Meeting Abstract
The membrane-pacemaker hypothesis proposes that membrane composition, particularly docosahexaenoic acid (DHA) content, functions as a controller of basal metabolism. We tested this hypothesis by altering the dietary lipid composition of red-winged blackbird hatchlings (Agelaius phoeniceus), predicting that supplemental DHA would incorporate into membranes and increase whole-animal and mitochondrial respiration rates. Beginning 1 or 2 days after hatching, nestlings were supplemented in the field with a daily oral dose (3% of body mass) of sunflower seed oil (high ω-6), fish oil (high ω-3, including DHA), or not supplemented (control). At 5, 7, or 9 days after hatching, we measured resting metabolic rate (in the thermoneutral zone and while decreasing ambient temperature to 15°C) and mitochondrial respiration using permeabilized fibers from pectoralis muscle. Dietary treatment did not have a main effect on metabolic rate (total, body-mass-specific, or pectoralis-mass-specific), but interacted with ambient temperature, such that differences among dietary treatments were apparent at low ambient temperatures but not in the thermoneutral zone. At all ages, birds that received the seed oil supplement tended to have higher VO2 than those that received fish oil. In permeabilized muscle fibers, mitochondrial respiration rates did not differ between seed and fish oil groups, but sometimes were higher for these groups compared to controls. Our dietary manipulation failed to support the membrane pacemaker hypothesis. This could be due to strong effects of the diet on unmeasured variables, such as eicosanoid production. Alternatively, the membrane-pacemaker hypothesis might need refinement.
