Morphophysiological dynamics of the proximal post‐testicular ducts in Crotalus durissus Linnaeus, 1758 (Squamata: Viperidae)

The organization and function of reptilian excurrent ducts remain poorly characterized, particularly in Neotropical snakes. We provide the first integrative morphological, histochemical, immunohistochemical, and ultrastructural analysis of the proximal post-testicular ducts of Crotalus durissus across reproductive stages. Using light, transmission electron, and confocal laser microscopy, we examined the rete testis, ductuli efferentes, ductuli epididymides, and ductus epididymis of adult males. The proximal post-testicular ducts are contained within the epididymal sheath alongside the adrenal gland. No anatomical regionalization was identified along the epididymis. The ductuli efferentes exhibited cuboidal epithelium with stereocilia-like projections, while the ductuli epididymides displayed simple columnar epithelium with abundant periodic acid-Schiff (PAS) and Bromophenol Blue (BB) positive secretory granules. The ductus epididymis consisted of pseudostratified epithelium with principal, basal, and clear cells. Confocal analyses revealed wheat germ agglutinin (WGA) in principal cells of the ductus epididymis and Concanavalin A (ConA) positive secretory granules in ductuli epididymides. Aquaporin-9 immunolabeling was detected in the epithelium of the ductus epididymis and ductuli efferentes, suggesting a role in luminal fluid regulation. Ultrastructural observations of the ductus epididymis revealed extensive rough endoplasmic reticulum, Golgi complexes, microvilli, and phagolysosomes in principal cells, supporting secretory, absorptive, and phagocytic functions. Seasonal variation was evident, with snakes in testicular activity exhibiting hypertrophy of all components analyzed. Collectively, our findings indicate that these ducts of C. durissus are functionally specialized for secretion and absorption, rather than sperm storage, thereby contributing to the establishment and regulation of a luminal microenvironment essential for sperm maturation in this seasonally reproducing viperid.