种间遗传分化与物种适应性机制是当代进化生物学重大科学问题之一。虽然近年来该领域研究取得了较大进展，但对于近缘姊妹种间遗传分化的定量研究仍较少，更缺乏基因分化模式与适应性进化之间关系信息。鹅掌楸与北美鹅掌楸为典型的东亚-北美间断分布树种，是种间遗传分化及适应性进化分歧研究的理想材料。本项目利用鹅掌楸、北美鹅掌楸全分布区采集的自然群体样本，选取与林木耐寒、耐旱相关的候选基因进行克隆测序与序列分析，结合叶绿体基因及核糖体DNA序列信息，分析鹅掌楸种间及种内不同种群间的核苷酸多态性类型与频率，连锁不平衡程度，单倍型及地理分布；同时，比较鹅掌楸属树种不同遗传体系基因进化速率差异与基因进化模式，定量分析种内群体遗传结构及种间遗传分化，推测鹅掌楸属树种的谱系地理，检测核苷酸突变位点的正选择作用。在此基础上，探讨基因分化与鹅掌楸种间适应性进化之间的关系。此外，研究结果也可为鹅掌楸育种群体的组建提供参考。

Understanding the mechanism of interspecies genetic divergence and how organisms adapt to changing environments is a fundamental topic in modern evolutionary biology. Despite the long-standing interest and significant progross in this area, there have been few attempts to objectively assess the amount of genetic divergence between vicariad species-pairs, and little attention has been paid to the relationship between nucleotide patterns and adaptive differentiation. The two extant species in Liriodendron i.e., L. tulipifera and L. chinense are typical eastern Asian-eastern North American floristic disjunction and ideal plants for exploring the underlying mechanism of genetic divergence and adaptive evolution. In this project, to reveal the nucleotide patterns related to adaptation differentiation to local environments in a set of genes including fourteen nuclear DNA genes related to cold and drought tolerance (dhn1,dhn2,dhn3,dhn4,dhn5,dhn7,dhn9, lea, lp3-2, abaR, gst1,gst2, Chs, Adh), one nrDNA ITS and two cpDNA genes (trnT-trnF, atpB-rbcL), we plan to assay dozens of natural populations covering their entire distribution area of these two species. The aims of this project are to search for patterns of selection in each gene by analyzing the types and frequency of nucleotide variation, linkage disequilibrium, and haplotype distributions，to compare the evolution pattern and rate at the DNA level, to detect the nucleotide variation loci related to positve selection, to assess the amount of interspecies genetic divergence and intraspecies variation, and to delineate the phylogeography of Liriodendron. The final goal is to explore the relationship between nucleotide diversity and adaptive evolution. Besides, we also hope that all these findings of this project will be used to guide the construction of breeding population in the long term breeding of Liriodendron.