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Acyl composition of muscle membranes varies with body size in birds
1 Metabolic Research Centre, University of Wollongong, Wollongong, NSW 2522,
Australia
2 Department of Biological Science, University of Wollongong, Wollongong,
NSW 2522, Australia
3 Department of Biomedical Science, University of Wollongong, Wollongong,
NSW 2522, Australia
* Author for correspondence (e-mail: hulbert{at}uow.edu.au)
Accepted 20 August 2002
The acyl composition of phospholipids from pectoral muscle of eight species of birds, ranging in size from the 13 g zebra finch to the 34 kg emu, were measured and combined with recent published results for a 3 g hummingbird. This represents an approximately 11000-fold range in body mass. Muscle phospholipids, and thus muscle membrane bilayers, from birds had a relatively constant unsaturated acyl chain content of 62% but exhibited a significant allometric decline in unsaturation index (number of double bonds per 100 acyl chains) with increasing body mass. There was a significant allometric increase in the percentage of mono-unsaturates and a significant allometric decline in the percentage of n-3 polyunsaturates with increasing body mass, whilst there were no significant allometric trends in either percentage of n-6 or percentage of total polyunsaturates in bird muscle. The relative content of the highly polyunsaturated docosahexaenoic acid (22:6 n-3) showed the greatest scaling with body mass, having an allometric exponent of -0.28. The contribution of this n-3 polyunsaturate to the unsaturation index varied with body size, ranging from less than a 6% contribution in the emu to approximately 70% in the hummingbird. Such allometric variation in the acyl composition of bird muscle phospholipids is similar to that observed in mammals, although birds have fewer n-3 polyunsaturates and more n-6 polyunsaturates than do mammalian phospholipids. This allometric variation in phospholipid acyl composition is discussed with respect to both the metabolic intensity and lifespan of different sized bird species.
Key words: muscle phospholipid, polyunsaturate, docosahexaenoic acid, allometry, basal metabolism, maximum lifespan, bird
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