Sperm morphology and some aspects of acrosomal complex development in four species of Heteronemertea (Pilidiophora, Nemertea)

Yurchenko, Olga V.; Chеrnyshev, Alexei V.

doi:10.1016/j.jcz.2022.05.005

Zoologischer Anzeiger

2022

DOI: 10.1016/j.jcz.2022.05.005

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Sperm morphology and some aspects of acrosomal complex development in four species of Heteronemertea (Pilidiophora, Nemertea)

Olga V. Yurchenko

Alexei V. Chеrnyshev

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2024

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Cited by 2 publications

References 40 publications

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Spermatozoa and Spermatogenesis in the Ribbon Worm Asteronemertes gibsoni (Hoplonemertea, Oerstediidae), a Symbiont of Sea Stars

Yurchenko,

Chernyshev

2024

Journal of Morphology

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In the phylum Nemertea, the class Hoplonemertea (former Enopla) comprises the largest number of studied species with complex spermatozoa. Asteronemertes gibsoni Chernyshev, 1991, a nemertean species having a symbiotic relationship with sea stars, is characterized by complex filiform spermatozoa. Here, spermatogenesis and spermatozoon structure in A. gibsoni have been examined using light and electron microscopy. Numerous proacrosomal vesicles of two kinds have been found in early spermatogenic cells. In spermatozoa, the elongated acrosomal complex consists of two components: a core, which is a spindle‐shaped electron‐dense acrosomal vesicle with a long anterior end, and its casing of moderate electron density that covers the acrosomal vesicle completely. The acrosomal complex is located laterally relative to the elongated nucleus. The acrosomal casing bears two rows of small, short channels between the nucleus and the electron‐dense acrosomal core. In late spermatids, the elongations of the acrosomal complex and the nucleus occur simultaneously and are mediated by numerous microtubules that disappear during the latest stages of spermiogenesis. The flagellum in spermatogenic cells and spermatozoa contains an axoneme with the usual 9 × 2 + 2 microtubular organization and is posteriorly oriented in spermatozoa. As known to date, A. gibsoni has the most modified spermatozoa among investigated Nemertea, and the complex structure of its sperm is suggested to be associated with the reproductive biology, in particular, with fertilization. Additionally, a number of similar ultrastructural features in spermatozoon organization have been found in A. gibsoni and Kurilonemertes phyllospadicola whose phylogenetic relationship was previously proven.

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Spermatozoa and Spermatogenesis in the Ribbon Worm Asteronemertes gibsoni (Hoplonemertea, Oerstediidae), a Symbiont of Sea Stars

Yurchenko,

Chernyshev

2024

Journal of Morphology

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Ultrastructure and phylogenetic significance of spermatozoa in Nemertea

Bartolomaeus,

Bronkars,

Adam

et al. 2024

Zoomorphology

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Sperm ultrastructure is frequently employed as a source for phylogenetic inference due to the ease of accessing spermatozoa. Despite being unicellular, sperm cells exhibit a relatively high number of diverse characters and character states. Spermatozoa are subject to strong sexual selection as they are finely tuned for maximizing male reproductive success. Given this strong functional constraint, one might anticipate the emergence of convergent characters in line with similar modes of reproduction. As a result, it might be expected that sperm cells do not possess substantial phylogenetic signal, with functional constraints overshadowing any evolutionary heritage. To test this assumption, we conducted a study on sperm ultrastructure in 11 nemertean species, representing closely related groups and major nemertean lineages. We analyzed these data for their phylogenetic signal within the context of the most recent nemertean phylogenies. Our findings demonstrate that, at all systematic levels, functional constraints imposed by sexual selection, or the mode of reproduction do not supersede the influence of historical constraints on sperm ultrastructure.

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Sperm morphology and some aspects of acrosomal complex development in four species of Heteronemertea (Pilidiophora, Nemertea)

Cited by 2 publications

References 40 publications

Spermatozoa and Spermatogenesis in the Ribbon Worm Asteronemertes gibsoni (Hoplonemertea, Oerstediidae), a Symbiont of Sea Stars

Spermatozoa and Spermatogenesis in the Ribbon Worm Asteronemertes gibsoni (Hoplonemertea, Oerstediidae), a Symbiont of Sea Stars

Ultrastructure and phylogenetic significance of spermatozoa in Nemertea

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