Structure, development, and evolutive patterns of spermatozoa in rhabditid nematodes (Nematoda: Rhabditida)

Abstract

Spermatogenesis of five rhabditid nematodes was studied using transmission electron microscopy and is described herein. Structure and development of nematode sperm in all available representatives of the extensive order Rhabditida have been analysed and the main characteristics of each infraorder are discussed. The ancestral sperm of the order Rhabditida was reconstructed using maximum likelihood and Bayesian methods based on 44 ultrastructural sperm characters. The hypothetical ancestral spermatogenesis of the order Rhabditida agrees with the previously suggested "rhabditid" pattern and appears to be conserved throughout the order Rhabditida. Despite the enormous variation of rhabditid nematodes, few groups deviate from the ancestral pattern. This conserved pattern can be informative within the phylum Nematoda at order level, but poses limitations when used in taxonomic and phylogenetic analysis within Rhabditida.

Spermatozoa in the Demanian system of free-living marine nematode Admirandus multicavus (Enoplida: Oncholaimidae)

“…Data on sperm structure and spermatogenesis are known to be informative to elucidate phylogenetic relations of many metazoans (Baccetti, 1985;Jamieson et al, 1995;Liana, Witalinski, 2005;Reunov, 2005;Schmidt-Rhaesa, 2007;Dallai et al, 2016;Bakhoum et al, 2017). Spermatozoon morphology and development have also been studied for taxonomic and phylogenetic analyses of nematodes (Foor, 1970;Anya, 1976;Baccetti et al, 1983;Justine, 2002;Yushin, Malakhov, 2004;Slos et al, 2020).…”

“…In the classification of nematodes proposed by De Ley and Blaxter (2002) and adapted in this study, the phylum Nematoda is subdivided into the classes Enoplea and Chromadorea. The description of spermatozoon structure and development is usually applied to the extensive order Rhabditida and several other orders of the nematode class Chromadorea (Yushin, Malakhov, 2014;Slos et al, 2020). The class Enoplea includes two well defined subclasses Enoplia and Dorylaimia where the former includes the order Enoplida that shows unusual structural diversity of male gametes (Justine, Jamieson, 1999;Yushin, Malakhov, 1999Justine, 2002;Yushin, 2003;Afanasiev-Grigoriev, Yushin, 2009).…”