“是什么引起生物遗传多样性的差异？”一直是进化生物学的核心问题。“近中性进化”理论曾是最接近实际的回答，但正面临巨大的挑战: 多物种全基因组扫描结果重新发现了正选择对维持遗传多样性的重要性。我们最新的理论研究表明正选择通过连锁不平衡影响了基因组不同区域的遗传多样性。全面认识这一课题要求对不同类型的基因组展开精确的定量分析。林木正是其中最具代表性的突破口，相比草本植物，它们的基因组具有更高的非同义突变率，意味着高遗传负荷与低竞争力。但这显然与木本植物，尤其是橡树，极强的抗性和悠久的树龄相矛盾。这看似相悖的特点可能体现了森林树种应对多种环境变化和病虫害入侵的机制，也反映了“自然选择论”和“中性进化论”的融合。我们以全面揭示这一机制为目标，计划首先以麻栎为研究对象，确立抗性性状的遗传机制和适应性进化过程，并深入探索连锁正选择在林木性进化过程中的作用形式和范围，为维护森林生态系统稳定提供理论指导。

The central question of evolutionary biology is “why some species have more genetic diversity than others?”. And a no less important question is “why selective efficacy varies among species?”. The Nearly Neutral Theory (NNT) of molecular evolution remains the most adequate model for explaining the amount of DNA polymorphism. However, it has been challenged by the mounting evidence of positive selection, which is believed to have a predominant role in the maintenance of genetic diversity by recent studies (reviewed in Kern and Hahn 2018). By showing the relationship of effective population size (Ne) and selective efficacy (PiN/PiS) using genomes of various species in a more careful study, we pointed out that positive selection takes effect mainly through linkage disequilibrium (e.g. Hitch-hiking or selective sweeps). To integrate linked positive selection into the current framework of NNT we must further study across various types of genomes with a large variation of Ne but similar life history traits in order to find out how one could evaluate its influence on genetic diversity. Based on our previous research (Chen et al 2017), we believe tree genomes provide the full potential for this purpose. Different from most animals and annual plants, genomes of forest trees harbor much higher genetic diversity as well as PiN/PiS, which in theory should cause a great genetic load and thus reduce their survival rates. However, in reality this is certainly not the case, especially for Quercus that has the longest lifespan and widest distribution range of all plants. Such conflict sheds us a light that high PiN/PiS could be the very reason how forest trees can deal with all kinds of pathogens and environmental changes in their long lifespan and where positive selection takes its place. Aiming at revealing this mechanism, we plan to first study the adaptive evolution of resistant genes in sawtooth oak (Q. acutissima), which distributes widely from tropical area to northernmost China and exhibits great diversity in leaf morphology as a reflect of local adaptation. To understand the mechanisms of the adaptation of its resistant traits shall help us search for the optimal genotypes for the maintenance of forest ecosystem under the circumstance of global climate changes. Based on these findings, we will further explore the role of linked positive selection in the evolution of forest tree genomes and try to integrate it into the current framework of NNT.