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）框架下划定物种界限，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，该模型的基础假设为物种形成后不存在基因流，而这一假设在植物演化过程中往往难以满足。本研究针对围绕短毛滨菊（Leucanthemum ageratifolium Pau）的近缘滨菊类群，评估了BEAST软件中集成的现有物种界定方法（BFD、BFD与DISSECT）的稳健性。该类群包含5个分类单元，在西班牙北部至意大利南部呈异地分布格局，且与广布且同域分布的普通滨菊（Leucanthemum vulgare (Vaill.) Lam.）存在不同程度的杂交迹象。
正如预期，本研究基于扩增片段长度多态性（Amplified Fragment Length Polymorphism, AFLP）指纹与序列数据开展的实证分析显示，物种界定结果的稳健性显著受物种间杂交强度及纳入分析的杂交个体数量影响。因此，我们构建了一套方法学分析流程：首先利用AFLP指纹与形态计量数据，识别并剔除因真实种间杂交产生遗传混合模式的个体；随后针对剩余个体，同时基于AFLP指纹与序列数据（4个核标记、5个拼接的质体基因组（plastid genome）基因间隔区），应用多种贝叶斯多物种溯祖（Bayesian MSC）物种界定方法。
研究结果支持将裂叶滨菊（Leucanthemum laciniatum）、莱格兰滨菊（Leucanthemum legraeanum）与利古里亚滨菊（Leucanthemum ligusticum）认定为独立物种，显示短毛滨菊、蒙彼利埃滨菊（Leucanthemum monspeliense）与普通滨菊之间亲缘关系密切，并首次描述了3个科学新杂种分类群（nothospecies）。