Data from: Intra-ejaculate sperm selection in female zebra finches

Among internal fertilizers, typically fewer than 1% sperm survive the journey through the oviduct. Several studies suggest that the sperm reaching the ovum—the ‘fertilizing set’—comprise a non-random sub-population, but the characteristics of this group remain unclear. We tested whether oviductal selection in birds results in a morphologically distinct subset of sperm, by exploiting the fact that the fertilizing set are trapped by the perivitelline layer of the ovum. We show that these sperm have remarkably low morphological variation, as well as smaller head size and greater tail length, compared with those inseminated. Our study shows that the morphological composition of sperm—rather than length alone—influences success in reaching the ovum.在体内受精（internal fertilization）的类群中，通常仅有不足1%的精子能够通过输卵管（oviduct）并存活下来。多项研究显示，抵达卵细胞的精子——即所谓的‘受精种群（fertilizing set）’——并非随机的亚群，但该类精子的具体特征仍未明确。我们借助受精种群会被卵细胞卵黄膜（perivitelline layer）捕获这一特性，检验鸟类的输卵管选择是否会催生形态特征独特的精子亚群。研究结果表明，与经输精的精子相比，这类精子的形态变异程度显著更低，同时头部尺寸更小、尾部长度更长。本研究证实，精子的形态构成——而非单纯的长度——会影响其抵达卵细胞的成功率。