Dobes C H, Mitchell-Olds T, Koch M A
Institute of Botany, University of Natural Resources and Applied Life Sciences Vienna, Gregor-Mendel-Strasse 33, A-1180 Vienna, Austria.
Mol Ecol. 2004 Feb;13(2):349-70. doi: 10.1046/j.1365-294x.2003.02064.x.
Arabis drummondii, A. holboellii and their hybrid A. x divaricarpa are widespread perennials of open habitats in North America. A phylogenetic analysis based on noncoding chloroplast DNA sequences (trnL intron and trnL/F intergenic spacer) resolved A. drummondii as a monophyletic taxon, but found A. holboellii to bear chloroplast haplotypes from highly diverged evolutionary lineages. This raised the question of a possible polyphyletic origin of A. holboellii. Arabis x divaricarpa was found to be of recent and polytopic origin, a result consistent with its presumed hybrid origin. One hundred and three chloroplast haplotypes were detected within 719 Arabis accessions investigated. The majority of chloroplast-types were estimated to have arisen prior to the Wisconsin glaciation. Phylogeographical analysis using nested clade analysis, suggested for A. holboellii (i). past fragmentation events, partitioning genetic variation in several instances between the Sierra Nevada, the Southern Rocky Mountains and the Colorado Plateau on the one hand and the Central to Northern Rockies of the United States and adjacent Cascades on the other; and for both parental species (ii). recolonization of major areas formerly covered by the Wisconsin glaciation by three haplotypes; and (iii). restricted gene flow indicating isolation by distance in areas south of the last glacial maximum. Arabis x divaricarpa is closely codistributed with its parental species and resampled their haplotypes. The highest genetic diversity was found in the Rocky Mountains from Idaho and Montana south to Utah and Colorado. This area was further hypothesized to have played a major role in the origin of both parental species and probably represented an important glacial refugium. However, evidence for glacial refugia was also found in arctic and boreal regions of Alaska and near the Great Lakes. In comparison to nuclear ribosomal internal transcribed spacer data, chloroplast DNA divergence was very high and evidently predated the origin of A. drummondii and possibly A. holboellii. Divergence of major chloroplast lineages dates back to the middle of the Pleistocene at least. Extensive hybridization is the most likely evolutionary factor working on A. holboellii to explain the revealed discrepancy in nuclear DNA and chloroplast DNA diversification.
德拉蒙德南芥、霍尔博尔南芥及其杂交种叉状南芥是北美开阔生境中广泛分布的多年生植物。基于非编码叶绿体DNA序列（trnL内含子和trnL/F基因间隔区）的系统发育分析将德拉蒙德南芥解析为一个单系类群，但发现霍尔博尔南芥带有来自高度分化进化谱系的叶绿体单倍型。这就引发了霍尔博尔南芥可能具有多系起源的问题。叉状南芥被发现是近期多源起源的，这一结果与其假定的杂交起源相符。在所研究的719份南芥材料中检测到了103种叶绿体单倍型。大多数叶绿体类型估计在威斯康星冰川期之前就已出现。使用嵌套分支分析的系统地理学分析表明，对于霍尔博尔南芥：（i）过去的片段化事件，在几种情况下将遗传变异一方面在内华达山脉、南落基山脉和科罗拉多高原之间，另一方面在美国中部到北部落基山脉及相邻的喀斯喀特山脉之间进行了划分；对于两个亲本物种：（ii）由三种单倍型对以前被威斯康星冰川覆盖的主要区域进行了重新定殖；以及（iii）有限的基因流表明在末次盛冰期以南的区域存在距离隔离。叉状南芥与其亲本物种紧密同域分布，并重新采样了它们的单倍型。在从爱达荷州和蒙大拿州向南到犹他州和科罗拉多州的落基山脉中发现了最高的遗传多样性。该区域进一步被推测在两个亲本物种的起源中发挥了主要作用，并且可能代表了一个重要的冰川避难所。然而，在阿拉斯加的北极和北方地区以及五大湖附近也发现了冰川避难所的证据。与核糖体DNA内转录间隔区数据相比，叶绿体DNA分歧非常高，显然早于德拉蒙德南芥的起源，甚至可能早于霍尔博尔南芥的起源。主要叶绿体谱系的分歧至少可追溯到更新世中期。广泛的杂交是作用于霍尔博尔南芥的最可能的进化因素，以解释所揭示的核DNA和叶绿体DNA多样化方面的差异。
