Differential effects of vitamins E and C and carotenoids on growth, resistance to oxidative stress, fledging success and plumage colouration in wild great tits

INTERACTIVE EFFECTS OF INCREASED NESTBOX TEMPERATURE AND VITAMIN E ON NESTLING GROWTH ARE ATTENUATED BY PLASTICITY IN FEMALE INCUBATION EFFORT

In recent years, temperatures have increased globally, and nestlings of many bird species are likely regularly exposed to increased temperatures both pre- and postnatally. Even small increases in nest temperature during incubation affect offspring growth and survival in a variety of species, one cause of which is thought to be increased production of prooxidants in embryos and nestlings. Defences marshalled in response to this oxidative stress could, in turn, result in trade-offs that lead to reduced survival or growth. If so, any downstream negative effects on nestlings of increased ambient temperatures during incubation could be counteracted by increasing their antioxidant intake. We predicted, therefore, that dietary supplements of an antioxidant would reduce or eliminate any detrimental effects on nestling growth and survival of experimentally increased nest temperature during the incubation period. We employed a split-brood design in which we increased nest temperature of entire clutches and, after hatching, provided dietary supplements of the antioxidant vitamin E to half of the nestlings within broods. We also recorded female incubation and provisioning behaviour to control for the possibility that heating nests might also influence maternal behaviour. There was a significant interaction between nestbox heating treatment and vitamin E treatment in their effect on nestling mass, a trait that is positively correlated with survival and future reproductive success in the study population. Vitamin E supplementation promoted increased nestling mass in heated nests, whereas it had the opposite effect in control nests, but these effects were weak. Heating significantly affected female incubation behaviour, with females in heated nestboxes investing less in incubation than those in unheated boxes. These results suggest that within at least some range of expected increased ambient temperatures during the 21st century, effects of climate change on nestling bird development can be mitigated by adjustments in female incubation behaviour.

Glycine Improved Cryopreserved Spermatozoa Quality in Achai Bull

Achai is a small size cattle breed, resilient to harsh and cold environment. Cryopreservation of Achai bull semen may help to improve its genetics and preserve the germplasm. Reactive oxygen species (ROS) affects the structural and functional integrity of the spermatozoa. During freezing and thawing processes, the ROS make changes in the spermatozoa quality parameters and reduce total antioxidant capacity (T-AOC) of semen that is considered as marker of oxidative stress. This study was designed to determine the effect of glycine along with vitamin E on post-thawed spermatozoa quality and total antioxidant capacity in Achai cattle. The semen collection was done twice a week from four mature fertile Achai cattle bulls (n = 4). The glycine was utilized as 0 mM, 5 mM, 10 mM, 15 mM, and 20 mM along with vitamin E @ 2.3 mM added constantly in each concentration. The control group contained all extenders except glycine. The results revealed that post-thawed spermatozoa motility was found significantly higher (P < 0.05) at 10 mM as compared to 5 mM, 15 mM, and 20 mM. Compared with control group, glycine concentration at 10 mM and other concentrations increased progressive and fast motility (%), curvilinear, straight line, and average path velocity (μm/s). Moreover, beat cross frequency (Hz) was higher (P < 0.05), and post-thaw viability (%), plasma membrane integrity, and mitochondrial membrane potential were significantly higher (P < 0.05) at 10 mM of glycine concentration in comparison to control and other glycine concentrations. Besides, acrosome integrity (%) and DNA integrity (%) as well as post-thawed T-AOC were also significantly higher (P < 0.05) at 10 mM of glycine concentration as compared to other glycine concentrations and control group. It is concluded that 10 mM of glycine along with vitamin E @ 2.3 mM improved cryopreserved semen quality of Achai bull.

Ecological effects on female bill colour explain plastic sexual dichromatism in a mutually-ornamented bird

Sex differences in ornamentation are common and, in species with conventional sex roles, are generally thought of as stable, due to stronger sexual selection on males. Yet, especially in gregarious species, ornaments can also have non-sexual social functions, raising the possibility that observed sex differences in ornamentation are plastic. For example, females may invest in costly ornamentation more plastically, to protect body and reproductive ability in more adverse ecological conditions. We tested this hypothesis with experimental work on the mutually-ornamented common waxbill (Estrilda astrild), supplementing their diets either with pigmentary (lutein, a carotenoid) or non-pigmentary (vitamin E) antioxidants, or alleviating winter cold temperature. We found that both lutein and vitamin E supplementation increased red bill colour saturation in females, reaching the same mean saturation as males, which supports the hypothesis that female bill colour is more sensitive to environmental or physiological conditions. The effect of vitamin E, a non-pigment antioxidant, suggests that carotenoids were released from their antioxidant functions. Alleviating winter cold did not increase bill colour saturation in either sex, but increased the stability of female bill colour over time, suggesting that female investment in bill colour is sensitive to cold-mediated stress. Together, results show that waxbill bill sexual dichromatism is not stable. Instead, sexual dichromatism can be modulated, and even disappear completely, due to ecology-mediated plastic adjustments in female bill colour.

Dietary vitamin E reaches the mitochondria in the flight muscle of zebra finches but only if they exercise

Whether dietary antioxidants are effective for alleviating oxidative costs associated with energy-demanding life events first requires they are successfully absorbed in the digestive tract and transported to sites associated with reactive species production (e.g. the mitochondria). Flying birds are under high energy and oxidative demands, and although birds commonly ingest dietary antioxidants in the wild, the bioavailability of these consumed antioxidants is poorly understood. We show for the first time that an ingested lipophilic antioxidant, α-tocopherol, reached the mitochondria in the flight muscles of a songbird but only if they regularly exercise (60 min of perch-to-perch flights two times in a day or 8.5 km day-1). Deuterated α-tocopherol was found in the blood of exercise-trained zebra finches within 6.5 hrs and in isolated mitochondria from pectoral muscle within 22.5 hrs, but never reached the mitochondria in caged sedentary control birds. This rapid pace (within a day) and extent of metabolic routing of a dietary antioxidant to muscle mitochondria means that daily consumption of such dietary sources can help to pay the inevitable oxidative costs of flight muscle metabolism, but only when combined with regular exercise.

Oxidative Stress Experienced during Early Development Influences the Offspring Phenotype

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

Does Vitamin E Supplementation Enhance Growth Benefits of Breeding Helpers at No Oxidative Costs?

During early postnatal development, biomolecules are particularly exposed to the detrimental actions of unneutralized reactive oxygen species. These prooxidant molecules have been claimed to mediate the trade-off between growth and somatic maintenance. Vitamin E is a key exogenous antioxidant that plays an important role in protecting biological membranes against oxidative damage. However, evidence of the effect of vitamin E supplementation during early life on growth and oxidative status in wild populations is equivocal. We tested the effect of supplementing western bluebird nestlings (Sialia mexicana) with vitamin E on growth rate, antioxidant capacity, and oxidative damage to lipids. During the period of accelerated growth (5-8 d), bill growth rate was 21% higher in supplemented nestlings from nests with breeding helpers than in supplemented nestlings from unassisted nests. Vitamin E also boosted tarsus growth rate during the period of slow growth (11-18 d), and this effect was independent of the presence of breeding helpers. Differences in body size and mass, oxidative damage to lipids, and antioxidant capacity were not evident between supplemented and control nestlings at 18 d. Therefore, we conclude that vitamin E promoted faster bill and tarsus growth, but this transient effect disappeared as soon as the supplementation ceased. Our experimental study also supports the idea that tocopherols are rapidly metabolized, since we failed to detect any evident increase of vitamin E in supplemented nestlings at age 18 d. These results provide partial support for the hypothesis that growth rate is constrained by its costs in terms of increased susceptibility to oxidative stress.

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.

Effects of co-exposure to lead and zinc on redox status, kidney variables, and histopathology in adult albino rats

Lead (Pb) is a toxic metal that induces a wide range of biochemical and physiological effects in humans. Oxidative damage has been proposed as a possible mechanism involved in Pb toxicity. The current study was carried out to evaluate the antioxidant activities of zinc (Zn) supplement against lead acetate-induced kidney injury in rats. In this study, adults male rats were treated for 15 days with Pb (0.344 g/kg body weight (bw)) associated or not with Zn (10 mg/kg bw). Our study showed that supplementation with Zn prevented renal dysfunction as indicated by plasma biomarkers (urea, uric acid, creatinine, lactate dehydrogenase, and alkaline phosphatase levels) and oxidative stress-related parameters (thiobarbituric acid reactive substances, protein carbonyl, advanced oxidation protein product, superoxide dismutase, catalase, glutathione peroxidase, and vitamins (A, E)) in kidney tissue. The corrective effect of Zn on Pb-induced kidney nephrotoxicity recovered normal kidney histology. Overall, this study indicates that Zn alleviated the toxic effects of this heavy metal on renal tissue, suggesting its role as a potential antioxidant and nephroprotective agent.

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.

Effects of dietary lead exposure on vitamin levels in great tit nestlings - An experimental manipulation

Exposure to metal pollution negatively affects animal physiology, including nutrient metabolism, but in the wild an effect can seldom be attributed to a single metal. Moreover, little is known about how the metabolism of vitamins, essential micronutrients for developing juveniles, is affected by toxic metals. Therefore we experimentally investigated the effects of lead (Pb), a widespread toxic metal, on four fat-soluble vitamins A (total and retinol), D3, E (total and α-tocopherol) and K and carotenoids (lutein, zeaxanthin and unidentified) in great tit (Parus major) nestlings. In addition to a control group where no Pb was provided, two Pb-dosed groups were compared to a metal exposed group in the vicinity of a Ni-Cu smelter. We examined whether Pb treatment affects vitamin homeostasis and how the response of Pb-treated birds relates to that of a population under industrial exposure of Pb and other metals. For this purpose, vitamin and carotenoid levels were quantified with UPLC-MS from plasma of 7 days-old nestlings. All metal exposed groups showed increased vitamin A and retinol levels. However, vitamin levels were not directly associated with fecal Pb levels, with the exception of retinol, which was positively correlated with fecal Pb. Alpha-tocopherol, lutein and zeaxanthin levels were positively associated with body mass and wing growth rate. To conclude, Pb exposure increased plasma vitamin A and retinol levels while the levels of other vitamins and carotenoids rather reflected secondary pollution effects via differences in habitat and diet quality at the smelter site. Our findings suggest Pb exposed nestlings may allocate the vitamins needed for growth and development to fight the physiological stress thus compromising their fitness.

Maternal effects as drivers of sibling competition in a parent-offspring conflict context? An experimental test

Maternal effects occur when the mother's phenotype influences her offspring's phenotype. In birds, differential allocation in egg yolk components can allow mothers to compensate for the competitive disadvantage of junior chicks. We hypothesize that the parent-older chick conflict peaks at intermediate conditions: parents benefit from the younger chick(s) survival, but its death benefits the older chick in terms of growth and survival. We thus expect maternal compensation to follow a bell-shaped pattern in relation to environmental conditions. We studied a black-legged kittiwake (Rissa tridactyla) population where previous results revealed increased allocation of yolk testosterone in younger as compared to older chicks in intermediate conditions, in line with our theoretical framework. We therefore predicted a maternally induced increase in aggressiveness, growth, and survival for younger chicks born in intermediate environmental conditions. Controlling for parental effects and chick sex, we manipulated food availability before egg laying to create a situation with intermediate (Unfed group) and good (Fed group) environmental conditions. Within each feeding treatment, we further created experimental broods where the natural hatching order was reversed to maximize our chances to observe an effect of feeding treatment on the younger chicks' aggressiveness. As predicted, we found that chick aggressiveness was higher in younger chicks born from the Unfed group (i.e., in intermediate environmental conditions), but only when they were put in a senior position, in reversed broods. Predictions on growth and survival were not confirmed. Mothers thus seem to favor the competitiveness of their younger chick in intermediate conditions via egg yolk components, but our study also suggests that hatching asynchrony need to be small for maternal compensation to be efficient. We emphasize the need for further studies investigating other chick behaviors (e.g., begging) and focusing on the relative role of different yolk components in shaping parent-offspring conflict over sibling competition.

Plasma markers of oxidative stress are uncorrelated in a wild mammal

Oxidative stress, which results from an imbalance between the production of potentially damaging reactive oxygen species versus antioxidant defenses and repair mechanisms, has been proposed as an important mediator of life‐history trade‐offs. A plethora of biomarkers associated with oxidative stress exist, but few ecological studies have examined the relationships among different markers in organisms experiencing natural conditions or tested whether those relationships are stable across different environments and demographic groups. It is therefore not clear to what extent studies of different markers can be compared, or whether studies that focus on a single marker can draw general conclusions regarding oxidative stress. We measured widely used markers of oxidative damage (protein carbonyls and malondialdehyde) and antioxidant defense (superoxide dismutase and total antioxidant capacity) from 706 plasma samples collected over a 4‐year period in a wild population of Soay sheep on St Kilda. We quantified the correlation structure among these four markers across the entire sample set and also within separate years, age groups (lambs and adults), and sexes. We found some moderately strong correlations between some pairs of markers when data from all 4 years were pooled. However, these correlations were caused by considerable among‐year variation in mean marker values; correlation coefficients were small and not significantly different from zero after accounting for among‐year variation. Furthermore, within each year, age, and sex subgroup, the pairwise correlation coefficients among the four markers were weak, nonsignificant, and distributed around zero. In addition, principal component analysis confirmed that the four markers represented four independent axes of variation. Our results suggest that plasma markers of oxidative stress may vary dramatically among years, presumably due to environmental conditions, and that this variation can induce population‐level correlations among markers even in the absence of any correlations within contemporaneous subgroups. The absence of any consistent correlations within years or demographic subgroups implies that care must be taken when generalizing from observed relationships with oxidative stress markers, as each marker may reflect different and potentially uncoupled biochemical processes.

Testing the interactive effects of carotenoids and polyunsaturated fatty acids on ejaculate traits in the guppy Poecilia reticulata (Pisces: Poeciliidae)

Using the polyandrous livebearing guppy Poecilia reticulata, this study revealed no main effects of carotenoids in the diet on ejaculate traits, but significant main effects of polyunsaturated fatty acids (PUFAs) on sperm viability and weak but significant interacting effects of both nutrients on sperm length. Collectively, these findings not only add evidence that PUFAs are critical determinants of sperm quality, but also provide tentative evidence that for some traits these effects may be moderated by carotenoid intake.

Interactive effects of early and later nutritional conditions on the adult antioxidant defence system in zebra finches

In vertebrates, antioxidant defences comprise a mixture of endogenously produced components and exogenously obtained antioxidants that are derived mostly from the diet. It has been suggested that early life micronutritional conditions might influence the way in which the antioxidant defence system operates, which could enable individuals to adjust the activity of the endogenous and exogenous components in line with their expected intake of dietary antioxidants if the future environment resembles the past. We investigated this possibility by experimentally manipulating the micronutrient content of the diet during different periods of postnatal development in the zebra finch (Taeniopygia guttata). Birds that had a low micronutrient diet during the growth phase initially had a lower total antioxidant capacity (TAC) than those reared under a high micronutrient diet, but then showed a compensatory response, so that by the end of the growth phase the TAC of the two groups was the same. Interestingly, we found an interactive effect of micronutrient intake early and late in development: only those birds that continued with the same dietary treatment (low or high) throughout development showed a significant increase in their TAC during the period of sexual maturation. A similar effect was also found in the level of enzymatic antioxidant defences (glutathione peroxidase; GPx). No significant effects were found in the level of oxidative damage in lipids (MDA). These findings demonstrate the importance of early and late developmental conditions in shaping multiple aspects of the antioxidant system. Furthermore, they suggest that young birds may adjust their antioxidant defences to enable them to ‘thrive’ on diets rich or poor in micronutrients later in life.