Pizzari Tommaso, Worley Kirsty, Burke Terry, Froman David P
Edward Grey Institute, Department of Zoology, University of Oxford, Oxford, UK.
BMC Evol Biol. 2008 Dec 16;8:332. doi: 10.1186/1471-2148-8-332.
A fundamental challenge in evolutionary biology is to resolve the mechanisms that maintain paternity a hypervariable fitness component. Because females are often sexually promiscuous, this challenge hinges on establishing the mechanisms through which the ejaculates of different males compete for fertilisation (sperm competition). The competitive quality of an ejaculate is mediated by the relative number of live sperm and their motile performance. The differential rate at which rival ejaculates lose their fertilising efficiency over time is therefore expected to influence the outcome of sperm competition.
Here, we artificially inseminated into sets of replicate domestic hens, Gallus gallus domesticus, experimentally engineered heterospermic ejaculates containing a large number of low-quality sperm from one male, and a lower number of high-quality sperm from another male. Large, low-quality ejaculates fertilised the first eggs produced after insemination, but small, high-quality ejaculates prevailed in the long run despite their numerical disadvantage.
Together, these results provide the first experimental demonstration that the relative competitive value of an ejaculate changes drastically over the time during which competing ejaculates are stored within the reproductive tract of a female, resulting in a marked temporal pattern of variation in paternity. A high level of replication makes these results robust. However, our study was restricted to few males of a well characterised study population, and future work should explore the generality of these results.
进化生物学中的一个基本挑战是解析维持父权这一高度可变的适合度成分的机制。由于雌性通常具有性乱交行为，这一挑战取决于确定不同雄性的射精如何竞争受精的机制（精子竞争）。射精的竞争质量由活精子的相对数量及其运动性能介导。因此，随着时间推移，竞争对手的射精失去受精效率的差异速率预计会影响精子竞争的结果。
在这里，我们将经过实验设计的异精混合精液人工授精到多组重复的家鸡（Gallus gallus domesticus）中，这些精液包含来自一只雄性的大量低质量精子和来自另一只雄性的少量高质量精子。大量的低质量射精使授精后产生的第一批蛋受精，但从长远来看，少量的高质量射精尽管数量处于劣势却占了上风。
总之，这些结果首次通过实验证明，在雌性生殖道中储存竞争射精的时间段内，射精的相对竞争价值会急剧变化，从而导致父权出现显著的时间变化模式。高度的重复性使这些结果具有可靠性。然而，我们的研究仅限于一个特征明确的研究群体中的少数雄性，未来的工作应探索这些结果的普遍性。
