Known as the ‘third polar region’, the Qinghai-Tibet Plateau represents one of the harshest highland environments in the world and yet a number of organisms thrive there. Previous studies of birds, animals and humans have focused on well-differentiated populations in later stages of phenotypic divergence. The adaptive processes during the initial phase of highland adaptation remain poorly understood. We studied a human commensal, the Eurasian Tree Sparrow, which has followed human agriculture to the Qinghai-Tibet Plateau. Despite strong phenotypic differentiation at multiple levels, in particular in muscle-related phenotypes, highland and lowland populations show shallow genomic divergence and the colonization event occurred within the past few thousand years. In a one-month acclimation experiment investigating phenotypic plasticity, we exposed adult lowland tree sparrows to a hypoxic environment and did not observe muscle changes. Through population genetic analyses, we identified a signature of polygenic adaptation, whereby shifts in allele frequencies are spread across multiple loci, many of which are associated with muscle-related processes. Our results reveal a case of positive selection in which polygenic adaptation appears to drive rapid phenotypic evolution, shedding light on early stages of adaptive evolution to a novel environment.

中文翻译：

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欧亚树麻雀高海拔适应早期阶段的快速表型进化与浅层基因组分化

青藏高原被称为“第三极区”，是世界上最恶劣的高原环境之一，但仍有许多生物在那里繁衍生息。先前对鸟类、动物和人类的研究集中在表型分化后期阶段的分化良好的种群。高原适应初始阶段的适应过程仍然知之甚少。我们研究了一种人类共生体——欧亚树麻雀，它跟随人类农业来到青藏高原。尽管在多个水平上有强烈的表型分化，特别是在肌肉相关的表型中，高地和低地种群显示出浅的基因组差异，并且殖民事件发生在过去几千年。在为期一个月的研究表型可塑性的驯化实验中，我们将成年低地树麻雀暴露在缺氧环境中，没有观察到肌肉变化。通过群体遗传分析，我们确定了多基因适应的特征，即等位基因频率的变化分布在多个基因座上，其中许多基因座与肌肉相关过程有关。我们的结果揭示了一个积极选择的案例，其中多基因适应似乎推动了快速的表型进化，揭示了对新环境的适应性进化的早期阶段。