Body building and concurrent mass loss: flight adaptations in tree sparrows

In small resident bird species living at northern latitudes, winter cold acclimatization is associated with an increase in pectoral muscle size and haematocrit level, and this is thought to drive the seasonal increase in summit metabolic rate (Ṁ sum , a measure of maximal shivering thermogenic capacity). However, evidence suggesting that pectoral muscle size influences Ṁ sum is correlational and the link between haematrocrit level and Ṁ sum remains to be demonstrated. We experimentally tested the relationship between pectoral muscle size and Ṁ sum by manipulating muscle size using a feather clipping protocol in free-living wintering black-capped chickadees (Poecile atricapillus). This also allowed us to investigate the link between haematocrit and thermogenic capacity. After a first series of measures on all birds, we cut half of the flight feathers of experimental individuals (N=14) and compared their fat and pectoral muscle scores, Ṁ sum and haematocrit level at recapture with their previous measures and with those of control birds (N=17) that were captured and recaptured at comparable times. Results showed that: (1) experimental birds developed larger pectoral muscles than control individuals and (2) mass-independent Ṁ sum was up to 16% higher in birds expressing large pectoral muscles. Ṁ sum was also positively correlated with haematocrit, which was not affected by the experimental manipulation. These findings demonstrate that, for a given body mass, large pectoral muscles are associated with a higher Ṁ sum in black-capped chickadees and that oxygen carrying capacity likely supports thermogenesis in this species.

Section: Discussionsupporting

confidence: 80%

Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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Phenotype manipulations confirm the role of pectoral muscles and haematocrit in avian maximal thermogenic capacity

Petit

Vézina

2013

“…In neither Eurasian tree sparrows nor hummingbirds does relative flight muscle mass increase with elevation, which could otherwise potentially compensate for the increased power demands of hypodense air. Molting Eurasian tree sparrows are known to increase their relative pectoral muscle size, enabling escape flights dynamically comparable to those in non-molting conditions (Lind, 2001;Lind and Jakobsson, 2001). Such an increase is not, however, characteristic among sparrow populations at different elevations (Table 1), consistent with a relative decline in load-lifting performance.…”

Section: Discussionmentioning

confidence: 46%

Flying high: Limits to flight performance by sparrows on the Qinghai-Tibet Plateau

Sun

Ren

et al. 2016

Limits to flight performance at high altitude potentially reflect variable constraints deriving from the simultaneous challenges of hypobaric, hypodense and cold air. Differences in flight-related morphology and maximum lifting capacity have been well characterized for different hummingbird species across elevational gradients, but relevant within-species variation has not yet been identified in any bird species. Here we evaluate load-lifting capacity for Eurasian tree sparrow (Passer montanus) populations at three different elevations in China, and correlate maximum lifted loads with relevant anatomical features including wing shape, wing size, and heart and lung masses. Sparrows were heavier and possessed more rounded and longer wings at higher elevations; relative heart and lung masses were also greater with altitude, although relative flight muscle mass remained constant. By contrast, maximum lifting capacity relative to body weight declined over the same elevational range, while the effective wing loading in flight (i.e. the ratio of body weight and maximum lifted weight to total wing area) remained constant, suggesting aerodynamic constraints on performance in parallel with enhanced heart and lung masses to offset hypoxic challenge. Mechanical limits to take-off performance may thus be exacerbated at higher elevations, which may in turn result in behavioral differences in escape responses among populations.

“…In this study, BMR was lower for exercise-trained than for control birds, which is consistent with such an energy conservation strategy, despite the increase in M pec and higher maximum metabolic outputs for exercise-trained birds. Feather clipping to increase flight costs in birds also produces increases in M pec (Lind and Jakobsson, 2001;Petit and Vézina, 2014) and migratory birds also consistently show pectoralis muscle hypertrophy during migration to help support prolonged flights (reviewed in Swanson, 2010;Piersma and van Gils, 2010). The exercise-induced increase in M pec in this study is thus consistent with these latter adjustments to increase power production for extended flights.…”

Section: Among Birds Tufted Ducksmentioning

confidence: 99%

Cross-training in birds: cold and exercise training produce similar changes in maximal metabolic output, muscle masses and myostatin expression in house sparrows,Passer domesticus

Zhang

Eyster

Liu

et al. 2015

Maximal metabolic outputs for exercise and thermogenesis in birds presumably influence fitness through effects on flight and shivering performance. Because both summit (M sum , maximum thermoregulatory metabolic rate) and maximum (MMR, maximum exercise metabolic rate) metabolic rates are functions of skeletal muscle activity, correlations between these measurements and their mechanistic underpinnings might occur. To examine whether such correlations occur, we measured the effects of experimental cold and exercise training protocols for 3 weeks on body (M b ) and muscle (M pec ) masses, basal metabolic rate (BMR), M sum , MMR, pectoralis mRNA and protein expression for myostatin, and mRNA expression of TLL-1 and TLL-2 (metalloproteinase activators of myostatin) in house sparrows (Passer domesticus). Both training protocols increased M sum , MMR, M b and M pec , but BMR increased with cold training and decreased with exercise training. No significant differences occurred for pectoralis myostatin mRNA expression, but cold and exercise increased the expression of TLL-1 and TLL-2. Pectoralis myostatin protein levels were generally reduced for both training groups. These data clearly demonstrate cross-training effects of cold and exercise in birds, and are consistent with a role for myostatin in increasing pectoralis muscle mass and driving organismal increases in metabolic capacities.