Spermatological characters of the digenean Rubenstrema exasperatum (Rudolphi, 1819) (Plagiorchioidea, Omphalometridae)

Abstract

We present the first ultrastructural description of spermiogenesis and of the spermatozoon of Rubenstrema exasperatum (Omphalometridae), an intestinal parasite of Sorex araneus (Soricidae). Spermiogenesis begins with the formation of the differentiation zone delimited at the base by the ring of the arched membranes and bordered by cortical microtubules. This area contains two centrioles associated with striated rootlets and with an intercentriolar body. It also contains the nucleus and numerous mitochondria. The intercentriolar body is made up of seven electron-dense layers. The two centrioles give rise to two free flagella that grow orthogonally to the median cytoplasmic process. Additionally, flagellar rotation is followed by the proximodistal fusion of the flagella with the median cytoplasmic process, while the nucleus and mitochondria migrate along the spermatid. The constriction of the ring of arched membranes gives rise to the young spermatozoon. The mature spermatozoon of R. exasperatum shows several ultrastructural characters found in digenean spermatozoa such as two axonemes, mitochondrion, two bundles of parallel cortical microtubules, nucleus, and granules of glycogen. External ornamentation of the plasma membrane and spinelike bodies are also present in the spermatozoon of this species. In the present study, we produced additional spermatological data concerning a previously unexplored family, and we also compare our data to the existent ultrastructural descriptions within the Digenea in order to assess the use of several characters proposed as phylogenetic tools.

Spermiogenesis and ultrastructure of the spermatozoon of Wardula capitellata (Digenea, Mesometridae), an intestinal parasite of the sparid teleost Sarpa salpa in Senegal

“…Moreover, in several sections during the final stages of spermiogenesis, the mitochondrion is observed in migration. Contrarily, a mitochondrial migration before nuclear migration has been reported in the spermiogenesis of Dicrocoelium dendriticum (Cifrian et al 1993), Postorchigenes gymnesicus (Gracenea et al 1997) and R. exasperatum (Bakhoum et al 2011b).…”

“…In this anterior extremity there are two lateral expansions with external ornamentation and the centrioles are surrounded by a continuous layer of cortical microtubules. Two slightly longitudinally shifted axonemes have been reported for example, in H. medioplexus (Justine and Mattei 1982), Metorchis orientalis (Liu and Pan 1990), Echinostoma caproni (Iomini and Justine 1997), Nicolla testiobliquum (Quilichini et al 2007c) or R. exasperatum (Bakhoum et al 2011b). However, the particularity of W. capitellata sperm is the presence of two lateral expansions at centriolar level.…”

“…Other digeneans exhibit two mitochondria, one being located at the level of the ornamented region and the other in the area containing the nucleus. This is the case of the opecoelids P. furcatum, N. wisniewskii, N. testiobliquum (Levron et al 2004b;Quilichini et al 2007a, c), the dicrocoeliid D. hospes (Agostini et al 2005), the troglotrematid T. acutum (Miquel et al 2006), the apocreadiid N. chabaudi (Kacem et al 2010) or the omphalometrid R. exasperatum (Bakhoum et al 2011b). Additionally, a spermatozoon with three mitochondria has recently been described in B. ectorchus, S. sudanensis, A. capitellatum and E. squamula (Ashour et al 2007, Bakhoum et al 2009, Ternengo et al 2009).…”

“…In some digeneans with several mitochondria, the external ornamentation is observed in the area containing the first mitochondrion (see Agostini et al 2005, Miquel et al 2006or Bakhoum et al 2011b.…”

Ultrastructural characters of the spermatozoon of the digenean Hypocreadium caputvadum Kacem et al., 2011 (Lepocreadioidea: Lepocreadiidae), an intestinal parasite of Balistes capriscus in Tunisia

“…On the other hand, taking into account several incongruences in the described posterior sperm types, several authors discussed the consideration of only the terminal character [37] instead of the sequence of characters towards the posterior spermatozoon tip. With respect to the remaining Lepocreadioidea, all the studied species exhibit the second axoneme as terminal character except R. fractum (Gyliauchenidae), which presents a nucleus extremity in the posterior spermatozoon tip [24].…”