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    Corticosterone responses to different stimuli and phenotypic plasticity in corticosterone responses in the kororā (little penguin, Eudyptula minor) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physiology at Massey University, Manawatu, New Zealand
    (Massey University, 2018) Choi, MinSeo
    The overall aims of the research presented in this thesis were to compare in little penguins (Eudyptula minor) corticosterone concentrations following exposure to a variety of stimuli with corticosterone responses to handling, to investigate the relationship between corticosterone response to handling and corticosterone concentrations after exposure to different stimuli, and to examine plasticity in corticosterone responses. The study involved measurement of corticosterone concentrations in blood samples collected after a 15 min stimulus. Handling resulted in a greater mean plasma corticosterone concentration than all other stimuli. Plasma corticosterone concentrations in little penguins in nestboxes after the presentation of a novel object were greater than concentrations after the sound of dog barking and the sound of human talking. Corticosterone concentrations were higher in birds that were exposed to penguin alarm calls than birds exposed to human talking. Differences between mean corticosterone concentrations after human talking and dog barking, and between mean concentrations after the penguin alarm call and the novel object, were not significant. The mean concentration after human talking was the lowest and the mean concentration after novel object was the highest relative to responses to handling. Corticosterone concentrations after handling and concentrations after exposure to other stimuli were not correlated. A reaction norm revealed the existence of plasticity in corticosterone concentrations in little penguins. The reaction norm approach used to determine plasticity in this study did not allow for the quantification of the degree of plasticity. The findings of the present study have provided information about the way little penguins respond to different type of stimuli, whether responses to handling are similar to responses to other stimuli in the same bird, and show that the use of a reaction norm approach can provide useful information about plasticity in corticosterone responses to different stimuli in birds.
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    The development of the corticosterone stress response of kororā (little penguin, Eudyptula minor) chicks in response to frequent handling : a thesis presented in partial fulfilment of the requirements of the degree of Master of Science in Physiology at Massey University
    (Massey University, 2018) Ogle, Shelley
    In birds, when a stressor is encountered, the hypothalamo-pitiutary-adrenal (HPA) axis is activated to produce the corticosteroid, corticosterone. The production of this hormone incites a flight or fight response in order to best avoid long-term damage from the stressor. However, prolonged or repeated exposure to high levels of corticosterone can have damaging behavioural and physiological effects. For this reason, high levels of the hormone should be avoided where possible in developing chicks. Chicks of altricial species in particular, seldom hatch with a highly functioning HPA axis so as to avoid these detrimental effects while their parents are still protecting them from major stressors such as predators, adverse weather and low food availability. Previously, studies have mapped the development of the HPA axis in a range of species or studied the effects of stress from a young age on future behavioural or physiological responses. This current study aimed to not only describe any adverse effects observed as a result of increased encounters with stressors but also track the development of the HPA axis in kororā (little penguin, Eudyptula minor) chicks. Kororā chicks from the Oamaru Blue Penguin Colony were selected from both available sites and grouped based on their age at the time of sampling, 2 weeks old, 4 weeks old and 6 weeks old and a further two groups were formed for chicks that were handled twice a week from 2 weeks of age until 4 weeks or 6 weeks at which point they were sampled. Blood sampling and handling and capture stress responses were done following a modified standard protocol of a blood sample at 0 mins, 15 mins and 30 mins at which point they were returned to their nest to avoid over or under heating depending on the age and weather. The chicks being exposed to frequent human interactions were weighed twice a week and also had their flipper length and beak width, length and depth measured to graph the growth rates and body condition indices which has never previously been done in penguin chicks. It was found that frequent interactions with people did not have a significant effect on the stress responses when comparing previously handled chicks with unhandled chicks of the same age and that the previously handled chicks developed their adult-like stress response at a similar age to those that had not been previously handled. With regards to body condition indices and growth rates, this study showed that the parents leave the nest just after body condition indices drop to the low point in the chicks’ development.
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    The time course of corticosterone responses in kororā (little penguin, Eudyptula minor) : a thesis presented in partial fulfilment of the requirements of the degree of Master of Science in Zoology at Massey University
    (Massey University, 2017) Long, Kar Hui
    When birds and other vertebrates perceive a situation to be threatening the hypothalamopituitary-adrenal (HPA) axis is activated and glucocorticoid hormones are secreted from the adrenal gland. Activation of the HPA axis in response to a stimulus perceived to be threatening is called a stress response. The main glucocorticoid hormone in birds is corticosterone. Corticosterone responses of birds are typically measured by the collection of an initial blood sample when a bird is captured or picked up, then the collection of further blood samples until 30 to 60 minutes has elapsed, at which time the bird is released. Whilst this standard sampling protocol provides information on the size of the corticosterone response, it does not provide any indication of how long it takes for corticosterone concentrations to return to initial values. The main objective of this thesis was to characterise the total duration of the corticosterone response of free-living kororā (little penguins, Eudyptula minor). Little penguins at Oamaru were picked up from their nestboxes and initial blood samples collected. Birds were handled and then restrained by being placed in a box. Further blood samples were collected 15, 30 and 60 min after the birds were first picked up. Birds were then returned to their nest boxes and an additional blood sample collected 15, 30, 60, 120, 240, or 360 min later. Mean corticosterone concentrations declined to initial values two hours after birds were returned to nest boxes. The rates at which corticosterone concentrations increased when a stressor was present and then decreased when the stressor was no longer present were positively correlated. Seasonal changes in corticosterone responses in little penguins were also investigated in this study. Mean corticosterone responses were similar in winter and in the pre-laying period, whereas mean responses were lower in birds during early chick rearing. Corticosterone responses during the pre-laying period were greater in male than female little penguins. The current study is the first to document the complete corticosterone responses of free-living penguins and provides information about changes of corticosterone concentrations after a stressor is removed from the free-living individuals. It is also the first to reveal that free-living penguins with relatively high corticosterone responses to a stressor had relatively high rates of corticosterone decline.
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    Corticosterone responses to handling, and effects of corticosterone injections in the Japanese quail (Coturnix xoturni japonica) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physiology at Massey University
    (Massey University, 2000) Boyd, Raewyn Anne
    These studies examined the effects of corticosterone on the reproductive system, investigated the relationship between plasma and faecal corticosterone levels and defined corticosterones response to handling in the Japanese quail (Coturnix coturnix japonica). Six days of daily corticosterone injections decreased the area of the cloacal protuberance in both seven week old and six month old male quail. However, plasma testosterone levels 24 hours after an injection were only decreased in the six month old birds. There was a strong correlation between basal plasma and faecal corticosterone concentrations in the six month old birds. The effects of corticosterone during the 24 hours after an injection were then examined before and after six days of corticosterone injections in male quail. Corticosterone injections decreased plasma testosterone levels three-fold for 6-12 hours both after a single corticosterone injection and after six days of treatment. However, there were no changes in plasma luteinising hormone levels during the 24 hours after an injection. This result is consistent with corticosterone acting directly on the testes to decrease testosterone release. The rate of corticosterone removal from the blood after an injection increased after six days of corticosterone injections. Handling female Japanese quail for 15 minutes resulted in increased plasma corticosterone levels for less than 30 minutes. Mean corticosterone response curves were almost identical when the same birds were handled on three occasions. Although corticosterone response curves were similar during the early afternoon and during the night, basal corticosterone levels and the area under the corticosterone response curves were lower at night. Plasma corticosterone levels 0 and 15 minutes after the initiation of handling were more than twice as high in birds with large gonads than birds with small gonads. This study provides the first information in birds of a decrease in plasma testosterone levels within three hours of a corticosterone injection, independent of changes in plasma LH levels. It is also the first study in a domestic species to show larger corticosterone responses in female birds with large gonads than in birds with small gonads.
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    Corticosterone responses of captive and wild northern brown kiwi (Apteryx mantelli) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Zoology at Massey University, Palmerston North, New Zealand
    (Massey University, 2000) Adams, Dominic Christian
    Conservation strategies should work to mmnruse the occurrence of stressful situations, which are likely to result in chronic elevations of corticosterone. Consequently, identification of such situations would yield important information for conservation management. The objective of this study was to compare the basal levels of corticosterone and the corticosterone response of kiwi (Apteryx mantelli) in different management systems. Repeated blood sampling enabled us to describe the magnitude and duration of the corticosterone response, which is a measure of the sensitivity of the hypothalamic-pituitary-adrenal (HP A) axis to stress. All kiwi responded to capture and handling with a rise in plasma levels of corticosterone, which peaked 30 min after capture. Corticosterone levels immediately after capture in wild kiwi were significantly higher than those of captive kiwi. This was most likely due to the method of capture, as wild kiwi took considerably longer to catch than captive kiwi. The plasma level of corticosterone 30 min after capture in nocturnal house kiwi was significantly lower than wild kiwi, but similar to those in outdoor penned kiwi. The cause of these differences is unclear. Nocturnal house kiwi may have become habituated to the presence of humans. Alternatively, it may be due to nocturnal house kiwi being held on a different light cycle to outdoor pen and wild kiwi. In addition, corticosterone levels in nocturnal house kiwi returned to basal levels 2 h after capture and handling. There was no significant difference in the binding affinity (I(I) and binding capacity (Bmax) of corticosteroid binding globulin (CBG) between nocturnal house, outdoor pen and wild kiwi. Furthermore, at no stage did maximum plasma levels of corticosterone exceed Bmax· Therefore, the Bmax of kiwi CBG was not a major factor when interpreting corticosterone responses of kiwi. Regularly handled kiwi do not respond to public display and handling with an increase in plasma levels of corticosterone. Therefore, these kiwi appear to have become habituated to this procedure. Elevated corticosterone levels in wild kiwi immediately after capture indicate that determining the precise location of wild kiwi is sufficient to induce a stress response. Therefore this practice should be kept to a minimum. Low basal levels of corticosterone indicate that captive kiwi have acclimatised to captivity. Furthermore, these results indicate that captive kiwi are not exposed to chronic elevations in corticosterone.
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    Corticosterone responses, fear behaviour and sociality in laying hens : a thesis presented in partial fulfilment of the requirements of the degree of Master of Science in Physiology at Massey University
    (Massey University, 2006) McLaughlin, Lana Marie
    The overall aim of this thesis was to compare behavioural measures of fear and sociality and corticosterone responses to a stressor in white Leghorn and brown Hyline hens and to examine the relationship between corticosterone and these behaviours. The first set of experiments involved taking behavioural measures of fear and sociality. Tonic immobility and open field tests were conducted to measure fear whist a runway test was used to measure sociality. There was a distinct difference in underlying fear levels with white hens being more fearful than brown, principal components analysis further distinguished this difference. There was no difference in the levels of sociality between the two strains of hen. The second set of experiments investigated the hen's corticosterone response to a 15 min handling stressor and 15 min and 60 min restraint stressors. Corticosterone responses to these stressors were measured by the collection of blood samples at 0. 15, 30 and 60 min after the stressor had begun. Both strains of hen responded to the handling procedure with a greater corticosterone response than to either restraint procedure, with no difference between the strains of hen. There was no difference in corticosterone response to both the restraint procedures but the white hens had a greater corticosterone response than brown hens. The third part of this thesis investigated the repeatability of the tonic immobility test and examined the relationship between corticosterone and fear and sociality. No difference was found in the mean behavioural measures of the first and second tonic immobility test for either strain of hen, but correlations and statistical repeatability calculations indicated that the tonic immobility test was more repeatable for brown than white hens. Correlations were found between corticosterone and behavioural measures of fear and sociality in white hens only. Principal components analysis supported these findings and indicated that there was a positive relationship between corticosteroid and fear and a negative relationship between corticosterone and sociality. The findings of the present study have provided information about the behavioural and physiological responses of white Leghorn and brown Hyline hens and show that the use of derived measures such as principal components analysis can provide useful information about relationships between variables in laying hens.
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    Plasma and faecal corticosterone in chickens (Gallus domesticus) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physiology at Massey University
    (Massey University, 1998) Littin, Kate Elizabeth
    The overall aim of this thesis was to investigate stress, and plasma and faecal corticosterone secretion in chickens. It is known that social rank may be correlated with glucocorticoid levels and glucocorticoid responses to a stressor in both birds and mammals. The relationship between social rank and glucocorticoid secretion may only be evident during periods of increased environmental stress, such as that caused by social disruption. In the first experiment of the present study, the relationship between social rank index and corticosterone responses to a handling stressor was investigated before and after mixing together two unfamiliar groups of hens. Handling elicited corticosterone responses in most hens and the levels of corticosterone during a response and the magnitude of the response varied between individuals. Middle ranking hens tended to have elevated corticosterone responses to handling relative to low or high ranking birds, but overall, the results did not demonstrate a significant relationship between social rank and corticosterone levels during a corticosterone response or between social rank and the magnitude of the response. Mixing two groups of hens did not produce a sustained period of social stress so there was no concurrent increase in the number of aggressive interactions, corticosterone levels or corticosterone responses to handling after mixing. It was thought that this was because corticosterone responses and behavioural interactions were measured over days rather than hours, and the sampling protocol may have missed any changes in these variables that occurred within a few hours of mixing. The second experiment investigated the non-invasive measurement of corticosterone in cockerel droppings and the relationship between plasma and faecal corticosterone responses to an ACTH injection. An intramuscular dose of ACTH produced a peak in faecal corticosterone levels whereas two smaller intravenous doses of ACTH, which increased plasma corticosterone levels, did not significantly alter faecal corticosterone. This showed that faecal corticosterone levels may give a non-invasive measure of plasma corticosterone in chickens although the increase in plasma corticosterone levels might need to be large and sustained to be detected in the droppings. The magnitudes of the plasma and faecal corticosterone responses to ACTH were not correlated. Problems with the method used to extract corticosterone from droppings in this study may have affected faecal corticosterone measurements and the radioimmunoassay was not validated. As a result, a different extraction method is now used in our laboratory.
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    Shelter aggregations, social behaviour, and seasonal plasma corticosterone levels in captive and wild Duvaucel's geckos, Hoplodactylus duvaucelii : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Albany, New Zealand
    (Massey University, 2010) Barry, Manuela
    The development of effective conservation management strategies is reliant on a thorough understanding of the basic biology and life history of the species of concern. New Zealand’s endemic herpetofauna species have undergone severe range contractions since human arrival due to habitat modifications and predation by introduced mammalian pests. Current conservation management practice involves the eradication of such pests as well as the restoration of habitat involving native species reintroductions. Albeit these conservation attempts, detailed information on physiology, ecology and behaviour of most New Zealand’s lizards is scarce, including the Duvaucel’s gecko (Hoplodactylus duvaucelii). In recent years, several H. duvaucelii have been translocated to islands within their historical range as part of restoration projects and in 2006/7 a captive breeding‐for‐release programme has been established. This provided an excellent opportunity to explore some fundamental aspects of H. duvaucelii’s basic physiology and behavioural ecology. I investigated seasonal plasma corticosterone concentrations of captive and wild geckos in relation to several physiological and ecological factors to enhance our understanding of natural fluctuations of seasonal hormone patterns. Such information can aid in evaluating stress related changes in hormone patterns of individuals and populations, which is particularly relevant for the captive management. I compared plasma steroid hormone patterns of captive geckos from a breeding colony with their wild source population over several seasons to assess whether captive lizards suffered from chronic stress, which could compromise their wellbeing and the fitness of future offspring. Further, I explored several aspects of H. duvaucelii’s social behaviour, including diurnal shelter aggregations, scent communication and social interactions using experimental and exploratory studies on captive and wild geckos. The hormone study provided evidence that H. duvaucelii are suitable for captive breeding as they seem to have adapted well to captivity and did not show a chronic elevation of stress hormone levels. Moreover, my research has shown that H. duvaucelii are essentially social lizards that form shelter aggregations year‐round. Adults showed a high tolerance of juveniles in their diurnal shelters and geckos were able to detect and discriminate scents from conspecifics in several social contexts. These social traits as well as the year‐round occurrence of male‐female pairs combined with H. duvaucelii’s life history traits suggest that this species may possess a social system of high complexity. In conclusion, this dissertation provides a foundation for future research and delivers the first insight into the social behaviour and basic endocrinology of this New Zealand endemic lizard.
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    Corticosterone responses to stressors and the regulation of hypothalmic-pituitary-adrenal axis in Japanese quail : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Physiology at Massey University, Palmerston North, New Zealand
    (Massey University, 2003) Chua, Wei-Hang
    Corticosterone is the major adrenal glucocorticoid in birds. It is secreted in response to stressors, with plasma concentrations typically rising to a peak within 10 to 15 minutes and then declining over 30 to 60 minutes once the stressor is removed. The increase in corticosterone is thought to help the animal to adjust to the stressor, although corticosterone may also inhibit the reproductive axis. The corticosterone response to a stressor varies between individuals, although the level of the hypothalamic-pituitary-adrenal axis at which this variation arises in birds has not been identified. The goals of this research were to determine in Japanese quail (Coturnix coturnix japonica): (1) the effects of corticosterone and of various stressors on sex steroid secretion; (2) corticosterone responses to 5, 10 or 15 min exposure to manual restraint and 15 min exposure to different stimuli; (3) quantifying individual variation in the corticosterone response; and (4) whether individual variation in the corticosterone response to stimuli used in goal 2 is regulated by differences in pituitary or adrenal sensitivity to corticotropin releasing factor (CRF) and adrenocorticotropic hormone (ACTH) respectively. A prolonged elevation in plasma corticosterone concentrations can inhibit reproduction. The effects of a short elevation in corticosterone are less understood, so the relationship between corticosterone and sex steroid secretion in quail was characterised by administering 1.2 mg corticosterone injections. Corticosterone treatment stimulated an increase in plasma corticosterone, while testosterone declined in both corticosterone-treated and control birds. Plasma LH was unaffected by challenge with corticosterone. Collectively, these data suggest that repeated handling associated with frequent blood sampling inhibited testosterone secretion directly at the testis. Corticosterone responses to a variety of novel stimuli were characterised. Manual restraint for 10 or 15 min caused a significant response whereas restraint for 5 min or less did not lead to an increase in corticosterone 15 minutes from the start of the stressor. Corticosterone responses to 15 min of mechanical restraint varied between birds whereas 15 min of manual restraint elicited a maximal plasma corticosterone response in all birds. Manual and mechanical restraint caused declines in plasma testosterone of a similar magnitude. There was more variation within than between birds in their corticosterone response to mechanical restraint. Despite this, the general pattern of the corticosterone response was repeatable for individuals. Quail with low or high plasma corticosterone responses to 15 minutes of mechanical restraint were injected intrajugularly with a dose of ACTH that stimulated a sub-maximal corticosterone response. The plasma corticosterone response to ACTH did not differ between birds with low or high corticosterone responses to mechanical restraint, indicating that variation in corticosterone responses to restraint did not arise at the level of the adrenal gland. A preliminary study showed that injections of ovine CRF stimulated corticosterone secretion. However, CRF did not consistently stimulate an increase in plasma corticosterone in these birds and hence it was not possible to determine if pituitary responsiveness to CRF differed between birds with low or high corticosterone responses to restraint. These results indicate that variation in the corticosterone response between individual Japanese quail arises above the level of the adrenal gland in the HPA-axis, and may occur at the pituitary gland or due to differences in activation of neural pathways in the brain.