Data from: ‘Fix me another marguerite!’: species delimitation in a group of intensively hybridising lineages of ox-eye daisies (Leucanthemum Mill., Compositae-Anthemideae)

Delineating species boundaries in the framework of the multi-species coalescent (MSC) proves to be a reliable, objective, and reproducible method in an increasing number of studies. However, the underlying model assumes the lack of gene flow after speciation; an assumption which may be frequently violated in plant evolution. The present study evaluates the robustness of currently available species delimitation methods implemented in BEAST (BFD, BFD, and DISSECT) in the closely-knit ox-eye daisy group around Leucanthemum ageratifolium Pau. Comprising five taxa being allopatrically distributed between northern Spain and southern Italy this study group shows signs of hybridisation with the widespread and co-distributed species Leucanthemum vulgare (Vaill.) Lam. to various extent. As expected, our empirical analyses based on both AFLP fingerprinting and sequence data demonstrate that the robustness of species delimitation results is considerably influenced by the intensity of hybridisation among species and the number of hybrid individuals included. Therefore, we set up a methodological pipeline with a first step of identification and subsequent removal of individuals showing admixed genetic patterns caused by actual interbreeding using AFLP-fingerprint and morphometric data, followed by application of different Bayesian MSC species delimitation methods based on the remnant individuals using both AFLP-fingerprint and sequence data (four nuclear markers, five concatenated intergenic spacer regions of the plastid genome). The results argue for acknowledgement of Leucanthemum laciniatum, L. legraeanum, and L. ligusticum as independent species, show the close relationship of L. ageratifolium, L. monspeliense, and L. vulgare, and give rise to the description of three nothospecies new to science.在多物种溯祖（multi-species coalescent, MSC）框架下划定物种边界，在日益增多的研究中被证实为一种可靠、客观且可重复的方法。然而，该基础模型假设物种形成后不存在基因流——这一假设在植物演化过程中可能频繁被违背。本研究针对以Leucanthemum ageratifolium Pau为核心的紧密聚类滨菊类群，评估了当前在BEAST软件中实现的现有物种界定方法（含BFD、BFD及DISSECT）的稳健性。该研究类群包含5个分类单元，呈西班牙北部至意大利南部的异域分布格局，且与广布且同域分布的Leucanthemum vulgare (Vaill.) Lam.存在不同程度的杂交迹象。正如预期，我们基于扩增片段长度多态性（amplified fragment length polymorphism, AFLP）指纹图谱与序列数据开展的实证分析显示，物种界定结果的稳健性在很大程度上受物种间杂交强度及纳入分析的杂交个体数量影响。为此，我们搭建了一套标准化分析流程：首先利用AFLP指纹图谱与形态计量数据，鉴定并移除因实际种间杂交产生遗传混合模式的个体；随后基于剩余个体，同时利用AFLP指纹图谱与序列数据（4个核基因标记、5个拼接的质体基因组基因间隔区），应用多种贝叶斯MSC物种界定方法。研究结果支持将Leucanthemum laciniatum、L. legraeanum及L. ligusticum认定为独立物种，证实了L. ageratifolium、L. monspeliense与L. vulgare之间的近缘关系，并确立了3个科学新杂种物种。