Species radiations should be facilitated by short generation times and limited dispersal among discontinuous populations. Hawaii's hyper-diverse, landscape-dominant tree, Metrosideros, is unique among the islands' radiations for its massive populations that occur continuously over space and time within islands, its exceptional capacity for gene flow by both pollen and seed, and its extended life span (ca. >650 years). Metrosideros shows the greatest phenotypic and microsatellite DNA diversity on O`ahu, where taxa occur in tight sympatry or parapatry in mesic and montane wet forest on 2 volcanoes. We document the nonrandom distributions of 12 taxa (including unnamed morphotypes) along elevation gradients, measure phenotypes of ~6-year-old common-garden plants of 8 taxa to verify heritability of phenotypes, and examine genotypes of 476 wild adults at 9 microsatellite loci to compare the strengths of isolation across taxa, volcanoes, and distance. All 8 taxa retained their diagnostic phenotypes in the common garden. Populations were isolated by taxon to a range of degrees (pairwise FST between taxa: 0.004-0.267), and there was no pattern of isolation by distance or by elevation; however, significant isolation between volcanoes was observed within monotypic species, suggesting limited gene flow between volcanoes. Among the infraspecific taxa of Metrosideros polymorpha, genetic diversity and isolation significantly decreased and increased, respectively, with elevation. Overall, 5 of the 6 most isolated taxa were associated with highest elevations or otherwise extreme environments. These findings suggest a principal role for selection in the origin and maintenance of the exceptional diversity that occurs within continuous Metrosideros stands on O`ahu.

中文翻译：

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瓦胡岛 Metrosideros (ʻOhiʻa) 分类群的分离随着海拔和极端环境的增加而增加

物种辐射应该通过较短的世代时间和在不连续种群中的有限扩散来促进。夏威夷的高度多样化、占主导地位的树木 Metrosideros 在岛屿辐射中是独一无二的，因为它在岛屿内的空间和时间上不断出现大量种群，其通过花粉和种子进行基因流动的特殊能力以及延长的寿命（大约>650 年）。Metrosideros 在瓦胡岛显示出最大的表型和微卫星 DNA 多样性，其中的分类群出现在 2 座火山上的中生和山地潮湿森林的紧密交界处或副区系中。我们记录了 12 个分类群（包括未命名的形态型）沿海拔梯度的非随机分布，测量了 8 个分类群的~6 年生普通花园植物的表型，以验证表型的遗传性，并检查 9 个微卫星位点的 476 只野生成虫的基因型，以比较跨分类群、火山和距离的隔离强度。所有 8 个分类群都在公共花园中保留了它们的诊断表型。种群被分类群隔离到一定程度（分类群之间的成对 FST：0.004-0.267），并且没有按距离或海拔的隔离模式；然而，在单型物种中观察到火山之间的显着隔离，表明火山之间的基因流动有限。在 Metrosideros polymorpha 的种下分类群中，遗传多样性和隔离度分别随着海拔升高而显着降低和增加。总体而言，6 个最孤立的分类群中有 5 个与最高海拔或其他极端环境有关。