Naturally Occurring Constraints on Development in a Model Learning System

科学价值：使用复杂的声音信号进行交流在动物中很普遍。在鸣禽中，这种声音信号被称为“歌声”，并且还有一个额外的有趣的方面，那就是它们是学习的。鸟类如何学习和发展它们的歌声是研究进化、生态学和一般学习的神经生理学基础的重要模型。然而，我们对这一模型的理解是有限的，因为大多数关于鸟类鸣唱学习的研究都是基于实验室实验，其中基本上所有的生态和社会变量都被控制或删除。最近，越来越明显的是，鸣禽在自然界中经历的复杂的社会和生态因素会影响其发育过程，并产生不同于实验室观察到的模式。过去对褐头燕八哥的研究非常清楚地证明了这一点。在实验室里，燕八哥遵循一条发育途径，导致年轻的雄性在一岁的时候就开始唱成年人的歌，就像许多其他鸣禽一样。然而，野外研究表明，大多数燕八哥在野外需要两年的时间才能发育成一个成年的剧目。据推测，燕八哥中观察到的延长的歌曲发展是由于两种限制的综合影响。第一次发生在鸟类孵化的一年，是一个有限的，甚至完全缺乏，接触当地的歌曲，因为成年人不再唱歌的时候，许多青少年是足够大的记忆当地的歌曲。第二个原因是，由于睾丸激素水平自然升高，年轻雄性在第一个繁殖季节显然无法改变它们的歌曲曲目。本项目继续调查这些自然的限制，在男性燕八哥的歌曲发展，也对女性的歌曲偏好的发展。拟议的研究将作出重大贡献的鸟鸣模型的理解，可以说是卓越的模型系统的实验研究的学习，通过：1）通过确定自然界正常的发展过程，并通过识别已经并继续塑造歌曲学习进化的因素，最大限度地发挥鸟鸣模型的效用，2）阐明敏感期的性质，这是语言习得、印记和正常感觉功能发育的重要特征; 3）确定高睾酮水平是否是繁殖季节行为可塑性丧失的近因; 4）探索雌性对雄性歌曲变体偏好的发育基础。最后一个目标是特别重要的，因为虽然人们普遍认为，在鸟类的歌曲的主要功能之一是吸引和性刺激的女性，很少有人知道的个体发育的女性的喜好，即使鸟类的歌曲是一个主要的模型系统的研究sexualselection.Broader影响：该项目将导致带薪培训的研究生和本科生。此外，这项研究将用于教育公众有关鸟类繁殖生物学，包括文化和遗传进化。 研究结果还将纳入加州大学针对小学生的外展计划。 由于研究物种，褐头燕八哥参与了其他几种鸟类的衰落，并且在美国的一些地区受到了严重的管理，这项研究可能有助于濒危物种的管理工作。

Scientific Merit: The use of complex acoustic signals for communication is widespread in animals. In songbirds, such vocal signals are called 'song' and have an additional, intriguing aspect in that they are learned. How birds learn and develop their songs is an important model used for studying the evolution, ecology and neuro-physiological bases of learning in general. However, our understanding of this model is limited because most studies of song learning in birds have been based on laboratory experiments in which essentially all ecological and social variables have been controlled or removed. Recently, it has become increasingly evident that the complex social and ecological factors songbirds experience in nature can affect the course of development and produce a pattern different from that observed in the lab. Past studies of brown-headed cowbirds demonstrate this point very clearly. In the lab, cowbirds follow a developmental pathway that results in young males singing adult songs by the time they are one year old, as is the case in many other songbirds. Field studies, however, show that most cowbirds take two years to develop an adult repertoire in the wild. It has been hypothesized that the extended song development observed in cowbirds is due to the combined effects of two constraints. The first occurs during a bird's hatching year and is a restricted, or even complete lack of, exposure to local songs because adults are no longer singing by the time many juveniles are old enough to be memorizing local songs. The second is the apparent inability of young males to alter their song repertoires during their first breeding season because of naturally elevated levels of testosterone. The present project continues investigations into these natural constraints on song development in male cowbirds and also, on the development of female song preferences. The proposed research will make significant contributions to understanding of the birdsong model, arguably the pre-eminent model system for experimental studies of learning, by: 1) Maximizing the utility of the birdsong model by determining the normal course of development in nature and by identifying factors that have and continue to shape evolution of song learning, 2) Elucidating the nature of sensitive periods, which are an important characteristic of language acquisition, imprinting and development of normal sensory function, 3) Determining whether high testosterone levels are the proximate cause of the loss of behavioral plasticity during the breeding season, 4) Exploring the developmental bases of female preferences for variants of male song. The last objective is particularly important because although it is generally accepted that one of the prime functions of song in birds is attraction and sexual stimulation of females, little is known about the ontogeny of female preferences even though bird song is a major model system for studies of sexual selection.Broader Impacts: The project will result in salaried training for graduate and undergraduate students. In addition, the research will used to educate the public about avian breeding biology, including cultural and genetic evolution. Results will also be incorporated into a University of California outreach program for elementary school students. Because the study species, the brown-headed cowbird is involved in the decline of several other bird species and is managed heavily in some regions of the US, the research may contribute to management efforts for endangered species.