Sperm characteristics in the yellow-spotted mountain newt, Neurergus derjugini (Salamandridae) through light and electron microscopy

Amphibians exhibit a wide range of sperm morphologies due to their diverse habitats and reproductive strategies. This study provides the first comprehensive morphological and ultrastructural analysis of the spermatozoon and spermatophore in the yellow-spotted mountain newt ( Neurergus derjugini ). After collecting sperm samples, we used Giemsa, Eosin 5%, and Diff-Quick stains for morphological examination, and electron microscopy for ultrastructural analysis. The results revealed that N. derjugini sperm have a relatively long head, a midpiece, and a tail with a wavy membrane; however, the end of the tail is short and lacks a membrane. The sperm head comprises distinct structures such as an acrosome, acrosomal barb, perforatorium, nucleus, and nuclear ridge. The tail is surrounded by a wavy membrane and contains an axoneme connected to an axial fibre by an undulating membrane with a half-moon-shaped marginal strand. The axial fibre’s shape changes from horseshoe-shaped near the head to crescentic distally. Additionally, the spermatophore is characterized by a conical cap of spermatozoa on a short stalk. The study highlights the adaptive diversity in sperm structure and function, influenced by reproductive strategies, mating systems, and environmental conditions. Understanding these characteristics is crucial for insights into fertilization and potential reproductive barriers. The findings also lay the groundwork for future research on related newt species, offering valuable insights into their evolutionary and phylogenetic relationships.