Age and food deprivation affects expression of the glucocorticosteroid stress response in Magellanic penguin (Spheniscus magellanicus) chicks.
We examined how the glucocortical stress response in free-living Magellanic penguin (Spheniscus magellanicus) chicks changes with age and whether adrenocortical function of chicks within a brood varies in relation to food provisioned by adults. Chicks showed little corticosterone response to capture stress shortly after hatching, an intermediate response around 45-d posthatch, and a robust stress response near fledging. However, in response to an adrenocorticotropic hormone (ACTH) challenge, hatchlings were capable of secreting corticosterone at adult-like levels. The larger sibling in broods of two showed a similar gradual stress-response development pattern. In contrast, by day 45, when differences in body condition were well established between siblings, the smaller, food-deprived chicks significantly increased baseline levels of corticosterone but showed normal stress-induced levels. Near fledging, baseline levels had returned to normal, but stress-induced levels were lower than expected. Similar to altricial species, normally developing semialtricial Magellanic penguin chicks do not express a robust corticosterone stress response until near fledging. Chronic stressors such as food deprivation cause corticosterone use to be up-regulated earlier than expected. However, in cases of extended chronic stress, down-regulation may ensue, thus avoiding the negative effects of chronically elevated levels of corticosterone.
Walker
Brian G
BG
Department of Biology, Box 351800, University of Washington, Seattle, WA, 98195, USA. bwalker@u.washington.edu
Wingfield
John C
JC
Boersma
P Dee
PD
D000324:Adrenocorticotropic Hormone; D000367:Age Factors; D000704:Analysis of Variance; D000818:Animals; D001118:Argentina; D003345:Corticosterone / Q000097:blood* / Q000378:metabolism; D005508:Food Deprivation / Q000502:physiology; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology*; D010913:Pituitary-Adrenal System / Q000502:physiology*; D011863:Radioimmunoassay; D013048:Specimen Handling; D046429:Spheniscidae / Q000097:blood / Q000502:physiology*; D013312:Stress, Physiological / Q000503:physiopathology*
D000324:Adrenocorticotropic Hormone; D003345:Corticosterone