Division of Molecular Ecology, Key Laboratory of Arid and Grassland Ecology, School of Life Science, Lanzhou University, Lanzhou, 730000, China.
BMC Evol Biol. 2010 Jun 22;10:194. doi: 10.1186/1471-2148-10-194.
Although allopatric speciation is viewed as the most common way in which species originate, allopatric divergence among a group of closely related species has rarely been examined at the population level through phylogeographic analysis. Here we report such a case study on eight putative cypress (Cupressus) species, which each have a mainly allopatric distribution in the Qinghai-Tibetan Plateau (QTP) and adjacent regions. The analysis involved sequencing three plastid DNA fragments (trnD-trnT, trnS-trnG and trnL-trnF) in 371 individuals sampled from populations at 66 localities.
Both phylogenetic and network analyses showed that most DNA haplotypes recovered or haplotype-clustered lineages resolved were largely species-specific. Across all species, significant phylogeographic structure (N(ST) > G(ST), P < 0.05) implied a high correlation between haplotypes/lineages and geographic distribution. Two species, C. duclouxiana and C. chengiana, which are distributed in the eastern QTP region, contained more haplotypes and higher diversity than five species with restricted distributions in the western highlands of the QTP. The remaining species, C. funebris, is widely cultivated and contained very little cpDNA diversity.
It is concluded that the formation of high mountain barriers separating deep valleys in the QTP and adjacent regions caused by various uplifts of the plateau since the early Miocene most likely promoted allopatric divergence in Cupressus by restricting gene flow and fixing local, species-specific haplotypes in geographically isolated populations. The low levels of intraspecific diversity present in most species might stem from population bottlenecks brought about by recurrent periods of unfavorable climate and more recently by the negative impacts of human activities on species' distributions. Our findings shed new light on the importance of geographical isolation caused by the uplift of the QTP on the development of high plant species diversity in the QTP biodiversity hotspot.
尽管异域物种形成被视为物种起源的最常见方式，但通过系统地理学分析很少在种群水平上研究一组密切相关物种的异域分歧。在这里，我们报告了一个关于八个假定的柏科（柏木属）物种的案例研究，这些物种在青藏高原（QTP）及其周边地区的分布主要是异域的。该分析涉及对来自 66 个地点的 371 个个体的三个质体 DNA 片段（trnD-trnT、trnS-trnG 和 trnL-trnF）进行测序。
系统发育和网络分析均表明，大多数回收的 DNA 单倍型或单倍型聚类谱系在很大程度上是种特异性的。在所有物种中，显著的地理结构（N（ST）>G（ST），P<0.05）表明单倍型/谱系与地理分布之间存在高度相关性。分布在青藏高原东部的两个物种，即翠柏和丽江柏，包含的单倍型和多样性比分布在青藏高原西部高地的五个物种更高。其余物种，岷江柏，广泛种植，含有很少的 cpDNA 多样性。
可以得出结论，由于早中新世以来高原的各种抬升导致 QTP 和周边地区高山深谷的形成，很可能通过限制基因流和固定地理上隔离的种群中具有特定物种的单倍型来促进翠柏的异域分歧。大多数物种中存在的种内多样性水平较低可能源于不利气候引起的种群瓶颈，以及人类活动对物种分布的负面影响。我们的研究结果为青藏高原隆升引起的地理隔离对青藏高原生物多样性热点地区高植物物种多样性的发展的重要性提供了新的认识。
