Comparison of Body Reserve Buildup in Prefasting Chicks and Adults of King Penguins (Aptenodytes patagonicus)

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Abstract
Like other penguin species, adult king penguins (Aptenodytes patagonicus) fast several weeks when they molt and at the beginning of their breeding cycle. Moreover, chicks of this species can withstand up to 5 mo of food deprivation during the austral winter. To assess possible variation in the prefasting amounts of nutrient reserves, we determined body composition (water, protein, total lipid, and ash contents) of adults and chicks of king penguins at the beginning of their long-term fasts. Accumulation of subcutaneous fat stores anticipates each of these periods and appears to be an obligatory prerequisite to fasting However, prewinter chicks contained 1 kg more fat and, consequently, had a higher adiposity (34%) than premolting chicks (22%) and prebreeding adults (18%), indicating that the higher the fat stores, the higher the fast resistance. Prewinter chicks also possess a 19% lower lean body mass (6 61 vs. 8.12 kg in premolting chicks), that is, a low amount of metabolically active tissues, thus minimizing their fasting energy expenditure. When compared with adult breeding fast, adult molt is anticipated by a 3.3-kg body mass increase due mainly to water (67%) and protein (23%). Two tissues (integument and pectoral muscles) account for 84% of this body mass difference. The increase in integument (feather, skin, and subdermal fat) mass involves water and fat (59% and 28% of the mass increase, respectively), whereas that in breast muscle mass involves protein and water (32% and 68% of the increase, respectively). Such protein stores anticipate the use of endogenous body protein for new feather synthesis during the molting fast. This study clearly shows that different amounts of fat and protein are builtup in anticipation of fasts of different durations and nutrient needs in king penguins.

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