Kohn Joshua R, Graham Sean W, Morton Brian, Doyle Jeff J, Barrett Spencer C H
University of California at San Diego, Department of Biology, 9500 Gilman Drive, La Jolla, California, 92093-0116.
Department of Botany, University of Toronto, Toronto, Ontario, M5S 3B2, Canada.
Evolution. 1996 Aug;50(4):1454-1469. doi: 10.1111/j.1558-5646.1996.tb03919.x.
We reconstructed the phylogenetic history of Pontederiaceae using chloroplast DNA restriction-site variation from approximately two-thirds of the species in this family of aquatic monocotyledons. The molecular phylogeny was used to evaluate hypotheses concerning the evolution of reproductive characters associated with the breeding system. The family has four main genera, two of which (Eichhornia and Pontederia) have tristylous, predominantly outcrossing species, while two (Monochoria and Heteranthera) have enantiostylous taxa. Self-incompatibility is restricted to some but not all tristylous species. In Eichhornia and Pontederia, predominantly selfing species with small monomorphic flowers (homostyly) have been hypothesized to result from the multiple breakdown of tristyly. Restriction-site variation provided a well supported phylogeny of ingroup taxa, enabling the mapping of reproductive characters onto trees. Two contrasting optimization schemes were assessed, differing in the relative weights assigned to shifts in character states. The reconstructed sequence of floral character-state change was used to assess competing hypotheses concerning the origin and breakdown of tristyly, and the relationships between tristylous and enantiostylous syndromes. Our results indicate that the class of optimization scheme used was the most critical factor in reconstructing character evolution. Despite some topological uncertainties and difficulty in reconstructing the primitive floral form in the family, several broad conclusions were possible when an unordered, unequally-weighted optimization scheme was used: (1) tristyly originated either once or twice, while the occurrence of enantiostyly in Monochoria and Heteranthera was always found to have independent origins; (2) tristyly has repeatedly broken down leading to selfing, homostylous taxa; and (3) self-incompatibility probably arose after the origin of floral trimorphism, a sequence of events that conflicts with some evolutionary models.
我们利用水生单子叶植物这一科中约三分之二物种的叶绿体DNA限制性位点变异，重建了雨久花科的系统发育史。分子系统发育被用于评估与繁殖系统相关的生殖特征进化的假说。该科有四个主要属，其中两个属（凤眼莲属和梭鱼草属）具有三型花柱，主要为异交物种，而另外两个属（雨久花属和异蕊花属）具有对花柱类群。自交不亲和仅限于部分而非全部三型花柱物种。在凤眼莲属和梭鱼草属中，具有小型单态花（同型花柱）的主要自交物种被认为是由三型花柱的多次崩溃导致的。限制性位点变异为类群内分类单元提供了一个得到充分支持的系统发育，从而能够将生殖特征映射到树上。评估了两种截然不同的优化方案，它们在赋予特征状态变化的相对权重上有所不同。重建的花特征状态变化序列被用于评估关于三型花柱的起源和崩溃以及三型花柱和对花柱综合征之间关系的相互竞争的假说。我们的结果表明，所使用的优化方案类别是重建特征进化的最关键因素。尽管在重建该科原始花形态时存在一些拓扑不确定性和困难，但当使用无序、不等加权的优化方案时，仍有可能得出几个广泛的结论：（1）三型花柱要么起源一次，要么起源两次，而雨久花属和异蕊花属中对花柱的出现总是独立起源；（2）三型花柱多次崩溃导致自交、同型花柱类群；（3）自交不亲和可能在花三态性起源之后出现，这一系列事件与一些进化模型相冲突。
