The Taxonomic Position and Phylogenetic Relationship between Digramma interrupta and Ligula intestinalis Based on Morphological and Molecular Diagnosis

Background: The position of Digramma interrupta remains disputable as it was raised by Cholodkovsky from Ligula alternans. This study aimed to survey the evolutionary relationships and the taxonomic position of D. interrupta and L. intestinalis. It also intended to support or reject the validity of D. interrupt as an independent genus and its correlation with L. intestinalis on the basis of their morphological characiteristics and a study on molecular data. Methods: Overall, 1301 fish varieties, including 883 Alburnoides bipunctatus and 418 Abramis brama, were collected from north and north-western parts of Iran. A. bipunctatus samples were obtained from fresh water sources of the Maragheh dam (northwest) and the Ramesar Lake (north). Moreover, samples of A. brama were captured from the Aras Dam (northwest) and the Bandar-e-Anzali lagoon (north) PCR was used to generate a fragment spanning two independent ITS-inclusive parts: ITS1-5.8S and ITS2 with two pairs of primers. Results: Nucleotide variation between L. intestinalis and D. interrupta samples amounts to about 3% to 7%. Between samples of L. intestinalis and GenBank data, and also between D. interrupta specimens and GenBank data, the diversity was seen for about 1% to 3%. Moreover, about 1% to 4% nucleotide variation was seen only in L. intestinalis samples caught from the same host, which could be supplementary to the presence of a species and/or strains in this genus. Conclusion: Maybe D. interrupta was just a rare diplogonadic form of the Ligula species, not a different genus and not synonymous with the Ligula genus, but only another species of the Ligula genus.