Data from: Polyspermy in birds: sperm numbers and embryo survival

Polyspermy is a major puzzle in reproductive biology. In some taxa, multiple sperm enter the ovum as part of the normal fertilisation process, while in others, penetration of the ovum by more than one sperm is lethal. In birds, several sperm typically enter the germinal disc, yet only one fuses with the female pronucleus. It is unclear whether supernumerary sperm play an essential role in the avian fertilisation process and, if they do, how females regulate the progression of sperm through the oviduct to ensure an appropriate number reach the ovum. Here we show that when very few sperm penetrate the avian ovum, embryos are unlikely to survive beyond the earliest stages of development. We also show that when the number of inseminated sperm is limited, a greater proportion than expected progresses to the site of fertilisation, indicating that females compensate for low sperm numbers in the oviduct. Our results confirm an essential role for supernumerary sperm in the processes of fertilisation and early embryogenesis, providing an exciting expansion of our understanding of sperm function in birds.多精入卵（Polyspermy）是生殖生物学领域的重大未解之谜。在部分生物类群中，多精子进入卵细胞是正常受精过程的固有环节；而在另一些类群中，多条精子穿透卵细胞则会引发致死性后果。在鸟类中，通常会有多条精子进入卵细胞的胚盘（germinal disc），但最终仅一条精子与雌原核（female pronucleus）融合。目前学界尚未明确多余精子（supernumerary sperm）在鸟类受精过程中是否发挥不可或缺的关键作用；即便确有作用，雌性个体如何调控精子在输卵管（oviduct）内的运行路径，以确保适量精子抵达卵细胞，这一问题也仍未得到解答。本研究证实，当仅有极少量精子穿透鸟类卵细胞时，胚胎难以存活至发育早期阶段之后。本研究同时发现，当授精精子（inseminated sperm）总量有限时，能够抵达受精位点（site of fertilisation）的精子比例高于预期，这表明雌性可在输卵管内对精子数量不足进行代偿。本研究结果确认了多余精子在鸟类受精及早期胚胎发生（embryogenesis）过程中的关键作用，为深化我们对鸟类精子功能的认知提供了令人振奋的全新视角。