Sperm storage in birds and mammals: comparative evolutionary and physiological insights

Sperm storage is a crucial reproductive adaptation that ensures fertilization success by maintaining viable sperm until ovulation.Birds and mammals have evolved anatomically distinct yet functionally analogous structures, sperm storage tubules (SSTs) in the avian female reproductive tract and the epididymis in the mammalian male reproductive tract, that represent a striking example of convergent evolution.These systems prolong sperm lifespan and regulate fertilization timing through shared physiological strategies.While each system has been studied independently, a direct comparison between SSTs and the epididymis has not been thoroughly explored.This review proposes that, although structurally distinct, SSTs and the epididymis exhibit shared physiological strategies such as metabolic suppression, pH and ion regulation, oxidative stress control, and hormonally mediated sperm release.By highlighting these parallels, we present a novel perspective on sperm storage as a case of evolutionary convergence in reproductive physiology.Understanding these shared mechanisms provides new insights into sperm viability regulation and offers practical implications for assisted reproductive technologies (ARTs), such as improved cryopreservation strategies and biomimetic sperm storage platforms designed to mimic SST or epididymal conditions.