Is the genus Digramma synonymous to the genus Ligula (Cestoda: Pseudophyllidea)?

Abstract

The genus Digramma (Cestoda: Pseudophyllidea) described by Cholodkovsky in 1915 differs from the genus Ligula only by the number of the reproductive organs per proglottis. However, the occurrence of transitional forms in Digramma raises much confusion concerning its generic validity. In the present study, cestodes previously designated as Digramma and Ligula were collected from lakes in the lower and middle reaches of the Yangtze River, and also from Qinghai Lake on Qingzang plateau, China. The entire internal transcribed spacer of the ribosomal DNA (ITS rDNA) and 5¢ end of 28S rDNA were compared between the Digramma and Ligula specimens. The low level of nucleotide variation between the two genera may imply that cestodes in the genus Digramma are paraphyletic to the Ligula genus, and Digramma is a synonym of Ligula. However, whether previously identified Digramma cestodes represent different species in the genus Ligula requires further investigation.The genus Digramma was erected by Cholodkovsky (1915) for Ligula alternans Rudolphi, 1810, an adult cestode of a gull Larus tridactylus in Europe. The only morphological difference considered to be of generic importance is the number of reproductive complexes per proglottis: one row of reproductive organs in Ligula, but two in Digramma. Although the reproductive organ is a relatively stable character, Wardle and Meleod (1952) speculated that Digramma was merely an uncommon diplogonadic morph of Ligula Bloch, 1782. Dubinina (1980) reported sexual dimorphism in Digramma. In bream (Abramis brama L.) they are found with reproductive organs in one row, whereas two rows occur in those from carp (Cyprinus carpio L.) and goldfish [Carassius auratus (L.)] over the entire length of the worm. In the same locality, Tai Hu lake on the lower and middle reaches of the Yangtze River, Liao and Liang (1987) found that plerocercoids in fish of the family Salangidae possess only a single row of reproductive complexes, but two regular rows are always present in those from Hemiculter and Acanthorhodeus. Thus, much confusion remains on the status of the genus Digramma. On the other hand, since the erection of the genus, the tapeworm has only been reported from cyprinid hosts in Russia and China (Dubinina 1980;Liao and Liang 1987). Studies on this cestode have been related to its geographical distribution and the pathological effect on its fish hosts (Evlanov and Kolokol'nikova 1990;Krylov et al. 1993), but little has been done on the redescription or validity of the genus. The objective of this study was to compare the phylogenetic differences in sequences of the entire internal transcribed spacer of the ribosomal DNA (ITS rDNA) and 5¢ end of 28S rDNA between Digramma and Ligula groups, and to determine whether the differences vary at the intergeneric and/or intra-and interspecific levels.Plerocercoids of Digramma and Ligula were collected from the body cavities of cyprinid fish from lakes on the lower and middle reaches of the Yangtze River in Hubei, Jiangxi provinces, China and also fro...

Historical dispersal and host-switching formed the evolutionary history of a globally distributed multi-host parasite – The Ligula intestinalis species complex

“…The taxonomy of Ligula tapeworms has always been complicated due to the general uniformity of their plerocercoids and adults (Dubinina, 1980), resulting in a lack of suitable morphological features to determine species boundaries using traditional methods, except for an already known trait, the duplicated reproductive complexes in L. alternans (Luo et al, 2003). Indeed, numerous species of Ligula have been proposed to accommodate plerocercoids from different fish hosts (see Dubinina, 1980 for their extensive list), but almost all these taxa have been synonymised with L. intestinalis.…”

Historical dispersal and host-switching formed the evolutionary history of a globally distributed multi-host parasite - theLigula intestinalisspecies complex

“…The taxonomy of Ligula tapeworms has always been complicated due to the general uniformity of their plerocercoids and adults (Dubinina, 1980), resulting in a lack of suitable morphological features to determine species boundaries using traditional methods, except for an already known trait, the duplicated reproductive complexes in L. alternans (Luo et al, 2003). Indeed, numerous species of Ligula have been proposed to accommodate plerocercoids from different fish hosts (see Dubinina, 1980 for their extensive list), but almost all these taxa have been synonymised with L. intestinalis .…”

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

“…Bykhovskaya-Pavlovskaya et al suggested that at least two genera ( Digramma and Ligula ) and five species, including L. intestinalis , are involved and that the plerocercoid of each species is restricted to a relatively narrow range of host species. However, Luo et al (2003) compared Digramma and Ligula specimens based on ITS and the 5’ end of 28S rDNA sequences and found that low level nucleotide variation between the two genera may imply that cestodes in the genus Digramma are paraphyletic to the Ligula genus, and that Digramma is a synonym of Ligula . To obtain definitive information regarding the taxonomy of Ligula plerocercoid obtained in this survey, we also analyzed the partial nucleotide sequence of mitochondrial Cox 1 and Cytb genes.…”