Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, Apartado Postal 70-275, México, D.F., Mexico.
Mol Phylogenet Evol. 2012 Jan;62(1):263-74. doi: 10.1016/j.ympev.2011.09.021. Epub 2011 Oct 10.
The genus Abies is distributed discontinuously in the temperate and subtropical montane forests of the northern hemisphere. In Mesoamerica (Mexico and northern Central America), modern firs originated from the divergence of isolated mountain populations of migrating North American taxa. However, the number of ancestral species, migratory waves and diversification speed of these taxa is unknown. Here, variation in repetitive (Pt30204, Pt63718, and Pt71936) and non-repetitive (rbcL, rps18-rpl20 and trnL-trnF) regions of the chloroplast genome was used to reconstruct the phylogenetic relationships of the Mesoamerican Abies in a genus-wide context. These phylogenies and two fossil-calibrated scenarios were further employed to estimate divergence dates and diversification rates within the genus, and to test the hypothesis that, as in many angiosperms, conifers may exhibit accelerated speciation rates in the subtropics. All phylogenies showed five main clusters that mostly agreed with the currently recognized sections of Abies and with the geographic distribution of species. The Mesoamerican taxa formed a single group with species from southwestern North America of sections Oiamel and Grandis. However, populations of the same species were not monophyletic within this group. Divergence of this whole group dated back to the late Paleocene and the early Miocene depending on the calibration used, which translated in very low diversification rates (r(0.0)=0.026-0.054, r(0.9)=0.009-0.019 sp/Ma). Such low rates were a constant along the entire genus, including both the subtropical and temperate taxa. An extended phylogeographic analysis on the Mesoamerican clade indicated that Abies flinckii and A. concolor were the most divergent taxa, while the remaining species (A. durangensis, A. guatemalensis, A. hickelii, A. religiosa and A. vejari) formed a single group. Altogether, these results show that divergence of Mesoamerican firs coincides with a model of environmental stasis and decreased extinction rate, being probably prompted by a series of range expansions and isolation-by-distance.
冷杉属间断分布于北半球的温带和亚热带山地森林中。在中美洲（墨西哥和中美洲北部），现代冷杉起源于北美的孤立山地种群的分化。然而，这些类群的祖先是多少，迁徙的波次，以及分化的速度是未知的。在这里，叶绿体基因组的重复（Pt30204、Pt63718 和 Pt71936）和非重复（rbcL、rps18-rpl20 和 trnL-trnF）区域的变异被用于在属范围内重建中美洲冷杉的系统发育关系。这些系统发育和两个化石校准的方案进一步被用来估计属内的分化时间和多样化速率，并检验这样的假说，即与许多被子植物一样，针叶树可能在亚热带地区表现出加速的物种形成速度。所有的系统发育都显示了五个主要的聚类，这些聚类与冷杉属的目前公认的分类群和物种的地理分布大部分一致。中美洲类群与来自北美西南部的 Oiamel 和 Grandis 分类群的物种形成了一个单一的群体。然而，同一物种的种群在这个群体中不是单系的。这个整个群体的分化可以追溯到晚古新世到早始新世，这取决于所使用的校准，这转化为非常低的多样化速率（r(0.0)=0.026-0.054，r(0.9)=0.009-0.019 sp/Ma）。这种低速率在整个属中都是恒定的，包括亚热带和温带类群。对中美洲类群的扩展系统地理学分析表明，Abies flinckii 和 A. concolor 是最具分化的类群，而其余的物种（A. durangensis、A. guatemalensis、A. hickelii、A. religiosa 和 A. vejari）形成了一个单一的群体。总的来说，这些结果表明，中美洲冷杉的分化与环境稳定和灭绝率下降的模式相吻合，可能是由一系列的范围扩张和距离隔离所推动的。
