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的时期，它们就会受到压力。在此期间，称为应激激素的特定化学信使在称为下丘脑-垂体-肾上腺轴的激素系统内发生一系列复杂的相互作用后被释放到血液中。在短期内，这些荷尔蒙可以使动物受益，因为它们促进了帮助动物生存的觅食等活动。然而，如果压力持续数小时或数天，这些荷尔蒙可能会产生有害影响。如果母亲生活在充满压力的环境中，她会将增加的压力荷尔蒙传递给正在发育的后代，我们知道，如果动物在成长过程中经历了高水平的这些荷尔蒙，这可能会对它们成年后的行为产生长期影响。这些行为的变化与压力环境中应激激素的长时间释放有关，这是由于监管系统的中断。其中一些影响是有害的，早期应激与高血压或糖尿病等健康问题有关，因此我们了解这一系统背后的生理机制非常重要。我的研究的中心目的是通过观察应激激素对动物整个生命周期的影响来研究这一点，将我的注意力集中在不同的生物水平，量化基因表达、生理、行为和繁殖成功的变化。这项研究的一个令人兴奋的方面是，我将能够直接控制个人的压力荷尔蒙水平，并在一生中跟踪他们的发展和行为。这是可能的，因为我选择了在鸟类身上工作；因为当母亲下蛋时，她一次性转移了胚胎生长所需的所有营养和激素，我们知道这包括应激激素。我将通过向这些鸡蛋中注入少量已知的压力荷尔蒙来模拟压力环境。虽然发展压力的传统观点是有害的，但还有一种耐人寻味的替代观点。母亲可以利用暴露在压力荷尔蒙下后发生的生理变化来“改造”她们的后代，以便让他们为出生后将生活的环境做好准备，最大限度地增加他们的生存机会。因此，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经历的环境不匹配。这是一个新的想法，它被提出来解释为什么压力荷尔蒙对动物有如此长期的影响。然而，很少有实验对此进行研究，尽管它可以提供关于压力荷尔蒙如何导致以后的健康问题的信息。我将通过进行实验来解决这个重要的问题，这些实验创造出与动物的出生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过程，测试它们在有利和不利条件下的繁殖情况。最后，我还可以追踪这些鸟的后代的发育情况。这将有助于我们理解如何在不改变遗传密码的情况下发生世代持久的变化，这种现象被称为表观遗传。我的研究将提供关于早期生活条件在塑造帮助个人应对环境方面的重要性的新信息。这对人类和动物健康方案以及动物繁育项目具有重大影响。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。这是因为它对种群在不确定环境条件下的生存有潜在影响，这种情况可能在未来几年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.