Sperm storage causes sperm senescence in human and non-human animals

In animals, mature sperm are stored in males before ejaculation, and sometimes in females before fertilisation. Sperm storage provides evolutionary advantages; however, storage can also cause sperm deterioration due to post-meiotic sperm ageing. Yet, the extent of such deterioration, the mechanisms driving it, and its consequences remain poorly understood. We perform a meta-analysis across humans (115 studies) and non-human animals (56 studies, 30 species) to understand the impacts of sperm storage. In men, storage via sexual abstinence increases sperm oxidative stress and DNA damage, reduces sperm viability and motility. In other animals, sperm storage in males and females reduces sperm performance and embryo quality. The duration of storage, the method of sampling individuals, and the sperm-storing sex also impact observed outcomes. The results have implications for fertility clinics, sperm selection, captive breeding, and understanding adaptations evolved to mitigate stored-sperm deterioration.