Higher Corticosterone Concentrations Research Articles

Recovery from Disrupted Ultradian Glucocorticoid Rhythmicity Reveals a Dissociation Between Hormonal and Behavioural Stress Responsiveness

Ultradian release of glucocorticoids is thought to be essential for homeostasis and health. Furthermore, deviation from this pulsatile release pattern is considered to compromise resilience to stress-related disease, even after hormone levels have normalised. In the present study, we investigate how constant exposure to different concentrations of corticosterone affects diurnal and ultradian pulsatility. The rate of recovery in pulsatile hypothalamic-pituitary-adrenal (HPA) activity after withdrawal of exogenous corticosterone is also examined. Finally, the behavioural and neuroendocrine responsiveness to an audiogenic stressor is studied. Adrenally intact male rats were subcutaneously implanted with vehicle, 40% or 100% corticosterone pellets for 7 days. The continuous release of corticosterone from these implants abolished diurnal and ultradian corticosterone variation, as measured with high-frequency automated blood sampling. Pellet removal on post-surgery day 8 allowed rapid recovery of endogenous rhythms in animals previously exposed to daily average concentrations (40%) but not after exposure to high concentrations (100%) of corticosterone. Behavioural and neuroendocrine responsiveness to stress was distinctly different between the treatment groups. Audiogenic stimulation 1 day after pellet removal resulted in a similar corticosterone response in animals previously exposed to 40% corticosterone or vehicle. The 40% pellet group, however, showed less and shorter behavioural activity (i.e. locomotion, risk assessment) to noise stress compared to 100% corticosterone and vehicle-treated animals. In conclusion, unlike the animals impanted with 100% corticosterone, we find that basal HPA axis activity in the 40% group, which had mean daily levels of circulating corticosterone in the physiological range, rapidly reverts to the characteristic pulsatile pattern of corticosterone secretion. Upon reinstatement of the ultradian rhythm, and despite the fact that these animals did not differ from controls in their response to noise stress, they did show substantial changes in their behavioural response to stress.

Yolk and albumen corticosterone concentrations in eggs laid by white versus brown caged laying hens

Maternal stress in birds can have permanent transgenerational effects through the transmission of stress hormones to offspring via the egg yolk. Previous studies have shown that White Leghorn hens show a heightened response to stress compared with Hy-Line Brown hens, producing significantly more corticosterone and displaying longer bouts of tonic immobility after handling, whereas baseline levels of corticosterone are similar between the strains. We tested the hypothesis that higher stress responsiveness would correspond to chronic accumulation and thus higher concentrations of corticosterone in egg yolks after exposure to stressors associated with routine maintenance. Eggs were collected from white and brown hens that were undisturbed except for daily feeding and routine egg collections. Corticosterone was quantified in plasma, egg yolks, and albumen and compared between strains. We predicted that corticosterone concentrations in yolk would be higher in eggs from white versus brown hens but that albumen corticosterone would not differ between strains due to the short term of albumen deposition. As predicted, yolk corticosterone concentrations were significantly higher in eggs produced by white hens, approximately twice those found in eggs laid by brown hens. Plasma and albumen concentrations of corticosterone were similar between groups. These results suggest that offspring hatching from eggs laid by White Leghorn hens are exposed to significantly more corticosterone through concentration in the egg yolk, which could permanently imprint offspring physiology and behavior.

Variation in the hormonal stress response among larvae of three amphibian species

In a series of studies, we examined how larval corticosterone treatment for several species of amphibians can impact fitness parameters both during exposure and after metamorphosis. We completed confinement stress series on larvae of three species in natural/semi-natural conditions: wood frogs (Rana sylvatica), Jefferson salamanders (Ambystoma jeffersonianum), and Eastern spadefoot toads (Scaphiopus holbrooki). Two of the species had a typical vertebrate response of increasing corticosterone with confinement. However, Eastern spadefoot toads, which have a very short developmental period before metamorphosis, did not show any increase in corticosterone in response to confinement. In a second study, we treated the three species with a low and a high concentration of corticosterone (0.001 and 0.01 µM dissolved in tank water) in the laboratory and examined effects on growth. Although we were successful in raising baseline corticosterone levels with our high corticosterone concentrations, this did not translate into changes in mean larval growth for any of the three species. The larval treatments also did not appear to translate into differences in the juvenile response to confinement stress after metamorphosis. Although juvenile wood frogs did respond to confinement with increasing corticosterone, there was no variation based on larval treatment. As with the larval responses, the juvenile Eastern spadefoot toads did not have a hormonal response to confinement. In summary, while our larval corticosterone exposures did elevate baseline corticosterone levels, we did not see effects of exposure on growth or any latent effects of larval exposure on juvenile responses to confinement.

Carotenoid-based coloration, oxidative stress and corticosterone in common lizards

Environmental factors including stressors, health status and social context significantly affect carotenoid-based coloration. For instance, stressors may induce the diversion of carotenoids from pigmentation pathways, potentially explaining why stressed animals often exhibit reduced coloration. However, we recently showed that high blood corticosterone concentrations, which are part of the physiological stress response, are associated with increased redness of the belly in the common lizard (Lacerta vivipara). This result clearly contrasts with the findings of many studies of carotenoid-based coloration because corticosterone is believed to increase oxidative stress. Here, we examined whether these positive effects are influenced by differences in food availability. We tested the effect of high corticosterone levels on carotenoid-based coloration, antioxidant enzyme activity and oxidative damage in common lizards subject to low and high food availability. Food restriction abolished the carotenoid-based color enhancement when corticosterone concentrations in animals were high. We discuss how carotenoid-based color can honestly signal individual quality in this species and how the increased redness induced by corticosterone could be a terminal investment in an environment where long-term survival prospects are poor but not when immediate survival is endangered.

Are increased concentrations of maternal corticosterone adaptive to offspring? A test using a placentotrophic lizard

Summary 1. Maternal hormones during embryogenesis act as a bridge between the maternal and the offspring environment and consequently may allow maternal pre‐programming of offspring phenotype to the environment, assuming that maternal environment is a reliable predictor of offspring environment. 2. We use an orthogonal experimental design in which we increase plasma corticosterone concentration (vs. control) in placentotrophic gravid female spotted skinks (Niveoscincus ocellatus) and their offspring. We hypothesize that high concentrations of maternal corticosterone allow offspring phenotype to be pre‐programmed to better cope with high concentrations of corticosterone after birth and, consequently, offspring would not suffer from its deleterious effects. We use growth as a measure of performance as corticosterone typically affects growth in reptiles. 3. High concentrations of maternal corticosterone had significant effects on offspring body condition at birth which could have resulted from corticosterone passing through the complex placenta and/or from the indirect effects of corticosterone on maternal body condition. 4. There was no indication of maternal pre‐programming to high concentrations of corticosterone postpartum: growth rate of offspring placed in the same treatment (corticosterone vs. control) than their mother was not different to growth rate of offspring placed in a different treatment than their mother. 5. Maternal pre‐programming to corticosterone may not have been selected for in this species either because maternal chronic stress is not a reliable predictor of offspring chronic stress or because maternal pre‐programming does not outweigh the costs of having reduced sensitivity to the hormone, resulting in slower, less appropriate reactions in stressful conditions. This study further demonstrates the highly versatile and context‐dependent nature of maternal effects and the trade‐offs between costs and benefits of maternal pre‐programming.

Adrenocortical function of Arctic-breeding glaucous gulls in relation to persistent organic pollutants

Unpredictable changes in the environment stimulate the avian hypothalamo–pituitary–adrenal axis to produce corticosterone, which induces behavioural and metabolic changes that enhance survival in the face of adverse environmental conditions. In addition to profound environmental perturbations, such as severe weather conditions and unpredictable food shortages, many Arctic-breeding birds are also confronted with chronic exposure to persistent organic pollutants (POPs), some of which are known to disrupt endocrine processes. This study investigated the adrenocortical function of a top predator in the Arctic marine environment, the glaucous gull ( Larus hyperboreus). High concentrations of organochlorines, brominated flame retardants and metabolically-derived products in blood plasma of incubating glaucous gulls were associated with high baseline corticosterone concentrations in both sexes and a reduced stress response in males. Contaminant-related changes in corticosterone concentration occurred over and above differences in body condition and seasonal variation. Chronically high corticosterone concentrations and/or a compromised adrenocortical response to stress can have negative effects on the health of an individual. The results of the present study suggest that exposure to POPs may increase the vulnerability of glaucous gulls to environmental stressors and thus could potentially compromise their ability to adapt to the rapidly changing environmental conditions associated with climate change that are currently seen in the Arctic.

Fasting suppresses T cell-mediated immunity in female Mongolian gerbils ( Meriones unguiculatus)

Immune defense is important for organisms' survival and fitness. Small mammals in temperate zone often face seasonal food shortages. Generally fasting can suppress immune function in laboratory rodents and little information is available for wild rodents. The present study tested the hypothesis that Mongolian gerbils ( Meriones unguiculatus) could inhibit T cell-mediated immunity to adapt to acute fasting. Forty-two females were divided into the fed and fasted groups, in which the latter was deprived of food for 3 days. After 66 h fasting, half of the gerbils in each group were injected with phosphate buffered saline or phytohaemagglutinin (PHA) solution. T cell-mediated immunity assessed by PHA response was suppressed in the fasted gerbils compared with the fed gerbils. The fasted gerbils had lower body fat mass, wet and dry thymus mass, dry spleen mass, white blood cells, serum leptin and blood glucose concentrations, but higher corticosterone concentrations than those of the controls. Moreover, PHA response was positively correlated with body fat mass and serum leptin levels in the immunochallenged groups. Taken together, acute fasting leads to immunosuppression, which might be caused by low body fat mass and low serum leptin concentrations in female Mongolian gerbils.

Critical time-window for the actions of adrenal glucocorticoids in behavioural sensitisation to cocaine

Glucocorticoids, secreted by the adrenals in response to stress, have profound effects on behavioural responsiveness to psychostimulant drugs. We have studied the critical time-window for the influence of corticosterone on behavioural sensitisation to cocaine in relation to i) the stage of behavioural sensitisation, and ii) the time of drug exposure. Previously, we have identified a mouse strain (DBA/2) in which surgical removal of the adrenals (adrenalectomy) fully prevented locomotor sensitisation to cocaine. To investigate the role of corticosterone in expression of behavioural sensitisation, the glucocorticoid receptor antagonist mifepristone (RU38486) was administered to previously sensitised mice prior to a cocaine challenge. Furthermore, adrenalectomised mice were given corticosterone replacement at different intervals prior to each drug administration, to investigate the role of the glucocorticoid in initiation of behavioural sensitisation, and in relation to the time of drug exposure. Administration of mifepristone to previously sensitised animals failed to block expression of cocaine-induced behavioural sensitisation. In adrenalectomised mice, intermittent replacement of corticosterone (1 mg/kg i.p., either 2 h or 5 min prior to each cocaine administration), did not reverse the sensitisation deficit. By contrast, chronic corticosterone replacement (20% pellet) partially restored initiation of behavioural sensitisation. These data indicate that the presence of corticosterone facilitates the initiation rather than the expression of behavioural sensitisation to cocaine. However, because high corticosterone concentrations only partially reversed the sensitisation deficit of adrenalectomised mice, the adrenal glucocorticoid seems necessary, but not sufficient, for full behavioural sensitisation to cocaine in the DBA/2 strain.

Corticosteroids modulate Seoul virus infection, regulatory T-cell responses and matrix metalloprotease 9 expression in male, but not female, Norway rats

Human hantaviral disease is mediated by excessive proinflammatory and CD8+ T-cell responses, which can be alleviated by administration of corticosteroids. In contrast with humans, male rats that are infected with their species-specific hantavirus, Seoul virus (SEOV), have reduced proinflammatory and elevated regulatory T-cell responses in tissues where virus persists. To determine the effects of glucocorticoids on SEOV persistence and immune responses during infection, male and female Norway rats received sham surgeries (sham) or were adrenalectomized (ADX0), in some of which corticosterone was replaced at low (ADX10) or high (ADX80) doses. Rats were inoculated with SEOV and serum corticosterone, SEOV RNA, gene expression and protein production were measured at different time points post-inoculation. We observed that SEOV infection suppressed corticosterone in sham males to concentrations seen in ADX0 males. Furthermore, males with low corticosterone had more SEOV RNA in the lungs than either females or males with high corticosterone concentrations during peak infection. Although high concentrations of corticosterone suppressed the expression of innate antiviral and proinflammatory mediators to a greater extent in females than in males, these immunomodulatory effects did not correlate with SEOV load. Males with low corticosterone concentrations and high viral load had elevated regulatory T-cell responses and expression of matrix metalloprotease (MMP)-9. MMP-9 is a glycogenase that disrupts cellular matrices and may facilitate extravasation of SEOV-infected cells from circulation into lung tissue. Suppression of glucocorticoids may thus contribute to more efficient dissemination of SEOV in male than in female rats.

Proestrous compared to diestrous wildtype, but not estrogen receptor beta knockout, mice have better performance in the spontaneous alternation and object recognition tasks and reduced anxiety-like behavior in the elevated plus and mirror maze

17β-Estradiol (E 2) may influence cognitive and/or affective behavior in part via the β isoform of the estrogen receptor (ERβ). Endocrine status and behavior in cognitive (object recognition, T-maze), anxiety (open field, elevated plus maze, mirror maze, emergence), and motor/coordination (rotarod, activity chamber) tasks of proestrous and diestrous wildtype (WT) and ERβ knockout (βERKO) mice was examined. Proestrous (WT or βERKO), versus diestrous, mice had higher E 2 and progestin levels in plasma, hippocampus, and cortex. The only effect of genotype on hormone levels was for corticosterone, such that βERKO mice had higher concentrations of corticosterone than did WT mice. Proestrous WT, but not βERKO, mice had improved performance in the object recognition (greater percentage of time with novel object) and T-maze tasks (greater percentage of spontaneous alternations) and less anxiety-like behavior in the plus maze (increased duration on open arms) and mirror chamber task (increased duration in mirror) than did diestrous mice. This pattern was not seen in the rotarod, open field, or activity monitor, suggesting effects may be specific to affective and cognitive behavior, rather than motor behavior/coordination. Thus, enhanced performance in cognitive tasks and anti-anxiety-like behavior of proestrous mice may require actions of ERβ in the hippocampus and/or cortex.

Chronic Stress in Battery Hens: Measuring Corticosterone in Laying Hen Eggs

There has been growing social and scientific interest in recent years in laying hen welfare. Stress is an animal welfare parameter that has been found to alter laying hens’ physiology and social behaviour. Our study aims to test the effects of the different housing systems (laying cage, barn and free range) on the laying hens’ welfare. In this study we have taken a new approach to determine stress levels by measuring corticosterone and androgen concentrations in the eggs laid by hens housed in different farming systems. We found no relationship between commercial egg production type and androgen (testosterone and androstenedione) levels. Contrary to our expectations, we observed an almost significant positive trend between corticosterone levels and welfare quality: free range eggs contained the highest corticosterone concentrations. This would initially suggest that free range hens are more stressed than battery or barn hens. However, considering that chronic stressors can reduce an organism’s hormonal output, our results could suggest that the low levels of corticosterone in battery hens are an indication of a chronic stress situation. Our data suggest that measuring corticosterone in eggs is a novel non-invasive method to determine stress levels in laying hens. This study would however need to be combined with a number of parameters (health, production and behaviour) to get an encompassing measure of laying hen welfare.

Deleterious effects of high-fat diet on perinatal and postweaning periods in adult rat offspring

Pre- and postnatal environmental changes can reset the developmental path during intrauterine development leading to obesity and cardiovascular and metabolic disorders later in life. The effects of high-fat diets on body mass, fat mass, the plasma level of glucose, insulin and leptin, as well as the insulin/glucose ratio and cardiovascular parameters in adult rat offspring were studied. Pregnant Wistar rats in a standard chow group (SC) or high-fat chow group (HFC), at weaning their SC and HFC offspring were randomly divided into two postnatal groups: fed on SC or HFC. With euthanasia at 6-month-old, three-way ANOVA there were three-factor interactions among gender, perinatal diet and postweaning diet to body mass (BM), BP, left ventricle (LV) thickness, carbohydrate metabolism, plasma corticosterone concentrations and leptin/fat mass/adipocyte size pattern. HFC/SC and SC/HFC offspring of both genders had high BM and BP, which were increased in HFC/HFC offspring. There was hyperinsulinism, hyperleptinemia, as well as high insulin/glucose ratio and high plasma corticosterone concentrations mainly in HFC/HFC offspring with adipocytes and LV hypertrophy. Postweaning HFC was deleterious to the health of adult offspring from dams fed HFC during pregnancy and then during the first half of lactation period. HFC administrated in both periods shows supplementary effects, elevating BP with consequent LV hypertrophy, altering carbohydrate metabolism, plasma corticosterone concentrations and disturbing leptin/fat mass/adipocyte size pattern.

The effect of plant polyphenolic compounds on the proliferation and DNA methylation in MCF7 cells

Pre- and postnatal environmental changes can reset the developmental path during intrauterine development leading to obesity and cardiovascular and metabolic disorders later in life. The effects of high-fat diets on body mass, fat mass, the plasma level of glucose, insulin and leptin, as well as the insulin/glucose ratio and cardiovascular parameters in adult rat offspring were studied.Pregnant Wistar rats in a standard chow group (SC) or high-fat chow group (HFC), at weaning their SC and HFC offspring were randomly divided into two postnatal groups: fed on SC or HFC. With euthanasia at 6-month-old, three-way ANOVA there were three-factor interactions among gender, perinatal diet and postweaning diet to body mass (BM), BP, left ventricle (LV) thickness, carbohydrate metabolism, plasma corticosterone concentrations and leptin/fat mass/adipocyte size pattern.HFC/SC and SC/HFC offspring of both genders had high BM and BP, which were increased in HFC/HFC offspring. There was hyperinsulinism, hyperleptinemia, as well as high insulin/glucose ratio and high plasma corticosterone concentrations mainly in HFC/HFC offspring with adipocytes and LV hypertrophy.Postweaning HFC was deleterious to the health of adult offspring from dams fed HFC during pregnancy and then during the first half of lactation period. HFC administrated in both periods shows supplementary effects, elevating BP with consequent LV hypertrophy, altering carbohydrate metabolism, plasma corticosterone concentrations and disturbing leptin/fat mass/adipocyte size pattern.

Rapid changes in hippocampal CA1 pyramidal cell function via pre‐ as well as postsynaptic membrane mineralocorticoid receptors

Corticosterone (100 nm) rapidly increases the frequency of miniature excitatory postsynaptic currents in mouse CA1 pyramidal neurons via membrane-located mineralocorticoid receptors (MRs). We now show that a presynaptic ERK1/2 signalling pathway mediates the nongenomic effect, as it was blocked by the MEK inhibitors U0126 (10 microm) and PD098059 (40 microm) and occluded in H-Ras(G12V)-mutant mice with constitutive activation of the ERK1/2 presynaptic pathway. Notably, the increase in mEPSC frequency was not mediated by retrograde signalling through endocannabinoids or nitric oxide, supporting presynaptic localization of the signalling pathway. Unexpectedly, corticosterone was also found to have a direct postsynaptic effect, rapidly decreasing the peak amplitude of I(A) currents. This effect takes place via postsynaptic membrane MRs coupled to a G protein-mediated pathway, as the effect of corticosterone on I(A) was effectively blocked by 0.5 mm GDP-beta-S administered via the recording pipette into the postsynaptic cell. Taken together, these results indicate that membrane MRs mediate rapid, nongenomic effects via pre- as well as postsynaptic pathways. Through these dual pathways, high corticosterone concentrations such as occur after stress could contribute to enhanced CA1 pyramidal excitability.

Effects of dehydroepiandrosterone on aldosterone release in rat zona glomerulosa cells

The present study was to investigate the effects and action mechanisms of dehydroepiandrosterone (DHEA) on steroidogenesis in rat adrenal zona glomerulosa cells (ZG). ZG cells were incubated with DHEA in the presence or absence of angiotensin II (AngII), a high concentration of potassium, 8-Br-cAMP, forskolin, 25-OH-cholesterol, pregnenolone, progesterone, deoxycorticosterone, corticosterone, A23187, or cyclopiazonic acid (CPA) at 37 degrees C for 1 h. The concentration of aldosterone or pregnenolone in the culture medium was then measured by radioimmunoassay (RIA). The cells were used to determine the cellular cAMP content. The data demonstrated that: (1) DHEA inhibited AngII-, high concentration of KCl-, forskolin-, 8-Br-cAMP-, 25-OH-cholesterol-, pregnenolone-, progesterone-, deoxycorticosterone-, corticosterone-, A23187-, or CPA-stimulated aldosterone release; (2) DHEA increased 25-OH-cholesterol-stimulated pregnenolone release but not when 25-OH-cholesterol was combined with trilostane; (3) DHEA noncompetitively inhibited aldosterone synthase but showed uncompetitive inhibition of P450scc. These results suggest that DHEA acts directly on rat ZG cells to diminish aldosterone secretion by inhibition of a post-cAMP pathway or by acting on intracellular Ca2+ mobilization. In addition it affects the function of post-P450scc steroidogenic enzymes.

A combination of body condition measurements is more informative than conventional condition indices: Temporal variation in body condition and corticosterone in brown tree snakes ( Boiga irregularis)

The body condition index is a common method for quantifying the energy reserves of individual animals. Because good body condition is necessary for reproduction in many species, body condition indices can indicate the potential reproductive output of a population. Body condition is related to glucocorticoid production, in that low body condition is correlated to high concentrations of corticosterone in reptiles. We compared the body condition index and plasma corticosterone levels of brown tree snakes on Guam in 2003 to those collected in 1992/1993 to determine whether that population still showed the chronic stress and poor condition apparent in the earlier study. We also examined the relationship between fat mass, body condition and plasma corticosterone concentrations as indicators of physiological condition of individuals in the population. Body condition was significantly higher in 2003 than in the earlier sample for mature male and female snakes, but not for juveniles. The significantly lower levels of corticosterone in all three groups in 2003 suggests that although juveniles did not have significantly improved energy stores they, along with the mature males and females, were no longer under chronic levels of stress. Although the wet season of 2002 was unusually rainy, low baseline levels of corticosterone measured in 2000 indicate that the improved body condition of snakes in 2003 is likely the result of long-term changes in prey populations rather than annual variation in response to environmental conditions.

Opposite effects of glucocorticoid receptor activation on hippocampal CA1 dendritic complexity in chronically stressed and handled animals

Remodeling of synaptic networks is believed to contribute to synaptic plasticity and long-term memory performance, both of which are modulated by chronic stress. We here examined whether chronic stress modulates dendritic complexity of hippocampal CA1 pyramidal cells, under conditions of basal as well as elevated corticosteroid hormone levels. Slices were prepared from naïve, handled or chronically stressed animals and briefly treated with vehicle or corticosterone (100 nM); neurons were visualized with a fluorescent dye injected into individual CA1 pyramidal cells. We observed that 21 days of unpredictable stress did not affect hippocampal CA1 apical or basal dendritic morphology compared with naïve animals when corticosteroid levels were low. Only when slices from stressed animals were also exposed to elevated corticosteroid levels, a significant reduction in apical (but not basal) dendritic length became apparent. Unexpectedly, animals that were handled or 3 weeks showed a reduction in both apical dendritic length and number of apical branch points when compared with naïve animals. Apical dendritic length and number of branch points were restored to levels found in naïve animals several hours after in vitro treatment with 100 nM corticosterone. All effects of acute corticosterone administration could be prevented by the glucocorticoid receptor antagonist RU38486 given during the last 4 days of the stress or handling protocol. We conclude that brief exposure to high concentrations of corticosterone can differently affect apical dendritic structure, depending on the earlier history of the animal, a process that critically depends on involvement of the glucocorticoid receptor.

Glucocorticoids exert opposing effects on macrophage function dependent on their concentration

Glucocorticoids (GCs) are involved in the modulation of macrophage function and thereby control the host's immune responses to pathogens. However, neither the role of hormone concentration nor the differential contribution of the glucocorticoid (GR) and the mineralocorticoid receptors (MR) to these activities are known. Here we show that low levels of corticosterone enhance NO production as well as mRNA expression of pro-inflammatory cytokines, chemokines and enzymes required for mediator synthesis. In contrast, at high corticosterone concentrations macrophage function was strongly repressed. Importantly, inactivation of the GR by lentiviral delivery of siRNAs abrogated both the immunostimulatory and the immunosuppressive GC actions whereas inactivation of the MR had no effect. Furthermore, removal of endogenous GCs by adrenalectomy in vivo induced a preactivated state in macrophages that could be modulated by corticosterone. We conclude that GCs exert distinct effects on macrophage function dependent on their concentration, and that they primarily act through the GR despite concomitant expression of the MR.

Elevated hormonal stress response and reduced reproductive output in Yellow-eyed penguins exposed to unregulated tourism

The endangered, endemic Yellow-eyed penguin ( Megadyptes antipodes) is one of the flagship species for New Zealand’s wildlife tourism, and recently concern has been raised that tourism-related pressures may be becoming too great. We compared two neighbouring breeding areas exposed to different levels of human disturbance. Penguins at the site exposed to unregulated tourism showed significantly lower breeding success and fledging weights than those in an area visited infrequently for monitoring purposes only. High parental baseline corticosterone concentrations correlated with lower fledgling weights at both sites. Stress-induced corticosterone concentrations were significantly higher at the tourist-exposed site, suggesting birds have been sensitized by frequent disturbance. Consequences are likely to include reduced juvenile survival and recruitment to the tourist site, while the changed hormonal stress responses may ultimately have an effect on adult fitness and survival. For maintenance of attractive Yellow-eyed penguin-viewing destinations we recommend that tourists stay out of breeding areas and disturbance at penguin landing beaches is reduced.

Blood metabolite levels in normal and handicapped pied flycatchers rearing broods of different sizes

We measured levels of select metabolites (glucose, triglycerides, free fatty acids, glycerol, uric acid) and corticosterone in the blood plasma of adult pied flycatchers Ficedula hypoleuca while they were rearing broods whose sizes were modified experimentally. We also made it more difficult than normal for some pairs of birds to forage by removing certain wing and tail feathers (handicapping them). Both procedures have been shown previously to change parental workload. We did this in order to determine if the birds alter their use of nutrients in response to differences in their workload. Metabolite levels were not influenced by handicapping or brood size. However, the concentration of free fatty acids in the plasma of females and of triglycerides in the plasma of males was directly related to the frequency with which the adults fed their nestlings. These findings suggest that the two sexes have different ways of coping with the work associated with rearing the brood: females apparently undergo brief daily fasts while feeding their chicks, whereas males take more time to feed themselves while providing food for their young, and spend more time doing so as their workload increases. The flycatchers exhibited high concentrations of uric acid and corticosterone in the blood plasma; corticosterone and glycerol were positively correlated in females; and corticosterone and triglyceride levels were negatively correlated in males; all of which suggest that gluconeogenesis provides some of the energy required for their parental activities.