The turnover and distribution of labelled corticosterone during post-natal development of the duckling (Anas platyrhynchos)

Pre- and post-natal stress in context: effects on the stress physiology in a precocial bird

Developmental stress can significantly influence physiology and survival in many species. Mammalian studies suggest that pre- and post-natal stress can cause different effects (i.e. hyper- or hypo-responsiveness) on the Hypothalamic-Pituitary-Adrenal axis (HPA axis), the main mediator of the stress response. In mammals, the physiological intimacy between mother and offspring constrains the possibility to control, and therefore to manipulate, maternal pre- and post-natal influences. Here, by using the Japanese quail (Coturnix c. japonica) as our model, we elevated the glucocorticoid stress hormone corticosterone in ovo and/or in the endogenous circulation of hatchlings. We examined the effects of treatments on corticosterone and glucose stress responses at two different ages, in juvenile and adult quail. In juveniles, corticosterone data revealed a sex-specific effect of post-natal treatment regardless of the previous pre-natal protocol, with post-natally treated females showing shorter stress responses in comparison with the other groups, while no differences were observed among males. In adulthood, birds previously stressed as embryos showed higher corticosterone concentrations over the stress response compared with controls. This effect was not evident in birds subjected to either post- or the combined treatments. There were no effects on glucose in the juveniles. However, adult birds previously stressed in ovo showed opposite sex-specific basal glucose patterns compared with the other groups. Our results demonstrate that (1) early glucocorticoid exposure can have both transient and long-term effects on the HPA axis, depending upon the developmental stage and sex and (2) post-natal stress can modulate the effects of pre-natal stress on HPA activity.

Plasma corticosterone in American kestrel siblings: effects of age, hatching order, and hatching asynchrony

Although it is well documented that hatching asynchrony in birds can lead to competitive and developmental hierarchies, potentially greatly affecting growth and survival of nestlings, hatching asynchrony may also precipitate modulations in neuroendocrine development or function. Here we examine sibling variation in adrenocortical function in postnatally developing, asynchronously hatching American kestrels (Falco sparverius) by measurements of baseline and stress-induced levels of corticosterone at ages 10, 16, 22, and 28 days posthatching. There was a significant effect of hatching order on both baseline and stress-induced corticosterone levels during development and these effects grew stronger through development. First-hatched chicks exhibited higher baseline levels than later-hatched chicks throughout development and higher stress-induced levels during the latter half of development. Furthermore, there was significant hatching span (difference in days between first- and last-hatched chicks) x hatching order interaction on both baseline and stress-induced corticosterone levels during development. Hatching span was also positively correlated with both measures of corticosterone and body mass in first-hatched chicks, but was negatively correlated with these factors through most of the development in last-hatched chicks. It is known that hatching asynchrony creates mass and size hierarchies within kestrel broods and we suggest that hierarchies in adrenocortical function among siblings may be one physiological mechanism by which these competitive hierarchies are maintained.

Corticosterone levels during post-natal development in captive American kestrels (Falco sparverius)

We investigated post-natal development of the adrenocortical stress-response system in captive American kestrels (Falco sparverius) by measurements of baseline and stress-induced levels of corticosterone at ages 10, 16, 22, and 28 days post-hatching. Baseline levels of corticosterone increased significantly during post-natal development and although chicks aged 10- and 16-days old exhibited comparable baseline corticosterone levels, those of 22-day-old chicks were significantly higher and those of 28-day-old chicks close to fledging were higher than all younger groups. Chicks in this study exhibited low levels of stress-induced corticosterone early in development and did not exhibit adult-type stress-induced levels of corticosterone until 22 days of age post-hatching. Finally, although baseline and stress-induced levels of 28-day-old birds were significantly higher than one-year-old adults, there was no relationship between baseline corticosterone concentrations and time to nest departure. The fact that baseline levels of corticosterone are low during early development and then increase during later development may be an adaptation to the negative effects of chronically elevated corticosterone levels and as previously noted in other studies may minimize these negative effects on rapid growth and development in young birds, potentially maximizing normal growth. The ability of even young kestrel chicks to elevate corticosterone levels in response to stress suggests that they may be able to physiologically cope with food shortages associated with unpredictable food resources which wild kestrels often face.

Developmental changes and among-sibling variation of corticosterone levels in an altricial avian species

The postnatal development of the activity of the brain-pituitary-adrenal axis was investigated in an altricial bird species by measurements of plasma corticosterone levels in nestling and fledgling canaries, Serinus canaria. Corticosterone was detectable (>2.6 ng/ml) in 30% of 5-day-old, 67% of 10-day-old, 72% of 15-day-old, and 88% of 23-day-old birds. When detectable, the corticosterone levels of 5-day-old nestlings were comparable to the baseline levels of adult birds. Levels were higher in 10- and 15- than in 5-day-old nestlings. The levels of 23-day-old fledglings (about 6 to 7 days after fledgling) were significantly higher than those of 15-day-old nestlings. They were intermediate between adult baseline and stress-induced levels. Sex did not influence this general profile, but levels varied with the order of hatching within broods. At the age of 15 and 23 days first hatched chicks had higher corticosterone levels than last hatched chicks, while second hatched chicks had intermediate levels. These differences were not correlated with body mass. The results suggest that (1) the brain-pituitary-adrenal axis of this altricial bird becomes fully functional after hatching and (2) birth order within broods influences corticosterone secretion during subsequent stages of development. It is unlikely that the brain-pituitary-adrenal axis matures at different rates in first and later hatched chicks or that the different levels of first and later hatched chicks were caused by capture and handling stress. Rather, they may result from such maternal effects as hatching asynchrony or differential concentrations of yolk steroids among the eggs in a clutch. Further studies will have to show whether this systematic variation of corticosterone levels among siblings during early life persists into adulthood and how it is related to behavior and fitness.

Changes in the adrenal steroidogenic responsiveness of the mallard duck (Anas platyrhynchos) during early post-natal development

1. Plasma concentrations of corticosterone (B), aldosterone (Aldo) and deoxycorticosterone (DOC) were measured in mallard ducklings immediately before and after exposure to acute immobilization stress. 2. Except for transient declines in B and DOC between the 4th and 14th days after hatching, the resting concentration of each hormone did not change significantly during post-natal development. 3. The stress-induced in Aldo was maximal at hatching while maximal increases in B and DOC did not occur until one day later. 4. Thereafter the magnitude of the stress-induced increases in the concentrations of all of the hormones decreased steadily and on the 21st and 28th days after hatching only B increased significantly in response to stress.

Maturation of the diurnal rhythm of corticosterone in female domestic fowl

The purpose of this study was to examine the maturation of the avian corticosterone diurnal rhythm in relation to other indices of adrenocortical maturation. Female chickens were studied at 1, 5, 11, 17, 23, and 55 weeks of age. Blood samples were drawn at 4-hr intervals during a 24-hr (14 hr light: 10 hr dark) photoperiod. The diurnal rhythm in corticosterone concentration was not apparent until 11 weeks of age. At this age, unlike at 17 weeks of age, the maximal corticosterone concentration occurred during the light period. This indicates that although a rhythm is present at 11 weeks, a phase shift apparently occurs before the adult-like diurnal rhythm is attained. Injection of adrenocorticotropin (ACTH) produced an increase in the circulating corticosterone concentration in chickens at all ages. These results indicate 1) a phase shift must occur between the time of the initial emergence of a diurnal corticosterone rhythm and the attainment of the characteristic adult-like diurnal rhythm, and 2) the avian adrenal cortex is capable of responding to an ACTH stimulus with an increase in circulating corticosterone before the central nervous system rhythmically controls the pattern of circulating ACTH or corticosterone.

Effects of testosterone propionate and pituitary-adrenal hormones on the social behaviour of male ducklings (Anas platyrhynchos L.) in two test situations

This experiment was designed to study in male ducklings the behavioural influence of testosterone propionate (= TP) injections, combined with pituitary-adrenal hormones administration, in two test situations: in groups of birds from the same residence cage or from visually isolated cages. It appears from the results that TP administration increased sexual but not aggressive behaviour, while pituitary-adrenal hormones induced very few effects. The responses of the birds were however modulated to a large extent by the type of test situation.