Systematics and Biodiversity, Department of Biological and Environmental Sciences, University of Gothenburg, Box 463, SE-405 30, Göteborg, Sweden.
BMC Evol Biol. 2020 Sep 14;20(1):116. doi: 10.1186/s12862-020-01678-5.
Deep mitochondrial divergences were observed in Scandinavian populations of the terrestrial to semi-aquatic annelid Fridericia magna (Clitellata: Enchytraeidae). This raised the need for testing whether the taxon is a single species or a complex of cryptic species.
A total of 62 specimens from 38 localities were included in the study, 44 of which were used for species delimitation. First, the 44 specimens were divided into clusters using ABGD (Automatic Barcode Gap Discovery) on two datasets, consisting of sequences of the mitochondrial markers COI and 16S. For each dataset, the worms were divided into six not completely congruent clusters. When they were combined, a maximum of seven clusters, or species hypotheses, were obtained, and the seven clusters were used as input in downstream analyses. We tested these hypotheses by constructing haplowebs for two nuclear markers, H3 and ITS, and in both haplowebs the specimens appeared as a single species. Multi-locus species delimitation analyses performed with the Bayesian BPP program also mainly supported a single species. Furthermore, no apparent morphological differences were found between the clusters. Two of the clusters were partially separated from each other and the other clusters, but not strongly enough to consider them as separate species. All 62 specimens were used to visualise the Scandinavian distribution, of the species, and to compare with published COI data from other Fridericia species.
We show that the morphospecies Fridericia magna is a single species, harbouring several distinct mitochondrial clusters. There is partial genetic separation between some of them, which may be interpreted as incipient speciation. The study shows the importance of rigorous species delimitation using several independent markers when deep mitochondrial divergences might give the false impression of cryptic speciation.
在斯堪的纳维亚地区的陆生和半水生环节动物 Fridericia magna（Clitellata：Enchytraeidae）种群中观察到了深刻的线粒体分歧。这就需要检验该分类单元是否是单一物种还是隐藏物种的复合体。
本研究共包括 38 个地点的 62 个标本，其中 44 个标本用于物种划定。首先，使用 ABGD（自动条码间隙发现）在两个数据集上将 44 个标本分为聚类，这两个数据集由线粒体标记 COI 和 16S 的序列组成。对于每个数据集，将蠕虫分为六个不完全一致的聚类。当它们合并时，最多可以获得七个聚类，或物种假设，并且将这七个聚类作为下游分析的输入。我们通过构建两个核标记 H3 和 ITS 的 haplowebs 来测试这些假设，在两个 haplowebs 中，标本都表现为一个单一的物种。使用贝叶斯 BPP 程序进行的多基因座物种划定分析也主要支持一个单一的物种。此外，在聚类之间没有发现明显的形态差异。两个聚类部分彼此分开，其他聚类也是如此，但没有强到足以将它们视为单独的物种。所有 62 个标本都用于可视化该物种在斯堪的纳维亚地区的分布，并与其他 Fridericia 物种的已发表的 COI 数据进行比较。
我们表明，形态物种 Fridericia magna 是一个单一的物种，拥有几个不同的线粒体聚类。它们中的一些之间存在部分遗传分离，这可以解释为初步的物种形成。该研究表明，在可能出现隐藏物种的情况下，使用几个独立的标记进行严格的物种划定的重要性。
