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%）脊椎动物物种栖息在热带和南半球地区，并且通常具有“缓慢”的发展速度。相比之下，北温带物种通常具有“快速”的发育速度。本项目将结合对照比较分析和操作实验，研究由母体激素介导的表观遗传母性效应是否是导致不同纬度发育速率和相关生活史策略变化的近似机制。它探索和实验测试了假设，即鸟类胚胎暴露于母源性卵子激素的变化解释了后代发育率的变化。选择用于研究的母源激素有：i)雄激素，因为它们与温带雀形目动物的发育率有很强的相关性；二是甲状腺激素，因为它们是脊椎动物发育和代谢的调节器。该假说预测：1)热带雀形目动物的卵细胞激素低于温带雀形目动物；Ii)引起胚胎发育速率的变异；Iii)在发育速度和后代质量（如免疫功能）之间进行权衡，从而也解释了其他生活史特征的变化。拟议的研究将与Thomas Martin博士（U. Montana）正在进行的长期调查结合起来进行，该调查将通过项目和方法的紧密整合，解决同一模型系统中发育速度变化的最终原因（例如后代和父母死亡率）。这将为检验生命史进化假说提供一个强大而独特的工具，对表观遗传母性对生命史进化的影响产生新颖而关键的见解，并评估选择压力驱动亲代（生殖生理学）和后代（发育生理学）母性影响的近似机制进化。该项目为研究生和本科生提供综合方法和分析复杂生物学问题的培训。

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.