Age and Food Deprivation Affects Expression of the Glucocorticosteroid Stress Response in Magellanic Penguin (Spheniscus magellanicus) Chicks

Abstract

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.

Comparing plasma and faecal measures of steroid hormones in Adelie penguins Pygoscelis adeliae

“…This point, of the inadequacy of a single plasma sample for making sound inferences about baseline steroid hormone concentrations, has been outlined previously (von Holst, 1998;Harper & Austad, 2000;Goymann, 2005;Palme et al, 2005), yet studies still report baseline steroid hormone concentrations based on single plasma samples (e.g. Vleck et al, 2000;Walker et al, 2005b;Raouf et al, 2006;Ellenberg et al, 2007).…”

“…As penguins are commonly used as model species for hormonal and stress studies in birds (e.g. Holberton et al, 1996;McQueen et al, 1998;Fowler, 1999;Walker et al, 2005b;Walker et al, 2006), our results will be particularly valuable for the interpretation of previous studies, and for the undertaking of future studies.…”

Corticosterone Predicts Foraging Behavior and Parental Care in Macaroni Penguins

“…Implants were sealed at both ends, but N p 8 one end was opened at the time of implantation to allow corticosterone release. Our goal was to temporarily increase plasma corticosterone titers above baseline within a physiologically realistic range (Holberton et al 1996;Walker et al 2005;Cockrem et al 2006;Angelier et al 2008; other seabird species: Chastel et al 2005;Angelier et al 2007a) and not to supraphysiological levels. The 15-mg dose that we applied was approximately 50% and 83% smaller than the doses used previously to manipulate corticosterone levels in seabirds ) and sea ducks (Criscuolo et al 2005).…”

Experimental effects of early‐life corticosterone on the hypothalamic–pituitary–adrenal axis and pre‐migratory behaviour in a wild songbird

“…Early life conditions influence developmental programming of the HPA axis (Matthews 2002, Seckl 2004, and exposure to early life stressors can disrupt HPA axis regulation, resulting in elevated basal glucocorticoids (Kitaysky et al 2005;Walker et al 2005;Quillfeldt et al 2007;Rensel, Boughton & Schoech 2010) and increased magnitude of the glucocorticoid response to acute stressors (Pravosudov & Kitaysky 2006;Vieau et al 2007, reviewed in Schoech, Rensel & Heiss. 2011).…”