Naturally Occurring Constraints on Development in a Model Learning System

科学价值：动物广泛使用复杂的声音信号进行交流。在鸣禽中，这种声音信号被称为“歌声”，并且有一个额外的，有趣的方面，因为它们是习得的。鸟类如何学习和发展它们的歌曲是一个重要的模型，用于研究进化、生态学和学习的神经生理基础。然而，我们对这个模型的理解是有限的，因为大多数关于鸟类鸣叫学习的研究都是基于实验室实验，在实验室实验中，基本上所有的生态和社会变量都被控制或删除了。近年来，越来越多的研究表明，鸣禽在自然界中经历的复杂的社会和生态因素会影响鸣禽的发育过程，并产生与实验室观察不同的模式。过去对棕头牛鹂的研究非常清楚地证明了这一点。在实验室里，牛郎鸟遵循着一种发育途径，在它们一岁的时候，年轻的雄性会唱成年的歌曲，就像许多其他的鸣禽一样。然而，实地研究表明，大多数牛郎鸟需要两年的时间才能在野外发展成成年曲目。据推测，在牛郎鸟中观察到的延长的歌声发展是由于两个约束的综合影响。第一次发生在鸟类的孵化年，这是一个有限的，甚至完全没有接触到当地歌曲的机会，因为成年鸟在许多幼鸟长大到足以记住当地歌曲的时候不再唱歌。其次，由于雄性激素水平自然升高，年轻的雄性在第一个繁殖季节显然无法改变它们的鸣叫声。目前的项目继续调查这些对雄性牛郎鸟鸣叫发展的自然限制，以及雌性鸣叫偏好的发展。本文提出的研究将对理解鸟鸣模型做出重大贡献，鸟鸣模型可以说是学习实验研究中最杰出的模型系统。1)通过确定自然界的正常发展过程和确定已经并继续影响鸣叫学习进化的因素，最大限度地发挥鸟鸣模型的效用；2)阐明敏感期的本质，这是语言习得、印迹和正常感觉功能发展的重要特征；3)确定高睾丸激素水平是否是繁殖季节行为可塑性丧失的直接原因。4)探索雌性对雄性歌曲变体偏好的发育基础。最后一个目标尤其重要，因为尽管人们普遍认为鸟类鸣叫的主要功能之一是吸引和性刺激雌性，但尽管鸟类鸣叫是研究性选择的主要模型系统，但对雌性偏好的个体发生知之甚少。更广泛的影响：该项目将为研究生和本科生提供带薪培训。此外，这项研究还将用于教育公众有关鸟类繁殖生物学的知识，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。由于研究物种棕头牛鹂与其他几种鸟类的数量下降有关，并且在美国一些地区受到严格管理，因此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.