State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; University of Chinese Academy of Sciences, Beijing 100049, China.
School of Earth Sciences, East China University of Technology, Nanchang 330013, China.
Mol Phylogenet Evol. 2021 Apr;157:107066. doi: 10.1016/j.ympev.2020.107066. Epub 2020 Dec 31.
The disjunct distribution between East Asia and North America is one of the best established biogeographic patterns. A robust phylogeny is fundamental for understanding the biogeographic histories of taxa with this distribution pattern. Tsuga (hemlock) is a genus of Pinaceae with a typical intercontinental disjunct distribution in East Asia and eastern and western North America, and its phylogeny has not been completely reconstructed in previous studies. In this study, we reconstructed a highly resolved phylogeny of Tsuga using 881 nuclear genes, 60 chloroplast genes and 23 mitochondrial genes and explored its biogeographic and reticulate evolutionary history. The results of phylogenetic analysis, molecular dating and ancestral area reconstruction indicate that Tsuga very likely originated from North America in the late Oligocene and dispersed from America to East Asia via the Bering Land Bridge during the middle Miocene. In particular, we found complex reticulate evolutionary pattern among the East Asian hemlock species. T. sieboldii possibly originated from hybridization with the ancestor of T. chinensis from mainland China and T. forrestii as the paternal donor and the ancestor of T. diversifolia and T. ulleungensis as the maternal donor. T. chinensis (Taiwan) could have originated by hybridization together with T. sieboldii and then evolved independently after dispersal to the Taiwan Island, subsequently experiencing mitochondrial DNA introgression with T. chinensis from mainland China. Moreover, our study found that T. chinensis from western China is more closely related to T. forrestii than to T. chinensis from eastern China. The nonmonophyletic T. chinensis needs taxonomic reconsideration.
东亚和北美之间的间断分布是最具确立性的生物地理模式之一。一个稳健的系统发育对于理解具有这种分布模式的分类群的生物地理历史至关重要。铁杉（枞树）是松科的一个属，具有典型的洲际间断分布，分布于东亚和北美东部和西部，其系统发育在以前的研究中尚未完全重建。在本研究中，我们使用 881 个核基因、60 个叶绿体基因和 23 个线粒体基因重建了铁杉的高度分辨率系统发育，并探讨了其生物地理和网状进化历史。系统发育分析、分子定年和祖先区重建的结果表明，铁杉很可能起源于晚渐新世的北美，并在中新世中期通过白令陆桥从中美洲扩散到东亚。特别是，我们发现东亚铁杉种间存在复杂的网状进化模式。T. sieboldii 可能起源于与中国大陆的 T. chinensis 和 T. forrestii 的祖先的杂交，父本供体为 T. forrestii，母本供体为 T. diversifolia 和 T. ulleungensis 的祖先。T. chinensis（台湾）可能是通过与 T. sieboldii 的杂交起源的，然后在传播到台湾岛后独立进化，随后与中国大陆的 T. chinensis 发生线粒体 DNA 渗入。此外，我们的研究发现，来自中国西部的 T. chinensis 与 T. forrestii 的亲缘关系比来自中国东部的 T. chinensis 更为密切。非单系的 T. chinensis 需要进行分类学上的重新考虑。
