The Taxonomic Status of Digramma (Pseudophyllidea: Ligulidae) Inferred From Dna Sequences

Abstract

The traditional classification of the ligulid tapeworms into 2 genera, Ligula Bloch, 1782 and Digramma Cholodkovsky, 1914, remains controversial. Molecular data of sequences for the 5' end of the nuclear 28S ribosomal ribonucleic acid (rRNA) gene, the mitochondrial cytochrome c oxidase subunit I (COI) gene, and the nicotinamide adenine dinucleotide dehydrogenase subunit 1 (ND1) gene, as well as the first internal transcribed spacer (ITS1) of the nuclear ribosomal deoxyribonucleic acid (DNA), were used to characterize Digramma and to investigate its relationship with Ligula. Digramma spp. exhibited identical sequences with Ligula intestinalis both in the 28S rRNA and the COI gene and differed from L. intestinalis by 0.7% in the ITS1 region and 7.4% in the ND1 gene, respectively. A high degree of genetic conservation within 28S ribosomal DNA, COI, ITS1, and even ND1 genes, was found in Ligula and Digramma. The low genetic divergence in the 4 genes between Ligula and Digramma indicates that Digramma is probably not an independent genus. Therefore, it is proposed that Ligula and Digramma should be considered as 2 species within the genus Ligula and the tapeworms of Digramma collected from diverse localities in China belong to the same species. The present study also suggests that ITS1 and ND1 sequences can act as useful genetic markers to distinguish Ligula and Digramma.

Genetic diversity ofLigula intestinalis(Cestoda: Diphyllobothriidea) based on analysis of inter-simple sequence repeat markers

“…samples from roach from France formed the same cluster with samples from Czech Republic). A possible explanation, which was also suggested for Digramma (a sister genus of Ligula) (Li and Liao 2003), for this low genetic variability is the migration of the definitive hosts of Ligula (e.g. Larus ridibundus, Ardea cinerea and Phalacrocorax carbo).…”

“…Indeed, recent studies support such a view by the recovery of genetically distinct plerocercoid isolates (Olson et al. 2002; Li and Liao 2003; Logan et al. 2004).…”

“…Given the extensive host and geographic ranges of this parasite, distinct strains⁄species are supposed to exist. Indeed, recent studies support such a view by the recovery of genetically distinct plerocercoid isolates (Olson et al 2002;Li and Liao 2003;Logan et al 2004). For instance, Olson et al (2002) used the entire ITS region and the partial ribosomal 28S and found reliable genetic differences of Ligula populations between two sympatric fish hosts, namely roach (R. rutilus) and the gudgeon (Gobio gobio Linnaeus, 1758) in Northern Ireland.…”

Integrating molecular and morphological approaches for characterizing parasite cryptic species: implications for parasitology

“…2000; Desdevises et al . 2000; Bell and Summerville, 2002; Li and Liao, 2003). This documentation of parasite phenotypic plasticity (e.g.…”

Infection status with plerocercoid of ligulid tapeworm in cyprinid fish from three lakes in Republic of Korea

“…These organisms are flat, unsegmented and have a tapering anterior end with two bothridia pleurocercoids from different host fish that vary in size from 10 – 100 cm in length, and 3 – 1.2 cm in width (Hajirostamloo, 2009). Recently, genetic analysis has been employed to distinguish Ligula species (Lee et al, 2000; Li and Liao, 2003; Bouzid, 2008). Since Ligula intestinalis represents a complex of cryptic/sibling species, it is difficult to distinguish.…”