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 fertilization. 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 ‘old’ and ‘young’ ejaculates from individual male guppies (Poecilia reticulata). We show that older sperm exhibit significant reductions in sperm velocity compared with 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 minimize the likelihood of being fertilized by aged sperm.精子衰老可通过损害精子质量与后代表现产生重要进化意义。据此，有观点提出：当多雄性射精竞争受精时，一妻多夫制（polyandry，即雌性多次交配）可促进对更年轻、因而竞争优势更强的精子的选择。然而令人意外的是，目前仍缺乏确凿证据表明精子衰老会影响支撑精子竞争力的相关性状。本研究采用配对实验设计，比较了单个雄性孔雀鱼（Poecilia reticulata）的"衰老精液"与"年轻精液"的精子质量差异。结果显示，与同一雄性的年轻精子相比，衰老精子的运动速度显著降低。我们未发现雄性的橙色类胡萝卜素（carotenoid）斑点亮度可指示其抵御精子衰老有害影响的能力——尽管这类斑点此前被认为是雄性抗氧化应激能力的信号，进而可反映精子适合度随衰老发生的下降趋势。相较之下，一妻多夫制或许是雌性降低被衰老精子受精概率的更有效策略。