Luminal composition and maturation of spermatozoa in the male genital ducts of the Port Jackson shark, Heterodontus portusjacksoni

Abstract

AbstractThe functions of the epididymis of H. portusjacksoni were studied to assess the significance of its structural differentiation and to provide a basis for assessing the evolution of the vertebrate epididymis. It was shown that posttesticular sperm maturation occurs within the epididymis. The maturation process involves the development of the capacity for motility, and the formation of sperm bundles. However, the process does not involve ultrastructural changes. Micropuncture studies of the epididymal luminal fluids showed that in the region where sperm mature the ducts absorb most of the extracellular fluid leaving the testis, and secrete a denser proteinaceous fluid. Determinations of sodium and potassium showed that there is a barrier to the free movement of these ions between blood and the lumen of the genital ducts. The ratio of sodium:potassium was high (36.6:1) in the ductuli efferentes, but reduced to a ratio of 3.4:1 at the distal end of the epididymis. The epididymal fluids contain membrane‐bound, cytoplasmic bodies 3–4 μm in diameter which form a separate layer from spermatozoa during centrifugation. The bodies contain mitochondria, ribosomes, endoplasmic reticulum, lipid droplets, and a lower concentration of sodium than the surrounding fluid. It is concluded that the epididymis in the shark carries out some of the main functions of the mammalian epididymis.