The membrane pacemaker hypothesis: novel tests during the ontogeny of endothermy.
The 'membrane pacemaker' hypothesis proposes a biochemical explanation for among-species variation in resting metabolism, based on the positive correlation between membrane docosahexaenoic acid (DHA) and metabolic rate. We tested this hypothesis using a novel model, altricial red-winged blackbird nestlings, predicting that the proportion of DHA in muscle and liver membranes should increase with the increasing metabolic rate of the nestling as it develops endothermy. We also used a dietary manipulation, supplementing the natural diet with fish oil (high DHA) or sunflower oil (high linoleic acid) to alter membrane composition and then assessed metabolic rate. In support of the membrane pacemaker hypothesis, DHA proportions increased in membranes from pectoralis muscle, muscle mitochondria and liver during post-hatch development. By contrast, elevated dietary DHA had no effect on resting metabolic rate, despite causing significant changes to membrane lipid composition. During cold challenges, higher metabolic rates were achieved by birds that had lower DHA and higher linoleic acid in membrane phospholipids. Given the mixed support for this hypothesis, we conclude that correlations between membrane DHA and metabolic rate are likely spurious, and should be attributed to a still-unidentified confounding variable.
['Price|Edwin R|ER|0000-0001-6042-7020', 'Sirsat|Tushar S|TS|', 'Sirsat|Sarah K G|SKG|', 'Curran|Thomas|T|', 'Venables|Barney J|BJ|', 'Dzialowski|Edward M|EM|']
D000821:Animal Feed D000818:Animals D000831:Animals, Newborn D001481:Basal Metabolism D003080:Cold Temperature D004032:Diet D019587:Dietary Supplements D004281:Docosahexaenoic Acids D005260:Female D008099:Liver D008563:Membrane Lipids D008931:Mitochondria, Muscle D010369:Pectoralis Muscles D010743:Phospholipids D020308:Songbirds
Membrane pacemaker hypothesis Ontogeny Docosahexaenoic acid Linoleic acid Mitochondria Agelaius phoeniceus