Marcussen Thomas, Meseguer Andrea S
Monrads gate 21a, 0564 Oslo, Norway.
INRA, UMR 1062 CBGP (INRA, IRD, CIRAD, Montpellier SupAgro), The Center for Biology and Management of Populations (CBGP), Avenue du Campus Agropolis, 34980 Montferrier-sur-Lez, France.
Mol Phylogenet Evol. 2017 May;110:134-149. doi: 10.1016/j.ympev.2017.03.012. Epub 2017 Mar 10.
The cosmopolitan genus Geranium L. (Geraniaceae) consists of c. 350 species distributed in temperate habitats worldwide, with most of its diversity concentrated in the Mediterranean region. Unlike other genera in Geraniaceae, the species of Geranium present contrasting seed discharge syndromes, i.e. the 'Erodium-type' (ET), the 'carpel-projection type' (CP), the 'seed-ejection type' (SE), and the 'inoperative type' (IT), which have been used to delimit major groups within the genus. However, phylogenetic relationships within Geranium are unknown and so is the evolution of the different seed discharge mechanisms. Here, we used a calibrated multispecies coalescent approach to infer the species-level phylogeny and divergence times of the genus based on chloroplast (rbcL, trnL-trnF) and nuclear (ITS) DNA sequences. Our sampling represents most of the morphological variation described in the genus. We reconstruct the evolution of the seed discharge mechanism using ancestral state reconstruction (ASR) techniques on the multispecies coalescent tree, and assess the association between fruit type evolution and species diversification using stochastic birth-death and trait-dependent diversification models. Finally, we reconstruct the early biogeographic history of the genus using discrete and continuous biogeographic analyses of species distribution centroids, including fossil evidence and tip dates. Our results show that fruit type is homoplasious and that the classification based on fruit type in Geranium is artificial. The taxonomy and putative apomorphic characters for Geranium are discussed. ASR of the fruit characters suggests that ET may represent the ancestral state in Geranium and from which CP originated twice, IT presumably once, and SE twice. The independent appearance of the SE syndrome is in both cases associated with increases in diversification rates in the genus. The biogeographic analysis centers the origin and early 10Ma diversification of Geranium on the Mediterranean region. The evolution of seed discharge mechanism about 5Ma might have allowed the species of Geranium to increase in geographic range and to ultimately, diversify.
全球广布的老鹳草属（牻牛儿苗科）约有350个物种，分布于世界各地的温带生境，其多样性大多集中在地中海地区。与牻牛儿苗科的其他属不同，老鹳草属的物种呈现出截然不同的种子传播综合征，即“牻牛儿苗型”（ET）、“心皮弹射型”（CP）、“种子喷射型”（SE）和“无功能型”（IT），这些已被用于界定该属内的主要类群。然而，老鹳草属内的系统发育关系尚不清楚，不同种子传播机制的进化情况也不明。在此，我们采用校准的多物种溯祖方法，基于叶绿体（rbcL、trnL-trnF）和核（ITS）DNA序列推断该属的物种水平系统发育和分歧时间。我们的采样涵盖了该属所描述的大部分形态变异。我们在多物种溯祖树上使用祖先状态重建（ASR）技术重建种子传播机制的进化，并使用随机出生-死亡和性状依赖的多样化模型评估果实类型进化与物种多样化之间的关联。最后，我们利用物种分布中心的离散和连续生物地理分析，包括化石证据和枝端时间，重建该属早期的生物地理历史。我们的结果表明，果实类型是同形的，基于果实类型对老鹳草属进行的分类是人为的。讨论了老鹳草属的分类学和假定的近裔性状。果实性状的ASR表明，ET可能代表老鹳草属的祖先状态，CP由此起源了两次，IT大概起源了一次，SE起源了两次。在这两种情况下，SE综合征的独立出现都与该属多样化速率的增加有关。生物地理分析将老鹳草属的起源和1000万年前早期的多样化定位于地中海地区。约500万年前种子传播机制的进化可能使老鹳草属的物种扩大了地理范围，并最终实现了多样化。
