Glucocorticoids and phenotypic programming in birds

当动物的环境发生不可预测的变化时，例如在恶劣天气或食物短缺期间，它们就会遭受压力。在这段时间里，被称为应激激素的特定化学信使，在被称为下丘脑-垂体-肾上腺轴的激素系统中，经过一系列复杂的相互作用，被释放到血液中。在短期内，这些激素可以促进动物的活动，如觅食，帮助它们生存。然而，如果压力持续数小时或数天，这些激素就会产生有害影响。如果一个母亲生活在一个充满压力的环境中，她会将更高水平的压力激素传递给她正在发育的后代，我们知道，如果动物在成长过程中经历高水平的压力激素，这将对它们成年后的行为产生长期影响。这些行为上的变化与在紧张的情况下，由于调节系统的破坏，压力激素的释放时间延长有关。其中一些影响是有害的，早期压力与高血压或糖尿病等健康问题有关，所以我们了解这个系统背后的生理机制是非常重要的。我研究的中心目标是通过观察应激激素对动物整个生命周期的影响来调查这一点，将我的注意力集中在不同的生物水平上，量化基因表达、生理、行为和繁殖成功率的变化。这项研究的一个令人兴奋的方面是，我将能够直接操纵个体的压力激素水平，并跟踪他们一生的发展和行为。这是可能的，因为我选择研究鸟类；因为当母亲下蛋时，她一次传递了胚胎发育所需的所有营养和激素，我们知道这包括应激激素。我将通过向这些卵子中注射少量已知的应激激素来模拟压力环境。虽然传统观点认为发育压力是有害的影响之一，但有一个有趣的替代观点。母亲可以利用暴露于压力激素后发生的生理变化来“改造”后代，让他们为出生后的生活环境做好准备，最大限度地提高他们的生存机会。在许多研究中看到的负面影响可能是出生后的环境与母亲所经历的环境不匹配的情况。这是一个新颖的想法，用来解释为什么应激激素对动物有如此长期的影响。然而，很少有实验研究过这一点，尽管它可以提供压力激素如何导致后来的健康问题的信息。我将通过进行实验来解决这个重要的问题，这些实验创造了与动物的产前条件相匹配或不匹配的产后环境。然后，我将跟踪鸟类的成长，测试它们在有利和不利的条件下繁殖得如何。最后，我还可以跟踪这些鸟的后代的发展。这将有助于我们理解如何在不改变遗传密码的情况下，在几代人之间发生持续的变化，这种现象被称为表观遗传。我的研究将提供新的信息，说明早期生活条件在塑造帮助个人应对环境方面的重要性。这对人类和动物健康规划以及动物育种项目具有重大影响。更好地理解表观遗传不仅对科学界很重要，而且可能与那些关注气候变化的人有关。这是由于它在不确定的环境条件下对种群生存的潜在影响，这种情况在未来几年可能与人类和非人类动物有关。

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.