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 three-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 with when fed diets with less PUFA. (H3) Songbirds fed dietary anthocyanins gain additional antioxidant protection and thus upregulate their endogenous antioxidant system less compared with 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.
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 (
- NSF-PAR ID:
- 10449851
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 10
- Issue:
- 3
- ISSN:
- 2045-7758
- Page Range / eLocation ID:
- p. 1552-1566
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Songbirds meet the extreme metabolic demands of migration by burning both stored fat and protein. However, catabolizing these endogenous tissues for energy leads to organ atrophy, and reductions in gastrointestinal tissue can be as great as 50% of the pre-flight mass. Remarkably, during stopover refuelling birds quickly regain digestive mass and performance. Aminopep- tidase-N (APN) is a brush-border enzyme responsible for late-stage protein digestion and may critically assist tissue reconstruction during the stopover, thus compensating for reduced gut size. We hypothesized that birds recover- ing from a fast would differentially upregulate APN activity relative to disaccharidases to rapidly process and assimilate dietary protein into lean mass. We fasted 23 wild-caught migratory white-throated sparrows (Zonotrichia albicollis) for 48h to mimic mass reductions experienced during migratory flight and measured intestinal APN activity before the fast, immediately after the fast, and during recovery at 24 h and 48 h post- fast. Total fat mass, lean mass and basal metabolic rate were measured daily. We show that fasted birds maintain APN activity through the fast, despite a 30% reduction in intestine mass, but during refuelling, APN activity increases nearly twofold over pre-fasted individuals. This suggests that dynamically regulating APN may be necessary for rapid protein reconstruction during the stopover.more » « less
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null (Ed.)ABSTRACT Migratory birds catabolize large quantities of protein during long flights, resulting in dramatic reductions in organ and muscle mass. One of the many hypotheses to explain this phenomenon is that decrease in lean mass is associated with reduced resting metabolism, saving energy after flight during refueling. However, the relationship between lean body mass and resting metabolic rate remains unclear. Furthermore, the coupling of lean mass with resting metabolic rate and with peak metabolic rate before and after long-duration flight have not previously been explored. We flew migratory yellow-rumped warblers ( Setophaga coronata ) in a wind tunnel under one of two humidity regimes to manipulate the rate of lean mass loss in flight, decoupling flight duration from total lean mass loss. Before and after long-duration flights, we measured resting and peak metabolism, and also measured fat mass and lean body mass using quantitative magnetic resonance. Flight duration ranged from 28 min to 600 min, and birds flying under dehydrating conditions lost more fat-free mass than those flying under humid conditions. After flight, there was a 14% reduction in resting metabolism but no change in peak metabolism. Interestingly, the reduction in resting metabolism was unrelated to flight duration or to change in fat-free body mass, indicating that protein metabolism in flight is unlikely to have evolved as an energy-saving measure to aid stopover refueling, but metabolic reduction itself is likely to be beneficial to migratory birds arriving in novel habitats.more » « less
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Rationale Ecologists increasingly determine the δ15N values of amino acids (AA) in animal tissue; “source” AA typically exhibit minor variation between diet and consumer, while “trophic” AA have increased δ15N values in consumers. Thus, trophic‐source δ15N offsets (i.e., Δ15NT‐S) reflect trophic position in a food web. However, even minor variations in δ15Nsource AAvalues may influence the magnitude of offset that represents a trophic step, known as the trophic discrimination factor (i.e., TDFT‐S). Diet digestibility and protein content can influence the δ15N values of bulk animal tissue, but the effects of these factors on AA Δ15NT‐Sand TDFT‐Sin mammals are unknown.
Methods We fed captive mice (
Mus musculus Results As dietary protein increased, Δ15NConsumer‐Dietslightly declined for bulk muscle tissue in both experiments; increased for AA in the low‐fat, high‐fiber diet (A); and remained the same or decreased for AA in the high‐fat, low‐fiber diet (B). The effects of dietary protein on Δ15NT‐Sand on TDFT‐Svaried by AA but were consistent between variables.
Conclusions Diets were less digestible and included more protein in Experiment A than in Experiment B. As a result, the mice in Experiment A probably oxidized more AA, resulting in greater Δ15NConsumer‐Dietvalues. However, the similar responses of Δ15NT‐Sand of TDFT‐Sto diet variation suggest that if diet samples are available, Δ15NT‐Saccurately tracks trophic position. If diet samples are not available, the patterns presented here provide a basis to interpret Δ15NT‐Svalues. The trophic‐source offset of Pro‐Lys did not vary across diets, and therefore may be more reliable for omnivores than other offsets (e.g., Glu‐Phe).
