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Abstract
In this study, the sperm ultrastructure of three species of Idarnes genus was investigated using light and transmission electron microscopy. Spermatozoon morphology of the three species was similar to that of most Chalcidoidea, with helicoidally twisted nucleus and flagellum. The head region consists of an acrosome and a nucleus; the nucleus-flagellum transition region characterized by the presence of mitochondrial derivatives and the centriolar adjunct; a flagellum region, which includes the axoneme with microtubular arrangement 9 + 9 + 2 and two mitochondrial derivatives. However, the sperm of these three species exhibit features that discriminate one species from each other: (1) only one species, Idarnes sp. 2 (carme group) exhibited an extracellular sheath surrounding the anterior portion of the nucleus, which extends to the anterior region of the flagellum, but it did not present filaments; (2) the acrosome in the three species was quite different, Idarnes sp. 1 and Idarnes sp. 2 (carme group) has two compartments (acrosomal and subacrosomal vesicles) while Idarnes sp. 3 (flavicollis group) has a third compartment (perforatorium); (3) the centriolar adjunct elongated and its location among the mitochondrial derivatives is similar for the three species analyzed; (4) mitochondrial derivatives differ between the species, with triangular (Idarnes sp. 1 and sp. 3) and elongated or flat shaped (Idarnes sp. 2) appearance. These data shows that sperm structure may differ within the same genus and confirms the potential of these cells in phylogenetic and taxonomic analyses in the Chalcidoidea superfamily, as well as in Hymenoptera in general.
Highlights
Idarnes is the second most common genus within the subfamily Sycophaginae, with 23 described species for the Americas (Bouček, 1993; Farache et al, 2017)
Male specimens of the three species (Idarnes sp. 1, Idarnes sp. 2—both belonging to carme group; and Idarnes sp. 3— flavicollis group) were collected at the University of São Paulo (USP) campus located in the city of Ribeirão Preto (São Paulo, Brazil) during the months of April 2008 and January, June, August, and September of 2009
Sperm cells are divided into three regions: the anterior region, which corresponds to the head, where the nucleus and the acrosome are found; the nucleus-flagellum transition presenting the centriolar adjunct and mitochondrial derivatives; and the posterior, corresponding to the flagellum, which in turn is composed of the axoneme, with a 9 + 9 + 2 microtubular arrangement, and a pair of mitochondrial derivatives (Fig. 1)
Summary
Idarnes is the second most common genus within the subfamily Sycophaginae, with 23 described species for the Americas (Bouček, 1993; Farache et al, 2017). The genus Idarnes is subdivided into three species-groups (incertus, flavicollis and carme) and considered monophyletic (Cruaud et al, 2011a; Cruaud et al, 2011b). The spermatozoon morphology of Idarnes wasps was first described by Pereira et al (2008) using light microscopy. The ultrastructural investigation of spermatozoa is widely accepted as a feasible approach by which to better comprehend and resolve the phylogeny and taxonomy of insects. Spermatozoa are commonly understood as holders of a species-specific set of features (Jamieson, 1987, Dallai et al, 2011; Gottardo et al, 2012)
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