Vieu Julien C, Koubínová Darina, Grant Jason R
Institute of Biology, University of Neuchâtel, Rue Emile Argand 11, 2000 Neuchâtel, Switzerland.
Biology (Basel). 2021 Aug 25;10(9):825. doi: 10.3390/biology10090825.
The evolutionary processes responsible for the extraordinary diversity in the middle elevation montane forests of the Tropical Andes (MMF; 1000-3500 m) remain poorly understood. It is not clear whether adaptive divergence, niche conservatism or geographical processes were the main contributors to the radiation of the respective lineages occurring there. We investigated the evolutionary history of plant lineages in the MMF. We used the vascular plant genus (Gentianaceae) as a model, as it consists of 118 morphologically diverse species, a majority of which are endemic to the MMF. We used a time-calibrated molecular phylogeny and morphological and climatic data to compare a set of evolutionary scenarios of various levels of complexity in a phylogenetic comparative framework. In this paper, we show that the hypothesis of adaptive radiation for in the MMF is unlikely. The genus remained confined to the upper montane forests (UMF > 1800 m) during more than a half of its evolutionary history, possibly due to evolutionary constraints. Later, coinciding with the beginning of the Pleistocene (around 2.58 Ma), a phylogenetically derived (recently branching) clade, here referred to as the clade (25 species), successfully colonized and radiated in the lower montane forests (LMF < 1800 m). This colonization was accompanied by the evolution of a new leaf phenotype that is unique to the species of the clade that likely represents an adaptation to life in this new environment (adaptive zone). Therefore, our results suggest that niche conservatism and geographical processes have dominated most of the diversification history of , but that a rare adaptive divergence event allowed a transition into a new adaptive zone and enabled progressive radiation in this zone through geographical processes.
热带安第斯山脉中海拔山地森林（MMF；1000 - 3500米）存在着非凡的生物多样性，然而导致这种多样性的进化过程仍鲜为人知。目前尚不清楚适应性分化、生态位保守性或地理过程是否是该地区各谱系辐射的主要促成因素。我们研究了MMF中植物谱系的进化历史。我们以维管植物龙胆属（龙胆科）为模型，该属由118个形态各异的物种组成，其中大多数是MMF特有的。我们使用了经过时间校准的分子系统发育树以及形态和气候数据，在系统发育比较框架中比较了一系列不同复杂程度的进化情景。在本文中，我们表明MMF中龙胆属适应性辐射的假说是不太可能的。在其超过一半的进化历史中，该属一直局限于高海拔山地森林（UMF > 1800米），这可能是由于进化限制。后来，在更新世开始时（约258万年前），一个系统发育衍生的（最近分支的）分支，这里称为龙胆分支（25个物种），成功地在低海拔山地森林（LMF < 1800米）中定殖并辐射。这种定殖伴随着一种新叶表型的进化，这种表型是龙胆分支物种所特有的，可能代表了对这种新环境（适应区）生活的一种适应。因此，我们的结果表明，生态位保守性和地理过程在龙胆属的大部分多样化历史中占主导地位，但一次罕见的适应性分化事件使得其能够过渡到一个新的适应区，并通过地理过程在该区域实现渐进辐射。
