, and ceased this behaviour with egg deposition. The total amount of greenery deposited in a nest-box was a function of the number of days of courtship a male needed to attract a female. 3. Polygynous males deposited the same amount of greenery in their first nest as monogynous males. In additional nests polygynous males deposited more greenery. However, this was due to the fact that these additional nests were advertised for a longer time.
We examined the pattern of song output of male European starlings during different stages of the breeding cycle. Song activity dropped dramatically at pairing, suggesting that the song has an important mate-attraction function. Singing in the nest box occurred almost only when males were unpaired and when prospecting females were in the vicinity of the nest box. Pairing in starlings had several other effects on male behaviour: the occurrence of wingwaving (a visual display sometimes associated with singing) and of carrying green nest materials dropped significantly after pairing. Unpaired males sang significantly more close (less-than-or-equal-to 1 m) to the nest box than paired males. After pair formation, an increase in singing activity was observed in the period coinciding with the presumed fertile period of the female. Evidence is presented that by singing males try to stimulate their females to solicit copulations during this period. Monogamous males almost completely stop singing after the egg laying period, whereas males attempting to become polygynous start/continue singing at another nest box at a level comparable to that of unpaired males.
Summary • Carotenoids are fat-soluble pigments that stimulate the immune system and can act as antioxidants. Carotenoids are thus expected to buffer the effects of environmental stressors on health. As carotenoids are a limited resource, the ability of an individual to use and metabolize carotenoids is assumed to influence its stress-resistance. Accordingly, it has been found that nestlings hatched from eggs with increased carotenoid concentration, show an enhanced ability to use carotenoids and a lower susceptibility of tissues to lipid peroxidation. • We tested the prediction that nestling great tits (Parus major), hatched from eggs laid by carotenoid-supplemented mothers, cope better with a transient stressor encountered after hatching. We supplemented half of the breeders with carotenoids during egg production (C+), used the other half as a control (C–), and cross-fostered the eggs between nests after clutch completion. Three days after hatching, we applied a stressor in two-third of the nests either by increasing brood size, or by infesting nests with hen fleas (Ceratophyllus gallinae) during five consecutive days. A third group was kept as a control. We then assessed the responses of C+ and C– nestlings to each stressor by measuring mass gain, body condition, plumage coloration, humoral immune response and fever response to a lipopolysaccharide injection. • In control nests, C+ and C– nestlings showed similar body condition but C+ nestlings had a higher increase in body temperature and tended to have a higher wing web swelling in response to lipopolysaccharide injection. Under stress, however, there were no differences in overall condition between C+ and C– nestlings. The two stressors led to different responses: when sibling competition was increased, C– nestlings favoured immune development, whereas C+ nestlings favoured mass gain and body condition, while under parasite exposure C+ and C– nestlings seemed to invest in immune development and body growth similarly. • Our results support the hypothesis that carotenoid-induced maternal effects provide developmental benefits under natural conditions without additional stressors. Additionally, we show that the response to sudden environmental changes depends on the environment during the initial phases of development, which thus shape phenotype and individual variation.
Maternal diet can significantly influence the quality and size of eggs, and this may, in turn, influence the fitness of offspring. In this study, we show how antioxidants (vitamin E compounds and carotenoids) in the diet of female zebra finches influence the concentrations of antioxidants in their eggs. Antioxidants are biochemicals derived from the diet, which reduce damage to cell membranes caused by the free radicals produced during normal metabolism and growth.
Females were given either a seed‐only or a seed + rearing food diet prior to egg laying. The seed + rearing food diet was more enriched with carotenoids, but had lower amounts of less effective antioxidants, such as γ‐tocopherol. Eggs were collected as they were laid, then analysed to determine the concentrations of antioxidants using high‐performance liquid chromatography.
Females in the two food groups had similar rates of food consumption and laid similar sized clutches. Females on the seed‐only diet produced eggs of similar mass to that of females on the seed + rearing food diet.
The concentrations of the most effective antioxidant (α‐tocopherol) were higher in the eggs of females from the seed‐only group and, for both food groups, concentrations decreased with successively laid eggs within clutches. The concentration of carotenoids in egg yolks did not differ between food treatments, but also decreased with successive eggs. Less effective antioxidants were relatively under‐represented in eggs in relation to their availability in food, and were deposited in similar overall amounts between the two food treatments, and independently of laying sequence.
Our results indicate that egg size is not necessarily an accurate guide to egg quality, especially when comparing between clutches of different females or across species. Females may be able to adjust egg composition to influence offspring quality variation within broods, possibly traded‐off against their personal use of antioxidants, their future reproductive success, control over sibling competition within their brood and/or brood reduction.
1. We studied the changes in body mass, metabolizable energy intake rate (ME) and basal metabolic rate (BMR) of a Thrush Nightingale, Luscinia luscinia, following repeated 12-h migratory flights in a wind tunnel. In total the bird flew for 176 h corresponding to 6300 km. This is the first study where the fuelling phase has been investigated in a bird migrating in captivity.
2. ME was very high, supporting earlier findings that migrating birds have among the highest intake rates known among homeotherms. ME was significantly higher the second day of fuelling, indicating a build-up of the capacity of the digestive tract during the first day of fuelling.
3. Further indications of an increase in size or activity level of metabolically active structures during fuelling come from the short-term variation in BMR, which increased over the 2-day fuelling period with more than 20%, and in almost direct proportion to body mass. However, mass-specific BMR decreased over the season.
4. The patterns of mass change, ME and BMR of our focal bird following two occasions of 12-h fasts were the same as after flights, indicating that fast and flight may involve similar physiological processes.
5. The relatively low ME the first day following a flight may be a contributing factor to the well-known pattern that migrating birds during stopover normally lose mass the first day of fuelling.
1.
Small passerine migrants achieve endurance flight while fasting, together with one of the highest mass-specific energy rates. Metabolic responses to flight and fasting were examined in three species of free-living migrants (Sylvia borin, Ficedula hypoleuca, Erithacus rubecula) by measuring plasma concentrations of glucose, uric acid, triglycerides, glycerol, free fatty acids (FFA), and -hydroxybutyrate (-OHB) in three main physiological situations (feeding, overnight fasting, nocturnal flight) and while changing between these situations.
2.
Overnight-fasted birds showed low triglyceride and uric acid levels. Contrary to mammals, FFA and glycerol levels were not increased in agreement with published data on birds. The transition from feeding to fasting (post-feeding) was distinguished by a temporary rise in FFA and a drop in glucose levels.
3.
Birds utilize fat during migratory flight, indicated by high levels of FFA, glycerol, and -OHB. For the first time, high triglyceride levels were found in an exercising vertebrate. The use of protein during flight was demonstrated by high uric acid levels.
4.
Birds kept inactive after flight showed a more pronounced reduction of the fat and protein utilization and post-exercise ketosis than naturally landed birds.
5.
Differences among the three species in the metabolic pattern suggest that the garden warbler shows the greatest metabolic adaption to endurance flight, having the highest levels of fat metabolites and the highest body fat reserves.
Dietary carotenoids perform several important roles in animals including as antioxidants, immunostimulants and pigments responsible for sexual signals. However, carotenoids may be in limited supply because of foraging constraints and/or physiological trade-offs in their utilization. Studies of birds and fish have shown that females frequently prefer to mate with carotenoid-rich males, which may serve to ensure the acquisition of a healthier mate. Evidence suggests that antioxidant and immune defences can be constrained by carotenoid availability, but we still lack information about the functional consequences of such carotenoid limitation for health, or any measure of physiological performance at the behavioural level. We tested whether carotenoid availability influenced escape flight responses in captive male zebra finches. Birds were fed a control or carotenoid-supplemented diet for 8 weeks, before measurements of escape flight responses from a release chamber after a startle stimulus. Carotenoid supplementation enhanced flight performance: carotenoid-supplemented birds had shorter flight times than controls. In addition, compared to controls, carotenoid-supplemented birds less often required a repeat startle stimulus to elicit escape flight, and emerged sooner from the release chamber after a startle stimulus. Such effects of carotenoids could be ecologically important, since flight take-off performance is thought to be an important determinant of predator evasion and foraging, and thus of survival probability and the capacity to provide parental care. We discuss various putative physiological mechanisms to explain how carotenoids may influence flight behaviour and performance.
Although fat is the primary fuel for migratory flight in birds, protein is also used. Catabolism of tissue protein yields
five times as much water per kilojoule as fat, and so one proposed function of protein catabolism is to maintain water balance
during nonstop flights. To test the protein-for-water hypothesis, we flew Swainson’s thrushes (Catharus ustulatus) in a climatic wind tunnel under high- and low-humidity conditions at 18°C for up to 5 hours. Flight under dry conditions
increased the rates of lean mass loss and endogenous water production and also increased plasma uric acid concentration. These
data demonstrate that atmospheric humidity influences fuel composition in flight and suggest that protein deposition and catabolism
during migration are, in part, a metabolic strategy to maintain osmotic homeostasis during flight.
Selenium is an essential trace element for mammals. Through selenoproteins, this mineral participates in various biological processes such as antioxidant defence, thyroid hormone production, and immune responses. Some reports indicate that a human organism deficient in selenium may be prone to certain diseases. Adverse health effects following selenium overexposure, although very rare, have been found in animals and people. Contrary to selenium, arsenic and cadmium are regarded as toxic elements. Both are environmental and industrial pollutants, and exposure to excessive amounts of arsenic or cadmium can pose a threat to many people's health, especially those living in polluted regions. Two other elements, vanadium and chromium(III) in trace amounts are believed to play essential physiological functions in mammals. This review summarizes recent studies on selenium interactions with arsenic and cadmium and selenium interactions with vanadium and chromium in mammals. Human studies have demonstrated that selenium may reduce arsenic accumulation in the organism and protect against arsenic-related skin lesions. Selenium was found to antagonise the prooxidant and genotoxic effects of arsenic in rodents and cell cultures. Also, studies on selenium effects against oxidative stress induced by cadmium in various animal tissues produced promising results. Reports suggest that selenium protection against toxicity of arsenic and cadmium is mediated via sequestration of these elements into biologically inert conjugates. Selenium-dependent antioxidant enzymes probably play a secondary role in arsenic and cadmium detoxification. So far, few studies have evaluated selenium effects on chromium(III) and vanadium actions in mammals. Still, they show that selenium may interact with these minerals. Taken together, the recent findings regarding selenium interaction with other elements extend our understanding of selenium biological functions and highlight selenium as a potential countermeasure against toxicity induced by arsenic and cadmium.
Endurance exercise causes fatigue due to mitochondrial dysfunction and oxidative stress. In order to find an effective strategy to prevent fatigue or enhance recovery, the effects of a combination of mitochondrial targeting nutrients on physical activity, mitochondrial function and oxidative stress in exercised rats were studied.
Rats were subjected to a four-week endurance exercise regimen following four weeks of training. The effects of exercise and nutrient treatment in rat liver were investigated by assaying oxidative stress biomarkers and activities of mitochondrial complexes.
Endurance exercise induced an increase in activities of complexes I, IV, and V and an increase in glutathione (GSH) levels in liver mitochondria; however, levels of ROS and malondialdehyde (MDA) and activities of complexes II and III remained unchanged. Exercise also induced a significant increase in MDA and activities of glutathione S-transferase and NADPH-quinone-oxidoreductase 1 (NQO-1) in the liver homogenate. Nutrient treatment caused amelioration of complex V and NQO-1 activities and enhancement of activities of complex I and IV, but had no effect on other parameters.
These results show that endurance exercise can cause oxidative and mitochondrial stress in liver and that nutrient treatment can either ameliorate or enhance this effect, suggesting that endurance exercise-induced oxidative and mitochondrial stress may be either damaging by causing injury or beneficial by activating defense systems.
After intense physical activity animals generally experience a rise in metabolic rate, which is associated with a proliferation of pro-oxidants. If unchecked, these pro-oxidants can cause damage to DNA and peroxidation of lipids in cell walls. Two factors are thought to ameliorate post-exercise oxidative damage, at least in mammals: dietary antioxidants and exercise training. So far it is unknown whether birds benefit similarly from exercise training, although a positive effect of dietary antioxidants on take-off flight has been indicated. In this experiment, we maintained captive wildtype budgerigars Melopsittacus undulatus on enhanced (EQ) or reduced quality (RQ) diets differing in levels of the dietary antioxidants retinol, vitamin C and alpha-tocopherol for 12 months. Birds were then regularly trained to perform take-off escape flights, a strenuous and biologically relevant form of exercise. For these adult budgerigars, regular exercise training improved escape flight performance, particularly in males on the EQ diet. In terms of oxidative damage, post-exercise levels of malondialdehyde (MDA), a by-product of lipid peroxidation, were significantly decreased after 9 weeks of flight training than after a single exercise session. Thus, individuals achieved faster escape flights with lower oxidative damage, after training. Also, birds that were fatter for their skeletal size initially had higher post-exercise MDA levels than thinner birds, but this relationship was broken by 9 weeks of flight training. Interestingly, there was no impact of diet quality on levels of MDA, suggesting that improved protection against oxidative damage for all birds was due to an up-regulation of endogenous antioxidant systems. Given their diversity, bird species provide rich research opportunities for investigating the interactions between exercise training, pro-oxidants production and antioxidant defences.