Reproductive seasonality drives structural and functional shifts in spermatozoa of the Neotropical rattlesnake Crotalus durissus (Squamata: Viperidae).

In brief: Reproductive seasonality in snakes reflects evolutionarily conserved adaptive mechanisms that sustain sperm function despite seasonal environmental fluctuations. This study demonstrates structural and ultrastructural modifications in Crotalus durissus spermatozoa, providing novel insights into the mechanisms of sperm maintenance and their potential applications in reptile reproductive biotechnology. AbstractReproductive seasonality in snakes can result in dissociation between spermatogenesis and mating, making long-term sperm storage essential. Despite seasonal testicular regression in Crotalus durissus, spermatozoa persist in the distal segment of the ductus deferens year-round. This study evaluated structural and functional changes in sperm associated with this reproductive pattern. We analyzed 40 adult males with active (n = 21) or regressed (n = 19) testes. Morphological, morphometric, and ultrastructural assessments were performed, along with evaluations of motility, vitality, concentration, and viability after short-term cold storage. Sperm from males with regressed testes (autumn and winter) exhibited significantly longer heads and acrosomes, suggesting structural changes during storage. While total motility did not differ significantly between groups, sperm vitality was significantly higher in males with active testes (spring and summer). Additionally, sperm from both groups remained viable after 7 days of cold storage (2-8 °C), although motility declined over time. These findings suggest that the distal segment of the ductus deferens plays a role in sperm maintenance and potentially in sperm maturation. The extended viability of spermatozoa outside the active reproductive phase highlights key physiological adaptations and supports potential applications in reptile reproductive management and conservation.