UBC Botanical Garden & Centre for Plant Research, and Department of Botany, 6270 University Boulevard, University of British Columbia, Vancouver, BC, Canada.
Am J Bot. 2012 Apr;99(4):663-76. doi: 10.3732/ajb.1100524. Epub 2012 Apr 2.
Species relationships are unknown in Hydatellaceae, a small family of dwarf aquatics related to water lilies that arose near the base of angiosperm phylogeny. Here we use molecular evidence to infer a species tree for the family and apply this to reconstructing major transitions in morphology and sexual system in this early branch of angiosperms.
We assembled plastid (atpB, matK, ndhF, rbcL) and nuclear (ribosomal ITS) data for 50 samples (including outgroups) and estimated a species tree for Hydatellaceae using a Bayesian multispecies coalescent approach. We reconstructed the evolution of several morphological characters, then tested for associations between sexual system and reproductive morphology using phylogenetic ANOVA.
Dioecious species of Hydatellaceae have significantly greater stamen number and anther length than do cosexual species, suggesting changes in male function. The perennial habit that defines one subclade likely represents a reversion from annuality. Species relationships do not fall along traditional morphological divisions, but new sections proposed here are supported by fruit and seed synapomorphies. The earliest split in the family is reflected in geography and climate (i.e., tropical vs. subtropical/temperate clades). We found limited evidence of incongruence between plastid and nuclear trees, with one exception involving gene-tree nonmonophyly for two close relatives (Trithuria submersa, T. bibracteata).
While the direction of sexual-system evolution is ambiguous, transitions are significantly associated with changes in involucral phyllome length and proxies of pollen production. We propose a new sectional circumscription based on fruit, seed, and DNA evidence.
Hydatellaceae 是一个小型水生植物家族，与睡莲有关，睡莲起源于被子植物系统发育的基部。该家族的物种关系尚不清楚。本研究利用分子证据推断该科的物种树，并将其应用于重建该早期被子植物分支的形态和性系统的主要转变。
我们为 50 个样本（包括外群）组装了质体（atpB、matK、ndhF、rbcL）和核（核糖体 ITS）数据，并使用贝叶斯多物种合并方法估计了 Hydatellaceae 的物种树。我们重建了几个形态特征的进化，然后使用系统发育方差分析检验性系统与生殖形态之间的关联。
Hydatellaceae 的雌雄异株物种的雄蕊数量和花药长度明显大于雌雄同株物种，表明雄性功能发生了变化。定义一个亚科的多年生习性可能代表了从一年生向多年生的回归。物种关系不沿传统的形态学划分，但这里提出的新节段得到了果实和种子同源特征的支持。该科最早的分支反映在地理和气候上（即热带与亚热带/温带分支）。我们发现质体和核树之间的不一致证据有限，只有一个例外涉及两个近亲（Trithuria submersa、T. bibracteata）的基因树非单系性。
虽然性系统进化的方向尚不清楚，但转变与总苞片长度和花粉产量替代物的变化显著相关。我们根据果实、种子和 DNA 证据提出了一个新的分类学范围。
