Abstract
BackgroundDeep 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.ResultsA 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.ConclusionWe 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.
Highlights
Deep mitochondrial divergences were observed in Scandinavian populations of the terrestrial to semi-aquatic annelid Fridericia magna (Clitellata: Enchytraeidae)
During large-scale surveys of Clitellata in Scandinavia involving Deoxyribonucleic acid (DNA) barcoding (Erséus et al, ongoing work), we found deep divergence in the mitochondrial marker Cytochrome c Oxidase subunit I (COI) in the terrestrial worm, Fridericia magna Friend, 1899 [23], suggesting that this taxon is a species complex
The habitats are of Specimens, DNA extraction and assembly For all 62 specimens COI was obtained, 16S ribosomal DNA (16S) and H3 were successfully sequenced for 44 specimens, Internal Transcribed Spacer region (ITS) was successfully sequenced for 42 specimens
Summary
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. During large-scale surveys of Clitellata in Scandinavia involving DNA barcoding (Erséus et al, ongoing work), we found deep divergence in the mitochondrial marker Cytochrome c Oxidase subunit I (COI) in the terrestrial worm, Fridericia magna Friend, 1899 [23] (family Enchytraeidae), suggesting that this taxon is a species complex. The species is mainly found in moist mineral soils, rich in organic material, and near rivers and lakes [26]
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