Developmental plasticity of physiology and morphology in diet-restricted European shag nestlings (Phalacrocorax aristotelis).

Growing animals may exhibit developmental plasticity as an adaptation to variability in the environmental conditions during development. We examined physiological and morphological responses to short-term food shortage of 12-16-day-old European shag nestlings kept under laboratory conditions. After 4 days on a weight maintenance diet, the resting metabolic rate (RMR) of diet-restricted nestlings was 36.5% lower compared with control fed nestlings, after controlling for body mass. This response was accompanied by a reduction in body temperature (T(b)) and by reductions in the size of several visceral organs, muscles and lipid stores, while the overall structural growth was maintained almost in line with the age-specific growth rate of controls. Hence, the pattern of energy allocation reflected a very high priority to structural growth at the expense of visceral organs, lipid deposits and muscles. The reduced T(b) and size of the liver served as important physiological processes behind the observed reductions in RMR. We discuss the possible adaptive significance of this differential developmental plasticity during temporal food shortage. This is the first study of avian developmental plasticity to report substantial energy saving in combination with a high structural growth rate.