Dunbar-Co Stephanie, Wieczorek Ania M, Morden Clifford W
Department of Botany, University of Hawai'i, 3190 Maile Way, Honolulu, Hawai'i 96822 USA.
Am J Bot. 2008 Sep;95(9):1177-88. doi: 10.3732/ajb.0800132.
Insular oceanic islands provide excellent opportunities for the study of evolutionary processes and adaptive radiation. The Hawaiian Plantago radiation comprises six endemic taxa showing considerable inter- and intraspecific morphological and ecological diversity. The rDNA internal (ITS) and external (ETS) transcribed spacers and two recently described chloroplast spacers, ndhF-rpl32 and rpl32-trnL, were sequenced to study phylogenetic relationships within this morphologically complex group. Phylogenetic analysis provided strong evidence for the monophyly of Hawaiian Plantago, suggesting that the lineage arose from a single long-distance dispersal event. Inconsistencies between nuclear and chloroplast phylogenies suggest a history of hybridization. The basal, unresolved dichotomy of the combined phylogeny is consistent with rapid phenotypic diversification of the major lineages early in the history of this group. Speciation has largely occurred allopatrically, with divergence a result of intraisland ecological shifts between bog and woodland habitats and interisland dispersal events. Most interisland colonizations were from older to younger islands with initial colonization of Kaua'i. In our analysis, P. pachyphylla is paraphyletic and taxonomic separation of the distinct morphotypes of this species appears justified. Furthermore, the apparent hybrid ancestry and unique morphology and habitat of the endangered P. princeps var. longibracteata support its recognition at the specific rank.
孤立的海洋岛屿为研究进化过程和适应性辐射提供了绝佳机会。夏威夷车前草辐射包含六个特有分类群，它们在种间和种内表现出相当大的形态和生态多样性。对核糖体DNA的内部（ITS）和外部（ETS）转录间隔区以及最近描述的两个叶绿体间隔区ndhF-rpl32和rpl32-trnL进行了测序，以研究这个形态复杂的类群内部的系统发育关系。系统发育分析为夏威夷车前草的单系性提供了有力证据，表明该谱系起源于一次单一的长距离扩散事件。核基因和叶绿体基因系统发育之间的不一致表明存在杂交历史。联合系统发育中基部未解决的二分法与该类群历史早期主要谱系的快速表型多样化一致。物种形成主要发生在异域，分歧是岛内沼泽和林地生境之间的生态转变以及岛间扩散事件的结果。大多数岛间定殖是从较老的岛屿到较年轻的岛屿，最初定殖于考艾岛。在我们的分析中，厚叶车前草是并系的，对该物种不同形态型进行分类学分离似乎是合理的。此外，濒危的长苞车前草变种明显的杂交起源以及独特的形态和生境支持将其认定为一个独立的物种。
