Neuroendocrine Basis of Reproductive Flexibility

PI传送 原提案摘要 Coombs-Hahn，托马斯IBN 98-08470 波动的环境条件要求动物的时间要求活动，如繁殖，以配合食物丰富的时期。它们通过影响生殖生理和行为的神经内分泌调节对环境的提示做出反应来实现这一点。通过对温带鸟类的研究，人们已经对这些过程有了很多了解，这些鸟类每年春天都按照相对不变的时间表繁殖，但很少有人知道机会主义物种是如何在全年时间内灵活繁殖的。 这项研究探讨了大脑如何调节一个物种的繁殖，这个物种的繁殖时间表非常灵活。 红交嘴雀是一种高度专业化的雀鸟，以松树等针叶树的种子为食。 这些种子可能足够丰富的鸟类筑巢在几乎任何时间的一年。 然而，它们并不是在特定地点定期生产。 因此，这些鸟必须四处流浪，它们发现大量种子的季节可能每年都有很大的变化。 交嘴雀在一年中约10个月（12月下旬至10月上旬）定期繁殖，即使在剩下的两个月里也会偶尔筑巢。在本研究中，将讨论两个关于交嘴鸟如何实现这种生殖灵活性的补充问题。 首先，交嘴鸟对环境信号的生殖反应如何随季节变化？ 在其他温带鸟类中，春季白天长度的增加首先导致生殖发育，但随后诱导鸟类对长日照变得“顽固”。 也就是说，它们不再对长时间日照的刺激效应作出反应。 这一不应期确保了繁殖及时终止，以便鸟类更换羽毛并为秋季迁徙做准备。 它在温带鸟类中普遍存在，到目前为止已经研究过，并通过在夏末和秋季禁止繁殖几个月来限制灵活性。 在交嘴鸟中可能不存在或数量减少。 两个实验将测试交嘴鸟是否对白天长度的刺激效应以及非光线线索（如食物供应和配偶行为）产生抗性。 第二，交嘴鸟对环境因素的敏感性变化与大脑的变化有什么关系？ 所有其他温带鸟类的研究表明，在不应期大脑生殖激素的生产显着减少。 我将在一年中的几个时间检查交嘴鸟的这些激素，以确定交嘴鸟更大的生殖灵活性是否反映了相对恒定的激素产生，为它们非凡的生殖灵活性提供一个机械的解释。这项研究很重要，因为它解决了一个具有高度灵活的生殖时间表的物种的现象学和机械学问题。 这些结果将阐明生殖灵活性的生理基础，并有助于揭示基于严格季节性育种者研究的结果是否适用于鸟类，特别是生殖机会。研究动物对环境信息的反应有助于我们了解环境条件变化的短期和长期影响，因此具有保护意义。 他们还回答了关于对环境的反应的基本问题，这些问题继续提供关于所有动物（包括人类）如何受到环境影响的见解。

PI Transfer Abstract from original Proposal Coombs-Hahn, Thomas IBN 98-08470 Fluctuating environmental conditions require that animals time demanding activities such as breeding to coincide with periods when food is abundant. They achieve this by responding to cues from the environment with neuroendocrine adjustments that affect reproductive physiology and behavior. A great deal has been learned about these processes through studies of temperate zone birds that breed on relatively invariant schedules each spring, but little is known of how opportunistic species capable of breeding throughout the year time breeding flexibly. This study explores how the brain regulates reproduction in a species that breeds on an extremely flexible schedule. Red crossbills are finches that are highly specialized to feed on the seeds of coniferous trees such as pines. These seeds may be sufficiently abundant for the birds to nest at almost any time of year. However they are not produced regularly at particular locations. Consequently the birds must wander nomadically, and the season when they discover abundant seeds may vary dramatically from year to year. Crossbills regularly breed during about 10 months of the year (late December through early October), and apparently occasionally nest even during the remaining two months. Two complementary questions about how crossbills achieve this reproductive flexibility will be addressed in the present study. First, how does reproductive responsiveness to environmental cues change seasonally in crossbills? In other temperate zone birds, the spring increase in day length first leads to reproductive development, but then induces birds to become "refractory" to long days. That is, they cease to respond to the stimulatory effects of long days. This refractory period ensures that breeding terminates in time for birds to replace their plumage and prepare for fall migration. It is ubiquitous among temperate zone birds that have been studied thus far, and restricts flexibil ity by prohibiting breeding for several months in late summer and autumn. It may be absent or much reduced in crossbills. Two experiments will test to see whether crossbills become refractory to the stimulatory effects of day length, and of non-light cues such as food supply and behavior of mates. Second, how do changes in crossbill sensitivity to environmental factors relate to changes in the brain? All other temperate zone birds that have been studied show dramatic reduction in production of brain reproductive hormones during the refractory period. I will examine these hormones in crossbills at several times of year to determine whether the greater reproductive flexibility of crossbills reflects relatively constant hormone production, providing a mechanistic explanation for their extraordinary reproductive flexibility. This study is important because it addresses phenomenological and mechanistic questions in a species with a highly flexible reproductive schedule. The results will clarify the physiological basis of reproductive flexibility and help to reveal whether findings based on studies of rigidly seasonal breeders apply to birds generally, and to reproductive opportunists in particular. Studies of how animals respond to environmental information help us to understand the effects of changing environmental conditions in the short and long term, and therefore have conservation implications. They also answer basic questions about responses to the environment that continue to provide insight into how all animals, including humans, may be affected by their environment.