The Sperm Structure and Spermatogenesis of Trypophloeus klimeschi (Coleoptera: Curculionidae: Scolytinae)

Abstract

The male reproductive system, sperm structure, and spermatogenesis of Trypophloeusklimeschi (Coleoptera: Curculionidae: Scolytinae), which is one of the most destructive pests of Populus alba var. pyramidalis (Bunge), were investigated using light microscopy, scanning electron microscopy, and transmission electron microscopy. The male reproductive system of T.klimeschi is composed of testes, seminal vesicles, tubular accessory glands, multilobulated accessory glands, vasa deferentia, and a common ejaculatory duct. In spermatogenesis, two phenomena are apparent: The nuclear chromatin condenses into two different patterns, and an oval preacrosomal vesicle is present at the flank of the Golgi apparatus. The sperm are short, measuring 76.7 ± 1.8 μm in length, and are 508.1 ± 12.9 nm in width. The sperm are composed of a three-layer acrosomal complex, a cylindrical nucleus, two mitochondrial derivatives, a 9 + 9 + 2 axoneme, and two accessory bodies with a large "puff"-like expansion. Mature sperm are individually stored in seminal vesicles. During spermiogenesis, the similarities in the nuclear chromatin condensation characteristics of Curculioninae and Scolytinae are indicative of their close phylogenetic relationship. It appears that the preacrosomal vesicle being flanked by the Golgi apparatus is a characteristic of spermatogenesis in Curculionidae.

Keywords: Trypophloeus klimeschi (Coleoptera: Curculionidae: Scolytinae); male reproductive system; sperm ultrastructure; spermatogenesis.

Figure 1

The male reproductive system of T. klimeschi: (A) The male reproductive system on the 16th day after eclosion. (B) On the first day after eclosion, the seminal vesicles are only thin tubules (white arrow). (C) The cross section of the testis showing many cysts (CY). Testis (T); seminal vesicle (SV); tubular accessory gland (TAG); multilobulated accessory gland (MAG); vas deferens (VD); ejaculatory duct (EJ).

Figure 2

The spermatogenesis of T. klimeschi: (A) spermatogonia cyst; (B) spermatogonia; (C) primary spermatocytes; (D) secondary spermatocytes; (E) centrioles in spermatocytes; (F) spermatids. Cyst cell nucleus (CCN); centrioles (C); heterochromatin (H); mitochondria (M); Golgi apparatus (G); lysosomes (L); nucleus (N); synaptonemal complexes (SC); fusing mitochondria (black arrow).

Figure 3

Spermiogenesis of T. klimeschi: (A) The axoneme starts elongating from the concavity of nucleus. (B) Mitochondrial derivatives are located on both sides of the axoneme and parallel to the axoneme. (C) Spermatid at initial stage of differentiation showing that the preacrosomal vesicle is near to the nebenkern and Golgi apparatus. (D,E) In the early spermatid (nebenkern becomes two mitochondrial derivatives), the preacrosomal vesicle and axoneme are near to the Golgi apparatus (D) and nucleus (E). The preacrosomal vesicle has a dark-stained mantle and light core (E). (F) The preacrosomal vesicle under high magnification and its membrane structure (white arrow). (G) As the nucleus elongates, the preacrosomal vesicle becomes flat. (H) The spermatid components are surrounded by microtubules (black arrow). The bell-shaped nucleus with different chromatin aggregation states: homogeneously compact chromatin and fibrillar chromatin. The cross section of the axoneme under high magnification (white arrow). (I) The centriolar adjunct appears in the spermatid stage. Nucleus (N); axoneme (AX); preacrosomal vesicle (PAV); nebenkern (NE); Golgi apparatus (G); dark-stained mantle (DM); light core (LC); homogeneously compact chromatin (HCC); fibrillar chromatin (FC); mitochondrial derivatives (MD); centriolar adjunct (CA); basal body (BB).

Figure 4

Changes of mitochondria during spermiogenesis of T. klimeschi: (A) Mitochondria (M) gathered together; (B–F) changing mitochondria (black arrow). Nucleus (N).

Figure 5

SEM and TEM micrographs of T. klimeschi spermatozoa: (A) The appearance of spermatozoa; (B) Detailed view of spermatozoa; (C) TEM micrograph of spermatozoa in seminal vesicles. The black, round, and short strips are the sperm nuclei. Axoneme (AX); large mitochondrial derivative (LMD); small mitochondrial derivative (SMD).

Figure 6

The spermatozoa structure of T. klimeschi: (A,B) The longitudinal and cross sections of 3-layered acrosome complex. (C,D) The longitudinal and cross sections showing the junction of the nucleus and flagellar components. (E) The mitochondrial cristae (black arrow). (F) Cross section of the middle of the spermatozoa. (G) Cross section showing the disorganized axoneme (black arrow) at the end of the spermatozoa. Extra acrosomal layer (E); acrosomal vesicle (A); perforatorium (P); nucleus (N); basal lamina (BL); axoneme (AX); large mitochondrial derivative (LMD); small mitochondrial derivative (SMD); crescent accessory body (CAB); basal body (BB); small accessory body (SAB); puff-like expansion (PF).