Department of Biology, Duke University, Durham, North Carolina 27708 USA;
Am J Bot. 2003 Apr;90(4):540-50. doi: 10.3732/ajb.90.4.540.
This study focused on three species that occur disjunctly between western North America and the Mediterranean region of southern Europe, northern Africa, and western Asia, forming the so-called Madrean-Tethyan distribution pattern. Quantitative morphological characters were measured in New and Old World plants to find any subtle phenotypic differentiation between the disjunct populations. Sequences from the nuclear ribosomal internal transcribed spacer region were obtained from the same populations to assess differentiation at the molecular level and to compare molecular diversity with patterns of morphological similarity among plants. Little or no morphological differentiation existed between New and Old World plants in any of the species, but internal transcribed spacer (ITS) sequences revealed some phylogeographic structure. Patterns of morphological similarity in all three species were incongruent with phylogeographic structure revealed by sequence data. New World populations were more variable than Old World populations at the molecular level in the three species. Despite some evidence for differentiation between disjunct plants, no plausible mutation rate would date the divergence at ≥20 million years ago (MYA), as implied by the Madrean-Tethyan hypothesis. Recent long-distance dispersal is a more likely explanation for intercontinental disjunctions in these species.
本研究集中于三个物种，它们在北美西部和地中海地区的南欧、北非和西亚之间呈不连续分布，形成了所谓的中美洲-地中海分布模式。对新旧世界的植物进行了定量形态特征测量，以发现不连续种群之间的任何细微表型分化。从同一群体中获得了核核糖体内转录间隔区的序列，以评估分子水平的分化，并将分子多样性与植物之间形态相似性模式进行比较。在任何一个物种中，新旧世界的植物之间几乎没有或没有形态分化，但内转录间隔区（ITS）序列揭示了一些系统地理学结构。在所有三个物种中，形态相似性模式与序列数据揭示的系统地理学结构不一致。在三个物种中，新的世界种群在分子水平上比旧的世界种群更具变异性。尽管有证据表明不连续的植物之间存在分化，但没有合理的突变率可以将其追溯到≥2000 万年前（MYA），正如中美洲-地中海假说所暗示的那样。最近的长距离扩散更可能解释这些物种的洲际间断。
