The incorporation of molecular data into current taxonomic practise has unravelled instances of incongruence among different data sets. Here we report a case of mitochondrial discordance in cobweb spiders of the genus Theridion Walckenaer, 1805 from the Iberian Peninsula. Morphological examination of samples from a country-wide bioinventory initiative revealed the existence of a putative new species and two nominal species belonging to the Theridion melanurum species group. The morphological delineation was supported by the molecular analysis of a nuclear marker but was at odds with the groups circumscribed by a mitochondrial marker. The causes of this discordance remained uncertain, once sample and sequencing errors and the existence of pseudogenes were discarded. The full sorting observed in the alleles of the more slowly evolving nuclear marker ruled out incomplete lineage sorting, while the geographic patterns recovered were difficult to reconciliate with ongoing hybridization. We propose that the apparent incongruence observed is most likely the result of old introgression events in a group with high dispersal abilities. We further speculate that endosymbiont-driven cytoplasmatic incompatibility could be involved in the fixation of mitochondrial haplotypes across species barriers. Additionally, we describe the new species T. promiscuum sp. nov., based on the presence of diagnostic morphological traits, backed up by the nuclear data delimitation. Our study contributes yet another example of the perils of relying on single methods or data sources to summarise the variation generated by multiple processes acting through thousands of years of evolution and supports the key role of biological inventories in improving our knowledge of invertebrate biodiversity.

中文翻译：

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密切相关的 Theridion 蜘蛛（Araneae，Theridiidae）的线粒体不一致，描述了 T. melanurum 组的一个新物种

将分子数据结合到当前的分类实践中，已经解决了不同数据集之间不一致的情况。在这里，我们报告了 1805 年来自伊比利亚半岛的 Theridion Walckenaer 属蜘蛛网蜘蛛线粒体不一致的案例。来自全国范围的生物清单计划的样本的形态学检查显示存在一个推定的新物种和两个属于 Theridion melanurum 物种组的名义物种。形态学划分得到了核标记的分子分析的支持，但与线粒体标记限定的组不一致。一旦排除了样本和测序错误以及假基因的存在，这种不一致的原因仍然不确定。在进化较慢的核标记的等位基因中观察到的完全排序排除了不完整的谱系排序，而恢复的地理模式很难与正在进行的杂交相协调。我们认为观察到的明显不一致很可能是具有高分散能力的组中旧的基因渗入事件的结果。我们进一步推测，内共生体驱动的细胞质不相容性可能与跨物种障碍的线粒体单倍型固定有关。此外，我们描述了新物种 T. promiscuum sp。11 月，基于诊断形态特征的存在，并得到核数据定界的支持。