Glucocorticoids and phenotypic programming in birds

When an animal's environment changes unpredictably, for example during periods of bad weather or food shortages, they suffer stress. During this time specific chemical messengers, called stress hormones, are released into the bloodstream following a series of complex interactions within a hormonal system called the hypothalamic-pituitary-adrenal axis. In the short-term these hormones can benefit the animal as they promote activities such as foraging that help it survive. If the stress continues for a period of hours or days, however, these hormones can have harmful effects. If a mother lives in a stressful environment she can pass an increased level of stress hormones to her developing offspring, and we know that if animals experience high levels of these hormones while they are growing this can have long-term effects on how they behave when they are adults. These changes in behaviour are linked to a prolonged release of stress hormones in a stressful situation, due to a disruption in regulatory systems. Some of these effects are harmful, and early stress has been linked to health problems such as hypertension or diabetes, so it is very important that we understand the physiological mechanism underlying this system. The central aim of my research is to investigate this by looking at the effects of stress hormones on animals throughout their life cycle, concentrating my attention at different biological levels, quantifying changes in gene expression, physiology, behaviour and reproductive success. One exciting aspect of this study is that I will be able to directly manipulate the stress hormone levels of individuals and track their development and behaviour throughout life. This is possible as I have chosen to work on birds; because when the mother lays her egg she transfers all the nutrients and hormones required for embryonic growth at one time, and we know that this includes stress hormones. I will mimic a stressful environment by injecting small known amounts of stress hormones into these eggs. Whilst the traditional view of developmental stress is one of harmful effects, there is an intriguing alternative perspective. Mothers could capitalise on the physiological changes that occur following exposure to stress hormones to 'engineer' their offspring in order to prepare them for the environment they will live in once they are born, maximising their chances of survival. The negative effects seen in many studies could then be a case of the environment after birth not matching the one experienced by the mother. This is a novel idea that was proposed to explain why stress hormones have such long-term effects on animals. However, very few experiments have investigated this, even though it could provide information on how stress hormones might cause later health problems. I will tackle this important topic by carrying out experiments that create post-natal environments that match or mis-match the pre-natal conditions an animal experiences. I will then follow birds as they grow and test how well they breed under favourable and unfavourable conditions. Finally I can also track the development of these birds' offspring. This will be important in helping us understand how persistent change can occur across generations without changing the genetic code, a phenomenon called epigenetic inheritance. My research will provide novel information on the importance of early life conditions in shaping helping an individual to cope with its environment. This has significant implications for human and animal health programmes and animal breeding projects. A greater understanding of epigenetic inheritance is important not just to the scientific community but may be relevant to those concerned about climate change. This is due to its potential influence on the survival of populations under uncertain environmental conditions, a circumstance that may be relevant to human and non-human animals in the years to come.

The potential influence that physiological conditions experienced during early development may have on adult phenotypes has recently developed as an important research focus. Mothers experiencing stressful conditions during pregnancy or egg-laying can transfer stress hormones to their offspring, manipulating pre-natal developmental conditions. This project will investigate the long-term and transgenerational effects of pre-natal exposure to stress hormones, specifically corticosterone (CORT) via laboratory based experiments using an avian species the Japanese quail. In particular, this research will examine the role of pre-natal corticosterone exposure on embryonic development, the physiological and behavioural responses to a range of stressors in adulthood, as well as reproductive success and long-term effects on offspring quality. The objectives will be met by studying embryonic and post-natal responses following a standardised pre-natal manipulation, namely the intra-ovo injection of a known amount of exogenous glucocorticoids. Birds will then be studied using an interdisciplinary approach, combining behavioural assay with radioimmunoassay (RIA) hormone profiling, magnetic resonance imaging (MRI), reverse transcription polymerase chain reaction (RT-PCR) and in situ hybridisation (ISH) techniques to track individual changes in neural development, stress axis functionality, physiology, behaviour and breeding success. This study takes a multi-disciplinary approach, drawing on endocrinology, behavioural ecology and reproductive physiology. This research will therefore provide detailed information on how early life CORT exposure could program the physiology of a bird throughout its life and how these effects could be felt in future generations. Taking such a long term approach, tracking individuals throughout their life cycle and applying an integrated approach will enable me to determine the potential for transgenerational epigenetic change in populations.