Rapid Atrophy and Hypertrophy of an Avian Flight Muscle

Abstract

A•3STRACT.-Eared Grebes (Podiceps nigricollis) use Mono Lake in eastern California as a rest stop during spring migration. Some nonbreeders remain for the summer, and in the autumn the lake becomes a staging area that may accommodate 750,000 returning breeders and young of the year. There the birds become obese by feeding on invertebrates and, if they have not already done so, molt. Most grebes remain several months until a decline in prey populations stimulates further migration. During this period the birds become flightless, and the flight muscles may lose up to 50% of their mass. Myofibers from atrophic birds show evidence of mitochondrial division (or fusion). Even severely atrophic fibers retain a high mitochondrial density (27% vs. 33% in migratory condition), so that relative volume remains stable although absolute volume is reduced. In contrast, intracellular triglyceride droplets are extremely sparse in atrophic fibers, even though most of the birds are carrying >200 g of subcutaneous fat. Mean myofiber diameter increases and decreases with atrophy and hypertrophy. In late autumn, as food availability declines, the birds engage in conspicuous flapping exercises. In the same period, intracellular lipid reappears in the muscles. Within several weeks the muscles are rebuilt to full size and the grebes emigrate. The benefits, if any, of this cycle of muscle atrophy and concomitant obesity, followed by muscle hypertrophy and weight loss, remain obscure.

Mitochondrial function in sparrow pectoralis muscle

“…The determined sparrow pectoralis mitochondrial volume density corroborated a single study that determined English sparrow mitochondrial volume density to be 29.9%. This value is also comparable to reported values for the pigeon (30%), the eared grebe (32%) and the rufous hummingbird (33%) (Gaunt et al, 1990;James and Meek, 1979;Suarez et al, 1991 O2 for all substrates save PC+M and G3P, were not significantly different between species (Table2). Mitochondria isolated from both species maintained high functional integrity, with P+M RCR values of 10.9±2.9 for sparrow and 8.6±0.8 for rat (Table2).…”

Making Olympic lizards: the effects of specialised exercise training on performance

“…In conclusion, our results, combined with perspectives from studies of exercise in fishes (Davison, 1997;He et al, 2013;Palstra and Planas, 2013), amphibians (Cummings, 1979;Miller and Camilliere, 1981), crocodilians (Owerkowicz and Baudinette, 2008;Eme et al, 2009), and birds (e.g. Gaunt et al, 1990) …”

“…In humans, both endurance running and sprint training can result in dramatic changes to skeletal muscle organisation, from gene expression (Wang et al, 2004;Wilson, 2013) to contractile properties, hypertrophy and power output (Trappe et al, 2006;Harber and Trappe, 2008;Lundberg et al, 2013). There are several studies on the effects of exercise in non-mammalian tetrapods, demonstrating that exercise training can enhance endurance capacity in amphibians (Cummings, 1979;Miller and Camilliere, 1981), crocodilians (Owerkowicz and Baudinette, 2008;Eme et al, 2009) and birds (Gaunt et al, 1990), but such studies have been conducted on only a few very distantly related species. This, combined with equivocal results in some studies, makes it difficult to understand the origin and adaptive significance of skeletal muscle plasticity.…”

Testing the use/disuse hypothesis: pectoral and leg muscle changes in captive barnacle geese Branta leucopsis during wing moult

“…Guozhen and Hongfa, 1986). Furthermore, a common observation in wild moulting waterfowl is atrophy of the major flight muscles at the onset of the flightless period of wing moult, coupled with hypertrophy of the leg muscles, which has been linked to increased levels of terrestrial locomotion (Ankney, 1979;Ankney, 1984;Gaunt et al, 1990;Fox and Kahlert, 2005). Towards the end of wing moult, flight muscles of wild moulting waterfowl hypertrophy (Ankney, 1979).…”