Is oxidative status influenced by dietary carotenoid and physical activity after moult in the great tit (Parus major)?

Repeat Sampling of Female Passerines During Reproduction Reveals Surprising Higher Plasma Oxidative Damage During Resting Compared to Active State

Traditional models of oxidative stress predict accumulation of damage caused by reactive oxygen species (ROS) production as highly correlated with aerobic metabolism, a prediction under increasing scrutiny. Here, we repeat sampled female great tits (Parus major) at two opposite levels of energy use during the period of maximum food provisioning to nestlings, once at rest and once during activity. Our results were in contrast to the above prediction, namely significantly higher levels of oxidative damage during rest opposed to active phase. This discrepancy could not be explained neither using levels of "first line" antioxidant enzymes activity measured from erythrocytes, nor from total nonenzymatic antioxidant capacity measured from plasma, as no differences were found between states. Significantly higher levels of uric acid, a potent antioxidant, were seen in the plasma during the active phase than in rest phase, which may explain the lower levels of oxidative damage despite high levels of physical activity. Our results challenge the hypothesis that oxidative stress is elevated during times with high energy use and call for more profound understanding of potential drivers of the modulation of oxidative stress such as metabolic state of the animal, and thus also the time of sampling in general.

How Birds During Migration Maintain (Oxidative) Balance

Animals dynamically adjust their physiology and behavior to survive in changing environments, and seasonal migration is one life stage that demonstrates these dynamic adjustments. As birds migrate between breeding and wintering areas, they incur physiological demands that challenge their antioxidant system. Migrating birds presumably respond to these oxidative challenges by up-regulating protective endogenous systems or accumulating dietary antioxidants at stopover sites, although our understanding of the pre-migration preparations and mid-migration responses of birds to such oxidative challenges is as yet incomplete. Here we review evidence from field and captive-bird studies that address the following questions: (1) Do migratory birds build antioxidant capacity as they build fat stores in preparation for long flights? (2) Is oxidative damage an inevitable consequence of oxidative challenges such as flight, and, if so, how is the extent of damage affected by factors such as the response of the antioxidant system, the level of energetic challenge, and the availability of dietary antioxidants? (3) Do migratory birds ‘recover’ from the oxidative damage accrued during long-duration flights, and, if so, does the pace of this rebalancing of oxidative status depend on the quality of the stopover site? The answer to all these questions is a qualified ‘yes’ although ecological factors (e.g., diet and habitat quality, geographic barriers to migration, and weather) affect how the antioxidant system responds. Furthermore, the pace of this dynamic physiological response remains an open question, despite its potential importance for shaping outcomes on timescales ranging from single flights to migratory journeys. In sum, the antioxidant system of birds during migration is impressively dynamic and responsive to environmental conditions, and thus provides ample opportunities to study how the physiology of migratory birds responds to a changing and challenging world.

Potential Benefits of Acanthocephalan Parasites for Chub Hosts in Polluted Environments

Some parasites are expected to have beneficial impacts on wild populations in polluted environments because of their bioaccumulation potential of pollutants from their hosts. The fate of organic micropollutants in host-parasite systems and the combined effect of parasitism and pollution were investigated in chub Squalius cephalus, a freshwater fish, infected (n = 73) or uninfected (n = 45) by acanthocephalan parasites Pomphorhynchus sp. from differently contaminated riverine sites. Several ubiquitous pollutants (polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl-ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), phthalates, insecticides, pyrethroids, and N,N-diethyl-meta-toluamide (DEET)) and some of their metabolites were characterized for the first time in parasites and various fish matrices (muscle, liver, and stomach content). Most organic pollutants reached higher levels in parasites than in chub matrices. In contrast, metabolite levels were lower in parasite tissues compared to fish matrices. Infected and uninfected chub exhibited no significant differences in their pollutant load. Body condition, organo-somatic indices, and immunity were not affected by parasitism, and few correlations were found with chemical pollution. Interestingly, infected chub exhibited lower oxidative damage compared to uninfected fish, irrespective of their pollutant load. In light of these results, this correlative study supports the hypothesis that acanthocephalan parasites could bring benefits to their hosts to cope with organic pollution.

Varied effects of dietary carotenoid supplementation on oxidative damage in tissues of two waterfowl species

Carotenoids are regarded as a cornerstone of avian vitality and coloration. Currently, the antioxidant potential of dietary carotenoids is debated for birds. Although some studies support a protective role, others report either no effect or pro-oxidant effects. However, the majority of research on this topic has not analyzed the oxidative status of a series of tissues in animals nor considered a range of carotenoid dosages. We investigated the effects of three levels of carotenoid supplementation on plasma, liver, adipose, heart and breast muscle oxidative damage in two congeneric species of waterfowl that exhibit marked differences in carotenoid coloration. After a 6-week depletion period, captive adult northern pintail (Anas acuta) and mallard (A. platyrhynchos) ducks of both sexes were fed either a carotenoid-depleted diet (<3 μg/g xanthophylls, lutein and zeaxanthin), a carotenoid-supplemented diet (50 μg/g) within physiological range, or a carotenoid-rich diet (100 μg/g) within pharmacological range for 22 to 32 weeks. We hypothesized that these dosages of dietary carotenoids would differentially affect oxidative damage between species and sexes and among the tissues examined. We found that dietary xanthophyll supplementation had no significant effect on tissue pro-oxidation in males and females from both species. Moreover, sex or species differences in oxidative stress were only observed in two tissues (plasma and heart). Significant correlations in the levels of oxidative damage were not observed among the tissues examined. In conclusion, the current study does not support a consistent antioxidant role for dietary carotenoids in the tissues of these two waterfowl species. Instead, our results align with the notion that carotenoids play complex, tissue- and species-specific roles in oxidative status in birds.

Meta-analysis reveals that reproductive strategies are associated with sexual differences in oxidative balance across vertebrates

Oxidative stress is a key physiological mechanism underlying life-history tradeoffs. Here, I use meta-analytic techniques to test whether sexual differences in oxidative balance are common in vertebrates and to identify which factors are associated with such differences. The dataset included 732 effect size estimates from 100 articles (82 species). Larger unsigned effect size (meaning larger sexual differences in a given marker) occurred in: reptiles and fish; those species that do not provide parental care; and oviparous species. Estimates of signed effect size (positive values meaning higher oxidative stress in males) indicated that females were less resistant to oxidative stress than males in: reptiles while males and females were similar in fish, birds, and mammals; those species that do not provide parental care; and oviparous species. There was no evidence for a significant sexual differentiation in oxidative balance in fish, birds, and mammals. Effect size was not associated with: the number of offspring; whether the experimental animals were reproducing or not; biomarker (oxidative damage, non-enzymatic, or enzymatic antioxidant), the species body mass; the strain (wild vs. domestic); or the study environment (wild vs. captivity). Oxidative stress tended to be higher in females than males across most of the tissues analyzed. Levels of residual heterogeneity were high in all models tested. The findings of this meta-analysis indicate that diversification of reproductive strategies might be associated with sexual differences in oxidative balance. This explorative meta-analysis offers a starting platform for future research to investigate the relationship between sex and oxidative balance further.

The role of the antioxidant system during intense endurance exercise: lessons from migrating birds

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.