Morphology of the male reproductive tract in the water scavenger beetle <i>Tropisternus collaris</i> Fabricius, 1775 (Coleoptera: Hydrophilidae)

Members of the Hydrophilidae, one of the largest families of aquatic insects, are potential models for the biomonitoring of freshwater habitats and global climate change. In this study, we describe the morphology of the male reproductive tract in the water scavenger beetle Tropisternus collaris. The reproductive tract in sexually mature males comprised a pair of testes, each with at least 30 follicles, vasa efferentia, vasa deferentia, seminal vesicles, two pairs of accessory glands (a bean-shaped pair and a tubular pair with a forked end), and an ejaculatory duct. Characters such as the number of testicular follicles and accessory glands, as well as their shape, origin, and type of secretion, differ between Coleoptera taxa and have potential to help elucidate reproductive strategies and the evolutionary history of the group.

Keywords:
Accessory glands; Hydrophilid; Polyphaga; Reproductive system

Authorship

Vinícius Albano Araújo ^**Corresponding author.E-mail:vialbano@gmail.com (V.A. Araújo).

Universidade Federal do Rio de Janeiro, Instituto de Biodiversidade e Sustentabilidade (NUPEM), Macaé, RJ, Brasil.Universidade Federal do Rio de JaneiroBrasilMacaé, RJ, BrasilUniversidade Federal do Rio de Janeiro, Instituto de Biodiversidade e Sustentabilidade (NUPEM), Macaé, RJ, Brasil.

https://orcid.org/0000-0001-9387-7378

Igor Luiz Araújo Munhoz

Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil.Universidade Federal de Minas GeraisBrasilBelo Horizonte, MG, BrasilUniversidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil.

José Eduardo Serrão

Universidade Federal de Viçosa, Departamento de Biologia Geral, Viçosa, MG, Brasil.Universidade Federal de ViçosaBrasilViçosa, MG, BrasilUniversidade Federal de Viçosa, Departamento de Biologia Geral, Viçosa, MG, Brasil.

https://orcid.org/0000-0002-0477-4252

*Corresponding author.E-mail:vialbano@gmail.com (V.A. Araújo).

Associate Editor: Marcela Monné

Conflicts of interest The authors declare no conflict of interest.

VAA and ILAM conceived the research, dissections, photographs and the reproductive morphology work. ILAM realized illustrations and VAA the preparation of plates. VAA and JES improved the introduction, results and discussion of the document. All authors participated in the final redaction and critically reviewed the manuscript and accepted the final version of the paper.

SCIMAGO INSTITUTIONS RANKINGS

Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil.Universidade Federal de Minas GeraisBrasilBelo Horizonte, MG, BrasilUniversidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil.

Figures

Figures (5)

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Figure 1
Anatomy of the male reproductive tract of T. collaris. (A) Photograph of the anatomy of the male reproductive tract showing the testes (T), vasa deferentia (dd), seminal vesicles (sv), tubular accessory glands (ag), bean-shaped accessory glands (pg), and ejaculatory duct (ej). (B) Schematic drawing of the reproductive tract showing the position and direction of histological sections presented in Figures 2 –5. Bars: 0.4 cm.

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Figure 2
Histology of the male reproductive tract of T. collaris. (A) Longitudinal section of a testis showing the follicles (f); growth (a), maturation (b), and differentiation (c) zones; and vas efferens (ve) opening (arrow) into a vas deferens (vd) with lumen full of spermatozoa (asterisk). (B) Longitudinal section showing detail of the vasa efferentia (ve) in the confluence zone (black arrow) with the vas deferens (vd). The white arrow points to sperm bundles in the vas efferens. The asterisk indicates the lumen of a vas deferens with dissociated bundles. The arrowhead points to the epithelial of the vas deferens. (C and D) Details of the stages of spermatogenesis, showing zones of cell growth (a), maturation (b), and differentiation (c). The arrow points to a sperm bundle. Bars: A and B = 600 µm, C and D = 200 µm.

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Figure 3
Histology of the male reproductive tract of T. collaris. (A and B) Cross section of the glandular region showing the tubular accessory gland (ag1) and bean-shaped gland (ag2). The arrowhead indicates the epithelial folds, and the arrows point to the region of the secretory epithelium. Note the secretion accumulated in the lumen of the bean-shaped gland (asterisk). (C and D) Cross section of a seminal vesicle (sv) with simple epithelium (arrow), and lumen full of spermatozoa (asterisk). In (D) detail of the epithelium (ep) and the external muscular layer (m). Bars: A = 200 µm, B and C = 100 µm, D = 25 µm.

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Figure 4
Histology of the male reproductive tract of T. collaris. (A and B) Longitudinal section of the glandular region showing a tubular gland (ag1) with lumen full of secretion (black asterisk). The arrowhead points to the nucleus of the epithelium, and the black arrows to the opening of the common duct into the bean-shaped gland (ag2) in a region that precedes the ejaculatory duct (ej). Note the multilobed secretion (white arrow), lumen with secretion (white asterisk), and muscle layer (m) of the bean-shaped gland (ag2). (C) Cross section of the apical portion of the tubular gland showing apocrine secretion (dashed circle) and secretion granules in the lumen (asterisk). Longitudinal section of the ejaculatory duct (ej) showing the lumen (asterisk), simple cuboidal epithelium (arrow), and thick muscle layer (m). Bars: A = 200 µm, B = 150 µm, and C = 100 µm.

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Figure 5
Histology of the male reproductive tract of T. collaris. (A) Cross section of the confluence region of spermatic ducts and glands showing the presence of secretion (arrowhead) and spermatozoa (asterisk). (B) Cross and (C) longitudinal sections of the ejaculatory duct, indicating the cuboidal epithelium with basal nuclei (arrowhead), cuticle (arrowhead), and thick muscle layer (a = circular muscles, b = longitudinal muscles). Bars: A and B = 200 µm, C = 400 µm.

Figure 1 Anatomy of the male reproductive tract of T. collaris. (A) Photograph of the anatomy of the male reproductive tract showing the testes (T), vasa deferentia (dd), seminal vesicles (sv), tubular accessory glands (ag), bean-shaped accessory glands (pg), and ejaculatory duct (ej). (B) Schematic drawing of the reproductive tract showing the position and direction of histological sections presented in Figures 2 –5. Bars: 0.4 cm.

Figure 2 Histology of the male reproductive tract of T. collaris. (A) Longitudinal section of a testis showing the follicles (f); growth (a), maturation (b), and differentiation (c) zones; and vas efferens (ve) opening (arrow) into a vas deferens (vd) with lumen full of spermatozoa (asterisk). (B) Longitudinal section showing detail of the vasa efferentia (ve) in the confluence zone (black arrow) with the vas deferens (vd). The white arrow points to sperm bundles in the vas efferens. The asterisk indicates the lumen of a vas deferens with dissociated bundles. The arrowhead points to the epithelial of the vas deferens. (C and D) Details of the stages of spermatogenesis, showing zones of cell growth (a), maturation (b), and differentiation (c). The arrow points to a sperm bundle. Bars: A and B = 600 µm, C and D = 200 µm.

Figure 3 Histology of the male reproductive tract of T. collaris. (A and B) Cross section of the glandular region showing the tubular accessory gland (ag1) and bean-shaped gland (ag2). The arrowhead indicates the epithelial folds, and the arrows point to the region of the secretory epithelium. Note the secretion accumulated in the lumen of the bean-shaped gland (asterisk). (C and D) Cross section of a seminal vesicle (sv) with simple epithelium (arrow), and lumen full of spermatozoa (asterisk). In (D) detail of the epithelium (ep) and the external muscular layer (m). Bars: A = 200 µm, B and C = 100 µm, D = 25 µm.

Figure 4 Histology of the male reproductive tract of T. collaris. (A and B) Longitudinal section of the glandular region showing a tubular gland (ag1) with lumen full of secretion (black asterisk). The arrowhead points to the nucleus of the epithelium, and the black arrows to the opening of the common duct into the bean-shaped gland (ag2) in a region that precedes the ejaculatory duct (ej). Note the multilobed secretion (white arrow), lumen with secretion (white asterisk), and muscle layer (m) of the bean-shaped gland (ag2). (C) Cross section of the apical portion of the tubular gland showing apocrine secretion (dashed circle) and secretion granules in the lumen (asterisk). Longitudinal section of the ejaculatory duct (ej) showing the lumen (asterisk), simple cuboidal epithelium (arrow), and thick muscle layer (m). Bars: A = 200 µm, B = 150 µm, and C = 100 µm.

Figure 5 Histology of the male reproductive tract of T. collaris. (A) Cross section of the confluence region of spermatic ducts and glands showing the presence of secretion (arrowhead) and spermatozoa (asterisk). (B) Cross and (C) longitudinal sections of the ejaculatory duct, indicating the cuboidal epithelium with basal nuclei (arrowhead), cuticle (arrowhead), and thick muscle layer (a = circular muscles, b = longitudinal muscles). Bars: A and B = 200 µm, C = 400 µm.

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Morphology of the male reproductive tract in the water scavenger beetle <i>Tropisternus collaris</i> Fabricius, 1775 (Coleoptera: Hydrophilidae)

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[1] *Corresponding author.E-mail:vialbano@gmail.com (V.A. Araújo).