Long-term effects of elevated stress hormone levels in early development

幼小的动物在成长过程中会经历许多方面的压力，包括食物短缺和来自捕食者的高度干扰。此时所经历的压力水平本身可能在塑造动物的后续发育中发挥重要作用，从而使其在成年后暴露于压力环境中时能够更好地维持正常功能，或者对压力更敏感。在这项研究中，我们计划在自然范围内检查不同程度的压力的长期影响。研究压力对鸟类的影响可以帮助我们回答这样一个问题：当它们成年后，饲养条件是如何影响个体的。很难衡量婴儿期的压力对成年动物的“表现”和后代动物的长期“表现”的影响，因为许多物种寿命很长，需要数年才能达到性成熟。在这项研究中，我们计划在自然范围内，对一只相对较快成熟的鸟类进行不同程度的压力的长期影响。当动物的环境发生不可预测的变化时，例如恶劣的天气或食物短缺，它们就会承受压力。在此期间，被称为压力激素的特定化学信使从大脑、脑垂体和肾上腺释放到血液中。在短期内，这些激素对动物有益，因为它们促进了帮助动物生存的活动，但如果压力持续很长时间，它们就会产生有害的影响，甚至会使动物更容易感染。压力还会扰乱其他正常的生理系统，比如生殖系统，甚至可能导致动物停止繁殖。虽然我们知道很多关于即时压力如何改变动物的行为，但我们对发育过程中所经历的压力对成年行为和动物繁殖能力的长期影响知之甚少。此外，到目前为止，后代如何感受到这种影响的问题很少受到关注。我们建议将年轻的斑胸草雀暴露在自然条件下会经历的应激激素皮质酮浓度下，例如对人类干扰的反应，通过每天两次喂食非常少量的皮质酮。正是在这段时间里，鸟类体内调节应激反应的系统正在发育，可能会受到高水平应激激素的影响。然后，我们将收集这些鸟成年后的行为和繁殖成功的数据。由于应激激素在繁殖过程中也会增加，而繁殖也会受到压力的影响，我们将研究发育过程中应激激素的升高是否会影响生殖决策，并对成年后的繁殖成功产生影响。这项工作的结果将为我们提供信息，这将极大地增强我们对生命早期暴露于压力激素如何影响个体在以后的生活中对环境的反应的理解。

A young animal can experience stress in many ways whilst it is growing, including food shortages and high levels of disturbance from predators. The level of stress experienced at this time may itself play an important role in shaping the subsequent development of the animal such that it is either better able to maintain normal function when exposed to a stressful environment as an adult or more sensitive to stress. In this study we plan to examine the long-term effects of varying levels of stress, within the natural range. Studying the effects of stress in birds could help us answer the question of exactly how rearing conditions affect individuals when they are adults. It is difficult to measure the influence of stress in infancy on 'performance' as adults and the long-term 'performance of animals in future generations because many species are so long-lived, taking years to reach sexual maturity. In this study we plan to examine the long-term effects of varying levels of stress, within the natural range, in a relatively fast maturing bird. When an animal's environment changes unpredictably, e.g. bad weather or food shortages, they suffer stress. During this time specific chemical messengers, called stress hormones, are released into the bloodstream from the brain, pituitary and adrenal gland. In the short term these hormones can benefit the animal as they promote activities to help it survive, but if the stress continues for a long time, they can have harmful effects and can even make an animal more prone to infection. Stress can also disrupt other normal physiological systems like the reproductive system and may even stop animals breeding. Although we know a lot about how immediate stress changes an animal's behaviour, we know very little about the long-term effects of stress experienced during development on adult behaviour and an animal's ability to reproduce. Furthermore, the question of how such effects might be felt in future generations have received very little attention to date. We propose to expose young zebra finches to concentrations of the stress hormone corticosterone that would be experienced under natural conditions, in response for example to human disturbance, by feeding them very small amounts of corticosterone twice a day. It is during this time that the systems within the body that regulate a birds response to stress are developing and may be affected by exposure to high levels of stress hormones. We will then collect data on the behaviour and breeding success of these birds when they are adults. Since stress hormones also increase during breeding and breeding is known to be affected by stress we will examine whether exposure to elevated stress hormones during development will affect reproductive decision-making and have an impact on breeding success as an adult. The results of this work will provide us with information that will greatly enhance our understanding of how exposure to stress hormones early in life can program an individual response to it's environment in later life.