Data from: Long sperm fertilize more eggs in a bird

Sperm competition, in which the ejaculates of multiple males compete to fertilize a female's ova, results in strong selection on sperm traits. Although sperm size and swimming velocity are known to independently affect fertilization success in certain species, exploring the relationship between sperm length, swimming velocity and fertilization success still remains a challenge. Here, we use the zebra finch (Taeniopygia guttata), where sperm size influences sperm swimming velocity, to determine the effect of sperm total length on fertilization success. Sperm competition experiments, in which pairs of males whose sperm differed only in length and swimming speed, revealed that males producing long sperm were more successful in terms of (i) the number of sperm reaching the ova and (ii) fertilizing those ova. Our results reveal that although sperm length is the main factor determining the outcome of sperm competition, complex interactions between male and female reproductive traits may also be important. The mechanisms underlying these interactions are poorly understood, but we suggest that differences in sperm storage and utilization by females may contribute to the outcome of sperm competition.

精子竞争（sperm competition）是指多个雄性个体的精液竞相使雌性卵子受精的过程，该过程会对精子性状施加强烈的选择压力。尽管已有研究证实，在部分物种中精子大小与游泳速度可独立影响受精成功率，但厘清精子长度、游泳速度与受精成功率三者间的关联仍是一项亟待攻克的难题。本研究以斑胸草雀（Taeniopygia guttata）为实验对象，该物种中精子大小可影响精子游泳速度，借此我们探究了精子总长度对受精成功率的影响效应。我们开展了精子竞争实验：选取仅在精子长度与游泳速度上存在差异的雄性成对进行实验，结果显示，产生长精子的雄性在以下两方面表现更优：(i) 抵达卵子的精子数量更多；(ii) 成功完成卵子受精的比例更高。本研究结果表明，尽管精子长度是决定精子竞争结局的核心因素，但雌雄双方生殖性状间的复杂互作同样可能发挥关键作用。目前学界对这类互作背后的调控机制仍知之甚少，但我们推测，雌性对精子的储存与利用差异或许是影响精子竞争结局的重要因素之一。