Formation of sperm bundles in Pterostichus nigrita (Coleoptera: Carabidae)

Abstract

The formation and structure of sperm bundles (spermiozeugmata), and the structure of the vas deferens where bundles are formed, in Pterostichus nigrita is described by light and electron microscopy. The spermiozeugmata are of the sheet-like type consisting of a central rod (about 3 mm long) of electron-dense material (the spermatostyle), to which two bundles of spermatozoa (about 95 per bundle) are attached. The spermatostyle has a spoon-shaped head, and the rod material is differentiated into an electron-dense core and a more electron-lucent cortex. Spermatozoa (about 340 µm long) are attached to the anterior portion of the rod only. Spermiozeugma formation occurs in the upper vas deferens (before the seminal vesicle region) with the secretion of rod material by epithelial cells, which are characterized by well developed rough endoplasmic reticulum with distended cisternae, abundant mitochondria and Golgi bodies. Some cells contain numerous myeloid structures thought to be precursors of rod material, and coated vesicles. During spermiozeugma development, the heads of spermatozoa become embedded in the developing rod material, the anterior of which sits in one of the many diverticula of the mid-region of the vas deferens. Elongation of the rod proceeds by addition of material posteriorly.