Data from: Male sperm storage compromises sperm motility in guppies.

Sperm senescence can have important evolutionary implications due to its deleterious effects on sperm quality and offspring performance. Consequently, it has been argued that polyandry (female multiple mating) may facilitate the selection of younger, and therefore competitively superior, sperm when ejaculates from multiple males compete for fertilisation. Surprisingly, however, unequivocal evidence that sperm ageing influences traits that underlie sperm competitiveness is lacking. Here, we used a paired experimental design that compares sperm quality between experimentally ‘old’ and ‘young’ ejaculates from individual male guppies (Poecilia reticulata). We show that older sperm exhibit significant reductions in sperm velocity compared to younger sperm from the same males. We found no evidence that the brightness of the male’s orange (carotenoid) spots, which are thought to signal resistance to oxidative stress (and thus age-related declines in sperm fitness), signals a male’s ability to withstand the deleterious effects of sperm ageing. Instead, polyandry may be a more effective strategy for females to minimise the likelihood of being fertilised by aged sperm.