Aerobic metabolism in night migratory songbirds exhibit seasonal plasticity, which depends not only on annual life history stages (LHSs), viz., migratory/nonmigratory or breeding/ nonbreeding, but also on the time of the day. Initially, we studied daily changes in behavior/physiology alongside aerobic metabolism intermediates using gas chromatography−mass spectrometrybased chemometric analyses of serum of migratory male redheaded buntings during low-energy wintering, that is, the nonmigrating LHS. Then, the metabolic phenotype of nonmigrating birds was compared with that of photostimulated migrating buntings, the latter representing the high-energy LHS. Diurnal changes such as daytime feeding and activity were reflected by increased fatty acid (FA, viz., palmitic, oleic, and linoleic acids) levels and protein catabolites, whereas higher night-time levels of short-chain FAs indicated lipolysis in night-fasted birds. High night-time levels of taurine, a sulfur amino acid, suggested the endogenous metabolite rendering an adaptive advantage to hyperglycaemic night migratory songbirds during the LHS with low daily energy expenditure. Conversely, migrating birds, largely night-active, exhibited higher circulatory FA, its mobilization, and increased aerobic catabolism, and the adipocyte-secreted lipid, palmitoylethanolamide (PEA), capable of activating the peroxisome proliferator-activated receptor α−PGCα axis, showed elevated levels throughout the day. PEA is known for anti-inflammatory and cannabinomimetic properties, and we show, for the first time, circadian changes in PEA levels in any migrating bird. Significantly higher levels of pyridoxal phosphate also suggested the bird's protective ability to combat metabolic stress through high aerobic capacity during migration. This study elucidates putative "serum biomarkers" with a protective role in stress accrued by enhanced aerobic capacity requirements at the organismal level.
in 2 | P a g e ABSTRACT Daily behavioural and physiological changes in bird may reflect in biofluid metabolite composition. Locomotor activity, food intake and body temperature of group (n=7) of male migratory redheaded buntings held under short days (8L:16D, SD) were monitored besides blood sampling at midday (ZT4: 4 hours zeitgeber time starting ZT0 as lights 'on') and midnight (ZT16). The birds exhibited higher activity and increased feeding during daytime with negligible activity and feeding at night. Gas chromatography mass spectrometry and chemo-metric analyses of bird serum revealed higher levels of lipid (palmitic, oleic and linoleic acids) and protein (uric acid and proline) catabolites in daytime serum samples as compared to night samples. Higher night-time levels of short chain fatty acids indicated utilization of glucose and lipolysis in night fasted birds. High night-time levels of taurine, a sulphur amino acid has adaptive advantage to night migratory song birds. The diurnal differences in metabolite patterns suggests differential energy expenditure during day and renders survival benefit to buntings as night migrants. We propose a GCMS method that could be useful to unravel different annual life-history stages including migration.
Seasonal changes in daily food consumption have a direct bearing with energy requirement of bird that is in turn associated with life history stage of birds. We compared seasonal changes in daily food intake in adult male migratory redheaded bunting (Emberiza bruniceps) that over winters in Indian subcontinent with those in non-migratory blackheaded munia to reiterate the same. We also compared daily food eating pattern (DFEP) in wintering blackheaded and redheaded buntings, closely related Emberizidae finches to establish circadian nature of feeding behavior and how it varied at species level. The birds were held under short days (8L:16D; 8 h of light and 16 h of darkness) and two hourly food consumption was measured to profile their DFEP. Further, we extended the study to establish how the circadian pattern of food consumption varied depending on birds' physiological state and effect of photoperiod in adult male redheaded buntings. Redheaded buntings DFEP and locomotor activity were compared in pre-migratory months of February (spring) and September (autumn). The results suggest that September (photorefractory) birds exhibit clear bimodality in their feeding behavior as compared to (photosensitive) birds in February. Another experiment compared bird's DFEP held under short (8L:16D) and long (16L:8D) days for 5 weeks and suggested that under long days, prolonged hours of photophase render adaptive advantage to birds for positive energy budgeting. The present study clearly establishes the circadian nature of feeding behavior and that it modulates over seasons. The bimodal i.e. morning and evening peaks of food consumption suggest morning-evening food entrainable oscillators, however this needs to be investigated with mechanistic approach in future studies.
Circulatory system is the source of useful metabolites to enable organismal energy demands of muscle during different life states of birds including migration. In this study, we profiled the serum metabolites and fecal microbiome of redheaded buntings (Emberiza bruniceps) exhibiting diurnal non-migratory (nonM) pre-migratory (preM), migratory (M) and post-migratory (posM) states, when exposed to long days (14L:10D). Using gas chromatography, out of the identified 124 serum analytes, 38 showed significant variations (Fold change, VIP) between states. Out of these, 11 metabolites (short chain fatty acids, SCFAs- butanoate and hexanoate, lactate, pyruvate, ethylene and acetate oxime, pyridoxal phosphate (PLP), niacin, L-valine and carboximidic acids viz. phosphatidyl ethanolamine (PE) and diethyl carbamate) involved in energy pathways and enhanced immunity showed higher abundance in M state. While, upsurge of L-valine suggested energy contribution of glucogenic branched chain amino acids (BCAAs) in M state, that of leucine metabolite, was related to higher temperature in posM birds. Gut microbiota was analysed using faeces of buntings (n=6 each) during nonM and M states and alteration in bacterial compositions was observed; faeces of nonM birds were enriched in proteobacteria, while those of M were rich in firmicutes. This study reports the migratory state specific changes in the serum metabolome and faecal microbiome of the buntings and highlights the role of short chain fatty acids, SCFAs and branched chain amino acids, BCAAs during hypermetabolic state of migration.
Migratory birds need continued food supply and efficient metabolic machinery to meet high energy demands of the magnanimous feat of flight. Two questions are important i.e. as to 1) how a bird adapts to a temporary food constrain on a daily basis, and 2) how peripheral leptin, an anorectic hormone, impacted feeding and migratory behaviour in buntings? The aim of this study was to induce a non-photoperiodic tweak in the physiology of redheaded buntings through exogenous leptin administration and study its effect on their food intake and migratory behaviour. Groups of male redheaded buntings, Emberiza bruniceps (n=17) were transferred from short (8L: 16D) to long (16L: 8D) days and presented with food only either for first (morning food presence, MFP) or second (evening food presence, EFP) half of the 16h lighted phase, while control group received food ad libitum. Total daily food intake (FI) did not differ significantly between the MFP, EFP and controls, but hourly FI in MFP and EFP indicated increased activity differences based on time of food availability and bird’s tendency to cache food/ recompense for food scarcity during migration. In another experiment, a chemical tweak in bird’s FI was induced by peripheral administration of leptin, to add to current understanding of transition in buntings’ metabolic efficiency during high energy demanding migratory journey. Exogenous leptin appeared to safeguard cadaveric effect of exogenous injection in migrating buntings through promoting blood cholesterol and reduced liver fibrosis. Food restriction in the morning was better responded by buntings than that in evening. Therefore, migratory buntings exhibited diurnal variation in response to food scarcity.
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