Department of Plant and Environmental Sciences, University of Gothenburg, Box 461, 40530, Göteborg, Sweden.
BMC Biol. 2009 Nov 26;7:82. doi: 10.1186/1741-7007-7-82.
The tendency of animals and plants to independently develop similar features under similar evolutionary pressures - convergence - is a widespread phenomenon in nature. In plants, convergence has been suggested to explain the striking similarity in life form between the giant lobelioids (Campanulaceae, the bellflower family) of Africa and the Hawaiian Islands. Under this assumption these plants would have developed the giant habit from herbaceous ancestors independently, in much the same way as has been suggested for the giant senecios of Africa and the silversword alliance of Hawaii.
Phylogenetic analyses based on plastid (rbcL, trnL-F) and nuclear (internal transcribed spacer [ITS]) DNA sequences for 101 species in subfamily Lobelioideae demonstrate that the large lobelioids from eastern Africa the Hawaiian Islands, and also South America, French Polynesia and southeast Asia, form a strongly supported monophyletic group. Ancestral state reconstructions of life form and distribution, taking into account phylogenetic uncertainty, indicate their descent from a woody ancestor that was probably confined to Africa. Molecular dating analyses using Penalized Likelihood and Bayesian relaxed clock approaches, and combining multiple calibration points, estimate their first diversification at approximately 25-33 million years ago (Ma), shortly followed by several long-distance dispersal events that resulted in the current pantropical distribution.
These results confidently show that lobelioid species, commonly called 'giant', are very closely related and have not developed their giant form from herbaceous ancestors independently. This study, which includes the hitherto largest taxon sampling for subfamily Lobelioideae, highlights the need for a broad phylogenetic framework for testing assumptions about morphological development in general, and convergent evolution in particular.
动物和植物在相似的进化压力下独立发展出相似特征的趋势——趋同，是自然界中普遍存在的现象。在植物中，趋同被认为可以解释非洲巨型风铃草类（桔梗科，风铃草科）和夏威夷群岛之间在生活形态上的惊人相似性。根据这一假设，这些植物会从草本祖先独立地发展出巨大的习性，就像非洲的巨型千里光属和夏威夷的银剑联盟一样。
基于叶绿体（rbcL、trnL-F）和核（内部转录间隔区 [ITS]）DNA 序列对 101 种风铃草亚科植物的系统发育分析表明，来自东非、夏威夷群岛以及南美洲、法属波利尼西亚和东南亚的大型风铃草类形成了一个强烈支持的单系群。考虑到系统发育不确定性的生活形态和分布的祖先状态重建表明，它们来自一个可能局限于非洲的木本祖先。使用 Penalized Likelihood 和 Bayesian 松弛时钟方法，结合多个校准点的分子定年分析估计，它们的第一次多样化大约发生在 25-3300 万年前（Ma），随后紧接着发生了几次长距离扩散事件，导致了目前的泛热带分布。
这些结果有把握地表明，通常被称为“巨型”的风铃草类物种非常密切相关，它们并没有从草本祖先独立地发展出巨大的形态。本研究包括迄今最大的风铃草亚科分类群采样，突出了需要一个广泛的系统发育框架来检验一般形态发育的假设，特别是趋同进化的假设。
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