Maternal Effects as Mechanisms for Variation in Development rate ? A Study of Life Histories in Tropical and North Temperate Passerine Birds

世界上大多数（约75%）的脊椎动物栖息在热带和南半球地区，并且通常以“缓慢”的发育速度为特征。 相反，北温带的物种通常具有“快速”的发育速度。本计画将结合联合收割机控制比较分析与操作实验，以探讨由母体荷尔蒙介导的表观遗传母体效应是否为造成发育速率及相关生活史策略跨纬度变异的近似机制。它探讨和实验测试的假设，即在鸡蛋中的母体衍生激素的鸟类胚胎暴露的变化解释了后代发育速度的变化。选择用于研究的母体激素是：i）雄激素，因为它们在温带雀形目中显示出与发育速率的强相关性;和ii）甲状腺激素，因为它们是脊椎动物发育和代谢的调节剂。该假说预测这些卵激素i）在热带雀形目中低于温带雀形目; ii）导致胚胎发育速率的变化; iii）导致发育速率和后代质量（如免疫功能）之间的权衡，从而也解释了其他生活史特征的变化。拟议的研究将与托马斯马丁博士（美国）正在进行的长期研究结合进行。蒙大拿州），解决的最终原因（如后代和父母死亡率）的变化，在同一模型系统的项目和方法的紧密结合。这将提供一个强大的和独特的工具，用于测试假设的生活史的进化，产生新的和关键的见解表观遗传母性的影响，生活史的进化和评估选择压力驱动的近端机制的母亲的影响，在父母（生殖生理学）和后代（发育生理学）代的演变。该项目为研究生和本科生提供综合方法和分析复杂生物问题的培训。

Most (~75%) vertebrate species of the world inhabit tropical and southern hemisphere regions, and are generally characterized with a 'slow' development rate. North temperate species, in contrast, generally posses a 'fast' development rate. This project will combine controlled comparative analyses with manipulative experiments to examine whether epigenetic maternal effects, mediated by maternal hormones, are proximate mechanisms causing the variation of development rate and related life history strategies across latitudes. It explores and experimentally tests the hypotheses that variation in exposure of the avian embryo to maternally derived hormones in the egg explains variation in offspring development rate. Maternal hormones selected for study are: i) androgens because they show strong correlations with development rate in temperate zone passerines; and ii) thyroid hormones because they are regulators of vertebrate development and metabolism. The hypothesis predicts these egg hormones i) to be lower in tropical than temperate passerines; ii) to cause variation in rate of embryo development; iii) to cause trade-offs between development rate and offspring quality such as immune function, thereby explaining variation in other life history traits as well. Proposed studies will be conducted in conjunction with ongoing long-term investigations conducted by Dr. Thomas Martin (U. Montana) that address the ultimate causes (e.g. offspring and parent mortality) of variation in development rate in the same model systems with a tight integration of projects and approaches. This will provide a powerful and unique tool for testing hypotheses of evolution of life histories, generating novel and critical insights into epigenetic maternal effects on life history evolution and evaluating selection pressures driving evolution of proximate mechanisms of maternal effects in both the parent (reproductive physiology) and the offspring (developmental physiology) generations. The project provides training of graduate and undergraduate students in integrative approaches to, and analyses of, complex biological questions.