Research paperSpermatozoa morphology of the giant water bug Belostoma anurum (Herrich-Schäffer, 1848) (Heteroptera: Belostomatidae)
Introduction
Hemiptera has more than 100,000 described species with monophyly strongly supported by both morphological and molecular characters (Misof et al. 2014). However, phylogenetic relationships within the group are still discussed (Cryan & Urban, 2012).
The order is composed of three main clades: Sternorrhyncha, Auchenorrhyncha, and Heteropteroidea (Kristensen, 1975; Hennig, 1981), the last including Coleorrhyncha + Heteroptera (Kristensen, 1975). Heteroptera has seven infraorders: Enicocephalomorpha, Dipsocoromorpha, Gerromorpha, Nepomorpha, Leptopodomorpha, Pentatomomorpha and Cimicomorpha (Wheeler et al. 1993). In Nepomorpha, Belostomatidae has 11 genera and approximately 150 species (Estévez & Ribeiro, 2011; Moreira et al. 2011). Among the Belostomatidae, representatives of Belostoma are predators (Ohba et al. 2006; Ouyang et al. 2017; Ohba, 2019). These giant water bugs are natural enemies of insects of medical importance including the mosquitoes Culex quinquefasciatus Say, 1823 and Aedes aegypti (Linnaeus, 1762) (Valbon et al. 2019), vectors of filariasis, yellow fever, dengue fever, chikungunya and zika diseases.
The morphology of insect spermatozoa provides important characters for the systematic of some orders (see Jamieson et al., 1999; Birkhead et al. 2009; Dallai et al. 2016). The spermatozoa structure has been suggested to be conserved in Heteroptera, with some synapomorphies, such as the presence of two opposite bridges in the axoneme connecting the mitochondrial derivatives that have matrix rich in paracrystalline content, and the absence of accessory bodies throughout the flagellum (Dallai et al. 2016). However, the diversity of spermatozoa characters is important to understand the phylogenetic relationships in Heteroptera.
Intraspecific variations may occur in the spermatozoa morphology if insects (Hudgson, 1999) resulting in sperm polymorphism, which is characterized by different germ cell types, including their sizes and organelles (Jamieson et al. 1999).
This study describes the spermatozoa morphology of Belostoma anurum (Herrich-Schäeffer, 1848) (Nepomorpha: Belostomatidae), contributing to new data that can be useful in the future systematic studies of these important aquatic insects.
Section snippets
Material and methods
Adult males of B. anurum were obtained from a pond in the Federal University of Viçosa (20° 45′ S 42° 52′ W, 648 m asl), Viçosa, state of Minas Gerais, Brazil. Five insects were used for light microscopy and five for transmission electron microscopy.
Results
B. anurum has one spermatozoa morphotype, which are stored without sperm aggregation in the seminal vesicle. These germ cells measured 514.29 ± 9.35 (502.73–533.31) μm in length, including 35 ± 1.07 (34.88–38.55) μm of the nucleus (Fig. 1A and B).
The head of the spermatozoa is formed by a small acrosome that has a subacrosomal space and the nucleus. The acrosome has ca. 4.5 μm in length being 1.8 μm in the head apex and 1.5 μm in the region closely to the nucleus where they overlap (Fig. 1C–E).
Discussion
The absence of spermatozoa polymorphism in B. anurum has been also reported in other Heteroptera (Araújo et al. 2011; Dias et al. 2016; Novais et al. 2017; Santos & Lino-Neto, 2018; Munhoz et al., 2020), except in some representatives of Pentatomidae (Bowen, 1922; Schrader & Leuchtenberger, 1950; Araújo et al. 2011), Largidae (Araújo et al. 2012), and in the Auchenorrhynca Cicadidae (Kubo-Irie et al. 2003; Chawanji et al. 2005, 2006).
Individualized spermatozoa without bundles in the seminal
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors thank the Núcleo de Microscopia e Microanálise - UFV for technical assistance. This research was supported by CAPES (finance code 001), FAPEMIG (grants 00508-16) and CNPq (grants 155741/2018-7).
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