Spermatological characters of the digenean Lecithostaphylus retroflexus (Molin, 1859) (Microphalloidea: Zoogonidae), a parasite of the teleost fish Belone belone gracilis
Introduction
The family Zoogonidae includes digenean species mainly parasitizing marine fish. According to a recent review (Bray and Justine, 2014), this family contains 33 genera with a total of 159 species. Its placement as a microphalloidean has been demonstrated in several molecular analyses. The Microphalloidea includes two major clades. Three families are placed in the first clade (Pachypsolidae, Renicolidae and Eucotylidae). The Zoogonidae that was found closely related and probably paraphyletic to the Faustudidae is placed in the second clade. Thus, the second clade includes the Zoogonidae + Faustulidae as the most basal taxon with other taxa (Lecithodendriidae, Microphallidae, Pleurogenidae and Prosthogonimidae) as progressively more derived (see Olson et al., 2003, Bray and Justine, 2014).
In this context, the ultrastructural studies of species belonging to the Zoogonidae family are of great importance to bring additional information that complements the molecular results. The ultrastructural study of the mature spermatozoon provides numerous characters, which are useful for phylogenetic inference in parasitic Platyhelminthes (Justine, 1991, Justine, 1995, Levron et al., 2010, Quilichini et al., 2010, Quilichini et al., 2011).
Digenean trematodes have been the subject of numerous ultrastructural studies on spermatology. In fact, to our knowledge there are ultrastructural data of the spermatozoon for more than 75 species distributed among 45 families (Ndiaye et al., 2014). With respect to the Zoogonidae family and to the best of our knowledge, there is only one ultrastructural study on the sperm of Diphterostomum brusinae (Levron et al., 2004a).
The aim of the present study is to produce the first complete description of the ultrastructure of the spermatozoon of Lecithostaphylus retroflexus (Molin, 1859), contributing to the ultrastructural database concerning the Digenea. Our results were also compared with the available data on digenean spermatology, in particular, with those species belonging to the Microphalloidea superfamily in order to select the possible criteria useful for phylogeny.
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Materials and methods
Specimens of L. retroflexus (Molin, 1859) were collected from the digestive tract of Belone belone gracilis (Teleostei, Belonidae) caught from the Gulf of Gabès off Chebba (34°14′N, 11°06′E) (Tunisia).
The worms were isolated from their host. They were fixed in cold (4 °C) 2.5% glutaraldehyde in a 0.1 M sodium cacodylate buffer at pH 7.4 for a minimum of 2 h, rinsed in a 0.1 M sodium cacodylate buffer at pH 7.4. They were then postfixed in cold (4 °C) 1% osmium tetroxide (OsO4) with 0.9% potassium
Results
The observation of numerous ultrathin sections in the seminal vesicle of L. retroflexus allows the distinction of three different regions, I, II and III, from the anterior to the posterior spermatozoon extremities, considering the presence of different ultrastructural characteristics (Fig. 1, Fig. 2, Fig. 3, Fig. 4). The mature spermatozoon of L. retroflexus exhibits the usual structures found in numerous digeneans. Indeed, it contains two axonemes of the 9 + ‘1′ trepaxonematan pattern, external
Discussion
The mature spermatozoon of L. retroflexus shows the usual pattern described previously in the male gamete of digeneans so far: two axonemes of the 9 + ‘1′ pattern of trepaxonematan Platyhelminthes (Ehlers, 1984), nucleus, mitochondria, granules of glycogen, external ornamentation and two sets of parallel cortical microtubules. Additional aspects include the presence of spine-like bodies in the ornamented area of the sperm cell and the continuous distribution of cortical microtubules in the
Acknowledgements
The authors wish to thank the staff of the “Centres Científics i Tecnològics” of the University of Barcelona (CCTiUB) for their assistance. The study was partly supported by AECID (A/023585/09) and AGAUR (2014 SGR 1241).
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The Opecoelidae sperm model and its contribution to phylogeny: Spermatozoon ultrastructural particularities of Allopodocotyle pedicellata (Plagioporinae, Digenea, Platyhelminthes)
2017, Zoologischer AnzeigerCitation Excerpt :Among the digenean spermatozoa two other morphologies of the posterior spermatozoon extremity have been described. For example, digenean mature spermatozoa containing nucleus as the posterior character were reported in the Fasciolidae (Ndiaye et al., 2003b, 2004), Fellodistomidae (Kacem et al., 2015a), Mesometridae (Bakhoum et al., 2012, 2013a,b), Pronocephalidae (Ndiaye et al., 2011, 2012b) or Zoogonidae (Levron et al., 2004b; Kacem et al., 2015b), as well as in the recent study of the opecoelid P. magnatestis (Diagne et al., 2016). On the other hand, the presence of one axoneme was identified as the posterior character in the male gamete of species belonging to the Allocreadiidae (Quilichini et al., 2007c), Collyriclidae (Bakhoum et al., 2014), Pleurogenidae (Bruňanská et al., 2014; Miquel et al., 2013) or the Sclerodistomidae (Ndiaye et al., 2013b).