NUTRIENT RESERVE DYNAMICS AND ENERGETICS DURING LONG-TERM FASTING IN THE KING PENGUIN (APTENODYTES PATAGONICUS)

Males of king penguins (Aptemodytes patagonictus) naturally fast durin g one month of the beginning of their breeding cycle in the sub-Antarc tic islands. Previous qualitative data have shown that this species ad apts to prolonged fasting by mobilizing fat stores and minimizing prot ein loss and that this strategy ends with a progressive increase in pr otein utilization. In the present study, the quantification of nutrien t utilization from body composition of captive birds indicates that, d uring the phase of protein conservation, 93% of the energy produced de rives from the oxidation of fat stores, body protein accounting for th e remainder (7%). Tissue composition analysis shows that integument (f eathers, skin and subdermal fat) is the main lipid source (65% of the fat loss) during this period, and that pectoral muscles provide the ma jority of body protein (57% of the total loss). Ii. the fast is prolon ged until a body mass below 10 kg is reached, there is a progressive f our-fold increase (from 1.68 to 6.50 gN/24h) in nitrogen excretion, to gether with a progressive exhaustion of fat stores. This shift in fuel metabolism is not a direct consequence of total lipid depletion, beca use 22% of the initial fat content still remains when proteins are no longer spared. During this later metabolic phase, protein is not only provided by pectoral muscles (71% of the loss), but also by hindlimb m uscles (13%), and there remains only:2% of the initial amount of lipid in the integument at the end of the fast. Total energy expenditure is dose to the fasting basal metabolic rare during the phase of protein conservation (2.52 W/kg), but it increases by 33% (3.36 W/kg) during t he phase of protein wasting. This difference is probably due to a rise in locomotor activity, that is interpreted as reflecting a stimulatio n of food foraging behaviour before the lethal depletion of nutrient r eserves.