江孜沙棘和云南沙棘之间谱系分化和亲缘地理

MATERNAL DIVERGENCE AND PHYLOGEOGRAPHICAL RELATIONSHIPS BETWEEN HIPPOPHAE GYANTSENSIS AND H. RHAMNOIDES SUBSP. YUN-NANENSIS

研究具有邻近分布的近缘类群的遗传分化和谱系筛选对于进一步揭示物种形成机制具有重要意义。该文以沙棘属(Hippophae)临域分布的两个类群,江孜沙棘(H.gyantsensis)和云南沙棘(H.rhamnoides subsp.yunnanensis)为研究对象,进行群体水平上的母系分化研究。前一个种分布于西藏的中西部,而后者主要分布于青藏高原东南部的云南西北部、四川西部和西藏东南部。两个类群在叶和果实性状存在明显区别。叶绿体在沙棘属植物中为母系遗传。共研究了两个类群14种群109个沙棘个体的叶绿体trnL-F、trnS-G序列;序列排序后共发现11种单倍型,江孜沙棘和云南沙棘分别有7种和6种,两种单倍型为两个类群共享。分支分析和嵌套进化分析进一步表明,两个类群之间的单倍型相互交错,单倍型分化与形态上划分的两个类群不一致,表明它们之间具有十分复杂的谱系筛选过程。这些发现明显不支持以前提出的有关江孜沙棘系统位置的假设。但是,目前所获得的证据不能区分该物种究竟是通过异域分化还是同倍性杂交起源的。不同种群固定特有单倍型表明,两个类群都在最后一次冰期可能存在多个避难所。

Aims In order to understand complex speciation, it is critically important to investigate the corresponding genetic divergence and lineage sorting between close species or taxa distributed in parapatric regions. Our aim was to outline the distribution of the maternally inherited chloroplast haplotypes of Hippophae gyantsensis and H. rhamnoides subsp, yunnanensis and construct their phylogeographic relationships. The former species occurs in central and west Tibet, while the latter is distributed in northwest Yunnan and west Sichuan. These taxa are distinguished by leaf shape, trichomes and fruits. Methods We sequenced trnL-F and trnS-G DNA fragments for 109 trees of 14 populations from these two taxa. Important findings A total of 11 chlorotypes were identified, seven in H. gyantsensis and six in H. rhamnoides subsp, yunnanensis, with two shared. Phylogenetic and Nested Clade Analysis analyses further suggested that the divergence of these haplotypes is highly inconsistent with morphological differentiation of the two taxa, suggesting complex maternal lineage sorting between them. These findings refute the previous systematic placements of H. gyantsensis within the genus. However, the available data could not distinguish between two alterative hypotheses regarding origin of this species： homoploid hybrid versus allopatric speciation. In addition, the unique haplotypes recovered in separate populations within each of two taxa suggest that multiple refugia might have maintained both across their distributional ranges during the Last Glacial Maximum.