An Ultrastructural Investigation of Spermiogenesis and Sperm Structure in Asian Warty Newt (Paramesotriton chinensis)

Background: The Asian warty newt is a rare amphibian species endemic to China and is listed as a second-class national protected wild animal. This study observes the spermiogenesis and sperm ultrastructure of the Asian warty newt and explores the relationship between structure and function, elucidating the male reproductive biology of this rare amphibian at the cellular and molecular levels. Methods: The collected samples were fixed in 2.5% glutaraldehyde and stored at 4°C. The corresponding electron microscope samples were prepared respectively. The spermiogenesis and ultrastructure changes of spermatids were observed by transmission electron microscopy (TEM) and the morphology and structure of sperms were studied by scanning electron microscopy (SEM). Result: During spermiogenesis, the morphology and structure of spermatids undergo significant changes, ultimately forming mature sperm with highly condensed chromatin, an elongated nucleus and structures such as the acrosome and tail. The sperm ultrastructure of the Asian warty newt is divided into the head, neck and tail: the head is slender with an acrosome hook; the neck is short and not prominent; and the tail is divided into the middle piece, principal piece and end piece. The study found that certain structural features of the sperm are related to its fertilization method and reproductive habits and its morphological structure shares some common characteristics with the sperm of the Salamandridae family.