近日，从中科院昆明植物所获悉，该所孙航研究组在中国西南“生物地理线”，即田中—楷永线的研究上取得新突破，证实气候因子改变导致田中—楷永线两侧植物区系分异。相关成果发表在《分子生态学》杂志上。
据了解，田中—楷永线位于我国西南部，是东亚植物区系中中国—喜马拉雅和中国—日本区系一条最重要的生物地理分界线。由于地质历史和气候等因素，致使分界线东、西两侧区域植物区系的分异。通常认为，田中—楷永线以西的植物区系较年轻，有较多的新特有类群；而田中—楷永线以东的植物区系较为古老，并富有古特有或孓遗的类群。但目前尚不清楚田中—楷永线在促使种群谱系地理结构分化方面的重要性。
为此，孙航研究组利用叶绿体基因和核基因片段，对河谷优势、耐旱的灌木——苦刺花进行了遗传结构和谱系地理分析，重建了其种群分布和分化历史。结果表明，苦刺花种群在田中—楷永线两侧有显著的谱系地理分化，其分化时间大约在1.28个百万年，这个时间明显晚于喜马拉雅的最后一次抬升。
研究证明，导致田中—楷永线两侧植物区系分异是气候因子改变，如季风气候体系引起环境梯度变化，特别是最后一次冰期温度和植被类型的改变所致。
通过进一步分析，科研人员还发现，与田中—楷永线东侧的苦刺花种群相比，西侧种群长期以来较稳定，并存在多个避难所，特别是在横断山河谷。而东侧的种群受最后一次冰期影响，分化出了不同的区域谱系地理结构。
同时，核基因研究还表明田中—楷永线东部的居群可能来源于恰好位于该线以东的金沙江下游种群，从而验证了许多类群“冰期走出横断山”的假说，并不支持传统上认为田中—楷永线是一条古老的生物地理分界线的观点。（生物谷 Bioon.com）
生物谷推荐的英文摘要
Mol Ecol. doi: 10.1111/mec.12388
Phylogeography of Sophora davidii (Leguminosae) across the ‘Tanaka-Kaiyong Line’, an important phytogeographic boundary in Southwest China
Fan DM, Yue JP, Nie ZL, Li ZM, Comes HP, Sun H.
The 'Tanaka-Kaiyong Line' (TKL) is a major phytogeographic boundary in Southwest China, separating East Asia's Sino-Himalayan and Sino-Japanese Floras. However, little is known about the importance of this boundary in promoting intraspecific phylogeographic subdivision and divergence. Using chloroplast (cpDNA) and nuclear-intron (nDNA) sequence data, we reconstructed the population history of Sophora davidii, a drought-tolerant riparian shrub widely distributed on either side of the TKL. Specifically, we aimed at testing two long-standing explanations for possible vicariant events across the TKL: (i) Late Pliocene (c. 3 Ma) geological uplift of the eastern Qinghai-Tibetan Plateau (QTP) or (ii) a sharp environmental gradient associated with the establishment of different monsoon regimes on either side of the TKL during the (Late) Pleistocene. Our genealogical analyses detected a major west-east split in cpDNA, geographically largely consistent with the TKL, and dated to c. 1.28 Ma (95% HPD: 0.21-2.96 Ma), hence postdating the latest phase of eastern QTP uplift. Furthermore, integrating cpDNA phylogeographic patterns with mismatch analyses, we found multiple refugial isolation and long-term demographic stability of populations in the west (Hengduan Mountain Range) compared with extensive range expansions in the east, possibly during the last glacial period(s) and followed by differentiation into regional sublineages (southeast: Yunnan-Guizhou Plateau vs. northeast: Qinling Mts./Loess Plateau). Although nuclear differentiation was less marked, the geographical pattern of nDNA haplotypes provided some further indication of the species' eastward expansion, possibly from source populations located just east of the TKL (lower Jinshajiang region). Overall, the present data reject the geological (tectonic) explanation for the TKL and, instead, provide supportive evidence for its role as a climatically driven barrier to present-day plant dispersal. In addition, our study highlights changing temperatures and vegetation types during the last glacial period(s), along with aspects of regional topography, to be important determinants of the glacial eastward expansion of S. davidii. In consequence, our study lends support to a 'glacial out-of-Hengduan Mts'. hypothesis for the xerophytic-riparian flora of Southwest China, which in turn is inconsistent with the traditional view of the TKL as a 'classical' vicariant-biogeographic boundary.
