Testing species hypotheses for Fridericia magna, an enchytraeid worm (Annelida: Clitellata) with great mitochondrial variation

Abstract

Background 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. Results 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. Conclusion 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.

How complex is the Naineris setosa species complex? First integrative study of a presumed cosmopolitan and invasive annelid (Sedentaria: Orbiniidae)

“…For 16S, the interspecific distances ranged from 0 to 6%, which was considerably lower than in other species complexes of polychaetes (Drennan et al 2019;Radashevsky et al 2020). Still, they were comparable with those in Clitellata (Martinsson et al 2020). All Atlantic specimens shared the same haplotype in 16S, which could be explained by the low evolutionary rates in 16S in the Naineris setosa complex and possible recent speciation events between the two Atlantic species.…”