Hormone-Behavior Adaptations in Arctic Birds

北极夏季给利用冻土带丰富生产力进行繁殖的候鸟带来了一系列问题。繁殖期如此之短，以至于建立领地、结对和求爱所需的时间可能会缩短到几天甚至几个小时。鸟类必须早点到达才能开始筑巢，这样才能在条件仍然有利于它们生存的情况下生产出幼鸟。通常，北极春季的天气条件很恶劣，导致严重的新陈代谢问题，不仅对繁殖的开始，甚至对生存都是如此。这项研究将阐明北极鸟类抵抗北极夏季严酷天气的机制。其中涉及的问题包括：为什么肾上腺皮质对压力的反应在物种之间和物种内都存在差异，这是否与应激激素(如皮质酮)的行为效应和神经组织中受体的分布有关，以及这种差异是否通过性腺激素的作用受光周期调节。此外，繁殖策略变化的荷尔蒙基础将在白冠麻雀中进行探索，它在到达时表现出空间机会主义，然后既不保卫领土，也不保卫巢址；雪雀表现出中间策略，至少在产卵期间保卫巢址，但在季节晚些时候似乎不是领土。对这些物种的比较以及类固醇激素在大脑中的受体分布将为揭示北极鸟类激素行为适应的多样性提供新的线索，并将对一般脊椎动物生殖过程的调控具有相当大的意义。这两个目标都与极地生物学和医学的计划目标相一致。

The Arctic summer poses a number of problems for migratory birds that exploit the rich productivity of the tundra for reproduction. The breeding period is so brief that the time required for the establishment of a territory, pair bonding and courtship may be truncated into a few days or even hours. Birds must arrive early to begin nesting so that the young are produced while conditions are still favorable for their survival. Frequently, weather conditions in the Arctic spring are severe, resulting in serious metabolic problems not only for the onset of breeding but even for survival. This research will elucidate the mechanisms by which Arctic birds resist the rigors of the Arctic summer. Among the questions addressed are why there is variation in the adrenocortical responsiveness to stress both among and within species, whether this is related to behavioral effects of stress hormones such as corticosterone and the distribution of receptors in neural tissue, and whether the variability is regulated by photoperiod through the action of gonadal hormones. Additionally, the hormonal basis of variation in breeding strategy will be explored in the white-crowned sparrow that shows spatial opportunism on arrival and then defends neither a territory nor a nest site; and in the snow bunting that shows an intermediate strategy and defends a nest site at least during egg-laying, but does not appear to be territorial later in the season. Comparisons of these species, and receptor distributions for steroid hormones in the brain will shed new light on the diversity of hormone-behavior adaptations in Arctic birds, and will have considerable significance for the regulation of reproductive processes of vertebrates in general. Both of these objectives are alligned with program goals for Polar Biology and Medicine.