Department of Botany, University of Wisconsin-Madison, 53706, USA.
Am J Bot. 2012 Jan;99(1):152-64. doi: 10.3732/ajb.1100152. Epub 2011 Dec 20.
The American bulb-bearing Oxalis (Oxalidaceae) have diverse heterostylous breeding systems and are distributed in mountainous areas from Patagonia to the northeastern United States. To study the evolutionary processes leading to this diversity, we constructed the first molecular phylogeny for the American bulb-bearing Oxalis and used it to infer biogeographic history and breeding system evolution.
We used DNA sequence data (nuclear ribosomal internal transcribed spacer, trnL-trnL-trnF, trnT-trnL, and psbJ-petA) to infer phylogenetic history via parsimony, likelihood, and Bayesian analyses. We used Bayes Multistate to infer ancestral geographic distributions at well-supported nodes of the phylogeny. The Shimodaira-Hasegawa (SH) test distinguished among hypotheses of single or multiple transitions from South America to North America, and tristyly to distyly.
The American bulb-bearing Oxalis include sampled members of sections Ionoxalis and Pseudobulbosae and are derived from a larger clade that includes members of sections Palmatifoliae, Articulatae, and the African species. The American bulb-bearing Oxalis comprise two clades: one distributed in SE South America and the other in the Andes and North America. An SH test supports multiple dispersals to North America. Most sampled distylous species form a single clade, but at least two other independent distylous lineages are supported by the topologies and SH tests.
Phylogenetic results suggest the American bulb-bearing Oxalis originated in southern South America, dispersed repeatedly to North America, and had multiple transitions from tristyly to distyly. This study adds to our understanding of biogeographic history and breeding system evolution and provides a foundation for more precise inferences about the study group.
美洲含球菝葜属（菝葜科）具有多样化的异型花柱繁育系统，分布于从巴塔哥尼亚到美国东北部的山区。为了研究导致这种多样性的进化过程，我们构建了首个美洲含球菝葜属的分子系统发育，并利用它来推断生物地理历史和繁育系统进化。
我们使用 DNA 序列数据（核核糖体内转录间隔区、trnL-trnL-trnF、trnT-trnL 和 psbJ-petA）通过简约法、似然法和贝叶斯分析法推断系统发育历史。我们使用贝叶斯多态法推断系统发育树上支持度高的节点的祖先地理分布。Shimodaira-Hasegawa（SH）检验区分了从南美洲到北美洲的单一或多次跃迁假说，以及三型花柱到二型花柱的假说。
美洲含球菝葜属包括 Ionoxalis 和 Pseudobulbosae 两个节的样本成员，并且是从一个更大的分支中衍生而来的，这个分支包括 Palmatifoliae、Articulatae 以及非洲物种。美洲含球菝葜属包含两个分支：一个分布在南美洲东南部，另一个分布在安第斯山脉和北美洲。SH 检验支持多次向北美扩散。大多数取样的二型花柱物种形成一个单一的分支，但至少还有两个其他独立的二型花柱谱系得到了拓扑结构和 SH 检验的支持。
系统发育结果表明，美洲含球菝葜属起源于南美洲南部，多次向北美扩散，并且从三型花柱到二型花柱发生了多次转变。本研究增加了我们对生物地理历史和繁育系统进化的理解，并为更精确地推断研究群体提供了基础。
