Neuroendocrine Basis of Reproductive Flexibility

PI转移摘要自原始提案Coombs-Hahn，Thomas IBN 98-08470不断变化的环境条件要求动物需要时间的活动，如繁殖，与食物丰富的时期相吻合。它们通过影响生殖生理和行为的神经内分泌调节来对环境的提示做出反应，从而实现这一点。通过对每年春季按相对不变的时间表繁殖的温带鸟类的研究，人们对这些过程了解了很多，但对机会主义物种如何在一年中灵活繁殖却知之甚少。这项研究探索了大脑如何在一个极其灵活的时间表上繁殖的物种中调节生殖。红十字鸟是一种高度专门化的雀类，以松树等针叶树的种子为食。这些种子可能足够丰富，足以让鸟类在一年中的几乎任何时候筑巢。然而，它们并不是在特定地点定期生产的。因此，这些鸟必须游牧，它们发现丰富种子的季节可能每年都有很大的不同。十字鸟通常在一年中的10个月(12月下旬到10月初)繁殖，显然偶尔也会在剩下的两个月里筑巢。关于交叉鸟如何实现这种生殖灵活性的两个补充问题将在本研究中讨论。首先，交叉鸟对环境线索的生殖反应是如何季节性变化的？在其他温带鸟类中，春季日长的增加首先会导致生殖发育，但随后会诱导鸟类对长时间的日数变得“难耐”。也就是说，它们不再对漫长白天的刺激效应做出反应。这段难熬的时期确保了繁殖及时终止，以便鸟类更换羽毛，为秋季迁徙做准备。它在迄今已被研究的温带鸟类中普遍存在，并通过在夏末和秋季禁止繁殖几个月来限制灵活性。在交叉汇票中，它可能不存在或大大减少。两个实验将测试十字鸟是否会对白天的刺激作用以及食物供应和配偶行为等非光照因素的刺激作用产生抵抗力。第二，交叉鸟对环境因素敏感性的变化与大脑的变化有何关系？所有其他已被研究的温带鸟类都显示，在不应期，大脑生殖激素的产生显著减少。我将在一年中的几个时间段检查交叉鸟体内的这些激素，以确定交叉鸟更大的繁殖灵活性是否反映了相对持续的激素产生，为它们非凡的繁殖灵活性提供了一个机械的解释。这项研究很重要，因为它解决了繁殖时间表高度灵活的物种中的现象学和机械学问题。这些结果将澄清繁殖灵活性的生理基础，并有助于揭示基于对严格季节性繁殖者的研究结果是否适用于一般鸟类，特别是生殖机会主义者。研究动物对环境信息的反应有助于我们了解短期和长期环境条件变化的影响，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，这些问题继续为包括人类在内的所有动物可能会如何受到环境的影响提供洞察。

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.